# Heat Injury and Illness Prevention in Outdoor and Indoor Work Settings > Briefs, arguments, decisions, and more. URL: https://www.frixlaw.com/law-library/documents/fr%3A2024-14824 ## Record - **Collection:** Federal Register - **Document type:** Proposed Rule - **Published:** August 30, 2024 - **Citation:** 89 FR 70698 ## Text DEPARTMENT OF LABOR Occupational Safety and Health Administration 29 CFR Part 1910, 1915, 1917, 1918, 1926, and 1928 [Docket No. OSHA-2021-0009] RIN 1218-AD39 Heat Injury and Illness Prevention in Outdoor and Indoor Work Settings AGENCY: Occupational Safety and Health Administration (OSHA), Labor. ACTION: Notice of proposed rulemaking (NPRM); request for comments. SUMMARY: OSHA is proposing to issue a new standard, titled Heat Injury and Illness Prevention in Outdoor and Indoor Work Settings. The standard would apply to all employers conducting outdoor and indoor work in all general industry, construction, maritime, and agriculture sectors where OSHA has jurisdiction, with some exceptions. It would be a programmatic standard that would require employers to create a plan to evaluate and control heat hazards in their workplace. It would more clearly set forth employer obligations and the measures necessary to effectively protect employees from hazardous heat. OSHA requests comments on all aspects of the proposed rule. DATES: Comments to this NPRM (including requests for a hearing) and other information must be submitted by December 30, 2024. Informal public hearing: OSHA will schedule an informal public hearing on the proposed rule if requested during the comment period. If a hearing is requested, the location and date of the hearing, procedures for interested parties to notify the agency of their intention to participate, and procedures for participants to submit their testimony and documentary evidence will be announced in the Federal Register . ADDRESSES: Written comments: You may submit comments and attachments, identified by Docket No. OSHA-2021-0009, electronically at https://www.regulations.gov, which is the Federal e-Rulemaking Portal. Follow the instructions online for making electronic submissions. After accessing “all documents and comments” in the docket (Docket No. OSHA-2021-0009), check the “proposed rule” box in the column headed “Document Type,” find the document posted on the date of publication of this document, and click the “Comment Now” link. When uploading multiple attachments to regulations.gov, please number all of your attachments because regulations.gov will not automatically number the attachments. This will be very useful in identifying all attachments. For example, Attachment 1—title of your document, Attachment 2—title of your document, Attachment 3—title of your document. For assistance with commenting and uploading documents, please see the Frequently Asked Questions on regulations.gov. Instructions: All submissions must include the agency's name and the docket number for this rulemaking (Docket No. OSHA-2021-0009). All comments, including any personal information you provide, are placed in the public docket without change and may be made available online at https://www.regulations.gov . Therefore, OSHA cautions commenters about submitting information they do not want made available to the public, or submitting materials that contain personal information (either about themselves or others), such as Social Security Numbers and birthdates. Docket citations: This Federal Register document references material in Docket No. OSHA-2021-0009, which is the docket for this rulemaking. Citations to documents: The docket referenced most frequently in this document is the docket for this rulemaking, docket number OSHA-2021-0009, cited as Document ID OSHA-2021-0009. Documents in the docket get an individual document identification number, for example “OSHA-2021-0009-0047.” Because this is the most frequently cited docket, the citation is shortened to indicate only the document number. The example is cited in the NPRM as “Document ID 0047.” Documents cited in this NPRM are available in the rulemaking docket (Docket ID OSHA-2021-0009). They are available to read and download by searching the docket number or document ID number at https://www.regulations.gov . Each docket index lists all documents in that docket, including public comments, supporting materials, meeting transcripts, and other documents. However, some documents ( e.g., copyrighted material) in the dockets are not available to read or download from that website. All documents in the dockets are available for inspection at the OSHA Docket Office. This information can be used to search for a supporting document in the docket at www.regulations.gov . Contact the OSHA Docket Office at (202) 693-2350 (TTY number: 877-889-5627) for assistance in locating docket submissions. FOR FURTHER INFORMATION CONTACT: For press inquiries: Contact Frank Meilinger, Director, OSHA Office of Communications, Occupational Safety and Health Administration; telephone: (202) 693-1999; email: meilinger.francis2@dol.gov . General information and technical inquiries: Contact Stephen Schayer, Director, Office of Physical Hazards and Others, OSHA Directorate of Standards and Guidance; telephone: (202) 693-1950; email: osha.dsg@dol.gov . Copies of this Federal Register notice: Electronic copies are available at https://www.regulations.gov . This Federal Register notice, as well as news releases and other relevant information, also are available at OSHA's web page at https://www.osha.gov . The docket is available at https://www.regulations.gov, the Federal eRulemaking Portal. A “100-word summary” is also available on https://www.regulations.gov . For additional information on submitting items to, or accessing items in, the docket, please refer to the ADDRESSES section of this NPRM. Most exhibits are available at https://www.regulations.gov; some exhibits ( e.g., copyrighted material) are not available to download from that web page. However, all materials in the dockets are available for inspection and copying at the OSHA Docket Office. SUPPLEMENTARY INFORMATION: Table of Contents I. Executive Summary II. Pertinent Legal Authority A. Introduction B. Significant Risk C. Feasibility D. High Degree of Employee Protection III. Background A. Introduction B. Need for Proposal C. Events Leading to Proposal D. Other Standards IV. Health Effects A. Introduction B. General Mechanisms of Heat-Related Health Effects C. Identifying Cases of Heat-Related Health Effects D. Heat-Related Deaths E. Heat Stroke F. Heat Exhaustion G. Heat Syncope H. Rhabdomyolysis I. Hyponatremia J. Heat Cramps K. Heat Rash L. Heat Edema M. Kidney Health Effects N. Other Health Effects O. Factors That Affect Risk for Heat-Related Health Effects P. Heat-Related Injuries V. Risk Assessment A. Risk Assessment B. Basis for Initial and High Heat Triggers C. Risk Reduction VI. Significance of Risk A. Material Harm B. Significant Risk C. Preliminary Conclusions VII. Explanation of Proposed Requirements A. Paragraph (a) Scope and Application B. Paragraph (b) Definitions C. Paragraph (c) Heat Injury and Illness Prevention Plan D. Paragraph (d) Identifying Heat Hazards E. Paragraph (e) Requirements at or Above the Initial Heat Trigger F. Paragraph (f) Requirements at or Above the High Heat Trigger G. Paragraph (g) Heat Illness and Emergency Response and Planning H. Paragraph (h) Training I. Paragraph (i) Recordkeeping J. Paragraph (j) Requirements Implemented at no Cost to Employees K. Paragraph (k) Dates L. Paragraph (l) Severability VIII. Preliminary Economic Analysis and Initial Regulatory Flexibility Analysis A. Market Failure and Need for Regulation B. Profile of Affected Industries C. Costs of Compliance D. Economic Feasibility E. Benefits F. Initial Regulatory Flexibility Analysis G. Distributional Analysis H. Appendix A. Description of the Cost Savings Approach I. Appendix B. Review of Literature on Effects of Heat Exposure on Non-Health Outcomes J. Appendix C. Heat Exposure Methodology Used in Distributional Analysis K. Appendix D. Definitions of Core Industry Categories Used in Cost Analysis IX. Technological Feasibility X. Additional Requirements A. Unfunded Mandates Reform Act, 2 U.S.C. 1501 et seq. B. Consultation and Coordination With Indian Tribal Governments/Executive Order 13175 C. Consultation With the Advisory Committee on Construction