Dixie Divers, Inc.; Grant of Permanent Variance

SUMMARY: This notice announces the grant of a permanent variance to

Dixie Divers, Inc. (Dixie). The permanent variance is from the

Occupational Safety and Health Administration (OSHA) requirements for

decompression chambers during mixed-gas diving operations, including

paragraphs (b)(2) and (c)(3)(iii) of 29 CFR 1910.423 and paragraph

(b)(1) of 29 CFR 1910.426.

The permanent variance covers recreational diving instructors and

diving guides employed by Dixie. Using both classroom instruction and

practice dives, recreational diving instructors train novice divers

individually or in small groups in recreational diving knowledge and

skills, including conventional diving procedures and the safe operation

of diving equipment. Dixie's recreational diving instructors accompany

students during practice dives, which vary in depth from a few feet of

sea water (fsw) to 130 fsw, and last between 30 minutes and one hour.

Diving guides (who may also serve as recreational diving instructors)

lead small groups of trained sports divers to local undersea locations

for recreational purposes; the guides select the diving locations and

provide the sports divers with information regarding the dive site,

including hazardous conditions and safe diving practices. While leading

divers to a dive site, the guides dive to a maximum depth of 130 fsw

for periods of 30 minutes to one hour.

The permanent variance specifies the conditions under which Dixie's

recreational diving instructors and diving guides may conduct their

underwater training and guiding tasks using open-circuit, semi-closed-

circuit, or closed-circuit self-contained underwater breathing

apparatus (SCUBA) supplied with a breathing gas consisting of a high

percentage of oxygen (O2) mixed with nitrogen, and without a

decompression chamber near the dive site. These conditions address: The

requirements for SCUBA equipment, including carbon-dioxide canisters,

counterlungs, moisture traps, moisture sensors, carbon-dioxide and

O2 sensors, and information modules; depth limits for diving

operations; use of nationally-recognized no-decompression limits and

O2-exposure limits; the O2 and nitrogen

composition of the breathing-gas mixture; procedures and equipment for

producing and analyzing breathing-gas mixtures; emergency-egress

procedures and systems; management of diving-related medical

emergencies; procedures for maintaining diving logs; use of

decompression tables and dive-decompression computers; and training

requirements for recreational diving instructors and diving guides.

DATES: The effective date of the permanent variance is December 20,

1999.

FOR FURTHER INFORMATION CONTACT: Office of Information and Consumer

Affairs, Room N3647, U.S. Department of Labor, Occupational Safety and

Health Administration, 200 Constitution Avenue, NW, Washington, DC

20210, Telephone: (202) 693-1999.

Additional information also is available from the following

Regional and Area Offices:

Regional Office:

U.S. Department of Labor--OSHA, 61 Forsyth St., SW., Atlanta, GA 30303,

Telephone: (404) 562-2300

Area Offices:

U.S. Department of Labor--OSHA, 5807 Breckenridge Parkway, Suite A,

Tampa, FL 33610, Telephone: (813) 626-1177

U.S. Department of Labor--OSHA, 8040 Peters Road, Building H-100,

Jacaranda Executive Court, Fort Lauderdale, FL 33324, Telephone: (954)

424-0242

U.S. Department of Labor--OSHA, Ribault Building, suite 227, 1851

Executive Center Drive, Jacksonville, FL 32207, Telephone: (904) 232-

2895

SUPPLEMENTARY INFORMATION:

I. Table of Contents

The following Table of Contents identifies the major sections under

``Supplementary Information.'' To understand fully the information

presented in the following sections, we recommend reviewing the 40

conditions of the permanent variance listed below under section VI.

I. Table of Contents

II. Background

III. Application for a Permanent Variance

IV. Comments to the Proposed Variance

Part 1. Comments to proposed section I (Background).

Part 2. Comments to proposed section II (Proposed Alternative).

Part 3. Comments to proposed section III (Rationale for the

Proposed Alternative).

Part 4. Comments to proposed section VI (Issues).

Part 5. General comments to the proposed variance.

Part 6. Our revisions to the proposed variance.

V. Decision

VI. Order

VII. References

VIII. Authority and Signature

II. Background

Dixie Divers, Inc. (Dixie) applied for a permanent variance from

paragraphs (b)(2) and (c)(3)(iii) of 29 CFR 1910.423 and paragraph

(b)(1) of 29 CFR 1910.426 under Section 6(d) of the Occupational Safety

and Health Act of 1970 (29 U.S.C. 655) and 29 CFR 1905.11. These

paragraphs address the availability and use of decompression chambers

during mixed-gas diving operations.

Dixie operates six diving schools, either directly or as

franchises. The schools employ 18 skilled and experienced recreational

diving instructors to train novice divers in recreational diving

knowledge and skills. The same 18 employees also serve as diving guides

and lead groups of sport divers to local diving sites for recreational

purposes. (We also refer to recreational diving instructors and diving

guides jointly as ``employees'' or, more generally, as ``divers.'')

As recreational diving instructors, the employees train

recreational diving students in conventional diving procedures and the

safe operation of diving equipment. The diving students may use an

open-circuit, semi-closed-circuit, or closed-circuit self-contained

underwater breathing apparatus (SCUBA) during these training dives.

1 SCUBAs supply divers with compressed air or a breathing

gas consisting of a high percentage of oxygen mixed with nitrogen or

another inert gas. 2

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\1\ The acronym for ``self-contained underwater breathing

apparatus'' is ``SCUBA.'' The term ``SCUBA'' refers to open-circuit

diving equipment alone, or to open-circuit, semi-closed-circuit, and

closed-circuit diving equipment combined. The term ``rebreather''

refers to semi-closed-circuit or closed-circuit diving equipment

alone or combined; this diving equipment recycles part or all of the

exhaled breathing gas into the system that delivers the breathing

gas to the diver.

\2\ The abbreviation ``O2'' means ``oxygen,'' while

the phrase ``nitrox breathing-gas mixture'' or the term ``nitrox''

refers to a breathing-gas mixture composed of nitrogen and

O2 in varying proportions.

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Dixie's training program for diving students involves both

classroom instruction and practice dives in which the employees

accompany diving students to maximum depths of 130 feet of sea water

(fsw). These dives last between 30 minutes and one hour. During these

dives, the recreational diving instructors provide underwater

[[Page 71243]]

instruction in, and allow the diving students to practice using, diving

procedures and equipment. A recreational diving instructor may make as

many as three to four training dives a day while training diving

students either individually or in small groups.

As diving guides, the employees lead small groups of trained sports

divers to local undersea diving locations for recreational purposes.

The diving guide selects the diving location prior to departure, and

provides the sports divers with information regarding the dive site,

including hazardous conditions and safe diving practices. The divers in

the recreational diving groups use open-circuit, semi-closed-circuit,

or closed-circuit SCUBAs that supply compressed air or a nitrox

breathing-gas mixture during the dive. During these diving excursions,

diving guides dive to a maximum depth of 130 fsw for periods of 30

minutes to one hour. A diving guide may make as many as five

recreational diving excursions a day.

The places of employment affected by this permanent variance are:

Dixie Divers of Boca Raton, 8241 Glades Road, Boca Raton, FL 33434

Dixie Divers of Boynton Beach, 340 North Congress, Boynton Beach, FL

33426

Dixie Divers of Deerfield, 1645 Southeast 3rd Court, Deerfield Beach,

FL 33441

Dixie Divers of Key Largo, 103400 Overseas Highway, Key Largo, FL 33037

Dixie Divers of Palm Bay, 4651 Babcock Street, Northeast, Palm Bay, FL

32905

Dixie Divers of Panama City, 109B West 23rd Street, Panama City, FL

32405

III. Application for a Permanent Variance

In its application for a permanent variance (referred to as

``variance application,'' ``proposed variance,'' or ``proposal''),

Dixie proposed an alternative to the decompression-chamber requirements

of paragraphs (b)(2) and (c)(3)(iii) of 29 CFR 1910.423 and paragraph

(b)(1) of 29 CFR 1910.426. Paragraph (b)(2) of 29 CFR 1910.423 requires

that ``[f]or any dive outside the no-decompression limits, deeper than

100 fsw or using mixed gas as a breathing mixture, the employer shall

instruct the diver to remain awake and in the vicinity of the

decompression chamber which is at the dive location for at least one

hour after the dive (including decompression or treatment as

appropriate).'' Paragraph (c)(3)(iii) of 29 CFR 1910.423 requires that

the decompression chamber be ``[l]ocated within 5 minutes of the dive

location,'' while paragraph (b)(1) of 29 CFR 1910.426 permits mixed-gas

diving only when a ``decompression chamber is ready for use at the dive

location.'' The purpose of having a decompression chamber available and

ready for use at the dive site is to treat two conditions: (1)

Decompression sickness (DCS), which may occur from breathing air or

mixed gases at diving depths and durations that require decompression;

and (2) arterial-gas embolism (AGE), which may result from

overpressurizing the lungs, usually while ascending rapidly to the

surface during a dive.

In the variance application, Dixie proposed to implement

alternative procedures that meet or exceed the level of employee

protection afforded by OSHA's decompression-chamber requirements. As an

alternative to a decompression chamber, Dixie proposed to have its

employees use open-circuit, semi-closed-circuit, or closed-circuit

SCUBA supplied with breathing-gas mixtures that contain a fraction of

O2 ranging from 22 to 40 percent (22-40%) by volume, with

the remaining breathing-gas mixture consisting of nitrogen. In

addition, the partial pressure of O2 in the nitrox

breathing-gas mixture would never exceed 1.40 atmospheres absolute

(ATA) 3 for any SCUBA. Dixie would use one of the following

procedures to produce nitrox breathing-gas mixtures: Mixing pure

nitrogen with pure O2; removing O2 from air for

mixing with pure nitrogen; adding pure O2 to air; or de-

nitrogenating air (e.g., removing nitrogen from air using filter-

membrane systems 4). According to the proposal, Dixie would:

Analyze the O2 fraction in the breathing-gas mixtures for

accuracy; institute quality-assurance procedures for the analytic

processes; and use breathing-gas mixing systems rated for O2

service whenever the highest O2 fraction used in the mixing

process exceeds 40 percent (40%). Dixie also proposed to restrict

diving operations under the variance to depths of 130 fsw or less, and

to use the nationally-recognized no-decompression limits and

O2-exposure limits developed by the National Oceanic and

Atmospheric Administration (NOAA) and Diving Science and Technology

(DSAT).

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\3\ ATA, as used here, is the partial pressure of a constituent

gas in the total pressure of a breathing gas. If the percentage of

the constituent gas in the breathing gas remains constant throughout

a dive, its partial pressure or ATA, increases in proportion to

increases in diving depth.

\4\ Filter-membrane systems produce nitrox breathing-gas

mixtures in two steps: First, they route air through filters to

remove hydrocarbons and other contaminants, then they pass the

decontaminated air through membranes that transfer O2

across the membrane fibers at higher rates than nitrogen (hence,

``de-nitrogenating air''). As the rate of air flow across the

membrane fibers increases, the resulting ratio of O2 to

nitrogen also increases. Under the permanent variance, a filter-

membrane system will reduce the hazards associated with producing

high-O2 breathing-gas mixtures because the proportion of

O2 in the system will never exceed 40 percent (40%).

---------------------------------------------------------------------------

By increasing the O2 partial pressure and decreasing the

nitrogen partial pressure of the breathing-gas mixture compared to air,

and by restricting dives to no-decompression limits and depths of 130

fsw or less, Dixie asserted that both the rate and the severity of DCS

would be no greater for its employees than for divers who operate

according to paragraph (a)(2)(i) of 29 CFR 1910.401. In addition, Dixie

contended that using nationally-recognized O2-exposure

procedures would reduce the risk of O2 toxicity among its

divers to the rate expected among divers who use hyperbaric air.

Dixie proposed a number of other requirements to ensure that its

employees remain within safe diving parameters, thereby avoiding DCS

and AGE. These requirements included limiting the maximum carbon

dioxide (CO2) level in the inhaled nitrox breathing-gas

mixture to 0.01 ATA. Dixie would control excessive CO2

levels as follows: By using pre-packed sorbent materials to absorb

CO2 from the exhaled breathing gas prior to rebreathing; by

installing sensors for detecting high CO2 levels or

conditions that could result in high CO2 levels (such as

moisture sensors to detect flooding in the breathing loop); and by

using counterlungs to serve as low-breathing-resistance reservoirs for

the breathing gas. In addition, Dixie proposed that its divers use an

information module that provides them with critical dive information

(e.g., gas pressures, water-temperature); the required information

would vary with the type of SCUBA. For rebreathers, visual or auditory

warning devices would alert the diver to significant equipment problems

(e.g., solenoid failure, low battery levels) or deviations from

established diving parameters (e.g., diverging from the planned

O2 levels). Closed-circuit rebreathers would need to operate

using a gas-controller package, a manually-operated gas-supply bypass

valve, and separate O2 and diluent-gas cylinders.

Dixie proposed a number of other conditions to safeguard its

divers. For emergencies involving SCUBA malfunctions that could

endanger diver health and safety (e.g., high CO2 levels),

the proposed variance required that Dixie have a reliable ``bail-out

system'' available. The bail-out system would need to provide a

separate supply of

[[Page 71244]]

breathing gas to the second stage of the SCUBA regulator; when

rebreathers are used, the bail-out system could deliver a diluent

supply of breathing gas to the second stage of the regulator. Other

protective conditions, which refined or emphasized existing

requirements currently specified in OSHA's Commercial Diving Operations

Standard (CDO Standard), included the following: Maintaining

decompression tables and diving logs at the dive site; assuring the

availability of personnel, facilities, and equipment to treat DCS and

AGE; and providing quality control of diver training.

In summary, Dixie stated that the occurrence and severity of DCS

would be minimal when its divers breathe nitrox gas mixtures, while the

risk of AGE would be negligible when they use the equipment and

procedural safeguards specified in the variance application.

Consequently, divers who use SCUBAs according to the proposed variance

would experience a level of DCS and AGE that is equal to, or lower

than, the level experienced by recreational diving instructors who dive

under the conditions specified by the exemption to the CDO Standard at

29 CFR 1910.401(a)(2)(i). These conditions allow for the use of

compressed air supplied to open-circuit SCUBAs under no-decompression

diving limits. Dixie asserted, therefore, that it should not have to

maintain a decompression chamber at the dive location for its

recreational diving instructors and diving guides when it complies with

the conditions specified in the variance application.

In a Federal Register notice published on October 31, 1997, we

provided the public with a copy of Dixie's variance application (62 FR

58995). This notice invited interested parties, including affected

employers and employees, to submit written comments, data, views, and

arguments regarding the variance application. In addition, the notice

informed affected employers and employees of their right to request a

hearing on the variance application. At the request of several parties,

we extended the comment period for this notice until March 2, 1998 in a

Federal Register announcement dated January 6, 1998 (63 FR 579).

