General Motors Corp.; Receipt of Application for Determination of Inconsequential Noncompliance

DEPARTMENT OF TRANSPORTATION

National Highway Traffic Safety Administration

[Docket No. NHTSA 99-5862; Notice 1]

General Motors Corp.; Receipt of Application for Determination of

Inconsequential Noncompliance

General Motors Corporation (GM) of Warren, Michigan, has applied to

be exempted for the notification and remedy requirements of 49 U.S.C.

Chapter 301 ``Motor Vehicle Safety'' because of a noncompliance with,

Federal Motor Vehicle Safety Standard (FMVSS) No. 208, ``Occupant Crash

Protection.'' The basis of the application is that the noncompliance is

inconsequential to motor vehicle safety. GM has filed an appropriate

report pursuant to 49 CFR part 573, ``Defect and Noncompliance

Information Reports.''

This notice of receipt of an application is published under 49

U.S.C. 30118 and 30120 and does not represent any agency decision or

other exercise of judgment concerning the merits of the application.

Description of Noncompliance

On February 2, 1999, NHTSA tested a 1999 Chevrolet Tahoe to the

performance requirements of S13 of FMVSS No. 208 Alternative unbelted

test for vehicles manufactured before September 1, 2001. The test was

conducted at the Transportation Research Center of Ohio and the right

front passenger Anthropomorphic Test Dummy (ATD) registered a neck

extension moment of 67 Nm. This value exceeds the maximum limit of 57

Nm specified by S13.2(b) of the standard.

In response to the test failure, GM conducted an investigation to

understand the subject test results and to determine the cause of the

resultant neck extension moment of 67 Nm. After examining all the

relevant information and conducting additional tests, GM estimates that

50 percent of the 1999 model year (MY) Chevrolet and GMC

C/K vehicles manufactured between September 1, 1998 and May 5, 1999,

may produce similar results if all the subject vehicles were subjected

to the 30 mph Sled Test in accordance with S13.1 of FMVSS No. 208.

Supporting Information as Submitted by GM

There were 279,132 subject vehicles manufactured between

September 1, 1998 and May 5, 1999, with right front passenger

restraint systems that may not consistently meet the neck extension

moment prescribed in S13.2(b) of the standard. A neck extension

moment is produced during the test as a result of the reaction to

forces acting on the head in such a way as to rotate the head

rearward at the top of the neck. GM's analysis indicates that, due

to test and/or product variations, approximately 50 percent of the

right front passenger air bags could contribute to ATD kinematics

that could allow the passenger ATD to exceed the 57 Nm neck

extension value limit.

The prescribed Sled Test pulse is of a longer duration than a

typical 30 mph rigid barrier pulse for the subject vehicles (125

msec versus approximately 80 msec). Because of this, the air bag

must stay inflated longer during a test using the sled pulse to

allow the unbelted ATD's torso energy to dissipate over a longer

time period. Two design interventions involving the air bag system

could be used to address this. It would be possible to increase the

gas output into the deploying bag by adding more propellant to the

inflator. However, this would be counter to the reasons the agency

permitted less forceful air bags, and for the FMVSS 208 Sled Test

being allowed as an alternative test method with an unbelted, 50th

percentile ATD. The intent of the Sled Test provision, and the

ongoing rulemaking to address air bag aggressivity, is to allow and

encourage less aggressive air bag inflators in motor vehicles to

reduce the inflation induced injury risks to out-of-position small

adults and children.

A second possible approach is to reduce the venting capacity of

the air bag. By reducing the venting capacity, the inflation gas is

retained in the bag for a longer period of time resulting in bag

pressure being retained over a longer period. GM test results

(provided to NHTSA-OVSC in USG 3433; Part 5, dated May 7, 1999)

consistently provided neck extension moments well below the 57 Nm

limit when conducted with air bags having each of the two vent holes

reduced from a 60 mm diameter to a 30 mm diameter. Considering all

these resultant test values and the consistency of the neck

extension measurements from these tests, GM implemented this vent

size change in the subject vehicle production to further assure

compliance. The implementation of this change was completed in GM's

vehicle production facilities on May 5, 1999.

GM has examined the effect on motor vehicle safety involved in

this noncompliance and the appropriateness of field action. This

evaluation utilizes the total of 279,132 1999 MY Chevrolet and GMC

C/K vehicles that were manufactured between September 1, 1998 and

May 5, 1999 with the right front passenger air bag systems in

question and very conservative estimates for the remainder of the

analysis's multipliers. Approximately 50 percent of the subject

vehicles, or 139,566 vehicles, may have a passenger air bag that

could contribute to ATD kinematics that could allow the passenger

ATD to exceed the 57 Nm neck extension requirement if tested to the

S13 requirements of the standard. Projecting 5,700 deployments per 1

million car years for a 10 year vehicle life cycle, a total of 7,960

deployments can be expected. It is anticipated that one third of

these deployments (2,653) would have a right front passenger

present. Using the recognized current national seat belt use rate of

70 percent, 30 percent (or 796 occupants) of these deployments may

involve an unbelted occupant. Approximately 20 percent of the

deployments would be at a crash pulse similar to or more severe than

used for the FMVSS 208 Sled Test, resulting in the potential that

159 of the passengers may be involved in such a deployment. Assuming

60 percent of these passengers are the same size or larger than the

50th percentile male ATD, 95 right front occupants could be large

enough that sufficient torso energy may not be dissipated to meet

the specific neck extension requirement of the standard.