Safety and Health D. Environmental Impacts E. Consensus Standards F. Incorporation by Reference G. Protection of Children From Environmental Health Risks and Safety Risks H. Federalism I. Requirements for States With OSHA-Approved State Plans J. OMB Review Under the Paperwork Reduction Act of 1995 XI. Authority and Signature I. Executive Summary Heat is the leading cause of death among all weather-related phenomena in the United States. Excessive heat in the workplace can cause a number of adverse health effects, including heat stroke and even death, if not treated properly. Yet, there is currently no Federal OSHA standard that regulates heat stress hazards in the workplace. Although several governmental and non-governmental organizations have published regulations and guidance to help protect workers from heat hazards, OSHA believes that a mandatory Federal standard specific to heat-related injury and illness prevention is necessary to address the hazards posed by occupational heat exposure. OSHA has preliminarily determined that this proposed rule would substantially reduce the risk posed by occupational exposure to hazardous heat by clearly setting forth employer obligations and the measures necessary to effectively protect exposed workers. OSHA is proposing this standard pursuant to the Occupational Safety and Health Act of 1970, 29 U.S.C. 651 et seq. (OSH Act or Act). The Act authorizes the agency to issue safety or health standards that are “reasonably necessary or appropriate” to provide safe or healthful employment and places of employment (29 U.S.C. 652(8)). A standard is reasonably necessary or appropriate when a significant risk of material harm exists in the workplace and the standard would substantially reduce or eliminate that workplace risk. Applicable legal requirements are more fully discussed in Section II., Pertinent Legal Authority. Workers in both outdoor and indoor work settings without adequate climate controls are at risk of hazardous heat exposure. Certain heat-generating processes, machinery, and equipment ( e.g., hot tar ovens, furnaces) can also cause heat hazards when cooling measures are not in place. Based on the best available evidence, as discussed in this preamble, OSHA has preliminarily determined that exposure to hazardous heat in the workplace poses a significant risk of serious injury and illness. This finding of a significant risk of material harm is based on the health consequences associated with exposure to heat (see Section IV., Health Effects) as well as the risk assessment (see Section V., Risk Assessment and Section VI., Significance of Risk). In Section V.C., Risk Reduction, OSHA demonstrates the efficacy of the controls relied on in this proposed rule to reduce the risk of heat-related injury and illness in the workplace. Employees working in workplaces without these controls are at higher risk of severe health outcomes from exposure to hazardous heat. On October 27, 2021, OSHA published in the Federal Register an advance notice of proposed rulemaking (ANPRM) for Heat Injury and Illness Prevention in Outdoor and Indoor Work Settings (86 FR 59309). The ANPRM outlined key issues and challenges in occupational heat-related injury and illness prevention and aimed to collect evidence, data, and information critical to informing how OSHA proceeds in the rulemaking process. The ANPRM included background information on injuries, illnesses, and fatalities due to heat, underreporting, scope, geographic region, and inequality in exposures and outcomes. The ANPRM also covered existing heat injury and illness prevention efforts including OSHA's efforts, the National Institute for Occupational Safety and Health (NIOSH) criteria documents, State standards, and other standards. OSHA received 965 unique public comments, which largely supported the need for continued rulemaking. The agency then worked with the National Advisory Committee on Occupational Safety and Health (NACOSH) to assemble a Heat Injury and Illness Prevention Work Group. The Work Group was tasked with evaluating stakeholder input to the ANPRM and developing recommendations on potential elements of a proposed heat injury and illness prevention standard. The Work Group presented its recommendations on potential elements of a proposed heat injury and illness prevention standard for consideration by the full NACOSH committee. On May 31, 2023, NACOSH amended the report to ask OSHA to include a model written plan and then unanimously voted to submit the Work Group's recommendations to the Secretary of Labor. In accordance with the requirements of the Small Business Regulatory Enforcement Fairness Act (SBREFA), OSHA next convened a Small Business Advocacy Review (SBAR) Panel in August 2023. The Panel, comprised of members from the Small Business Administration's (SBA) Office of Advocacy, OSHA, and OMB's Office of Information and Regulatory Affairs, heard comments directly from Small Entity Representatives (SERs) on the potential impacts of a heat-specific standard. The Panel received advice and recommendations from the SERs and reported its findings and recommendations to OSHA. OSHA has taken the SER's comments and the Panel's findings and recommendations into consideration in the development of this proposed rule (see Section VIII.F., Initial Regulatory Flexibility Analysis). In accordance with 29 CFR parts 1911 and 1912, OSHA also consulted with and considered feedback from the Advisory Committee on Construction Safety and Health (ACCSH). On April 24, 2024, the Committee unanimously passed a motion recommending that OSHA proceed expeditiously with proposing a standard on heat injury and illness prevention. In addition, in accordance with Executive Order 13175, Consultation and Coordination with Indian Tribal Governments, 65 FR 67249 (Nov. 6, 2000), OSHA held a listening session on May 15, 2024, with Tribal representatives regarding this Heat Injury and Illness Prevention in Outdoor and Indoor Work Settings rulemaking and provided an opportunity for the representatives to offer feedback. The proposed rule is a programmatic standard that requires employers to create a heat injury and illness prevention plan to evaluate and control heat hazards in their workplace. It establishes requirements for identifying heat hazards, implementing engineering and work practice control measures at or above two heat trigger levels ( i.e., an initial heat trigger and a high heat trigger), developing and implementing a heat illness and emergency response plan, providing training to employees and supervisors, and retaining records. The proposed rule would apply to all employers conducting outdoor and indoor work in all general industry, construction, maritime, and agriculture sectors, with some exceptions (see Section VII.A., Paragraph (a) Scope and Application). Throughout this document, OSHA seeks input on alternatives and potential exclusions. Organizations affected by heat hazards vary significantly in size and workplace activities. Accordingly, many of the provisions of the proposed standard provide flexibility for affected employers to choose the control measures most suited to their workplace. The flexible nature of the proposed rule may be particularly beneficial to small organizations with limited resources. Additionally, to determine whether the proposed rule is feasible for affected employers, and in accordance with Executive Orders 12866 and 13563, the Regulatory Flexibility Act (RFA), and the Unfunded Mandates Reform Act (2 U.S.C 1501 et seq. ), OSHA has prepared a Preliminary Economic Analysis (PEA), including an Initial Regulatory Flexibility Analysis (see Section VIII., Preliminary Economic Analysis and Initial Regulatory Flexibility Analysis). Supporting materials prepared by OSHA are available in the public docket for this rulemaking, Document ID OSHA-2021-0009, through regulations.gov. II. Pertinent Legal Authority A. Introduction In the Occupational Safety and Health Act, 29 U.S.C. 651 et seq., Congress authorized the Secretary of Labor (“the Secretary”) “to set mandatory occupational safety and health standards applicable to businesses affecting interstate commerce” (29 U.S.C. 651(b)(3); see Nat'l Fed'n of Indep. Bus. v. Dep't of Labor, 595 U.S. 109, 117 (2022) (per curiam); see also 29 U.S.C. 654(a)(2) (requiring employers to comply with OSHA standards)). Section 6(b) of