IV. Comments on the Proposed Variance

We received 123 comments in response to the two Federal Register

notices. Of this total, two comments (Exs. 2-98 and 2-115) were

duplications, and one comment (Ex. 2-112) consisted solely of a request

to extend the comment period. (Exs. 6-1 to 6-17 also were requests to

extend the comment period.) Two additional comments (Exs. 2-118 and 2-

119) requested a hearing on the proposal. We denied these hearing

requests because neither of the two requestors employed recreational

diving instructors, the subject of this variance application. OSHA

received 103 comments that were general, non-specific endorsements of

the variance application; the vast majority of these comments varied

only slightly in content. The remaining 15 commenters submitted

detailed comments regarding the conditions and issues specified in the

variance application.

We have organized our discussion of the substantive comments to the

variance application into six parts. Comments concerning proposed

section I (Background) are in Part 1, while Part 2 consists of comments

made about the conditions specified in proposed section II (Proposed

Alternative). Part 3 discusses comments made regarding proposed section

III (Rationale for the Proposed Alternative), and Part 4 presents

comments to the issues raised in proposed section VI (Issues). No

commenters addressed sections IV and V of the variance application,

titled ``References'' and ``Additional Information'' respectively. Part

5 consists of general and miscellaneous comments. Throughout each of

these five parts, we explain the actions we are taking with regard to

individual comments or groups of comments. The last part, Part 6,

describes refinements to the proposed variance that we have made in

developing the permanent variance; these refinements are based upon our

interpretation of the proposed conditions and our overall review of the

record.

We and other parties submitted additional exhibits (Exs. 4, 4A, 5,

and 7 through 13) to the docket (see Table I). These exhibits, which

contain scientific and technical information, provided additional

information we used in replying to comments and discussing revisions to

the proposal. The principal topics covered by the exhibits are:

O2 toxicity; nitrogen narcosis; decompression procedures;

the operation and use of SCUBAs; and treatment of diving-related

medical emergencies. Table I below provides specific reference

information on these exhibits.

Table I.--Reference Information on Exhibits 4, 4A, and 5 Through 16

------------------------------------------------------------------------

Ex.

No. Reference information

------------------------------------------------------------------------

4 D. J. Kenyon and R. W. Hamilton. ``Managing Oxygen Exposure when

Preparing Decompression Tables.'' In: N. Bitterman and R.

Lincoln (eds.), Proceedings of the XVth Meeting of the European

Undersea Biomedical Society, pages 72-77. European Undersea

Biomedical Society, September 1989.

R. W. Hamilton. ``IV. Oxygen Physiology, Toxicity, and

Tolerance.'' In: R. W. Hamilton (author), Special Mix Diving:

Part One, pages 25-38. Hamilton Research and Life Support

Technologies, March 2, 1994.

4A R. W. Hamilton, R. E. Rogers, M. R. Powell, and R. D. Vann. The

DSAT Recreational Dive Planner: Development and Validation of No-

Stop Decompression Procedures for Recreational Diving. Diving

Science and Technology, Inc., and Hamilton Research, Ltd.,

February 28, 1994.

5 D. Richardson (ed.-in-chief). Proceedings of Rebreather Forum

2.0. Diving Science and Technology, Inc., 1996.

7 R. W. Hamilton. ``Tolerating Exposure to High Oxygen Levels:

Repex and Other Methods.'' Marine Technology Society Journal,

volume 23, number 4, pages 19-25, December 1989.

8 R. J. Kiessling and C. H. Maag. ``Performance Impairment as a

Function of Nitrogen Narcosis.'' Journal of Applied Psychology,

volume 46, number 2, pages 91-95, 1962.

9 A. D. Baddeley. ``Influence of Depth on the Manual Dexterity of

Free Divers: A Comparison Between Open Sea and Pressure Chamber

Testing.'' Journal of Applied Psychology, volume 50, number 1,

pages 81-85, 1966.

10 A. D. Baddeley, J. W. De Figueredo, J. W. Hawkswell Curtis, and

A. N. Williams. ``Nitrogen Narcosis and Performance Under

Water.'' Ergonomics, volume 11, number 2, pages 157-164, 1968.

11 W. B. Wright. ``Use of the University of Pennsylvania, Institute

for Environmental Medicine Procedure for Calculation of

Cumulative Pulmonary Oxygen Toxicity.'' U.S. Navy Experimental

Diving Unit, Report 2-72, 1972.

12 R. J. Biersner. ``Request for Your Recommendation Regarding

Acceptable Delay in Recompression Treatment of Diving-Related

Medical Emergencies.'' Memorandum to Dr. Edward D. Thalmann,

August 28, 1998.

[[Page 71245]]

13 E. D. Thalmann. Letter to R. J. Biersner Responding to the

Memorandum in Ex. 12, October 5, 1998.

14 J. R. Clarke. CO2 Canister Test Parameters and Procedure at NEDU.

Attachment to U.S. Navy Experimental Diving Unit E-mail

Memorandum, November 22, 1999.

15 J. R. Clarke. ``Statistically Based CO2 Canister Duration Limits

for Closed-Circuit Underwater Breathing Apparatus.'' U.S. Navy

Experimental Diving Unit, Report 2-99, 1999.

16 P. B. Bennett. ``Nitrox?'' Alert Diver, March/April, 1998.

------------------------------------------------------------------------

Part 1. Comments to proposed section I (Background).

(a) The skills and experience of, and the diving operations

performed by, the applicant's divers (62 FR 58996, second column)

received two comments. Both comments were primarily concerned about

Dixie's recreational diving instructors and diving guides engaging in

diving activity beyond the scope of the proposed variance. The

Association of Diving Contractors, Inc. (Ex. 2-99) contended that

recreational diving instructors and diving guides ``[engage] in

services of a commercial nature,'' and implied that the conditions of

the variance application would allow them to extend their commercial

diving activities beyond the scope of the proposed variance.

The second commenter (Ex. 2-105) did not object to the proposed

variance for no-decompression dives to depths of 130 fsw or less if

they are ``of an instructional, training, or scientific nature and [do]

not involve any form of salvage or underwater construction or related

working tasks.'' This commenter stated that the recreational diving

must ``not encompass working dives (i.e.[,] salvage, construction).

This is a very [important] distinction as the commercial diving

industry cannot bear the financial burden imposed by the insurance

companies who would lump professional recreational instructors in with

professional commercial divers.''

In reply to these commenters, we note that the permanent variance

will not cover recreational diving instructors and diving guides when

they engage in activities that do not involve recreational diving

instruction and diving guide activities. They must comply with our CDO

Standard as appropriate, including the decompression-chamber

requirements, while engaged in these other activities. To ensure that

Dixie understands under what conditions the permanent variance applies,

we are specifying in Condition (1) (see below at section VI, titled

``Order'') that the permanent variance covers only recreational diving

instructors and diving guides who are employees of Dixie Divers, Inc.,

and then only while they are performing as diving guides and

recreational diving instructors.

(b) The background information noted that the applicant's employees

``may make as many as three or four training dives a day while training

diving students'' and that ``[a] guide may make as many as five * * *

excursions a day'' (62 FR 58996, second column). This background

information elicited one comment. This commenter (Ex. 2-109) stated

that ``[b]oth NAUI [National Association of Underwater Instructors] and

PADI [Professional Association of Diving Instructors], the two largest

certifying agencies in the U.S., limit instructors teaching entry-level

classes to no more than two dives per day with a single class.'' The

commenter also noted that ``Dixie could hire more instructors, which

would lessen their time in the water, decreasing [their] nitrogen

exposure, lessening their susceptibility to DCS, thus obviating the

need for the variance.''

The basis for the NAUI and PADI limitations is unclear (e.g., do

these limits address diver safety or training effectiveness).

Nevertheless, we believe that adopting the no-decompression procedures

for repetitive diving published in the 1991 NOAA Diving Manual and by

DSAT (Ex. 4A) as a condition of the permanent variance will protect

Dixie's recreational diving instructors and diving guides at least as

well as recreational diving instructors who use compressed air supplied

to open-circuit SCUBAs under no-decompression diving limits specified

in paragraph (a)(2)(i) of 29 CFR 1910.401.

(c) The statement in this section that ``[e]mployees who use high-

oxygen breathing-gas mixtures will be able to make more or longer

repetitive-training [or] excursion dives than they would using

compressed-air open-circuit SCUBA'' (62 FR 58995, third column)

received one comment. This commenter (Ex. 2-109) disagreed with this

statement, claiming that nitrox breathing-gas mixtures may not reduce

susceptibility to DCS and that ``[w]e know of no studies or evidence to

show that diving to limits on the nitrox tables while breathing nitrox

produces a lower incidence of DCS than diving to limits on air tables

while breathing air.''

We agree that the mathematical probability of DCS is similar for

dives that result in equivalent levels of nitrogen saturation (e.g.,

dives made to a specific depth using air, and longer-duration dives

made to the same depth using nitrox breathing-gas mixtures).

Accordingly, for dives made using nitrox breathing-gas mixtures, the

risk of DCS is lower only when these dives are at the same depths and

for the same durations as the air dives. Note, however, that Condition

J of the proposed variance limits the risk of DCS by requiring that

divers remain within the no-decompression limits of NOAA's

decompression tables, or other tables or formulas that Dixie

demonstrates are equally effective in preventing DCS.

(d) We stated in the ``Background'' section of the proposed

variance that ``[a]s a result [of using nitrox breathing-gas mixtures],

the mathematical probability of developing decompression sickness (DCS)

is reduced compared to divers who use compressed air under the same

diving conditions (i.e., depth, bottom time, and descent and ascent

rates)'' (62 FR 58997, first column). This statement elicited two

comments. The first commenter (Ex. 2-98) stated that high-O2

nitrox breathing-gas mixtures will result in a reduced risk of DCS when

used at the same depths and for the same durations as air, but only if

the divers use the depth and duration limits specified for air

decompression and do not extend the duration of the dive. The reduction

in risk occurs because the nitrogen partial pressure in the nitrox

breathing-gas mixture is less than the partial pressure of nitrogen in

air at the specified depth. The second commenter (Ex. 2-109) asserted

that Dixie has economic incentives to extend the duration of dives.

We believe these commenters are correct that extending the duration

of dives using high-O2 nitrox breathing-gas mixtures would

increase the risk of DCS. However, we conclude that the

[[Page 71246]]

resulting risk would be comparable to using the equivalent partial

pressure of nitrogen in air for that extended period. The basis for

this conclusion is the equivalent-air-depth (EAD) formula published by

NOAA, which is the nation's lead Federal agency for developing mixed-

gas decompression schedules used in scientific and technical diving

operations. According to NOAA, EAD ``is the depth at which air will

have the same nitrogen partial pressure as the [oxygen-]enriched mix

has at the depth of the dive'' (1991 NOAA Diving Manual, page 15-7).

NOAA applies its EAD formula in determining what equivalent air

decompression limits to use with nitrox breathing-gas mixtures, and

assumes that equivalent nitrogen partial pressures and dive durations

will result in similar DCS risk. However, to provide Dixie's divers

with an added margin of safety against DCS, the permanent variance

requires that the partial pressure of nitrogen in the high-

O2 nitrox breathing-gas mixture used for a specific dive

duration must never exceed the no-decompression limits for the

equivalent partial pressure of nitrogen in air for that same duration

published in the 1991 NOAA Diving Manual.

Part 2. Comments to proposed section II (Proposed Alternative).

(a) Conditions A.1 and A.2 of the proposal, which specified

requirements for CO2 scrubbers, CO2 sensors,

moisture traps, moisture sensors, and over-pressure valves, received a

number of comments. Several commenters (Exs. 2-98, 2-99, 2-105, and 2-

117) pointed out a typographical error in the stated CO2

level in Condition A.1. The correct level is 0.01 ATA, not 0.1 ATA, and

we have corrected it in the permanent variance.

Condition A.1 in the proposed variance (Condition (4) in the

permanent variance) stated that rebreathers must use commercially-

available, pre-packed, disposable scrubber cartridges or an equally

effective alternative. Three commenters (Exs. 2-101, 2-105, and 2-114)

took exception to the requirement that CO2 scrubbers must

use sorbent cartridges that are commercially available, pre-packed, and

disposable. They contended that such cartridges are not available for

some rebreathers and, when available, are expensive. They also argued

that rebreather manufacturers do not require pre-packed, disposable

cartridges because many divers manually fill and pack most rebreather

canisters. One commenter (Ex. 2-105) stated that ``no scientific

evidence [shows that] a disposable[,] pre-packaged canister would

perform safer or with greater efficiency than one packed by the user.''

Another commenter (Ex. 2-117), however, stated that ``[u]se [of

disposable scrubber cartridges] in rebreathers reduces return to

service time and reduces human error during servicing,'' and that

[several manufacturers] have canisters that simplify replacement of

sorbent material, while [at least one manufacturer] uses a disposable

cartridge.''

In reply to these commenters, we note that Condition A.1 in the

proposed variance allowed Dixie to use an alternative to pre-packed

CO2-sorbent materials, including manually-filled cartridges;

Condition (4)(b) in the permanent variance will also permit this

alternative, if it is acceptable to the rebreather manufacturer.

However, Dixie bears the burden of demonstrating to us that its

manually-filled cartridges are at least as effective as pre-packed

sorbent materials in removing CO2 from the breathing loop;

Dixie likely would get this information from the rebreather

manufacturer.

Proposed Condition A.2 required the use of CO2 sensors.

One commenter (Ex. 2-25) endorsed this proposed requirement for closed-

circuit rebreathers, but claimed these sensors were unnecessary for

semi-closed-circuit rebreathers because these rebreathers ``are

regularly venting gas from the system which is replaced with high

oxygen content gas * * * to prevent the buildup of carbon dioxide.'' We

believe that CO2 sensors are necessary for semi-closed-

circuit rebreathers because divers can ``overbreathe'' these

rebreathers. Overbreathing occurs when the diver's breathing rate is

faster than the rate at which fresh breathing gas enters the inhalation

bag; consequently, overbreathing causes the diver to rebreathe exhaled

gas containing elevated levels of CO2. The information in

Ex. 5 (pages P-19 through P-22) supports this conclusion. Therefore,

CO2 sensors enable divers to detect increased CO2

before it reaches hazardous levels.

The commenter in Ex. 2-98 endorsed the use of CO2

sensors, but claimed that this technology is ``currently unavailable

even in the current U.S. Navy rebreathers.'' Two other commenters (Exs.

2-105 and 2-114) also asserted that continuously-functioning

CO2 sensors are not available commercially. However, another

commenter (Ex. 2-117) contradicted these assertions; this commenter

stated that CO2 sensors are available in several

rebreathers.

Four commenters (Exs. 2-99, 2-106, 2-113, and 2-114) claimed that

few, if any, rebreathers on the market met proposed Conditions A.1 and

A.2. One of these commenters (Ex. 2-106) stated, ``[M]any of the

specifications for rebreathers represent the manufacturer-specific

features of an intended unit that was never brought forward as a

production model. We also manufacture diving rebreathers and protest

any regulation that would arbitrarily bias compliance to one model.''