The risk of neck injury to these 95 occupants can be estimated

using the neck extension moment injury risk curve submitted to the

agency during the referenced rulemaking and provided as Attachment

A. It was also provided as Figure 4 of Attachment C--Proposal for

Dummy Response Limits for FMVSS 208 Compliance Testing--in the AAMA

response S98-13 to Docket No. NHTSA 98-4405; Notice 1 dated December

17, 1998. The risks of an AIS3 neck injury for the 50th

percentile adult male experiencing a neck extension moment of 57 Nm

(current FMVSS 208 requirement) and 67 Nm (measured during the

subject agency enforcement test) for both a relaxed and tensed

occupant are given in Table 1. Also shown are the estimated number

of the 95 occupants who may experience an AIS3 neck

injury.

[[Page 34310]]

Table 1.--Injury Risk Value for an AIS3 Neck Injury of Neck Extension Moments for No Muscle Tone and

for 80 Percent Muscle Tone Measured With the 50th Percentile Adult Male ATD

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

% Risk of AIS3 Neck Potential number of

Injury occupants with AIS3 neck injury

moment (Nm) ----------------------------

No muscle tone 80% muscle 80% muscle

tone No muscle tone tone

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

MVSS Req'mt........................ 57 0.8 0.09 3 neck injury

would be no more than one occupant, but more likely would be close

to zero depending on the degree of muscle tone involved. The reason

this increase is so small is that the current FMVSS 208 neck

extension moment limit of 57 Nm is an extremely conservative limit.

This value corresponds to only a 0.8 percent risk of an

AIS3 neck injury with no muscle tone assumed and only a

0.09 percent risk if 80 percent muscle tone is assumed.

As part of the aforementioned ongoing rulemaking, the agency is

currently considering the AAMA recommendation that an injury risk

level of 5 percent be used for setting regulated injury criteria

limits. This includes the recommendation that the neck extension

limit be set at a 5 percent risk of an AIS3 neck injury.

For out-of-position occupant measurements with the 50th percentile

male ATD, this would be a 77 Nm limit without consideration for

muscle tone, and the neck extension limit for in-position occupants

would be 96 Nm considering 80 percent muscle tone. For either case,

the resultant 67 Nm measurement from the agency's test is

substantially below these recommended limits.

These recommended neck extension limits of 77 and 96 Nm are also

exceptionally conservative compared to the risk level associated

with brain injury that is currently comprehended in FMVSS 208. The

current head injury criteria (HIC) limit of 1000 allows for a 16

percent risk of an AIS4 brain injury. Furthermore, the

current FMVSS 208 injury criteria for chest displacement and femur

loads are regulated at even higher risk levels than HIC. In fact,

the rigid barrier test methods prescribed in FMVSS 208 for both

belted and unbelted ATDs currently include these HIC, chest

displacement and femur injury criteria, but do not currently specify

any of the neck criteria associated with the Sled Test.

The current neck extension limit of 57 Nm is a very conservative

limit, especially when compared to the current HIC, chest

displacement and femur load limits required by FMVSS 208. Because of

this and because of no more that one occupant and possible zero

occupants may be at risk of an AIS 3 neck injury if

corrective action is not implemented for 279,132 subject vehicles,

GM believes this noncompliance is inconsequential as it relates to

motor vehicle safety. Therefore, GM requests the affected vehicles

be exempted from the recall and remedy provisions of Section 30120

of the Safety Act.

The agency is aware that significant controversy continues with

regard to the injury criteria currently specified for the neck. This

is a continuing topic of discussion between the agency and others in

the ongoing rulemaking regarding air bag related injuries and

fatalities to unbelted and out-of-position occupants. These ongoing

rulemaking discussions support GM's belief that the current limit of

57 Nm for the specified neck extension criteria is well below the

level necessary to meet the need for motor vehicle safety.

Interested persons are invited to submit written data, views and

arguments on the petition of GM, described above. Comments should refer

to the Docket Number and be submitted to: Docket Management, Room PL-

401, 400 Seventh Street, SW, Washington, DC 20590. It is requested that

two copies be submitted.

All comments received before the close of business on the closing

date indicated below will be considered. The application and supporting

materials, and all comments received after the closing date will also

be filed and will be considered to the extent practicable. When the

application is granted or denied, the Notice will be published in the

Federal Register pursuant to the authority indicated below.

Comment closing date: July 26, 1999.

(49 U.S.C. 30118, 30120; delegations of authority at 49 CFR 1.50 and

49 CFR 501.8)

Issued on: June 21, 1999.

L. Robert Shelton,

Associate Administrator for Safety Performance Standards.

[FR Doc. 99-16165 Filed 6-24-99; 8:45 am]

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