the Act authorizes the promulgation, modification or revocation of occupational safety or health standards pursuant to detailed notice and comment procedures (29 U.S.C. 655(b)). Section 3(8) of the Act defines a safety or health standard as a standard which requires conditions, or the adoption or use of one or more practices, means, methods, operations, or processes “reasonably necessary or appropriate” to provide safe or healthful employment and places of employment (29 U.S.C. 652(8)). A standard is reasonably necessary or appropriate within the meaning of section 3(8) when a significant risk of material harm exists in the workplace and the standard would substantially reduce or eliminate that workplace risk (see Indus. Union Dep't, AFL-CIO v. Am. Petroleum Inst., 448 U.S. 607 (1980) (“ Benzene ”)). OSHA's authority extends to, for example, removing workers from environments where workplace hazards exist (see, e.g., United Steelworkers of America v. Marshall, 647 F.2d 1189, 1228-38 (D.C. Cir. 1981); 29 CFR 1910.1028(i)(8); 29 CFR 1910.1024(l); cf. Whirlpool Corp. v. Marshall, 445 U.S. 1, 12 (1980) (upholding regulation allowing employees to refuse dangerous work in certain circumstances because “[t]he Act does not wait for an employee to die or become injured.”). In addition to the requirement that each standard address a significant risk, standards must also be technologically feasible (see UAW v. OSHA, 37 F.3d 665, 668 (D.C. Cir. 1994)). A standard is technologically feasible when the protective measures it requires already exist, when available technology can bring the protective measures into existence, or when that technology is reasonably likely to develop (see Am. Iron and Steel Inst. v. OSHA, 939 F.2d 975, 980 (D.C. Cir. 1991)). Finally, a standard must be economically feasible (see Forging Indus. Ass'n v. Secretary of Labor, 773 F.2d 1436, 1453 (4th Cir. 1985)). A standard is economically feasible if industry can absorb or pass on the costs of compliance without threatening its long-term profitability or competitive structure (see American Textile Mfrs. Inst., Inc., 452 U.S. 490, 530 n.55 (“ Cotton Dust ”)). Each of these requirements is discussed further below. B. Significant Risk As noted above, OSHA's workplace safety and health standards must address a significant risk of material harm that exists in the workplace (see Benzene, 448 U.S. at 614-15). The agency's risk assessments are based on the best available evidence, and its final conclusions are made only after considering all information in the rulemaking record. Reviewing courts have upheld the Secretary's significant risk determinations where supported by substantial evidence and “a reasoned explanation for [their] policy assumptions and conclusions” ( Bldg & Constr. Trades Dep't v. Brock, 838 F.2d 1258, 1266 (D.C. Cir. 1988) (“ Asbestos II ”)). The Supreme Court in Benzene explained that “[i]t is the agency's responsibility to determine, in the first instance, what it considers to be a `significant' risk” ( Benzene, 448 U.S. at 655). The Court declined to “express any opinion on the . . . difficult question of what factual determinations would warrant a conclusion that significant risks are present which make promulgation of a new standard reasonably necessary or appropriate” ( Benzene, 448 U.S. at 659). The Court stated, however, that the substantial evidence standard applicable to OSHA's significant risk determination (see 29 U.S.C. 655(b)(f)) does not require the agency “to support its finding that a significant risk exists with anything approaching scientific certainty” ( Benzene, 448 U.S. at 656). Rather, OSHA may rely on “a body of reputable scientific thought” to which “conservative assumptions in interpreting the data” may be applied, “risking error on the side of overprotection” ( Benzene, 448 U.S. at 656). The D.C. Circuit has further explained that OSHA may thus act with a pronounced bias towards worker safety in making its risk determinations ( Asbestos II, 838 F.2d at 1266). The Supreme Court also recognized that the determination of what constitutes “significant risk” is “not a mathematical straitjacket” and will be “based largely on policy considerations” ( Benzene, 448 U.S. at 655 & n.62). Once OSHA makes its significant risk finding, the standard it promulgates must be “reasonably necessary or appropriate” to reduce or eliminate that risk (29 U.S.C. 652(8)). In choosing among regulatory alternatives, however, “[t]he determination that [one standard] is appropriate, as opposed to a marginally [more or less protective] standard, is a technical decision entrusted to the expertise of the agency” ( Nat'l Mining Ass'n v. Mine Safety and Health Admin., 116 F.3d 520, 528 (D.C. Cir. 1997) (analyzing a Mine Safety and Health Administration standard under the Benzene significant risk standard)). C. Feasibility The statutory mandate to consider the feasibility of the standard encompasses both technological and economic feasibility; OSHA has performed these analyses primarily on an industry-by-industry basis ( United Steelworkers of Am., AFL-CIO-CLC v. Marshall, 647 F.2d 1189, 1264, 1301 (D.C. Cir. 1980) (“ Lead I ”)). The agency has also used application groups, defined by common tasks, as the structure for its feasibility analyses ( Pub. Citizen Health Research Grp. v. OSHA, 557 F.3d 165, 177-79 (3d Cir. 2009)). The Supreme Court has broadly defined feasible as “capable of being done” ( Cotton Dust, 452 U.S. at 509-10). I. Technological Feasibility A standard is technologically feasible if the protective measures it requires already exist, can be brought into existence with available technology, or can be created with technology that can reasonably be expected to be developed ( Lead I, 647 F.2d at 1272; Amer. Iron & Steel Inst. v. OSHA, 939 F.2d 975, 980 (D.C. Cir. 1991) (“ Lead II ”)). Courts have also interpreted technological feasibility to mean that a typical firm in each affected industry or application group will reasonably be able to implement the requirements of the standard in most operations most of the time (see Public Citizen v. OSHA, 557 F.3d 165, 170-71 (3d Cir. 2009); Lead I, 647 F.2d at 1272; Lead II, 939 F.2d at 990)). OSHA's standards may be “technology forcing,” so long as the agency gives an industry a reasonable amount of time to develop new technologies to comply with the standard. Thus, OSHA is not bound by the “technological status quo” ( Lead I, 647 F.2d at 1264). II. Economic Feasibility In addition to technological feasibility, OSHA is required to demonstrate that its standards are economically feasible. A reviewing court will examine the cost of compliance with an OSHA standard “in relation to the financial health and profitability of the industry and the likely effect of such costs on unit consumer prices” ( Lead I, 647 F.2d at 1265 (citation omitted)). As articulated by the D.C. Circuit in Lead I, “OSHA must construct a reasonable estimate of compliance costs and demonstrate a reasonable likelihood that these costs will not threaten the existence or competitive structure of an industry, even if it does portend disaster for some marginal firms” ( Lead I, 647 F.2d at 1272). A reasonable estimate entails assessing “the likely range of costs and the likely effects of those costs on the industry” ( Lead I, 647 F.2d at 1266). As with OSHA's consideration of scientific data and control technology, however, the estimates need not be precise ( Cotton Dust, 452 U.S. at 528-29 & n.54), as long as they are adequately explained. OSHA standards satisfy the economic feasibility criterion even if they impose significant costs on regulated industries so long as they do not cause massive economic dislocations within a particular industry or imperil the very existence of the industry ( Lead II, 939 F.2d at 980; see also Lead I, 647 F.2d at 1272; Asbestos I, 499 F.2d. at 478). As with its other legal findings, OSHA “is not required to prove economic feasibility with certainty, but is required to use the best available evidence and to support its conclusions with substantial evidence” ( Lead II, 939 F.2d at 980-81 (citing Lead I, 647 F.2d at 1267)). In addition to determining economic feasibility, OSHA estimates the costs and benefits of its proposed and final rules to ensure compliance with other requirements such as those in Executive Orders 12866 and 13563. D. High Degree of Employee