Four other commenters contended that the proposed variance favors or

enhances the competitive position of one or more rebreather

manufacturers (Exs. 2-99, 2-101, 2-105, and 2-114); no commenter,

however, indicated which manufacturer(s) would benefit. One commenter

(Ex. 2-114) stated that ``[implementing the proposed variance] would

put every dive store and instructor who teaches rebreather diving in

the U.S. out of business,'' and claimed that ``this [proposed] variance

would in essence be a restraint of trade.''

The information provided in Ex. 2-117 demonstrates that the

required components are commercially available and used in several

existing rebreathers. Other evidence in the record (Ex. 5, page 6-4)

also shows that effective CO2 sensors are commercially

available for closed-circuit rebreathers. We find that each proposed

condition is necessary for diver safety, and that Dixie can either

purchase rebreathers, or retrofit its existing rebreathers, to meet

these conditions. In addition, we observe that no commenter found that

any required component was unsafe.

While the proposed variance did not require any CO2

alarms, the commenter in Ex. 2-98 recommended that CO2

sensors activate two alarms: The first alarm when the inhaled

CO2 partial pressure is at 0.005 ATA (3.8 mmHg), to warn

divers that they are approaching the upper CO2 limit; and

the second alarm when inhaled CO2 reaches the partial

pressure limit of 0.01 ATA (7.6 mmHg), to alert the diver to terminate

the dive immediately. We agree with much of this comment, but we

believe that once the alarm is activated at a CO2 partial

pressure of 0.005 ATA, it must continue to provide a visual or auditory

warning to the diver to take corrective action or terminate the dive

before reaching the maximum CO2 limit of 0.01 ATA. The use

of an activation level is similar to the action-level requirement found

in many of OSHA's standards for toxic substances. Therefore, the

permanent variance requires Dixie to

[[Page 71247]]

integrate the CO2 sensors with an alarm (either visual or

auditory) that operates continuously at and above a CO2

partial pressure of 0.005 ATA.

The proposed variance did not specify calibration requirements for

CO2 sensors. Nevertheless, the commenter in Ex. 2-98 stated

that any CO2 sensor adopted for use in rebreathers must be

``tested both in the laboratory and in manned diving trials,'' and that

the ``[d]ata from these trials must support [the] accuracy, reliability

and ruggedness'' of CO2 sensors. While this commenter did

not specify a protocol or criteria for testing these factors, we agree

that, at a minimum, Dixie must determine the accuracy of CO2

sensors before its divers use them. Such a determination is necessary

to enable Dixie to eliminate sensors that are unreliable or that cannot

function under rugged diving conditions. Therefore, in developing

provisions for calibrating and maintaining the accuracy of

CO2 sensors (see Condition (9) in the permanent variance),

we have adopted the requirements that Dixie specified for O2

sensors in Condition A.4 of the variance application, with one major

revision: Instead of using an accuracy of 1 percent (1%) by volume,

Condition (9)(c) of the permanent variance requires that CO2

sensors be accurate ``to within 10 percent (10%) of a CO2

concentration of 0.005 ATA or less,'' based on the comments in Ex. 2-

98. Using a test or standard gas containing a CO2

concentration of 0.005 ATA or less will ensure that the sensors can

accurately detect CO2 levels that can be harmful to Dixie's

divers. Additionally, in view of the harmful effects that can result

from high levels of CO2, we consider a maximum error rate of

no more than 10 percent (10%) of a CO2 partial pressure of

0.005 ATA to be within acceptable limits.

The commenter in Ex. 2-98 also argued that, as an alternative to

CO2 sensors, ``the breathing apparatus manufacturer [must]

produce data from manned trials that substantiate [the] operational

CO2 canister-duration limits over the entire depth, water

temperature, and exercise range for which the breathing apparatus is

designed. Furthermore, the manufacturer must clearly state what these

limits are.'' While the proposed variance did not mention such an

alternative, we agree with the general approach recommended by this

commenter. However, we believe that valid and reliable data for

determining CO2-sorbent replacement schedules can be

obtained from carefully controlled and executed testing protocols that

use breathing machines instead of divers to evaluate the canisters.

Therefore, Condition (10)(a)(i) of the permanent variance permits Dixie

to use a schedule for replacing the CO2-sorbent material in

canisters if the rebreather manufacturer developed the replacement

schedule using the canister-testing protocol specified in Appendix A of

this notice. We adapted this protocol from the canister-testing

parameters and procedure provided by the U.S. Navy Experimental Diving

Unit (NEDU) (Ex. 14); NEDU is the lead federal agency for testing

CO2-sorbent replacement schedules, and the diving industry

recognizes the NEDU canister-testing protocol as the industry standard.

Additionally, the employer can use a CO2-sorbent replacement

schedule developed by a rebreather manufacturer only if the

manufacturer analyzed the protocol results using the statistical

procedures specified by NEDU (Ex. 14 and 15).

The canister-testing protocol developed by NEDU addresses the three

factors recommended by the commenter in Ex. 2-98: Depth, exercise level

(ventilation rate), and water temperature. Depth is the maximum depth

at which a diver would use the CO2-sorbent material, which

for the permanent variance is 130 fsw. We selected three combinations

of ventilation rates and CO2-injection rates from the NEDU

protocol to simulate three diverse levels of exercise (light, moderate,

and heavy). The four water temperatures used in the NEDU protocol are

40, 50, 70, and 90 degrees F (4.4, 10.0, 21.1, and 32.2 degrees C,

respectively); these temperatures represent the wide range of water

temperatures that Dixie's recreational diving instructors are likely to

encounter. We revised the NEDU protocol slightly by: Limiting the

maximum depth to 130 fsw; requiring an O2 fraction of 0.28

in a nitrox breathing gas (this fraction being the maximum

O2 concentration permitted at this depth by the permanent

variance); providing tolerance limits for water temperatures; and

defining canister duration as the time taken to reach 0.005 ATA of

CO2 (the CO2 level specified in the permanent

variance at which divers are to eliminate excessive CO2 in

the breathing gas or terminate the dive). In addition, our protocol

uses only mandatory language, and expressly prohibits the use of

replacement schedules based on extrapolation of the protocol results.

OSHA prohibits extrapolation of the protocol results because the

statistical-analysis procedures developed by NEDU (Ex. 15) do not

provide a method for estimating the duration of CO2-sorbent

materials beyond the results obtained during the canister-testing

trials. OSHA believes this approach significantly improves the validity

and reliability of the replacement schedules derived from these

results. After thoroughly reviewing the NEDU canister-testing protocol

and adapting it the conditions of the permanent variance, we believe

that CO2-sorbent replacement schedules based on the

requirements of Appendix A of the permanent variance will enable Dixie

to replace CO2-sorbent materials in a timely manner, thereby

ensuring the health and safety of its divers.

While we are confident that CO2-sorbent replacement

schedules developed according to Condition (10) of the permanent

variance will protect divers under ordinary diving conditions, we

believe that these schedules do not address a condition that can

seriously compromise canister effectiveness: Moisture in the canister,

which usually results from canister flooding. Based on our review of

the record, we find that moisture traps and moisture sensors can

effectively control this condition. In this regard, proposed Condition

A.2 required the use of moisture traps and moisture sensors. Several

commenters (Exs. 2-101, 2-105, and 2-117) claimed that existing

rebreathers already use moisture traps. The commenter in Ex. 2-101

stated, without explanation, that ``making them a requirement would be

restrictive.'' This commenter also asserted that moisture sensors are

unnecessary because CO2 sensors perform the same function.

(The commenter did not specify the term ``function,'' but we assume

that it refers to the capability to indicate canister flooding.) A

second commenter (Ex. 2-105) noted that moisture sensors would be an

important safety feature, but asserted that they were not available

commercially. However, another commenter (Ex. 2-117) claimed that

moisture sensors are available from several companies. One commenter

(Ex. 2-105) noted that excessive moisture can impair electrical systems

in rebreathers, and asked us to specify where to place the moisture

sensors to prevent these problems.

Moisture traps are necessary to keep water out of the canisters

because water leakage into canisters can substantially reduce the

CO2-absorbing properties of the sorbent material. Moisture

sensors, in turn, detect excessive water or flooding inside the

canister that can compromise the CO2-sorbent material.

Moisture sensors, therefore, warn the diver of hazardous water leakage

into the canister. The commenters in Exs. 2-101, 2-105, and 2-117 noted

that

[[Page 71248]]

moisture traps are available commercially and that existing rebreathers

routinely use them. The information in Ex. 2-117 also indicates that

moisture sensors are commercially available. While we believe that

rebreather manufacturers should place moisture sensors on the

inhalation side of the breathing loop, we leave the design and location

of moisture sensors and moisture traps to their technical expertise.

Dixie must ensure that its divers use these components consistent with

the rebreather manufacturer's instructions, and that the moisture

sensors alert the diver of moisture in the breathing loop in sufficient

time to terminate the dive and return safely to the surface. We have

incorporated these conditions into the permanent variance.

In the proposed variance, Condition A.2 specified that rebreathers

contain over-pressure valves. Regarding over-pressure valves, one

commenter (Ex. 2-101) asked us to define the term ``over-pressure

valve,'' while two commenters (Exs. 2-105 and 2-117) asserted that

existing rebreathers already have over-pressure valves. One of these

commenters (Ex. 2-105) noted that over-pressure valves are ``important

protection to reduce the risk of [AGE] and associated pressure[-

]induced injuries and [rebreather] damage.''

An over-pressure valve is a valve on the counterlung that releases

breathing gas from the counterlung when the pressure reaches a set

level; we have incorporated this meaning into the permanent variance.

Rebreathers routinely are designed with over-pressure valves. These

valves perform a critical safety function by helping to regulate

breathing-gas volume and pressure.

Condition A.2 of the proposed variance also specified that Dixie

use redundant (i.e., at least two) CO2 sensors and redundant

moisture sensors; it also required that these sensors function

continuously. One commenter (Ex. 2-101) agreed with the proposed

requirement for a continuously-functioning CO2 sensor, but

did not believe that additional CO2 sensors were necessary.

This commenter noted that both CO2 and moisture sensors will

alert the diver whenever the breathing loop, most likely the

CO2-sorbent material, is no longer capable of removing

exhaled CO2. We agree with this commenter that

CO2 and moisture sensors serve much the same purpose--to

inform the diver of conditions (for example, reduced efficiency of the

CO2-sorbent material) that may cause CO2 to

accumulate in the breathing loop. By measuring the amount of

CO2 in the inhaled breathing gas (after the gas passes

through the sorbent material in the canister to remove CO2)

CO2 sensors can detect an elevated CO2 level that

may indicate depletion of the CO2-sorbent material because

of canister flooding. An elevated CO2 level, in turn, warns

the diver to take corrective action, including terminating the

dive.5 As noted previously, moisture sensors detect

excessive water or flooding inside the canister that can reduce the

sorbent material's capacity to remove CO2 from the inhaled

breathing gas. The independent functions performed by these sensors

(i.e., a CO2 sensor measures CO2 in the breathing

gas, while a moisture sensor detects excessive moisture in the

canister) indicates that a malfunction in one sensor is unlikely to

result in a malfunction in the other sensor.

---------------------------------------------------------------------------

\5\ In addition, a CO2 sensor alerts the diver to

increased CO2 levels in the inhaled breathing gas that

may result from other conditions, including depleted sorbent

material (saturated with CO2) and channeling or

overbreathing (exhaled air bypassing the sorbent material).

---------------------------------------------------------------------------

Several other conditions make sensor redundancy unnecessary. First,

the symptoms of excessive CO2 do not develop as rapidly as

the symptoms of O2 toxicity; 6 consequently, a

properly trained and experienced diver will be able to recognize a

number of effects associated with excessive CO2 and take

appropriate action, including terminating the dive. These effects

include: Reduced buoyancy (from the increased weight caused by canister

flooding); shortness of breath (from CO2 displacing

O2 in the diver's lungs); an increase in breathing

resistance during inhalation (caused by difficulty moving the breathing

gas through wet CO2-sorbent material); and a large number of

bubbles vented through the rebreather's exhaust valve (venting related

to the increased exhaust pressure caused by exhaling against wet

CO2-sorbent material). Secondly, the permanent variance

(Conditions (7) and (8)) requires that both the moisture sensor and

CO2 sensor function continuously, ensuring early detection

of a CO2-related problem by the diver. Lastly, Condition

(30) of the permanent variance requires that the divers use an open-

circuit emergency-egress system (a ``bail-out'' system); this system

will provide the divers with the capability to shift to a known, safe,

and immediately-available breathing gas, and to terminate the dive

safely whenever a CO2-related problem occurs.

---------------------------------------------------------------------------

\6\ The rapid onset of symptoms resulting from O2

toxicity provides a major rationale for requiring redundant

O2 sensors.

---------------------------------------------------------------------------

Based on this record, we find that: Carbon-dioxide sensors and

moisture sensors provide independent means of detecting a

CO2-related problem; symptoms related to excessive levels of

CO2 develop more slowly than the symptoms of excessive

O2; a properly trained and experienced diver will recognize

the effects of excessive CO2 in sufficient time to take

correct action; the requirement that CO2 sensors and

moisture sensors be continuously functioning assures real-time

detection of CO2-related problems; and the required bail-out

system provides the diver with a safe means to terminate a dive

following detection of a CO2-related problem. This record

demonstrates that the proposed requirements for redundant

CO2 sensors and redundant moisture sensors are unnecessary;

we believe that the only basis for requiring redundant sensors is if

the rebreather manufacturer includes them in the equipment design or

specifications. Therefore, we have revised the conditions accordingly

in the permanent variance.

(b) Proposed Condition A.3, which required the use of flexible

breathing bags (also known as ``counterlungs'') with rebreathers,

elicited the following comment (Ex. 2-105):

Not all rebreathers use breathing bags. However, they all employ

some type of counter lung providing a compliant volume. Certain

types of rebreathers utilize a large diaphragm or bellows assembly.

There would be no purpose in mandating a particular counterlung

configuration. The only regulation that could be mandated might be a

minimum volumetric displacement.

We consider breathing bags to be a type of counterlung. Even though

the proposed variance used the terms ``breathing bags'' and

``counterlungs'' interchangeably, we agree with the commenter that the

permanent variance should not specify a particular counterlung

configuration. We have revised the condition accordingly in the

permanent variance. In addition, while we agree with the need to

specify a minimum volumetric displacement, we believe that the

rebreather manufacturer should determine this value. In this regard,

Dixie must ensure that its divers use the counterlung according to the

rebreather manufacturer's instructions, and the counterlung must

displace enough volume to sustain the diver's respiration rate during

any diving condition. We have incorporated these conditions into the

permanent variance.

(c) Proposed Condition A.4 addressed ``bail-out systems,'' which

are supplemental breathing-gas systems used by divers for emergency

ascent to the surface if the SCUBA malfunctions. The proposed condition

specified that bail-out systems must integrate the

[[Page 71249]]

second stage of the SCUBA regulator with either a separate supply of

emergency breathing gas or, for semi-closed-circuit and closed-circuit

rebreathers, a diluent supply of emergency breathing gas. Two

commenters (Exs. 2-100 and 2-105) responded to the proposed condition.