Protection Safety standards must provide a high degree of employee protection to be consistent with the purpose of the Act (see Control of Hazardous Energy Sources (Lockout/Tagout) Final Rule, Supplemental Statement of Reasons, 58 FR 16612, 16614-15 (March 30, 1993)). OSHA has preliminarily determined that this proposed standard is a safety standard because the health effects associated with exposure to occupational heat are generally acute. As explained in Section IV., Health Effects, the proposed standard aims to address the numerous acute health effects of occupational exposure to hazardous heat. These include, among other things, heat stroke, heat exhaustion, heat syncope, and physical injuries ( e.g., falls) due to fatigue or other heat-related impairments. These harms occur after relatively short-term exposures to hazardous heat and are typically apparent at the time of the exposure or shortly thereafter. Consequently, the link between these harms and heat exposures is also often apparent and they do not implicate the concerns about latent, hidden harms that underly health standards (see Benzene, 448 U.S. at 649 n. 54; UAW v. OSHA, 938 F.2d 1310, 1313 (D.C. Cir. 1991) (“ Lockout/Tagout I ”); National Grain & Feed Ass'n v. OSHA, 866 F.2d 717, 733 (5th Cir. 1989) (“ Grain Dust ”)). Finally, although OSHA acknowledges that there is growing evidence occupational exposure to hazardous heat may lead to some chronic adverse health outcomes like chronic kidney disease, much of the science in this area is still developing (see Section IV., Health Effects). In any event, the agency expects that addressing the acute hazards posed by heat would also protect workers from potential chronic health outcomes by reducing workers' overall heat strain. III. Background A. Introduction The Occupational Safety and Health Administration (OSHA) is proposing a new standard to protect outdoor and indoor workers from hazardous heat in the workplace. OSHA promulgates and enforces occupational safety and health standards under authority granted by the Occupational Safety and Health (OSH) Act of 1970 (29 U.S.C. 651 et seq. ). In the absence of a Federal occupational heat standard, five States have issued heat injury and illness prevention regulations to protect employees exposed to heat hazards in the workplace: Minnesota (Minn. R. 5205.0110 (1997)); California (Cal. Code of Regs. tit. 8, section 3395 (2005)); Oregon (Or. Admin. R. 437-002-0156 (2022); Or. Admin. R. 437-004-1131 (2022)); Colorado (7 Colo. Code Regs. section 1103-15 (2022)); and Washington (Wash. Admin. Code sections 296-62-095 through 296-62-09560; 296-307-097 through 296-307-09760 (2023)). Although Minnesota was the first State to adopt a standard covering employees exposed to indoor environmental heat conditions, California was the first State to adopt a standard covering employees exposed to outdoor environmental heat conditions. Washington, Oregon, and Colorado have since enacted similar regulations to California's, requiring employers to implement controls and monitor for signs and symptoms of heat-related injury or illness, among other requirements. In 2023, California proposed a new standard that would cover indoor work environments (California, 2023). In 2024, Maryland published a proposed standard that would cover both outdoor and indoor work environments (Maryland, 2024). Workers in many industries are at risk for heat-related injury and illness stemming from hazardous heat exposure (see Section V.A., Risk Assessment). While the general population may be able to avoid and limit prolonged heat exposure, workers across a wide range of indoor and outdoor settings often are required to work through shifts with prolonged heat exposure. Some workplaces have heat generation from industrial processes and expose workers to sources of radiant heat, such as ovens and furnaces. Additionally, employers may not take adequate steps to protect their employees from exposure to hazardous heat ( e.g., not providing rest breaks in cool areas). Many work operations also require the use of personal protective equipment (PPE) that can reduce the worker's heat tolerance because it can decrease the body's ability to cool down. Workers may also face pressure, or incentivization through pay structures, to push through and continue working despite high heat exposure, which can increase the risk of heat-related injury and illness (Billikopf and Norton, 1992; Johansson et al., 2010; Spector et al., 2015; Pan et al., 2021). OSHA uses several terms related to excessive heat exposure throughout this proposal. Heat stress is the combined load of heat that a person experiences from sources of heat ( i.e., metabolic heat and the environment) and heat retention ( e.g., from clothing or personal protective equipment). Heat strain refers to the body's response to heat stress (American Conference of Governmental Industrial Hygienists (ACGIH), 2023). Heat-related illness means adverse clinical health outcomes that occur due to heat exposure, such as heat exhaustion or heat stroke. Heat-related injury means an injury linked to heat exposure, such as a fall or cut. OSHA sometimes refers to these collectively as “heat-related injuries and illnesses.” B. Need for Proposal Occupational heat exposure affects millions of workers in the United States. Each year, thousands of workers experience heat-related injuries and illnesses, and some of these cases result in fatalities (BLS, 2023b; BLS, 2024c). OSHA has relied on the General Duty Clause of the OSH Act (discussed further below), as well as enforcement emphasis programs and hazard alerts and other guidance, to protect workers and inform employers of their legal obligations. However, a standard specific to heat-related injury and illness prevention would more clearly set forth enforceable employer obligations and the measures necessary to effectively protect employees from hazardous heat. Workers in both outdoor and indoor work settings without adequate climate controls are at risk of hazardous heat exposure. In addition to weather-related heat, certain heat-generating processes, machinery, and equipment ( e.g., hot tar ovens, furnaces) can cause hazardous heat exposure when cooling measures are not in place. An evaluation of 66 heat-related illness enforcement investigations from 2011-2016 found heat-related injuries and illnesses, including fatalities, occurring in both outdoor (n=34) and indoor (n=29) work environments (Tustin et al., 2018a). Excessive heat exacerbates existing health conditions like asthma, diabetes, kidney failure, and heart disease, and can cause heat stroke and death if not treated properly and promptly. Some groups may be more likely to experience adverse health effects from heat, such as pregnant workers (NIOSH, 2024), while others are disproportionately exposed to hazardous levels of heat, such as workers of color in essential jobs, who are more often employed in work settings with a high risk of hazardous heat exposure (Gubernot et al., 2015). The Bureau of Labor Statistics (BLS), in its Census of Fatal Occupational Injuries, documented 1,042 U.S. worker deaths due to occupational exposure to environmental heat from 1992-2022, with an average of 34 fatalities per year during that period (BLS, 2024c). In 2022 alone, BLS reported 43 work-related deaths due to environmental heat exposure (BLS, 2024c). The BLS Annual Survey of Occupational Injuries and Illnesses (SOII) estimates 33,890 work-related heat injuries and illnesses involving days away from work from 2011-2020, which is an average of 3,389 injuries and illnesses occurring each year during this period (BLS, 2023b). Workers across hundreds of industries are at risk for hazardous heat exposure and resulting heat-related injuries and illnesses. From January 1, 2017, to December 31, 2022, 1,054 heat-related injuries, illnesses, and fatalities were reported to and investigated by OSHA, including 625 heat-related hospitalizations and 211 heat-related fatalities, as well as 218 heat-related injuries and illnesses that did not result in hospitalization. During this time, hospitalizations occurred most frequently in construction, manufacturing, and postal and delivery service. Fatalities were most frequently reported in construction, landscaping, agriculture, manufacturing, and postal and delivery service (as identified by 2-digit NAICS codes). However, as explained in Section V.A., Risk Assessment, these statistics likely do not capture the true magnitude and prevalence of heat-related injuries, illnesses, and fatalities. Recent studies demonstrate significant undercounting of occupational injuries and illnesses by both the BLS SOII and OSHA's enforcement data. One reason for this undercounting is that the BLS SOII only reports the number of heat-related injuries and illnesses involving days away from work and thus does not capture the full picture of heat-related injuries and illnesses. An examination of workers' compensation claims in California, which include more than only cases involving days away from work, identified 3 to 6 times the number of annual heat-related illness and injury cases than reported by BLS SOII (Heinzerling et al., 2020). In addition, evidence has shown significant underreporting as employers and employees are disincentivized from reporting injuries and illnesses due to several factors, including potential increases in workers' compensation costs or impacts on the employer's reputation, or an employee's fear of retaliation or lack of awareness of their right to speak out about workplace conditions (BLS, 2020b). Heat-related injuries and illnesses may present unique challenges to surveillance efforts. As the nature of heat-related symptoms ( e.g., headache, fatigue) vary, some cases may be attributed to other illnesses rather than heat (as discussed in Section IV., Health Effects). Furthermore, heat is not always identified as a contributing factor to fatality, as heat exposure may exacerbate existing medical conditions and medical professionals may not witness the symptoms and events preceding death (Luber et al., 2006). Finally, exposure to heat can interfere with routine occupational tasks and impact workers' psychomotor and mental performance, which can lead to workplace injuries. Particularly, heat can impair performance of job tasks related to complex cognitive function (Hancock and Vasmatzidis, 2003; Piil et al., 2017) and reduce decision making abilities (Ramsey et al., 1983; Xiang et al., 2014a) and productivity (Foster et al., 2021). A growing body of evidence has demonstrated that heat-induced impairments may result in significant occupational injuries that are not currently factored into official statistics for heat-related cases (Spector et al., 2016; Calkins et al., 2019; Dillender, 2021; Park et al., 2021). See Section V.A., Risk Assessment, for further discussion on underreporting of heat-related injuries, illnesses, and fatalities. While a significant percentage of heat-related incidents are unreported, OSHA's investigations of reported heat-related fatalities point to many gaps in employee protections. OSHA has identified the following circumstances in its review of 211 heat-related fatality investigations from 2017-2022: employees left alone by employers after symptoms started; employers not providing adequate medical attention to employees with symptoms; employers preventing employees from taking rest breaks; employers not providing water on-site; employers not providing on-site access to shade; employers not providing cooling measures on-site; and employers not having programs to acclimatize employees to hot work environments ( https://www.osha.gov/fatalities ). OSHA has relied on multiple mechanisms to protect employees from hazardous heat, however, OSHA's efforts to prevent the aforementioned circumstances have been met with challenges without a heat-specific standard (as discussed in Section III.C.III., OSHA's Heat-Related Enforcement). Many U.S. States run their own OSHA-approved State Plans ( e.g., State heat standards, voluntary consensus standards) (see Section III.D., Other Standards), however OSHA has preliminarily determined that this standard is still needed to protect workers from the persistent and serious hazards posed by occupational heat exposure. As explained in Section VI., Significance of Risk, OSHA has preliminarily determined that a significant risk of material harm from occupational exposure to hazardous heat exists, and issuance of this standard would substantially reduce that risk. Therefore, to more clearly set forth employer obligations and the measures necessary to more effectively protect employees from hazardous heat, and reduce the number and frequency of occupational injuries, illness, and fatalities caused by exposure to hazardous heat, OSHA is proposing a Federal standard for Heat Injury and Illness Prevention for Outdoor and Indoor Work Settings. C. Events Leading to the Proposal I. History of Heat as a Recognized Occupational Hazard Heat exposure has long been recognized as an occupational hazard. For example, in the United States, the occupational hazards associated with the construction of the Hoover Dam between 1931 and 1935 brought attention to the effects of heat on worker health. The Bureau of Reclamation reported that 14 dam workers and two others residing in the work area died from “heat prostration” in 1931 (Bureau of Reclamation, 2015). According to a local newspaper, temperatures at the dam site that summer reached 140 °F in the sun and 120 °F in the shade (Turk, 2018; Rogers, 2012). In response to the extreme heat of the summer and other unsafe working conditions, the Industrial Workers of the World convinced Hoover Dam workers to strike over safety concerns (Turk, 2018; Rogers, 2012). Six Companies, the conglomerate of companies hired by the Bureau of Reclamation to construct most of the dam, was forced to make concessions, including protections against HRI such as providing potable water in dormitories, bringing ice water to workers at their work sites, and adding first aid stations closer to the job site (Rogers, 2012). The heat-related deaths that occurred during 1931 also prompted Harvard University researchers from the Harvard Fatigue Laboratory to travel to the Hoover Dam and study the relationship between hot, dry temperatures, physical performance, and heart rate (Turk, 2018). Heat-related illnesses were identified as a major concern for the U.S. military in the 1940s and 1950s. Between 1942 and 1944, 198 soldiers died of heat stroke at U.S.-based training camps, 157 of which did not have a known history of cardiac diseases or other conditions that may predispose them to heat illness (Schickele, 1947, p. 236). This led to investigations of the environmental conditions at the time of these deaths, and eventually to the development of wet bulb globe temperature (WBGT) to measure heat stress (Yaglou and Minard, 1957; Minard, 1961; Department of the Army, 2022; Department of the Navy, 2023). Research on the effects of occupational heat exposure continued in the 1960s, as researchers conducted trials examining the physiological effects of work at various temperatures ( e.g., Lind, 1963). Findings from these trials would eventually underpin the American Conference of Governmental Industrial Hygienists (ACGIH) Threshold Limit Value (TLV), as well as the National Institute of Occupational Safety and Health (NIOSH) Recommended Exposure Limit (REL) (Dukes-Dobos and Henschel, 1973). ACGIH first proposed guidelines for a TLV in 1971, which were later adopted in 1974. Heat was recognized as a preventable workplace hazard in the legislative history of the OSH Act. Senator Edmund Muskie submitted a letter in support of the OSH Act into the Congressional record on behalf of “a distinguished group of citizens, including a former Secretary of Labor and several noted scientists.” (Senate Debate on S. 2193, Nov. 16, 1970), reprinted in Legislative History of the Occupational Safety and Health Act of 1970, pp. 513-14 (1971) (Committee Print) (“Leg. Hist.”). The letter states, “Most industrial diseases and accidents are preventable. Modern technological and medical sciences are capable of solving the problems of noise, dust, heat, fumes, and toxic substances in the plants. However, existing legislation in this area does not begin to meet the problems” (Leg. Hist., pp. 513-14). In 1972, just two years after promulgation of the OSH Act, NIOSH first recommended a potential OSHA heat standard in its Criteria for a Recommended Standard (NIOSH, 1972). This criteria document, issued under the authority of section 20(a) of the OSH Act, recommended an OSHA standard based on a critical review of scientific and technical information. In