The first commenter (Ex. 2-100) recommended that the system contain at

least 35 cubic feet of emergency breathing gas. This volume was based

on maximum consumption rates related to a number of variables,

including water temperature, diver's thermal protection, speed of

current, lung volume, and psychological stress. The second commenter

(Ex. 2-105) stated that ``[a] bail-out system is a necessity for all

rebreather use.''

We agree that the bail-out system must enable the diver to

terminate the dive safely under ``worst-case'' conditions. We believe,

however, that the rebreather manufacturer is in the best position to

determine what capacity of breathing gas is needed for safe operation

of the bail-out system. In this regard, Dixie must ensure that its

divers use the bail-out system according to the rebreather

manufacturer's instructions. Dixie must also ensure that the bail-out

system supplies sufficient emergency breathing gas to enable a diver to

terminate the dive and return safely to the surface; the rebreather

manufacturer can make this determination after Dixie provides the

critical diving parameters (e.g., depth of dive and breathing rate). We

have revised this condition accordingly in the permanent variance.

(d) Proposed Condition A.5 specified requirements for information

modules, which provide divers with information about the dive,

including gas pressures, dive times, and descent and ascent rates. One

commenter (Ex. 2-114) stated that the information module is a dive

computer, that no rebreathers are available commercially that integrate

dive computers with breathing systems, and that no dive computer

``includes displays that directly warn of rebreather solenoid failure

and excessive descent rates.'' In response, although we believe that it

would be advantageous if dive computers included such information and

warning displays, neither the proposed nor the permanent variance

require it. The permanent variance requires Dixie to equip its divers

with sensor and display systems that provide information on time,

depth, ascent, and descent to divers who use closed-circuit

rebreathers, and time, ascent, and descent information to divers who

use semi-closed-circuit rebreathers. Both types of rebreathers must

also have alarms or visual displays that warn the diver about excessive

ascent and descent rates, as well as depth levels that are shallower

than the ceiling-stop depth. The permanent variance does not require

that a dive computer provide this capability.

(e) Proposed Condition B required that closed-circuit rebreathers

must use the following sensors: (1) Sensors that measure supply

pressures for O2 and diluent gas; (2) depth sensors; (3)

continuously-functioning and redundant temperature-compensated

O2 sensors; and (4) continuously-functioning gas-loop and

ambient water-temperature sensors. One commenter (Ex. 2-114) asserted

that no existing rebreathers have continuously-functioning sensors for

assessing gas-loop and ambient water temperatures. A second commenter

(Ex. 2-117) contradicted this assertion, claiming that ``transducers

and thermocouples are readily available from numerous companies'' for

sensing pressure, depth, and ambient water temperature.

We believe that temperature sensors are necessary for diver safety.

Water-temperature sensors alert divers to the possibility of

hypothermia. In addition, gas-loop temperature sensors and water-

temperature sensors allow divers to estimate the duration of their

CO2-sorbent material. Efficiency of the CO2-

sorbent material deteriorates with decreasing temperatures (1991 NOAA

Diving Manual, page 16-9). Thus, if divers are able to estimate the

duration of their CO2-sorbent material, they can judge how

long they can dive even if their CO2 sensors malfunction.

Even if no existing rebreather incorporates temperature sensors as

stated by the commenter in Ex. 2-114, Dixie's proposal to use such

sensors will provide its divers with additional protection from

temperature-related diving hazards; therefore, we have included this

condition in the permanent variance.

(f) For open-circuit SCUBA, proposed Condition C specified that the

concentration of O2 must not exceed 40 percent (40%) of the

breathing gas by volume, or, for any SCUBA, an O2 partial

pressure of 1.40 ATA. Three commenters (Exs. 2-104, 2-106, and 2-113)

recommended that we increase the partial pressure of O2 in

the breathing-gas mixture from 1.4 to 1.6 ATA; these commenters

asserted that recreational divers use the 1.6 ATA level regularly and

safely, and that this use conforms to prevailing rebreather practices.

In reply to these commenters, we believe that the research data

cited in the proposed variance support our conclusion that a maximum

O2 level of 1.40 ATA prevents O2 toxicity. The

commenters provided no data or studies to support a maximum

O2 exposure of 1.6 ATA, nor could we find any relevant data

or study to support this recommendation for SCUBA diving. Evidence in

the record (see Exs. 4, 4A, 5 (pages 3-5 through 3-15, P-15, and P-37

through P-43), and 7) also demonstrates that breathing 1.6 ATA of

O2 for extended periods increases the risk of O2

toxicity compared to breathing 1.4 ATA of O2. The increased

risk of O2 toxicity means that little tolerance exists for

errors in O2 control and delivery equipment (e.g.,

O2 sensors, solenoids) and in calculating O2

exposures.

One commenter (Ex. 2-106) noted that we should consider both

partial pressure and the duration of a dive when determining

O2 exposure limits. Another commenter (Ex. 2-109) maintained

that when they use high-oxygen breathing-gas mixtures, Dixie's

recreational diving instructors and diving guides can dive for longer

periods than when they use air as the breathing gas. Long dive

durations extend a diver's exposure to elevated levels of oxygen,

thereby increasing the diver's risk of developing O2

toxicity, as well as DCS. Regarding the first comment (Ex. 2-106), we

note that the O2 exposure limits specified in the proposed

variance address both duration and level of O2 exposure.

Similarly, in response to the second commenter (Ex. 2-109) we believe

that Conditions C and E in the proposed variance address the concern

about O2 toxicity expressed in Ex. 2-109; these proposed

conditions cited research studies attesting to the safety of breathing

O2 at a partial pressure of 1.40 ATA.

(g) Condition D in the proposal limited the diving depth to ``no

deeper than 130 fsw, or to a maximum oxygen partial pressure delivered

to the diver of 1.40 ATA, whichever is most restrictive.'' The proposed

condition elicited two comments. The first commenter (Ex. 2-99) stated

that the Association of Diving Contractors, a trade association for the

commercial-diving industry, requires decompression chambers at the dive

site for dives deeper than 80 fsw or for dives outside the no-

decompression limits because ``there is still a possibility of a rapid

ascent to the surface and hence, a [risk of AGE] brought on by

eliminated or accelerated decompression [during] the ascent.'' The

second commenter (Ex. 2-113) considered a maximum diving depth of 160

or 170 fsw to be safe.

The proposal reduced the risk of DCS resulting from ``eliminated or

accelerated decompression'' to minimal

[[Page 71250]]

levels by requiring Dixie to ensure that its divers use nationally-

recognized no-decompression diving limits. The proposal lowered the

risk of AGE by including a number of procedural and equipment

requirements (e.g., specified O2 levels in the breathing-gas

mixture and installation of O2 and CO2 sensors)

that would minimize the need to make rapid (emergency) ascents to the

surface during a dive; such ascents can cause AGE by overpressurizing

the lungs. We believe that these proposed requirements would protect

recreational diving instructors from the risks associated with DCS and

AGE as well as, or better than, the provisions of 29 CFR

1910.401(a)(2)(i) (the exemption in OSHA's CDO Standard for

recreational diving instructors who use open-circuit, air-supplied

SCUBA).

We are not extending the depth limit to 160 or 170 fsw because we

believe that doing so would place the diver at increased risk of

nitrogen narcosis (as well as DCS). This increased risk would occur

because the partial pressure of nitrogen in the breathing gas would be

higher at 160-170 fsw than at 130 fsw. Previous research (Exs. 8, 9,

and 10) demonstrates that hyperbaric air has significant narcotic

effects even at 100 fsw or about 4.00 ATA (which is equivalent to a

nitrogen partial pressure of 3.16 ATA). Using 28 percent (28%)

O2 at 130 fsw (equivalent to about 1.40 ATA O2),

the partial pressure of nitrogen would be 3.56 ATA, which is only

slightly above the narcotic threshold specified by the previous

research.

(h) Proposed Condition E established O2-exposure limits

for the breathing-gas mixtures, requiring that divers ``not exceed the

24-hour single-exposure time limits specified by the 1991 NOAA Diving

Manual or other oxygen-exposure limits, such as the Diving Science and

Technology (DSAT) Oxygen Exposure Table, that provide a level of

oxygen-toxicity protection at least equivalent to the level of

protection afforded by the 1991 NOAA Diving Manual.'' The proposed

condition received two comments. One commenter (Ex. 2-98) agreed with

using the NOAA O2-exposure limits and a maximum

O2 partial pressure of 1.4 ATA, stating that these limits

``should not make the probability of oxygen toxicity * * *

significantly different than when breathing air.'' At O2

partial pressures above 1.3 ATA, this commenter recommended using the

exposure durations specified in Table 15-1 of NOAA's 1991 Diving

Manual. According to this commenter, using the NOAA table ``would make

the probability of CNS O2 toxicity [extremely low].'' The

second commenter (Ex. 2-100) asserted that a commercial subsidiary of

the Professional Association of Diving Instructors developed the DSAT

O2-exposure limits. The commenter contended that this

subsidiary is not a recognized research authority and is ``motivated by

profit and not necessarily the public benefit.'' According to this

commenter:

NOAA is a highly regarded and recognized source of diving

research and operational protocol. If oxygen exposure limits are not

to exceed the 24-hour single exposure time limits specified in the

1991 NOAA Diving Manual[,] then citing additional sources of oxygen

exposure limits[] that[,] by default, can only be the same or more

conservative, is unnecessary and likely confusing.

The comments in Ex. 2-98 support the maximum O2-exposure

limit of 1.40 ATA specified in proposed Condition E. We agree with the

commenter that CNS toxicity is the principal basis for specifying

O2 exposure limits; accordingly, we discussed the need to

prevent O2-induced CNS toxicity in detail in the proposed

variance (62 FR 58999-59000).

Regarding the comments in Ex. 2-100, we find that the

O2-toxicity protection afforded to divers by the DSAT tables

under the diving conditions specified in the variance application is at

least equivalent to the level of safety that they get from the

O2-exposure limits specified in the 1991 NOAA Diving Manual.

The rationale provided in the proposed variance, as well as additional

evidence submitted to the record (Exs. 4 and 7), support this

conclusion.

We have deleted the proposed general language that would have

allowed Dixie to use non-NOAA O2-exposure limits (other than

DSAT's) when these limits ``provide a level of oxygen-toxicity

protection at least equivalent to the level of protection afforded by

the 1991 NOAA Diving Manual.'' We believe this provision would

introduce unnecessary uncertainty into the permanent variance when two

adequate sources of O2 limits are already available for

Dixie's use. Accordingly, we have revised this provision so that only

the O2-exposure limits identified in the proposal are

acceptable for the permanent variance; these limits are from the 1991

NOAA Diving Manual, and the Enriched Air Operations and Resources Guide

published in 1995 by the Professional Association of Diving Instructors

(commonly referred to as the ``1995 DSAT Oxygen Exposure Table''). If

other O2-exposure limits become available in the future,

Dixie may request us to amend the permanent variance if it provides

evidence that demonstrates their safety.

(i) Proposed Condition F, which required that ``[n]itrogen shall be

the only inert gas used to obtain the breathing-gas mixture,'' elicited

two comments. One commenter (Ex. 2-103) asserted that recreational

diving instructors and diving guides ``use gas blends to increase

safety,'' implying that we should allow divers to use additional inert

gases in the breathing-gas mixture. The second commenter (Ex. 2-113)

also noted that tri-mix breathing gases (usually consisting of

O2, N2, and He) have been used safely by many

divers.

Dixie proposed to use nitrogen as the only inert gas in the

breathing-gas mixture under the specified conditions encountered by its

divers (i.e., no-decompression dives to depths that do not exceed 130

fsw). We need not consider the use of other inert gases as part of

Dixie's permanent variance because Dixie did not seek our approval for

the use of these gases. In any case, we believe that other inert gases

(e.g., helium) have limited, if any, application under the conditions

of this variance.

(j) Proposed Conditions G, H, and I specified, respectively, the

requirements for: Mixing and analyzing nitrox breathing-gas mixtures;

compressors used to produce the nitrox breathing-gas mixtures; and

SCUBAs exposed to high-pressure (pressures exceeding 300 psi) nitrox

breathing-gas mixtures. These proposed conditions received four

comments. The first commenter (Ex. 2-99) contended that the proposal

did not provide specifications for O2-clean systems and

measurement accuracy, and did not require the delivery of pre-mixed

breathing gas ``from a reliable and competent source with high

standards of documented quality control in place.''

The second commenter (Ex. 2-105) asked: What is the basis for the

O2-cleaning and O2-service requirements and the

300 psi limit; at what minimum O2 level would these

requirements apply; and how does OSHA define ``O2

compatible.'' The commenter agreed with the use of oil-free compressors

for mixing nitrox breathing-gas mixtures. The commenter noted, however,

that employees who use these compressors need proper training and that

``[s]pecial consideration must be given * * * to material use, material

compatibility, system design, cleaning[,] and maintenance.'' The

commenter described several hazards associated with mixing nitrox

breathing gases, including: Partial-pressure blending into cylinders

not prepared properly for O2 service; inducing

O2-enriched breathing-

[[Page 71251]]

gas mixtures into the intake of compressors not designed for this

purpose; and contamination of mixtures with hydrocarbons or oil. The

commenter also recommended that we permit the use of O2

analyzers that involve processes or mechanisms other than fuel-cells

(e.g., gas chromatography, thermal conductivity), stating that such

analyzers are accurate and ``have been in use worldwide for many

years.''

A third commenter (Ex. 2-116) made a number of recommendations to

improve the safety of mixing nitrox breathing gases, including:

Prohibit the use of oil-lubricated air compressors for mixing nitrox

breathing gases containing 22-40 percent (22-40%) O2;

require compressor and filter-system manufacturers to certify that

their equipment is safe for the gases used in the breathing mixtures;

require filter-system manufacturers to certify that the equipment used

to clean air (for mixing with pure O2) produces

O2-compatible breathing gases (i.e., breathing gases with

low hydrocarbon levels); and require Dixie to monitor hydrocarbon

contamination continuously. The commenter also submitted suggested

revisions to the proposed text based on these recommendations.

In reply to the commenters who requested information on which

standards we would use to ensure accurate mixing and decontamination

(especially hydrocarbon removal) of nitrox breathing gases, we note

that Dixie must comply with 29 CFR 1910.101 (Compressed Gases (General

Requirements)) and 29 CFR 1910.169 (Air Receivers), and applicable

provisions of 29 CFR 1910.134 (Respiratory Protection). We agree with

the comment in Ex. 2-105 that Dixie must use only properly trained

personnel to mix breathing gases, and we have revised the permanent

variance accordingly.

To reduce the risk of O2 explosions, proposed Condition

I required that SCUBA using high-O2 breathing-gas mixtures

or pure O2 at pressures exceeding 300 psi be designed for

O2 service. We derived the 300 psi limit by interpolating

between the pressure limit (125 psi) for pure O2 and the

pressure limit (500 psi) for compressed air specified in paragraph

(i)(3) of 29 CFR 1910.430. We note, however, that Sec. 1910.430(i)(1)

requires that equipment using O2 mixtures exceeding 40

percent (40%) O2 by volume be designed for O2

service; this requirement is based on the serious explosion risk

associated with these O2 mixtures. Therefore, to reduce the

risk of an O2 explosion, we have revised the permanent

variance to require that SCUBA using breathing-gas mixtures that exceed

40 percent (40%) O2 by volume at pressures over 125 psi be

designed for O2 service.

The proposed variance explained that an O2 analyzer that

uses a fuel-cell process would be acceptable. However, O2

analyzers based on other processes are also acceptable if they meet the

requirements specified in Conditions 22 and 24(a) of the permanent

variance.

We agree with the commenter in Ex. 2-116 that Dixie must only use

compressors and filters that manufacturers have certified will produce

O2-compatible breathing-gas mixtures and will withstand the

pressures involved. We believe these requirements substantially reduce

the risk of O2-related explosions that can occur while

mixing nitrox breathing gases under high pressure. Accordingly, we have

incorporated these requirements into the permanent variance. Consistent

with existing requirements in our CDO Standard, the permanent variance

also requires an O2-service rating for compressors used for

mixing high-pressure O2 whenever O2 fractions

could exceed 40 percent (40%) by volume, as specified in paragraphs

(i)(1) and (i)(2) of 29 CFR 1910.430.

A fourth commenter (Ex. 2-117) stated that O2 analyzers,

oil-less compressors, and filter-membrane systems are available

commercially, and identified several companies that manufacture this

equipment. These comments demonstrate that Dixie can readily meet the

requirements in the permanent variance to use O2 analyzers,

oil-less compressors, and filter-membrane systems when mixing nitrox

breathing gases for rebreathers.

(k) Proposed Condition J, which identified the no-decompression

limits that Dixie must use, elicited three comments. One commenter (Ex.

2-98) asserted that using high-O2 breathing-gas mixtures and

diving in accordance with the no-decompression limits for air diving

specified in the 1991 NOAA Diving Manual would reduce the risk of

developing DCS. This commenter also recommended comparing other,

``equivalent,'' no-decompression limits to the NOAA limits using a

method that ``give[s] acceptable prediction of DCS probability when

applied to data bases * * * where the dive profile is accurately known

and the outcome (DCS or no DCS) is known.'' The commenter added that

``the employer must show through adequate records that the DCS

incidence using these other procedures [is] acceptably low,'' and

asserted that ``an ongoing evaluation of safety through record keeping

is essential.''

Another commenter (Ex. 2-109) stated that the ``DSAT [no-

decompression air] tables, [which] are based on a shorter tissue half-

time, predict more rapid out-gassing and therefore allow much longer

repetitive dives than the Navy [no-decompression air] tables would

following similar bottom times and surface intervals.'' This commenter

concluded, however, that the DSAT and U.S. Navy no-decompression limits

provide similar levels of diver protection.

The third commenter (Ex. 2-99) noted that the proposal did not

consider ``omitted decompression'' that may occur while instructing and

supervising novice divers. This commenter asserted that novice divers

are ``prone to panic and thus more susceptible to an occurrence that

[may require] * * * a decompression chamber on site.''

Based on these comments, we conclude that the permanent variance

needs to contain specific recommendations for no-decompression limits.

Therefore, we have decided to remove the provision for ``equivalent''

no-decompression limits from the permanent variance. In doing so, we

have carefully reviewed the findings and recommendations of Dr. R. W.

Hamilton et al. in Ex. 4A (``DSAT Recreational Dive Planner:

Development and Validation of No-Stop Decompression Procedures for

Recreational Diving'' or ``the Planner''). Based on evidence cited in

the Planner, we find that the scientific community accepts the DSAT no-

decompression tables; in addition, the program of extensive laboratory

and field testing described in the Planner has demonstrated that the

DSAT no-decompression tables are reliable and valid. Accordingly, the

permanent variance allows Dixie to use the DSAT no-decompression tables

and the no-decompression limits in the 1991 NOAA Diving Manual. Should

other no-decompression limits become available in the future, Dixie may

request us to amend the permanent variance. The application would need

to demonstrate that the alternative no-decompression limits are at

least as protective as the limits specified in the permanent variance.

In an earlier response to the commenter in Ex. 2-109 in paragraph

(d) of Part 1, we stated that NOAA's EAD formula can accurately

estimate the DCS risk associated with nitrox breathing-gas mixtures

based on equivalent nitrogen partial pressures and dive durations used

in air diving. In addition, we disagree with this commenter's

recommendation to adopt the U.S. Navy's no-decompression

[[Page 71252]]

limits. If we were to adopt these limits, we would unnecessarily

restrict a major application of rebreathers (i.e., to use high levels

of O2 in the breathing-gas mixture to extend the diving

duration at a specific depth beyond the duration limit specified for

air).

As previously noted, the commenter in Ex. 2-99 expressed concern

about diving-related incidents among novice divers, and implied that

recreational diving instructors could be placed at risk of DCS or AGE

under these conditions. We find that the risk of DCS is negligible

under these conditions because the recreational diving instructors and

novice divers will be using the NOAA or DSAT no-decompression tables

and, therefore, will have no need to decompress. If a novice diver

panics and makes a rapid ascent to the surface, the recreational diving

instructor has been trained and has the necessary experience to follow

the novice diver to the surface in an orderly fashion, thereby avoiding

AGE.

(l) Proposed Condition K.3, which specified the entries that divers

must make in the diving log, received only one comment (Ex. 2-109).

This commenter asked who would make the entries, stating that

``frequently, other than the paying passengers * * * there is only the

boat captain and the instructor [or] guide.'' Dixie Divers consists of

several small commercial diving businesses that may have difficulty

finding an employee to make entries in the diving log. After we

published the proposed variance, Dixie asked us to revise the proposed

condition to permit non-employees to make entries in the log. In

addition, Dixie asked for a similar revision to proposed Condition L,

which required the employer to verify the availability of treatment

resources for medical emergencies, and to enter the verification in the

diving log. Recognizing that any properly-qualified individual can make

such entries, we have revised these provisions to permit Dixie to use

non-employees to perform these tasks, but only after verifying their

qualifications to do so. As the employer, Dixie will be responsible for

assuring that the entries are made, regardless of who makes them.

(m) Proposed Condition L required that Dixie confirm, on a daily

basis before commencing diving operations, the availability of

resources to treat a diving-related medical emergency, including

``transportation * * * capable of delivering [an injured diver] to the

decompression chamber within two hours of the injury.'' A commenter

(Ex. 2-109) asked, ``Does this imply that if they are told a chamber is

down or the Coast Guard can't confirm readiness, that they'll cancel

the diving for that day?'' This commenter cautioned that ``if an

accident happens after a significant amount of time has passed since

the call, [a decompression chamber] may not be available at that time

[because it's in use or undergoing maintenance].'' Based on these

comments, we have clarified the requirement in the permanent variance

by specifying that Dixie must confirm that the required treatment

resources are ``available during each day's diving operations.''

This commenter (Ex. 2-109) also argued that a decompression chamber

should be within one hour from the dive site, instead of two hours,

because of the ``relatively short distance off-shore that most Florida

diving is done,'' and any ``[t]ime delay in getting an injured diver to

a chamber can severely lessen the chances of full recovery from DCS.''

In reviewing this recommendation, we asked the Divers Alert Network

(DAN) for assistance. DAN is the nation's leading private-sector

organization providing DCS treatment recommendations to recreational

divers and diving guides.

With DAN's assistance, we identified 13 locations in Florida where

suitable decompression chambers (6.0 ATA pressure capability, dual-

lock, multiplace) are available to the public for treating diving-

related medical emergencies. These chambers are in Pensacola, Panama

City, Tallahassee, Gainesville, Jacksonville, Inverness, Orlando,

Tampa, Fort Myers, Miami, Tavernier, Marathon, and Key West. These 13

decompression-facility sites are within two hours transit time of any

diving location in Florida, including off-shore, state-controlled

waters. This transit time assumes the use of surface vehicle

transportation traveling at the maximum legal speed limit, and includes

30 minutes to make land when diving off-shore. In response to the

commenter's statement that increases in treatment delay will ``severely

lessen the chances of full recovery from DCS,'' we sought evidence with

respect to one-hour or two-hour treatment delays from Dr. Edward D.

Thalmann (Ex. 12). Dr. Thalmann is a world-renowned expert in treating

diving-related medical emergencies among recreational divers; he is

also the author of a number of scientific publications that address the

causes and treatment of diving-related medical emergencies, especially

DCS.

In his reply (Ex. 13), Dr. Thalmann compared the risk of AGE and

DCS among recreational divers who breathe air as opposed to nitrox. He

then estimated the maximum delay in decompression treatment that would

not worsen the treatment outcome. Dr. Thalmann noted that AGE is the

most life-threatening diving-related medical emergency that can occur

and that, to treat the most serious cases, a decompression chamber

should be available at the dive site. He recognized that this

recommendation went far beyond our existing requirements for some types

of recreational diving (e.g., recreational diving instruction covered

by paragraph (a)(2)(i) of 29 CFR 1910.401). In this regard, Dr.

Thalmann stated that AGE ``is a rare occurrence and can be avoided with

proper training and experience.'' Dr. Thalmann concluded that AGE ``is

essentially independent of the time at depth'' and that ``there is no

evidence * * * [to] suggest that the occurrence and outcome of [AGE]

would be any different breathing a [n]itrox mixture [other] than air.''

Regarding DCS, Dr. Thalmann asserted that research data show that

the EAD approach (see the discussion above under paragraph (d) of Part

1) is valid for computing no-decompression limits for O2

partial pressures as high as 1.5 ATA. Based on this research and his

field experience, Dr. Thalmann stated that DCS associated with

breathing a nitrox gas mixture ``should not be substantially different

in incidence and severity compared to diving on air[,] provided the

[n]itrox no-decompression times are computed from accepted air no-

decompression limits using the [NOAA's] EAD [formula].'' Dr. Thalmann

concluded that, within these constraints, ``there is no rationale for

having different requirements for recompression chamber availability

for air and [n]itrox no-decompression diving.''

In addressing treatment delay, Dr. Thalmann reviewed available

research studies, as well as data from DAN. According to Dr. Thalmann,

the DAN data ``apply to recreational diving only where the vast

majority of diving is within no-decompression limits.'' The results

show that, for both pain-only DCS and DCS with severe neurological

symptoms, a treatment delay of four hours can occur without diminishing

treatment success (i.e., complete relief of symptoms). In conclusion,

Dr. Thalmann stated, ``There is no significant body of evidence to

suggest that, so long as one is diving within accepted no-decompression

limits breathing air or [n]itrox, having access to a recompression

facility within 4 hours is inadequate.''

Dr. Thalmann's reply demonstrates several points: (1) The risk of

AGE and DCS while breathing air or a nitrox gas

[[Page 71253]]

mixture should not differ when the dive conforms to accepted no-

decompression limits computed using the EAD approach; (2) maintaining a

decompression chamber at the dive site to treat AGE is unnecessary and

impractical because AGE is a rare occurrence that proper training and

diving experience can prevent; and (3) as much as a four-hour delay in

treating DCS does not diminish treatment outcomes. Based on this

evidence, as well as a complete review of the existing record, we have

decided to keep the provision permitting a two-hour timeframe for

treating DCS, as proposed by Dixie.

As part of his reply, Dr. Thalmann also recommended that we revise

the phrase ``within two hours of the injury'' in proposed Condition L.1

to read ``[2] hours after it is recognized that symptoms of [a

decompression incident] are present.'' We acknowledge that the proposed

language was unclear, but we also believe that the recommended wording

may be confusing as well. Therefore, we have adopted new language in

the permanent variance that expresses the requirement in terms of the

maximum delay permitted in transporting the injured diver to a suitable

decompression chamber; the revised language reads, ``* * * within two

(2) hours travel time from the dive site.''

(n) Proposed Condition N specified that Dixie was responsible for

initial treatment of diving-related medical emergencies, and that it

had to ensure that ``two personnel, one of whom shall be a diver

employed by [Dixie] and both of whom are qualified in first-aid and the

administration of treatment oxygen'' were available at the dive site

for this purpose. Two commenters responded to this provision. The first

commenter (Ex. 2-100) stated that the provision appears to be ``an

attempt by Dixie Divers * * * to use the process to gain an unfair

advantage in the recreational diving market by requiring all diving

operations to contract with a `diver employed by the applicant.' '' The

second commenter (Ex. 2-109) asserted that this requirement would be

difficult to satisfy because the ``typical crew on a Florida boat is

[a] captain and instructor.'' Dixie, as a small business with few

employees, supported the second commenter's assertion, and requested

that it be permitted to use qualified non-employees to meet this

requirement.

In reply to these comments, we note that Dixie and all other

employers engaged in commercial diving operations must already provide,

as appropriate, on-site support personnel to perform a variety of tasks

(see, e.g., the requirements in paragraph (c) of 29 CFR 1910.410 and

paragraph (c)(2) of 29 CFR 1910.426). These personnel can also perform

duties as specified in proposed Condition N. We recognize, however,

that the main purpose of this provision is to ensure that properly-

qualified personnel are available, regardless of their employment

status. Therefore, we have revised this provision to permit Dixie to

use non-employees for first-aid and O2 treatment. However,

Dixie may do so only if it verifies their qualifications to perform

these tasks before it starts the day's diving operations.

(o) Proposed Condition O specified the training requirements for

Dixie's recreational diving instructors and diving guides, including

the requirement that an industry-recognized training agency certify

that the divers are capable of using the diving equipment and

breathing-gas mixtures needed for their recreational diving operations.

The National Association of Underwater Instructors (NAUI) (Ex. 2-100)

noted its affiliates offer ``a full range of training programs from

Skin Diver through Instructor Course Director, including certification

in oxygen enriched air, semi-closed circuit and closed circuit

rebreather diver.'' Nonetheless, NAUI found the proposed condition

ambiguous because it ``does not provide a definition of the diving

industry or outline any process or criteria to evaluate and recognize a

training agency that would establish the legitimacy of its training.''

We agree with NAUI's comment that this provision in the proposed

variance was confusing. Additionally, we believe that an employer is in

the best position to determine if the training that its divers obtain

is adequate to perform their jobs safely and effectively. Therefore, we

have revised the proposed provision and have made the training

requirement in the permanent variance performance-based; that is, Dixie

must ensure that its employees receive training that enables them to

perform safely and effectively while using open-circuit SCUBAs or

rebreathers supplied with nitrox breathing-gas mixtures. However, we

specified several critical tasks that the recreational diving

instructors and diving guides employed by Dixie must be trained to

perform safely and effectively, including: Recognizing the effects

associated with breathing excessive CO2 and O2;

taking appropriate action after detecting the effects of breathing

excessive CO2 and O2; and properly evaluating,

operating, and maintaining their open-circuit SCUBAs and rebreathers.

We addressed the importance of recognizing and responding properly to

the effects of excessive CO2 and O2 in our

earlier discussions of Conditions A.2 and E of the proposed variance.