response, an OSHA Standards Advisory Committee on Heat Stress was appointed in 1973 and presented recommendations for a standard for work in hot environments in 1974. At the time, 12 of 15 members of the advisory committee agreed that occupational heat stress warranted a standard (Ramsey, 1975). NIOSH's criteria document for a recommended standard has since been updated in 1986 (NIOSH, 1986) and again in 2016 (NIOSH, 2016). The 2016 criteria document recommends various provisions to protect workers from heat stress, including rest breaks, hydration, shade, acclimatization plans, and worker training (NIOSH, 2016). The 2016 criteria document also recommends that no worker be “exposed to combinations of metabolic and environmental heat greater than” the recommended alert limit (RAL) for unacclimatized workers or the recommended exposure limit (REL) for acclimatized workers). The document recommends that environmental heat be assessed with measurements of WBGT (NIOSH, 2016). A detailed report of the history of heat as a recognized occupational hazard is available in the docket (ERG, 2024a). The report summarizes historical documentation of occupational heat-related illness beginning in ancient times and from the eighteenth century through the regulatory interest in the twentieth century. II. OSHA's Heat Injury and Illness Prevention Efforts In 2011, OSHA issued a memorandum to inform regional administrators and State Plan designees of inspection guidance for heat-related illnesses (OSHA, 2011). That same year, OSHA launched the Heat Illness Prevention Campaign ( https://www.osha.gov/heat ) to build awareness of prevention strategies and tools for employers and workers to reduce occupational heat-related illness. In its original form, the Campaign delivered a message of “Water. Rest. Shade.” The agency updated Campaign materials in 2021 to recognize both indoor and outdoor heat hazards, as well as the importance of protecting new and returning workers from hazardous heat with an acclimatization period. In addition, OSHA maintains on its website a Heat Topics page on workplace heat exposure ( https://www.osha.gov/heat-exposure/ ), which provides additional information and resources. The page provides information on planning and supervision in hot work environments, identification of heat-related illness and first aid, information on prevention such as training, calculating heat stress and controls, personal risk factors, descriptions of other heat standards and case study examples of situations where workers developed heat-related illness. OSHA and NIOSH also co-developed a Heat Safety Tool Smartphone App for both Android and iPhone devices (see www.osha.gov/heat/heat-app ). The app provides outdoor, location-specific temperature, humidity, and heat index (HI) readings. Measurements for indoor work sites must be collected and manually entered into the app by the user for accurate calculations. The app also provides relevant information on identifying signs and symptoms of heat-related illness and steps to prevent heat-related injuries and illnesses. Despite the strengths and reach of the Campaign, Heat Topics page, and Heat Safety Tool App, these guidance and communication materials are not legally enforceable requirements. III. OSHA's Heat-Related Enforcement Without a specific standard governing hazardous heat conditions at workplaces, the agency currently enforces section 5(a)(1) (the General Duty Clause) of the OSH Act against employers that expose their workers to this recognized hazard. Section 5(a)(1) states that employers have a general duty to furnish to each of their employees “employment and a place of employment which are free from recognized hazards that are causing or are likely to cause death or serious physical harm” to employees (29 U.S.C. 654(a)(1)). To prove a violation of the General Duty Clause, OSHA must establish—in each individual case—that: (1) the employer failed to keep the workplace free of a hazard to which its employees were exposed; (2) the hazard was recognized; (3) the hazard was causing or likely to cause death or serious injury; and (4) a feasible means to eliminate or materially reduce the hazard existed (see, e.g., A.H. Sturgill Roofing, Inc., 2019 O.S.H. Dec. (CCH) ¶  33712, 2019 WL 1099857 (No. 13-0224, 2019)). OSHA has relied on the General Duty Clause to cite employers for heat-related hazards for decades (see, e.g., Duriron Co., 11 BNA OSHC 1405, 1983 WL 23869 (No. 77-2847, 1983), aff'd, 750 F.2d 28 (6th Cir. 1984)). According to available OSHA enforcement data, between 1986 and 2023, Federal OSHA issued at least 348 hazardous heat-related citations under the General Duty Clause. Of these citations, 85 were issued between 1986-2000 (OSHA, 2024b). Citations were identified using multiple queries of OSHA enforcement data and then manually reviewed to ensure the inclusion of only citations due to heat exposure and no other exposures ( e.g., burns or explosions). Several keywords were utilized to filter the data for inclusion ( e.g., “heat,” “heat stress,” “heat illness,” “WBGT”) and exclusion ( e.g., “explosion,” “flash,” “electrical burn,” “fire”). Due to limitations of the data set on which OSHA relied, OSHA did not have access to violation text descriptions of citations issued before the mid-1980s and thus did not determine how many are related to heat exposure prior to this time period. Additionally, over half of the citations from 1986-1989 are missing violation text descriptions, which likely resulted in an undercount of heat-related citations. OSHA has used its general inspection authority (29 U.S.C. 657) to target heat-related injuries and illnesses in various Regional Emphasis Programs (REPs). OSHA enforcement emphasis programs focus the agency's resources on particular hazards or high-hazard industries (see Marshall v. Barlow's, Inc. , 436 U.S. 307, 321 (1978) (affirming OSHA's use of an administrative plan containing specific neutral criteria to focus inspections)). OSHA's Region VI regional office, located in Dallas, TX, has a heat-related special REP (OSHA, 2019). This region covers Texas, New Mexico, Oklahoma, Arkansas, and Louisiana. OSHA's Region IX regional office, located in San Francisco, CA, also has a heat-related REP (OSHA, 2022). This region covers American Samoa, Arizona, California, Guam, Hawaii, Nevada, and the Northern Mariana Islands. These REPs allow field staff to conduct heat illness inspections of outdoor work activities on days when the high temperature is forecasted to be above 80 °F. On September 1, 2021, OSHA issued updated Inspection Guidance for Heat-Related Hazards, which established a new enforcement initiative to protect employees from heat-related injuries and illnesses while working in hazardous hot indoor and outdoor environments (OSHA, 2021). The guidance provided that days when the heat index exceeds 80 °F would be considered heat priority days. It announced that enforcement efforts would be increased on heat priority days for a variety of indoor and outdoor industries, with the aim of identifying and mitigating potential hazards and preventing heat-illnesses before they occur. In April 2022, OSHA launched a National Emphasis Program (NEP) to protect employees from heat-related hazards and resulting injuries and illnesses in outdoor and indoor workplaces. The NEP expanded the agency's ongoing heat-related injury and illness prevention initiatives and campaign by setting forth a targeted enforcement component and reiterating its compliance assistance and outreach efforts. The NEP targets specific industries expected to have the highest exposures to heat-related hazards and resulting illnesses and deaths. This approach is intended to encourage early interventions by employers to prevent illnesses and deaths among workers during high heat conditions (CPL 03-00-024). As of June 26, 2024, OSHA has conducted 5,038 Heat NEP Federal inspections. More than 1,229 of these were initiated by complaints and 117 were due to the occurrence of a fatality or catastrophe. As a result of these inspections, OSHA issued 56 General Duty Clause citations and 736 Hazard Alert Letters (HALs). Inspections occurred across various industries (as identified by 2-digit NAICS codes) including construction, which had the highest number of inspections, as well as manufacturing, maritime, agriculture, transportation, warehousing, food