Based on our review of Ex. 5 (especially pages 11-1 through 11-15), we

believe that divers must also know how to evaluate, operate, and

maintain their rebreathers under the diving conditions that they

encounter as recreational diving instructors and diving guides. We have

specified these revisions in Condition 38 of the permanent variance.

Part 3. Comments to Proposed Section III (Rationale for the Proposed

Alternative)

(a) In discussing Conditions A and B in the proposed variance, we

noted that the existing exemption for recreational diving instructors

in paragraph (a)(2)(i) of 29 CFR 1910.401 in our CDO Standard does not

refer to rebreathers. We explained that ``such equipment was not

available or in common use by recreational diving instructors when

OSHA's [CDO] Standard was promulgated in 1977'' (62 FR 58999, first

column). A commenter (Ex. 2-109) noted that this statement gave the

false impression that rebreather equipment ``is readily used by the

recreational diving community.'' Regarding the experience of the

recreational diving community with rebreathers, this commenter asserted

that ``while the argument can be made that [rebreathers have] been used

safely within the scientific and commercial diving industries, it can

also be argued that those divers are more highly trained and the

operations more closely monitored than is the norm in the recreational

diving industry.''

Our discussion of the rationale for Conditions A and B as proposed

noted that ``data related to the reliability and safety of [rebreather

equipment] are difficult to obtain because its use by recreational

divers is still uncommon''; however, we now believe that data are

available showing that recreational diving instructors and diving

guides can use rebreathers safely and reliably. We revised our opinion

after reviewing Ex. 5 (especially pages 2-2, 7-1, and 7-2), which shows

that various military organizations have a 50-year history of using

rebreathers safely, scientific and technical divers have been doing so

for over 20 years, and, currently, recreational diving instructors and

diving students safely perform rebreather diving. We believe,

therefore, that we have sufficient knowledge about rebreather

technology and diving procedures to determine that the conditions

specified in the permanent

[[Page 71254]]

variance will protect Dixie's recreational diving instructors and

diving guides at least as well as having an on-site decompression

chamber.

(b) The rationale for proposed Conditions C through E justified the

use of DSAT's Oxygen Exposure Table (62 FR 58999, second and third

columns). This rationale elicited one comment (Ex. 2-109). This

commenter stated that specifying time limits in the DSAT Oxygen

Exposure Table in terms of total dive time ``is * * * a very common

industry practice and not some great concession on Dixie's part, as the

wording of the sentence would perhaps lead you to believe.'' In this

case, we agree that the use of a common industry practice will enable

Dixie to comply with the permanent variance without additional effort,

while providing adequate diver protection.

(c) Proposed Condition K provided a rationale for using dive-

decompression computers, noting that no-decompression limits for

repetitive dives can involve ``tedious and time-consuming calculations

* * * made by hand.'' It concluded that dive-decompression computers

would ``assist divers in decreasing their exposure to excessive ascent

rates, oxygen toxicity, and DCS that could result from errors in

calculating repetitive no-decompression diving schedules manually.''

(62 FR 59000, third column.) The single commenter (Ex. 2-109) on this

point claimed that manual calculations ``[can be] taught in the first

or second lecture of most entry-level [SCUBA] classes'' and performed

in a couple of minutes. This commenter also asserted that manual

calculations may provide an additional margin of safety from DCS

because they typically determine decompression using the deepest depth

attained during a dive. By contrast, dive-decompression computers may

reduce decompression (and therefore increase the risk of DCS) by

``measur[ing the] exact depth every few seconds and recalculat[ing

decompression] based on actual depth.''

In reply, we note that Condition K as proposed allowed Dixie the

flexibility to use either manual calculations or dive-decompression

computers. Nevertheless, manual calculation is subject to human error,

and computer use can reduce such error. The permanent variance will

reduce problems associated with using dive-decompression computers to

avoid decompression by restricting the no-decompression limits to the

most recent decompression tables and formulas published by NOAA and

DSAT.

(d) The rationale for proposed Conditions O and P addressed the

requirements for diver certification, noting that ``Condition O

provides general uniformity to the diver qualification and training

process, as well as quality control over the certifying agencies.'' (62

FR 59001, third column.) A commenter (Ex. 2-109) stated that the

certification requirement imposed no burden on Dixie because it was

consistent with existing industry practice; in addition, the

requirement was unlikely to bring uniformity to diver qualifications

because ``different dive stores, certifying under the same national

standards, can still turn out divers [and] instructors of varying

proficiency levels.'' In reply, we note that we do expect these

requirements to make training programs more uniform (than is presently

the case) in the way that they train recreational diving instructors

and diving guides, and this uniformity should substantially reduce much

of the variability in diver proficiency.

Part 4. Comments to Proposed Section VI (Issues)

In the proposal, we invited the public to submit information and

specific comments and rationale on nine other issues. Only one

commenter (Ex. 2-109) did so. This commenter addressed the first issue,

which requested commenters to differentiate the underwater tasks and

types of diving performed by recreational diving instructors and diving

guides, and to relate these differences to the probability of

experiencing diving-related medical problems. The commenter stated

that, during training dives, recreational diving instructors ``will

probably do multiple ascents * * * but may be exposed to less time in

the water than a dive guide since students generally are excited and

[consume more air] than experienced divers.'' The commenter stated

that, during the ascent-training phase, recreational diving instructors

must ``make multiple, generally rapid, ascents with each of the

students, increasing the chances of a DCS hit.'' The commenter added

that recreational diving instructors are ``at a slightly greater risk

[than diving guides] of AGE from the ascents and perhaps a slightly

elevated chance of DCS due to rapid ascents,'' although ``[t]he

likelihood of the instructor getting DCS or AGE * * * is probably

extremely small.''

Regarding diving guides, the commenter asserted that it escorts

experienced divers who, typically, are less excitable than novice

divers; based on this assumption, the commenter asserted that

experienced divers would consume breathing gases at slower rates than

novice divers. The commenter concluded that slow rates of gas

consumption would extend dive durations which, combined with the deeper

dives made by diving guides compared to recreational diving

instructors, would increase the diving guides' risk of DCS. In response

to this commenter, we refer to our earlier discussion of this issue in

Part I. In this discussion, we agreed that ``using high-O2

nitrox breathing-gas mixtures would increase the risk of DCS,'' but

concluded that ``the resulting risk would be comparable to using the

equivalent partial pressure of nitrogen in air for that extended

period.''

Part 5. General Comments to the Proposed Variance

One commenter (Ex. 2-105) indicated that a number of topics needed

clarification or were ``so controversial or comprehensive in nature

that this level of detail in a policy document may not be

appropriate.'' These areas are: Validating dive-decompression

computers, including the programmable safety factors used in these

computers; updating decompression data; identifying programmable gas-

percentage options; using failure mode and effects analysis of critical

components and assemblies to develop consensus regarding the general

safety and accuracy of dive-decompression computers; determining the

relevance of, and necessity for, monitoring environmental temperatures

and the breathing-loop gases in closed-circuit rebreathers; and

recognizing standards developed by the equipment manufacturers. The

commenter stated that ``[t]o expand on just a few of [these areas]

would make this document much [too long].'' Nevertheless, the commenter

asserted, without explanation, that ``from a standpoint of technical

diving facts [the proposed variance] is grossly inaccurate and in many

cases written with twisted facts,'' and that the ``[proposed] variance

as written has the potential to expose employees (i.e.[,] dive shop

technicians, instructors) to dangerous situations.''

In large part, these areas of concern address the safety and

standardization of dive-decompression computers. Under the permanent

variance, use of dive-decompression computers is optional; however, if

Dixie uses these computers, it must also provide its divers with

specific decompression information. Regardless of computer use or

availability, Dixie must have hard-copy decompression tables at the

dive site. Thus, the permanent variance specifies the conditions that

Dixie must meet to ensure that its employees' diving activities conform

to accepted

[[Page 71255]]

no-decompression practices, whether or not Dixie uses dive-

decompression computers.

Another commenter (Ex. 2-109) stated that ``[t]o retailers * * *

nitrox is marketed as a new profit center. In an industry with flat

growth over the past few years, and where profit margins are small to

begin with, nitrox * * * can be sold to the diving consumer as a

`safer' alternative to air, thus generating more profits * * * through

the sale of classes and equipment specific to nitrox.'' Regarding

diving safety, this commenter asserted that the high level of diving

skills acquired by commercial divers made them safer than recreational

diving instructors and diving guides, and referred to statistics from

the Divers Alert Network (DAN) to support this assertion:

[T]he statistics [for 1996] show that 0.2% of the reported accidents

involved commercial divers, but 17.1% of the accidents involved

Instructors or Divemasters (dive guides). The latter are the same two

categories * * * who make up Dixie Diver's employees who would be

exempt under the variance. In 1995, the numbers were 0.5% for

commercial divers versus 15.9% for instructors[-] divemasters. In 1994,

the numbers were 0.0% for commercial divers and 21.5% for instructors[-

]divemasters.

The statistics cited by this commenter do not address the principal

conditions specified in the permanent variance (i.e., recreational

diving instructors and diving guides who make no-decompression dives

using nitrox breathing-gas mixtures). In a recent editorial in Alert

Diver (Ex. 16, page 2), DAN's director (Dr. Peter B. Bennett) addressed

the safety of nitrox dives made by recreational divers (which includes

sports divers, as well as recreational diving instructors and diving

guides). Dr. Bennett stated that ``[b]etween 1990 and 1993 DAN

collected data on 21 cases of mixed-gas diving injuries. In 1994 there

were 10, and in 1996, 16 injuries occurred. The 1996 data [are] based

on 23 nitrox or mixed-gas injuries requiring recompression treatment. *

* * The International Association of Nitrox and Technical Divers * * *

certified 17,780 U.S. nitrox divers from 1985 to 1996.'' Based on this

information, an average of less than 0.001 per cent of recreational

divers who use nitrox breathing-gas mixtures are injured each year.

Additionally, both Dr. Bennett (Ex. 16, pages 2 and 6) and other DAN

representatives (Ex. 4A, page 60) admit that valid comparisons cannot

be made between different categories of divers because adequate

baseline data (e.g., the number and types of dives made by all divers

in a category) are not available. In conclusion, we believe that the

protections afforded by the conditions specified in the permanent

variance will reduce the prevalence of diving-related injuries among

Dixie's recreational diving instructors (who also have substantial

experience in using nitrox breathing-gas mixtures) below the already

low injury rates cited in Dr. Bennett's editorial.

Part 6. Our Revisions to the Proposed Variance

(a) When divers use rebreathers, proposed Condition A.4 provided

for a supplemental supply of breathable gas during emergency egress

(referred to as the ``bail-out system''); this supply would consist of

a diluent breathing gas connected to the second stage of the regulator.

We have added a phrase to the permanent variance to address alternative

means of emergency egress when open-circuit SCUBA provides the nitrox

breathing-gas mixture. It allows Dixie to use the reserve breathing-gas

supplies specified in paragraph (c)(4) of 29 CFR 1910.424 for this

purpose. This alternative, specified in Condition (30)(b)(i) in the

permanent variance, is an existing requirement for open-circuit SCUBA.

When the bail-out system consists of a separate supply of emergency

breathing gas, Condition A.1 of the proposed variance permitted Dixie

to use air as the emergency breathing gas. The permanent variance

retains this provision.

(b) Conditions A.5.a and A.5.b in the proposed variance specified

the use of an information module that provides time, depth, ascent, and

descent data to divers who use closed-circuit rebreathers, and time,

ascent, and descent information to divers who use semi-closed-circuit

rebreathers. Proposed Condition A.5.c required both types of

rebreathers to have alarms or visual displays that warn the diver about

excessive ascent and descent rates, as well as depth levels that are

shallower than the ceiling-stop depth. While Dixie's recreational

diving instructors and diving guides could use dive-decompression

computers for this purpose, we believe that such computers are

unnecessary because the divers will be diving within no-decompression

limits, and the technical capability of dive-decompression computers

exceeds the requirements of no-decompression dives. An information

module that provides the divers with the specified dive information

will permit them to remain within no-decompression limits and to

descend and ascend the water column at the rates specified by the

diving tables. We believe, therefore, that the information module will

ensure that Dixie's divers remain as safe as they would if they used

dive-decompression computers.

(c) Proposed Condition A.5.c also requires that, for both semi-

closed-circuit and closed-circuit rebreathers, the information module

must warn the diver of low battery voltage. As noted in Ex. 5 (page P-

59), a partial or total electronic failure interferes with sensor and

control systems and may have serious safety consequences for the diver.

We believe that the diver's safety depends on properly-operating

electrical power supplies and electrical and electronic circuits.

Accordingly, we have revised the proposal by requiring that Dixie

perform the following procedure: ``Before each day's diving operations,

and more often when necessary, * * * ensure that the electrical power

supplies and electrical and electronic circuits in each rebreather are

operating as required by the rebreather manufacturer's instructions.''

Condition (12) of the permanent variance contains this revision.

(d) Proposed Conditions B.1 and G.1.c addressed O2

sensor and control requirements for closed-circuit rebreathers.

Conditions (13) through (17) in the permanent variance consolidate

these requirements in a single location.

(e) For closed-circuit rebreathers, proposed Condition G.1.c

specifies the use of O2 sensors to assess the O2

fraction in the breathing loop, while proposed Condition G.1.d requires

Dixie to determine (i.e., calibrate) sensor accuracy according to the

rebreather manufacturer's instructions. As noted in the proposal,

maintaining accurate O2 partial pressures in the breathing

loop is critical to diver health and safety. To assure safe operation

of O2 sensors, we believe that the permanent variance must

specify the frequency for assessing the accuracy of O2

sensors. Such an approach is consistent with the rebreather community's

use of regular diving-equipment assessments (see Ex.5, pages 4-1

through 4-13, and 14-2). Condition (15) of the permanent variance,

therefore, requires that ``[b]efore each day's diving operations, and

more often when necessary, [Dixie] must calibrate O2 sensors

as required by the sensor manufacturer's instructions[.]'' Removing

inaccurate O2 sensors from service and replacing them with

correctly-calibrated sensors is a logical and expected consequence of

the calibration process; we are specifying this requirement in

Conditions (15)(d) and (15)(e) of the permanent variance.

[[Page 71256]]

(f) Proposed Condition G.1.c accepted O2 sensors only if

they were electromechanical. Evidence in the record (Ex. 5, page 5-11)

indicates that O2-sensor technology is undergoing continued

development and refinement. We believe, therefore, that specifying

``electromechanical'' O2 sensors is too limiting, and we

have revised this provision to specify that Dixie must use

O2 sensors approved by the rebreather manufacturer (see

Condition (14)(b) in the permanent variance).

(g) Condition G.1.d in the proposed variance required Dixie to

maintain the accuracy of the equipment used to analyze O2 in

the breathing-gas mixture ``in accordance with the manufacturer's

instructions.'' We intended this requirement to apply to the analytic

equipment used both to calibrate O2 sensors and to determine

the O2 fraction in nitrox breathing-gas mixtures. To clarify

this intention, we have included the requirement separately in

Conditions (15)(b) and (22)(b) in the permanent variance.

(h) We have clarified the provision in proposed Condition G.2.a

that addressed the analysis of O2 in nitrox breathing-gas

mixtures obtained from commercial suppliers. This revision requires

Dixie to ensure that the supplier of the mixture analyzes the

O2 fraction in the mixture in the charged tank after

disconnecting the tank from the charging apparatus. This clarification

prevents the supplier from using the O2 sensor on the

charging apparatus for this purpose, a procedure that could result in

an incorrect determination. The revised provision is in Condition

(23)(b) of the permanent variance.

(i) Proposed Conditions K.3 and K.4 required that Dixie maintain a

diving log and decompression tables at the dive site. The diving log

documents the critical dive parameters. Divers who do not use dive-

decompression computers must use the decompression tables; the tables

also serve as a back-up resource to divers with dive-decompression

computers. We have revised the proposed conditions to ensure that Dixie

maintains a diving log and decompression tables at the dive sites for

all diving operations covered by the permanent variance, whether or not

its divers use a dive-decompression computer. The revised provision

also clarifies that the decompression tables must be hard copies and

conform to the no-decompression limits specified in Condition (28) of

the permanent variance. Condition (37) of the permanent variance

contains the revised requirements.

(j) Regarding the term ``portable oxygen,'' proposed Condition M

specified that ``the oxygen shall be available for administration to

the diver during the entire period the diver is being transported to a

decompression chamber.'' The O2 supplied for this purpose

must be pure O2, and the injured diver must receive the

O2 continuously from the time Dixie detects the diving-

related medical emergency until the diver begins treatment in a

decompression chamber. We have revised the proposal to clarify these

requirements. Therefore, Condition (33) in the permanent variance

requires Dixie to ensure that the portable O2 equipment

supplies pure O2 to the injured diver's transparent mask,

and that sufficient O2 is available to treat injured divers

until they reach a decompression chamber.

(k) In the proposed variance, one provision (Condition G.1.d)

required Dixie to maintain the accuracy of the equipment used to

analyze the O2 fraction of the breathing gas ``in accordance

with the manufacturer's instructions.'' To clarify which manufacturer

is being addressed in this provision, we revised the relevant

conditions of the permanent variance (Conditions (15)(b) and (22)(b))

to refer specifically to the manufacturer of the O2 analyzer

(who seems to us to be in the best position to specify how its

O2 analyzer should be calibrated). We have made similar

revisions to other provisions of the permanent variance, including

Condition (9) (which specifies calibration requirements for

CO2 sensors) and to Condition (15) (which specifies the

calibration requirement for O2 sensors).

The permanent variance contains a general requirement (Condition

(3)) to use rebreathers according to the manufacturer's instructions.

We repeat this requirement in several other important conditions of the

permanent variance. We have added this provision because SCUBA

manufacturers select and develop the characteristics and parameters of

SCUBA equipment, design and integrate the equipment accordingly,

procure or manufacture the equipment components, and then assemble and

test the final products. There is a wide range of SCUBA designs and

capabilities, and there are no uniform standards for the design,

function, and use of SCUBA. We believe, therefore, that the SCUBA

manufacturer is in the best position to specify the components,

configuration, and operation of its product. In addition, the

rebreather conference held recently in Redondo Beach, California,

recommended that ``[m]anufacturers must provide written procedures, pre

and post dive checklists, and a schedule for required maintenance.''

The SCUBA manufacturers who attended the conference endorsed this

recommendation (see Ex. 5, page 14-2).

V. Decision

Dixie Divers, Inc. seeks a permanent variance from the

decompression-chamber requirements of paragraphs (b)(2) and (c)(3)(iii)

of 29 CFR 1910.423 and paragraph (b)(1) of 29 CFR 1910.426. These

provisions require an employer to have a decompression chamber

available and ready for use at the dive site to treat two diving-

related medical emergencies that employees may experience--

decompression sickness (DCS) and arterial-gas embolism (AGE). Divers

may develop DCS after decompressing inadequately during dives in which

they breathe a mixed gas (e.g., nitrox). AGE results from

overpressurizing the lungs, usually during a rapid ascent to the

surface; overpressurization causes the air sacs in the lungs to rupture

and disperse bubbles into the pulmonary veins.

These decompression-chamber provisions require employers to ensure

that: Employees remain awake and in the vicinity of a decompression

chamber for at least one hour after the dive whenever they make no-

decompression dives, dive to depths deeper than 100 feet of sea water,

or use a mixed-gas breathing mixture (paragraph (b)(2) of 29 CFR

1910.423); and a decompression chamber is located within five minutes

from the dive site and is ready for use (paragraph (c)(3)(iii) of 29

CFR 1910.423 and paragraph (b)(1) of 29 CFR 1910.426).

In its variance application, Dixie stated that nitrox breathing-gas

mixtures reduce the occurrence and severity of DCS, while the equipment

and procedural safeguards specified in the variance application lower

the risk of AGE. (See section II, ``Application for a Permanent

Variance,'' of this notice for a thorough review of Dixie's variance

application.) Dixie asserted that the risk of DCS and AGE for divers

who use the SCUBA equipment and diving procedures proposed in the

variance application would be equal to, or less than, that experienced

by divers exempted from our CDO Standard. This exemption, specified in

paragraph (a)(2)(i) of 29 CFR 1910.401, applies to recreational diving

instructors who use compressed air supplied to open-circuit SCUBAs

under no-decompression diving limits. Dixie concluded, therefore, that

we should not require it to maintain a decompression chamber at the

dive site if it complies with the

[[Page 71257]]

conditions proposed in the variance application.

After reviewing the variance application, comments made to the

record about the application, and other technical and scientific

information submitted to the record, we have revised the proposed

variance to require Dixie to use specific procedures and equipment

safeguards for its divers when they engage in recreational diving

instruction and perform services as diving guides. Therefore, under

Sec. 6(d) of the OSH Act, and based on the record discussed above, we

find that when Dixie complies with the conditions of the following

order, its divers will be exposed to working conditions that are at

least as safe and healthful as they would be if Dixie complied with

paragraphs (b)(2) and (c)(3)(iii) of 29 CFR 1910.423 and paragraph

(b)(1) of 29 CFR 1910.426.

VI. Order

We issue this order authorizing Dixie Divers, Inc. to comply with

the following conditions instead of complying with paragraphs (b)(2)

and (c)(3)(iii) of 29 CFR 1910.423 and paragraph (b)(1) of 29 CFR

1910.426:

Application of the Permanent Variance

(1) This permanent variance applies only to the recreational diving

instructors and diving guides (``divers'') employed by Dixie Divers,

Inc. (designated as ``you'' or ``your'') when your:

(a) Recreational diving instructors train diving students in the

use of recreational diving procedures and the safe operation of diving

equipment, including open-circuit, semi-closed-circuit, or closed-

circuit self-contained underwater breathing apparatus (SCUBA) during

these training dives;

(b) Diving guides lead small groups of trained sports divers who

use open-circuit, semi-closed-circuit, or closed-circuit SCUBAs to

local undersea diving locations for recreational purposes; and

(c) Divers use a nitrox breathing-gas mixture consisting of a high

percentage of oxygen (O2) (i.e., over 22 percent (22%) by

volume) mixed with nitrogen and supplied by an open-circuit, semi-

closed-circuit, or closed-circuit SCUBA.

(2) This permanent variance does not apply when your divers engage

in diving activities other than recreational diving instruction or

diving guide duties.

Equipment Requirements for Rebreathers

(3) You must ensure that your divers use rebreathers (i.e., semi-

closed-circuit and closed-circuit SCUBAs) in accordance with the

rebreather manufacturer's instructions.

(4) Regarding CO2-sorbent materials in canisters:

(a) You must ensure that each rebreather uses a manufactured (i.e.,

commercially pre-packed), disposable scrubber cartridge containing a

CO2-sorbent material that:

(i) Is approved by the rebreather manufacturer;

(ii) Removes CO2 from your divers' exhaled gas; and

(iii) Maintains the CO2 level in the breathable gas

(i.e., the gas that your divers are inhaling directly from the

regulator) below a partial pressure of 0.01 atmospheres absolute (ATA);

or

(b) You may use an alternative scrubber method if:

(i) The rebreather manufacturer permits such use;

(ii) You use the alternative method according to the rebreather

manufacturer's instructions; and

(iii) You demonstrate that the alternative method meets the

requirements specified above in Condition (4)(a) of this order.

(5) You must ensure that each rebreather has a counterlung that

supplies a volume of breathing gas to your divers that is sufficient to

sustain their respiration rate and contains an over-pressure valve.

(6) You must ensure that each rebreather uses a moisture trap in

the breathing loop, and that the moisture trap and its location in the

breathing loop are approved by the rebreather manufacturer.

(7) You must ensure that each rebreather has a continuously-

functioning moisture sensor that connects to a visual (e.g., digital,

graphic, or analog) or auditory (e.g., voice, pure tone) alarm that

warns your divers of moisture in the breathing loop in sufficient time

to terminate the dive and return safely to the surface.

(8) You must ensure that each rebreather contains a continuously-

functioning CO2 sensor in the breathing loop, and that the

CO2 sensor and its location in the breathing loop are

approved by the rebreather manufacturer. You must also integrate the

CO2 sensor used in a rebreather with an alarm that:

(a) Operates in a visual (e.g., digital, graphic, or analog) or

auditory (e.g., voice, pure tone) mode;

(b) Is readily detectable by your divers under the diving

conditions in which they operate; and

(c) Remains continuously activated when the inhaled

CO2 level reaches and exceeds 0.005 ATA.

(9) Before each day's diving operations, and more often when

necessary, you must calibrate the CO2 sensor according to

the sensor manufacturer's instructions. In doing so, you must:

(a) Ensure that the equipment and procedures used to perform this

calibration are accurate to within 10 percent (10%) of a CO2

concentration of 0.005 ATA or less;

(b) Maintain this accuracy as required by the sensor manufacturer's

instructions;

(c) Ensure that the calibration of the CO2 sensor

demonstrates an accuracy to within 10 percent (10%) of a CO2

concentration of 0.005 ATA or less;

(d) Replace the CO2 sensor when it fails to meet the

accuracy requirements specified above in Condition (9)(c) of this

order; and

(e) Ensure that the replacement CO2 sensor meets the

accuracy requirements specified above in Condition (9)(c) of this order

before you place a rebreather in operation.

(10) As an alternative to using a continuously-functioning

CO2 sensor, you may use schedules for replacing

CO2-sorbent material provided by the rebreather

manufacturer. You may use these CO2-sorbent replacement

schedules only if:

(a) The rebreather manufacturer has:

(i) Developed the replacement schedules according to the canister-

testing protocol provided below in Appendix A of this order;

(ii) Analyzed the canister-testing results using the statistical

procedures described in U.S. Navy Experimental Diving Unit Report 2-99

(see section VII (``References'') below); and

(iii) Specified the replacement schedule in terms of the lower

prediction line (or limit) of the 95% prediction interval. In this

regard, the rebreather manufacturer may derive replacement schedules by

interpolating among, but not by extrapolating beyond, the depth, water

temperatures, and exercise levels used during canister testing; and

(b) You replace the CO2-sorbent material in the canister

as required by Condition (4) of this order.

(11) You must ensure that each rebreather has an information module

that provides:

(a) Visual (e.g., digital, graphic, or analog) or auditory (e.g.,

voice, pure tone) displays that will effectively warn your divers of

solenoid failure (when the rebreather uses solenoids) and other

electrical weaknesses or failures (e.g., low battery voltage);

(b) For semi-closed circuit rebreathers, visual displays for the

partial pressure of CO2, or deviations

[[Page 71258]]

above and below a preset CO2 partial pressure of 0.005 ATA;

and

(c) For closed-circuit rebreathers:

(i) Visual displays for the partial pressures of O2 and

CO2, or deviations above and below a preset CO2

partial pressure of 0.005 ATA and a preset O2 partial

pressure of 1.40 ATA; and

(ii) A visual display for the gas temperature in the breathing

loop.

(12) Before each day's diving operations, and more often when

necessary, you must ensure that the electrical power supplies and

electrical and electronic circuits in each rebreather are operating as

required by the rebreather manufacturer's instructions.

Special Requirements for Closed-Circuit Rebreathers

(13) You must ensure that closed-circuit rebreathers use supply-

pressure sensors for the O2 and diluent (i.e., air or

nitrogen) gases and continuously-functioning sensors for detecting

temperature in the inhalation side of the gas-loop and the ambient

water.

(14) You must ensure that:

(a) At least two O2 sensors are located in the

inhalation side of the breathing loop;

(b) The O2 sensors are continuously-functioning,

temperature-compensated, and approved by the rebreather manufacturer.

(15) Before each day's diving operations, and more often when

necessary, you must calibrate O2 sensors as required by the

sensor manufacturer's instructions. In doing so, you must:

(a) Ensure that the equipment and procedures used to perform the

calibration are accurate to within 1 percent (1%) of the O2

fraction by volume;

(b) Maintain this accuracy as required by the manufacturer of the

calibration equipment;

(c) Ensure that the sensors are accurate to within 1 percent (1%)

of the O2 fraction by volume;

(d) Replace O2 sensors when they fail to meet the

accuracy requirements specified above in Condition (15)(c) of this

order; and

(e) Ensure that the replacement CO2 sensors meet the

accuracy requirements specified above in Condition (15)(c) of this

order before you place a rebreather in operation.

(16) You must ensure that closed-circuit rebreathers have:

(a) A gas-controller package with electrically-operated solenoid

O2-supply valves;

(b) A pressure-activated regulator with a second-stage diluent-gas

addition valve;

(c) A manually-operated gas-supply bypass valve to add

O2 or diluent gas to the breathing loop; and

(d) Separate O2 and diluent-gas cylinders to supply the

breathing-gas mixture.

O2 Concentration in the Breathing Gas

(17) You must ensure that the fraction of O2 in the

nitrox breathing-gas mixture:

(a) Is greater than the fraction of O2 in compressed air

(i.e., exceeds 22 percent (22%) O2 by volume);

(b) For open-circuit SCUBA, never exceeds a maximum fraction of

breathable O2 of 40 percent (40%) by volume or a maximum

O2 partial pressure of 1.40 ATA, whichever exposes your

divers to less O2; and

(c) For rebreathers, never exceeds a maximum O2 partial

pressure of 1.40 ATA.

Depth and O2 Partial Pressure Limits

(18) Regardless of the diving equipment your divers use, you must

ensure that they dive no deeper than 130 feet of sea water (fsw) or to

a maximum O2 partial pressure of 1.40 ATA, whichever exposes

them to less O2.

(19) Regarding O2 exposure, you must:

(a) Ensure that the exposure of your divers to partial pressures of

O2 between 0.60 and 1.40 ATA does not exceed the 24-hour

single-exposure time limits specified either by the 1991 National

Oceanic and Atmospheric Administration Diving Manual (the ``1991 NOAA

Diving Manual'') or by the report entitled Enriched Air Operations and

Resources Guide, published in 1995 by the Professional Association of

Diving Instructors (known commonly as the ``1995 DSAT Oxygen Exposure

Table'') (see section VII (``References'') below); and

(b) Determine your diver's O2-exposure duration using

the diver's maximum O2 exposure (partial pressure of

O2) during the dive and the total dive time (i.e., from the

time the diver leaves the surface until the diver returns to the

surface).