services, waste management, and remediation services. On July 27, 2023, OSHA issued a heat hazard alert to remind employers of their obligation to protect workers against heat injury and illness in outdoor and indoor workplaces. The alert highlights what employers can and should be doing to protect employees. It also serves to remind employees of their rights, including protections against retaliation. In addition, the alert highlights steps OSHA is currently taking to protect workers and directs employers, employees, and the public to OSHA resources, including guidance and fact sheets on heat. OSHA's efforts to protect employees from hazardous heat conditions using the General Duty Clause, although important, have limitations leaving many workers vulnerable to heat-related hazards. For example, the Commission has struggled to determine exactly what conditions create a recognized heat hazard under the General Duty Clause, and has therefore suggested the necessity of a standard (see, A.H. Sturgill Roofing, Inc., 2019 OSHD (CCH) ¶  33712, 2019 WL 1099857, at *2-5 and n.8 (No. 13-0224, 2019) (“The Secretary's failure to establish the existence of an excessive heat hazard here illustrates the difficulty in addressing this issue in the absence of an OSHA standard.”); U.S. Postal Service, 2023 OSHD (CCH) ¶ 33908, 2023 WL 2263313, at *3 n.7 (Nos. 16-1713, 16-1872, 17-0023,17-0279, 2023) (noting Commissioner Laihow's opinion that “A myriad of factors, such as the geographical area where the work is being performed and the nature of the tasks involved, can impact” whether excessive heat is present, and indicating that a standard is therefore necessary to define the hazard). Under the General Duty Clause, OSHA cannot require abatement before proving in an enforcement proceeding that specific workplace conditions are hazardous; whereas a standard would establish the existence of the hazard at the rulemaking stage, thus allowing OSHA to identify and require specific abatement measures without having to prove the existence of a hazard in each case (see Sanderson Farms, Inc. v. Perez, 811 F.3d 730, 735 (5th Cir. 2016) (“Since OSHA is required to determine that there is a hazard before issuing a standard, the Secretary is not ordinarily required to prove the existence of a hazard each time a standard is enforced.”)). Given OSHA's burden under the General Duty Clause, it is currently difficult for OSHA to ensure necessary abatement before employee lives and health are unnecessarily endangered. Further, under the General Duty Clause OSHA must largely rely on expert witness testimony to prove both the existence of a hazard and the availability of feasible abatement measures that will materially reduce or eliminate the hazard in each individual case (see, e.g., Industrial Glass, 15 BNA OSHC 1594, 1992 WL 88787, at *4-7 (No. 88-348, 1992)). Moreover, as OSHA has noted in similar contexts, standards have the advantage of providing greater clarity to employers and employees of the measures required to protect employees and are developed with the benefit of information gathered in the notice and comment process (see 86 FR 32376, 32418 (Jun. 21, 2021) (COVID-19 Healthcare ETS); 56 FR 64004, 64007 (Dec. 6, 1991) (Bloodborne Pathogens Standard)). OSHA currently has other existing standards that, while applicable to some issues related to hazardous heat, have not proven to be adequate in protecting workers from exposure to hazardous heat. For example, OSHA's Recordkeeping standard (29 CFR 1904.7) requires employers to record and report injuries and illnesses that meet recording criteria. Additionally, the agency's Sanitation standards (29 CFR 1910.141, 1915.88, 1917.127, 1926.51, and 1928.110) require employers to provide potable water readily accessible to workers. While these standards require that drinking water be made available in “sufficient amounts,” they do not specify quantities, and employers are not required to encourage workers to frequently hydrate on hot days. OSHA's Safety Training and Education standard (29 CFR 1926.21) requires employers in the construction industry to train employees in the recognition, avoidance, and prevention of unsafe conditions in their workplaces. OSHA's PPE standards (29 CFR 1910.132, 1915.152, 1917.95, and 1926.28) require employers to conduct a hazard assessment to determine the appropriate PPE to be used to protect employees from the hazards identified in the assessment. However, hazardous heat is not specifically identified as a hazard for which workers need training or PPE, complicating the application of these requirements to hazardous heat. IV. Rulemaking Activities Leading to This Proposal OSHA has received multiple petitions to promulgate a heat injury and illness prevention standard, including in 2018 from Public Citizen, on behalf of approximately 130 organizations (Public Citizen et al., 2018). OSHA has also been urged by members of Congress to initiate rulemaking for a Federal heat standard, as well as by the Attorneys General of several States in 2023. On October 27, 2021, OSHA published an advance notice of proposed rulemaking (ANPRM) for Heat Injury and Illness Prevention in Outdoor and Indoor Work Settings in the Federal Register (86 FR 59309) (referred to as “the ANPRM” hereafter). The ANPRM outlined key issues and challenges in occupational heat-related injury and illness prevention and aimed to collect evidence, data, and information critical to informing how OSHA proceeds in the rulemaking process. The ANPRM included background information on injuries, illnesses, and fatalities due to heat, underreporting, scope, geographic region, and inequality in exposures and outcomes. The ANPRM also covered existing heat injury and illness prevention efforts, including OSHA's efforts, the NIOSH criteria documents, State standards, and other standards. The initial public comment period was extended and closed on January 26, 2022. In response to the ANPRM, OSHA received 965 unique comments. The comments covered several topics, including the scope of a standard, heat stress thresholds for workers across various industries, heat acclimatization planning, and heat exposure monitoring, as well as the nature, types, and effectiveness of controls that may be required as part of a standard. Following the publication of the ANPRM, OSHA presented topics from the ANPRM and updates on the heat rulemaking to several stakeholders, including several trade associations, the Office of Advocacy of the Small Business Administration's (SBA's Office of Advocacy) Labor Safety Roundtable (November 19, 2021), and NIOSH National Occupational Research Agenda (NORA) councils, including the Construction Sector Council (November 17, 2021), Landscaping Safety Workgroup (January 12, 2022), and Oil and Gas Extraction Sector (April 7, 2022). On May 3, 2022, OSHA held a virtual public stakeholder meeting on the agency's “Initiatives to Protect Workers from Heat-Related Hazards.” A total of over 1,300 people attended the virtual meeting, and the recorded video has been viewed over 3,500 times (see www.youtube.com/watch?v=Ud29WsnsOw8 ) as of June 2024. The six-hour meeting provided stakeholders an opportunity to learn about and comment on efforts OSHA is taking to protect workers from heat-related hazards and ways the public can participate in the agency's rulemaking process. OSHA also established a Heat Injury and Illness Prevention Work Group of the National Advisory Committee on Occupational Safety and Health (NACOSH) to support the agency's rulemaking and outreach efforts. The Work Group was tasked with reviewing and developing recommendations on OSHA's heat illness prevention guidance materials, evaluating stakeholder input, and developing recommendations on potential elements of any proposed heat injury and illness prevention standard. On May 31, 2023, the Work Group presented its recommendations on potential elements of a proposed heat injury and illness prevention standard for consideration by the full NACOSH committee. The Work Group recommended that any proposed heat injury and illness prevention standard include: a written exposure control plan/heat illness prevention plan; training; environmental monitoring; workplace control measures; acclimatization; worker participation; and emergency response (Document ID OSHA-2023-0003-0007). After deliberations, NACOSH