Mixing and Analyzing the Breathing Gas

(20) You must ensure that only properly trained personnel mix

nitrox breathing gases, and that nitrogen is the only inert gas used in

the breathing-gas mixture.

(21) When mixing nitrox breathing gases, you must mix the

appropriate breathing gas before you deliver the mixture to the

breathing-gas cylinders, using the continuous-flow or partial-pressure

mixing techniques specified in the 1991 NOAA Diving Manual, or using a

filter-membrane system.

(22) Before the start of each day's diving operations, you must

determine the O2 fraction of the breathing-gas mixture using

an O2 analyzer. In doing so, you must:

(a) Ensure that the O2 analyzer is accurate to within 1

percent (1%) of the O2 fraction by volume; and

(b) Maintain this accuracy as required by the manufacturer of the

analyzer.

(23) When the breathing gas is a commercially-supplied nitrox

breathing-gas mixture, you must ensure that the supplier:

(a) Determines the O2 fraction in the breathing-gas

mixture using an analytic method that is accurate to within 1 percent

(1%) of the O2 fraction by volume;

(b) Makes this determination when the mixture is in the charged

tank and after disconnecting the charged tank from the charging

apparatus;

(c) Documents the O2 fraction in the mixture; and

(d) Provides you with a written certification of the O2

analysis.

(24) For commercially-supplied nitrox breathing-gas mixtures, you

must ensure that the O2 is Grade A (also known as

``aviator's oxygen'') or Grade B (referred to as ``industrial-medical

oxygen''), and meets the specifications, including the purity

requirements, found in the 1991 NOAA Diving Manual. In doing so, you

must:

(a) Ensure that the analytic method used to make this determination

is accurate to within 1 percent (1%) of the O2 fraction by

volume; and

(b) Obtain a written certificate to this effect from the supplier.

(25) Before producing nitrox breathing-gas mixtures using a

compressor in which the gas pressure in any system component exceeds

125 pounds per square inch (psi), you must:

(a) Have the compressor manufacturer certify in writing that the

compressor is suitable for mixing high-pressure air with the highest

O2 fraction used in the nitrox breathing-gas mixture;

(b) Ensure that the compressor is oil-less or oil-free and rated

for O2 service unless you comply with the requirements of

Condition (26) of this order; and

(c) Ensure that the compressor meets the requirements specified in

paragraphs (i)(1) and (i)(2) of 29 CFR 1910.430 whenever the highest

O2 fraction used in the mixing process exceeds 40 percent

(40%).

(26) Before producing nitrox breathing-gas mixtures using an oil-

lubricated compressor to mix high-pressure air with O2,

regardless of the

[[Page 71259]]

gas pressure in any system component you must:

(a) Have the compressor manufacturer certify in writing that the

compressor is suitable for mixing the high-pressure air with the

highest O2 fraction used in the nitrox breathing-gas

mixture;

(b) Filter the high-pressure air to produce O2-

compatible air;

(c) Have the filter-system manufacturer certify in writing that the

filter system used for this purpose is suitable for producing

O2-compatible air;

(d) Continuously monitor the air downstream from the filter for

hydrocarbon contamination; and

(e) Use only uncontaminated air (i.e., air containing no

hydrocarbon particulates) for the nitrox breathing-gas mixture.

(27) You must ensure that diving equipment using nitrox breathing-

gas mixtures or pure O2 under high pressure (i.e., exceeding

125 psi) conforms to the O2-service requirements specified

in paragraphs (i)(1) and (i)(2) of 29 CFR 1910.430.

Use No-Decompression Limits

(28) For diving conducted while using nitrox breathing-gas

mixtures, you must ensure that each of your divers remains within the

no-decompression limits specified for single and repetitive air diving

and published in the 1991 NOAA Diving Manual or the report entitled

Development and Validation of No-Stop Decompression Procedures for

Recreational Diving: The DSAT Recreational Dive Planner, published in

1994 by Hamilton Research Ltd. (known commonly as the ``1994 DSAT No-

Decompression Tables'') (see section VII (``References'') below).

(29) You may permit your divers to use a dive-decompression

computer designed to regulate decompression if the dive-decompression

computer uses the no-decompression limits specified above in Condition

(28) of this order and provides output that reliably represents those

limits.

Emergency Egress

(30) Regardless of the diving equipment your divers use (i.e.,

open-circuit SCUBA or rebreathers), you must ensure that the diving

equipment consists of:

(a) An open-circuit emergency-egress system (a ``bail-out'' system)

in which:

(i) The second stage of the regulator connects to a separate supply

of emergency breathing gas; and

(ii) The emergency breathing gas consists of air or the same nitrox

breathing-gas mixture used during the dive; or

(b) One of the following alternative bail-out systems:

(i) For open-circuit SCUBAs, the emergency-egress systems specified

in paragraph (c)(4) of 29 CFR 1910.424; or

(ii) For semi-closed-circuit and closed-circuit rebreathers, a

system configured so that the second stage of the regulator connects to

a diluent supply of emergency breathing gas.

(31) You must ensure that the bail-out system performs reliably and

provides sufficient emergency breathing gas to enable your diver to

terminate the dive and return safely to the surface.

Diving-Related Medical Emergencies

(32) Before each day's diving operations, you must ensure that:

(a) A hospital, qualified health-care professionals, and the

nearest Coast Guard Coordination Center (or an equivalent rescue

service operated by a state, county, or municipal agency) are available

for diving-related medical emergencies;

(b) These treatment resources are available when you notify them of

the diving-related medical emergency;

(c) A list of telephone or call numbers for these health-care

professionals and facilities is readily available at the dive site; and

(d) Transportation to a suitable decompression chamber is readily

available when no decompression chamber is at the dive site, and that

this transportation can deliver your injured diver to the decompression

chamber within two (2) hours travel time from the dive site.

(33) You must ensure that portable O2 equipment is

available at the dive site to treat your injured divers. In doing so,

you must ensure that:

(a) This equipment delivers pure O2 to a transparent

mask that covers the injured diver's nose and mouth; and

(b) Sufficient O2 is available for administration to the

injured diver from the time you recognize the symptoms of a diving-

related medical emergency until the injured diver reaches a

decompression chamber for treatment.

(34) Before each day's diving operations, you must:

(a) Ensure that at least two individuals, either employees or non-

employees, qualified in first-aid and administering O2

treatment are available at the dive site to treat diving-related

medical emergencies; and

(b) Verify their qualifications for this task.

Diving Logs and Decompression Tables

(35) You must maintain a diving log at the dive site and ensure

that:

(a) Before starting each day's diving operations, the individual

who verifies the availability of the treatment resources required above

under Condition (32) of this order makes a signed entry to this effect

in the diving log; and

(b) The diving log contains the following information for each

dive:

(i) The time when the diver left the surface, left the bottom, and

returned to the surface;

(ii) The maximum depth of the dive; and

(iii) If a diver uses a dive-decompression computer, the name of

the manufacturer and the model and serial numbers.

(36) Before starting each day's diving operations, you must:

(a) Designate an employee or a non-employee to make the entries in

the diving log; and

(b) Verify that the designee understands the:

(i) Diving and medical terminology required to make proper entries;

and

(ii) Procedures for making entries in the diving log.

(37) You must ensure that a hard-copy of the decompression tables

used for the dives (as specified above in Condition (28) of this order)

is readily available at the dive site, whether or not your divers use

dive-decompression computers.

Diver Training

(38) You must ensure that your divers receive training that enables

them to perform their work safely and effectively while using open-

circuit SCUBAs or rebreathers supplied with nitrox breathing-gas

mixtures. Accordingly, your divers must be able to perform critical

tasks safely and effectively, including, but not limited to:

(a) Recognizing the effects of breathing excessive CO2

and O2;

(b) Taking appropriate action after detecting the effects of

breathing excessive CO2 and O2; and

(c) Properly evaluating, operating, and maintaining their diving

equipment under the diving conditions they encounter.

The Order: Notification and Duration

(39) You must notify the divers affected by this order using the

same means that you used to inform them of the variance application.

(40) This order remains effective until modified or revoked under

section 6(d) of the Occupational Safety and Health Act of 1970.

Appendix A (Mandatory).--Testing Protocol for Determining the

CO2 Limits of Rebreather Canisters

If the employer replaces CO2-sorbent material using a

schedule provided by

[[Page 71260]]

the rebreather manufacturer (hereafter, manufacturer), then the

employer must ensure that the manufacturer developed the schedule

according to the protocol specified below in this appendix. The

employer must also: Use only the CO2-sorbent material

specified by the manufacturer (and that is consistent with the

requirements of Condition 10(b)(ii) of this order); ensure that the

manufacturer analyzes the canister-duration results using the

statistical analysis specified in U.S. Navy Experimental Diving Unit

(NEDU) Report 2-99 (see Section VII (``References'') of the permanent

variance); and ensure that the manufacturer specifies the replacement

schedule in terms of the lower prediction line (or limit) of the 95%

prediction interval.

1. The manufacturer must use the following procedures to ensure

that the CO2-sorbent material meets the specifications of

the material's manufacturer: NATO CO2 absorbent-activity

test; RoTap shaker and nested sieves to determine granule-size

distribution; NEDU-derived Schlegel test to assess friability; and

NEDU's MeshFit software to evaluate mesh size conformance to

specifications.

These procedures involve a quality-control assessment of the

CO2-sorbent material. Canister durations are suspect if

these procedures indicate that the CO2-sorbent material used

in canister testing either exceeds or falls below the specifications

provided by the material's manufacturer. Therefore, for the purposes of

this canister-testing protocol, rebreather manufacturers must use only

CO2-sorbent materials that meet the specifications provided

by the material's manufacturer.

2. While operating the rebreather at a maximum depth of 130 feet of

sea water (fsw), the manufacturer must use a breathing machine to

continuously ventilate the rebreather with breathing gas that is at

100% humidity and warmed to a temperature of 98.6 degrees F (37 degrees

C) in the heating-humidification chamber. The breathing gas must be a

nitrox mixture, with the oxygen (O2) fraction maintained at

0.28 (equivalent to 1.4 ATA of O2 at 130 fsw, the maximum

O2 concentration permitted at this depth by the permanent

variance); the manufacturer must measure the O2

concentration of the inhalation breathing gas delivered to the

mouthpiece.

3. The manufacturer must test canisters using the following three

ventilation rates (with required breathing-machine tidal volumes and

frequencies, and CO2-injection rates, provided for each

ventilation rate):

------------------------------------------------------------------------

Breathing

Ventilation rates Breathing-machine machine CO2-injection

(liters/min., tidal volumes frequencies rates (liters/

ATPS \1\) (liters) (breaths per min., STPD \2\)

min.)

------------------------------------------------------------------------

22.5 l.5 15 0.90

40.0 2.0 20 1.35

62.5 2.5 25 2.25

------------------------------------------------------------------------

\1\ ATPS means ambient temperature and pressure, saturated with water.

\2\ STPD means standard temperature and pressure, dry; the standard

temperature is 0 degrees C.

The manufacturer must perform the CO2 injection at a

constant (steady) and continuous rate during each testing trial. An

employer cannot use a rebreather at a work rate higher than the work

rates simulated in this testing protocol unless the manufacturer adds

the appropriate combinations of ventilation-CO2-injection

rates to the protocol.

4. The manufacturer must determine canister duration using a

minimum of four (4) water temperatures, including 40, 50, 70, and 90

degrees F (4.4, 10.0, 21.1, and 32.2 degrees C, respectively). An

employer cannot use a rebreather at a water temperature that is lower

than the minimum, or higher than the maximum, water temperature used in

this testing protocol unless the manufacturer adds a lower or higher

temperature to the protocol.

5. The manufacturer must monitor the breathing-gas temperature at

the rebreather mouthpiece (at the ``chrome T'' connector) and ensure

that this temperature conforms to the temperature of a diver's exhaled

breath at the water temperature and ventilation rate used during the

testing trial. (NEDU can provide the manufacturer with information on

the temperature of a diver's exhaled breath at various water

temperatures and ventilation rates, as well as techniques and

procedures used to maintain these temperatures during the testing

trials.)

6. Testing must consist of at least eight (8) testing trials for

each combination of temperature and ventilation-CO2-

injection rates. (For example, eight testing trials at 40 degrees F

using a ventilation rate of 22.5 lpm at a CO2-injection rate

of 0.90 liters/min.) While water temperature may vary slightly

( 2.0 degrees F or 1.0 degree C) between each of the eight

testing trials, the manufacturer must maintain strict control of water

temperature ( 1.0 degree F or 0.5 degree C) within each

testing trial. The rebreather manufacturer must use the average

temperature for each set of eight testing trials in the statistical

analysis of the resulting data.

7. The testing-trial result is the time taken for the inhaled

breathing gas to reach 0.005 ATA of CO2. Using the canister-

duration results from these testing trials, the rebreather manufacturer

must: Analyze the canister-duration results using the repeated-measures

statistics described in NEDU Report 2-99 (see Section VII

(``References'') of the permanent variance); and specify the

replacement schedule for CO2-sorbent materials in terms of

the lower prediction line (or limit) of the 95% confidence interval.

VII. References

This order cites the following references:

(1) National Oceanic and Atmospheric Administration (1991). NOAA

Diving Manual: Diving for Science and Technology. U.S. Government

Printing Office, Washington, D.C.

(2) Diving Science and Technology (1995). Analysis of Proposed

Oxygen Exposure Limits for DSAT Oxygen Exposure Table Against

Existing Database of Manned Oxygen Test Dives. Enriched Air

Operations and Resource Guide. International PADI, Inc., Rancho

Santa Margarita, California.

(3) R. W. Hamilton, R. E. Rogers, M. R. Powell, and R. D. Vann

(1994). Development and Validation of No-Stop Decompression

Procedures for Recreational Diving: The DSAT Recreational Dive

Planner. Hamilton Research, Ltd., Tarrytown, New York.

(4) J. R. Clarke. ``Statistically Based CO2 Canister

Duration Limits for Closed-Circuit

[[Page 71261]]

Underwater Breathing Apparatus.'' U.S. Navy Experimental Diving

Unit, Report 2-99, 1999.

Copies of these references are available from the Docket Office,

Room N-2625, Occupational Safety and Health Administration, U.S.

Department of Labor, 200 Constitution Avenue, NW, Washington, DC

20210; telephone (202) 693-2350 or fax (202) 693-1648.

VIII. Authority and Signature

The authority for this order is section 6(d) of the Occupational

Safety and Health Act of 1970 (29 USC 655), Secretary of Labor's Order

No. 6-96 (62 FR 111), and 29 CFR part 1905.

Signed at Washington, DC, this 9th day of December 1999.

Charles N. Jeffress,

Assistant Secretary of Labor.

[FR Doc. 99-32824 Filed 12-17-99; 8:45 am]

BILLING CODE 4510-26-P