amended the report to ask OSHA to include a model written plan and then submitted its recommendations to the Secretary of Labor (Document ID OSHA-2023-0003-0012). As an initial rulemaking step, OSHA convened a Small Business Advocacy Review Panel (SBAR Panel) on August 25, 2023, in accordance with the Regulatory Flexibility Act (RFA) (5 U.S.C. 601 et seq. ), as amended by the Small Business Regulatory Enforcement Act (SBREFA) of 1996. This SBAR Panel consisted of members from OSHA, SBA's Office of Advocacy, and the Office of Information and Regulatory Affairs (OIRA) in the White House Office of Management and Budget (OMB). The SBAR Panel identifies individual representatives of affected small entities, termed small entity representatives (SERs), which includes small businesses, small local government entities, and non-profits. This process enabled OSHA, with the assistance of SBA's Office of Advocacy and OIRA, to obtain advice and recommendations from SERs about the potential impacts of the regulatory options outlined in the regulatory framework and about additional options or alternatives to the regulatory framework that may alleviate those impacts while still meeting the objectives and requirements of the OSH Act. The SBAR Panel hosted six online meetings on September 9, 12, 13, 14, 18, and 19, 2023, with participation from a total of 82 SERs from a wide range of industries. A final report containing the findings, advice, and recommendations of the SBAR Panel was submitted to the Assistant Secretary of Labor for Occupational Safety and Health on November 3, 2023, to help inform the agency's decision making with respect to this rulemaking (Document ID OSHA-2021-0009-1059). In accordance with 29 CFR parts 1911 and 1912, OSHA presented to the Advisory Committee on Construction Safety and Health (ACCSH) on its framework for a proposed rule for heat injury and illness prevention in outdoor and indoor work settings on April 24, 2024. The Committee then passed unanimously a motion recommending that OSHA proceed expeditiously with proposing a standard on heat injury and illness prevention. The Committee also recommended that OSHA consider the feedback and questions discussed by Committee members during the meeting in formulating the proposed rule (see the minutes from the meeting, Docket No. 2024-0002). OSHA has considered the Committee's feedback in the development of this proposal. In accordance with Executive Order 13175, Consultation and Coordination with Indian Tribal Governments, 65 FR 67249 (Nov. 6, 2000), OSHA held a listening session with Tribal representatives regarding this Heat Injury and Illness Prevention in Outdoor and Indoor Work Settings rulemaking on May 15, 2024. OSHA provided an overview of the rulemaking effort and sought comment on what, if any, tribal implications would result from the rulemaking. A summary of the meeting and list of attendees can be viewed in the docket (DOL, 2024a). D. Other Standards Various other organizations have also either identified the need for standards to prevent occupational heat-related injury and illness or published their own standards. In 2024, the American National Standards Institute/American Society of Safety Professionals A10 Committee (ANSI/ASSP) published a consensus standard on heat stress management in construction and demolition operations. The International Organization for Standardization (ISO) also has a standard for evaluating heat stress: ISO 7243: Ergonomics of the thermal environments—Assessment of heat stress using the WBGT (wet bulb globe temperature) index (ISO, 2017). ISO 7243 uses WBGT values, along with metabolic rate, to assess hot environments, similar to ACGIH and NIOSH recommendations. Additional ISO standards address predicting sweat rate and core temperature (ISO 7933), and determining metabolic rate (ISO 8996), physiological strain (ISO 9886), and thermal characteristics for clothing (ISO 9920). In 2021, the American Society for Testing and Materials (ASTM) finalized its Standard Guide for Managing Heat Stress and Heat Strain in Foundries (E3279-21) which establishes “best practices for recognizing and managing occupational heat stress and heat strain in foundry environments.” The standard outlines employer responsibilities and recommends elements for a “Heat Stress and Heat Strain Management Program” (ASTM, 2021). ACGIH has identified TLVs for heat stress (ACGIH, 2023). The TLVs utilize WBGT and take into consideration metabolic rate or workload categories. Additionally, ACGIH provides clothing adjustment factors which are added to the measured WBGT for certain types of work clothing to account for the impaired thermal regulation. The U.S. Armed Forces has developed extensive heat-related illness prevention and management strategies. The Warrior Heat and Exertion Related Events Collaborative is a tri-service group of military leaders focused on clinical, educational, and research efforts related to exercise and exertional heat-related illnesses and medical emergencies (HPRC, 2023). The U.S. Army has a Heat Center at Fort Benning which focuses on management, research, and prevention of heat-related illness and death (Galer, 2019). In 2023, the U.S. Army updated its Training and Doctrine Command (TRADOC) Regulation 350-29 addressing heat and cold casualties. The regulation includes requirements for rest and water consumption according to specific WBGT levels and work intensity (Department of the Army, 2023). The U.S. Navy has developed Physiological Heat Exposure Limit curves that are based on metabolic and environmental heat loads and represent the maximum allowable heat exposure limits, which were most recently updated in 2023. The Navy monitors WBGT and has guidelines based on these measurements, with physical training diminishing as WBGTs increase and all nonessential outdoor activity stopped when WBGTs exceed 90 °F (Department of the Navy, 2023). The U.S. Marine Corps follows the Navy's guidelines for implementation of the Marine Corps Heat Injury Prevention Program (Commandant of the Marine Corps, 2002). In 2022, the U.S. Army and U.S. Air Force issued an update to their technical heat stress bulletin, which outlines measures to prevent indoor and outdoor heat-related illness in soldiers. The bulletin includes recommended acclimatization planning, work-rest cycles, fluid and electrolyte replacement, and limitations on work based on WBGT (Department of the Army, 2022). As of April 2024, five States have promulgated heat standards requiring employers in various industries and workplace settings to implement protections to reduce the risk of heat-related injuries and illnesses for their employees: California, Minnesota, Oregon, Washington, and Colorado. In addition, Maryland and California are currently engaged in rulemaking. State standards differ in the scope of coverage (see tables III-1 and 2). For example, Minnesota's standard covers only indoor workplaces. California and Washington standards cover only outdoor workplaces, although California's proposal would include coverage of indoor workplaces. Oregon's rule covers both indoor and outdoor workplaces. State rules also differ in the methods used for triggering protections against hazardous heat. Minnesota's standard considers the type of work being performed (light, moderate, or heavy) and provides WBGT trigger levels based on the type of work activity. California's heat-illness prevention protections go into effect at an ambient temperature of 80 °F. Washington's rule also relies on ambient temperature readings combined with considerations for the breathability of workers' clothing. Oregon's rule uses a heat index 80 °F as a trigger. California, Washington, Colorado, and Oregon all have additional protections that are triggered by high heat. However, they differ as to the trigger for these additional protections. In California, high heat protections are triggered at an ambient temperature reading of 95 °F (and only apply in certain industries). In Washington, high heat protections are triggered at an ambient temperature reading of 90 °F. In Colorado, additional protections are triggered at an ambient temperature reading of 95 °F or by other factors such as unhealthy air quality, length of workday, heaviness of clothing or gear, and acclimatization status. These additional protections only apply to the agricultural industry. Finally, in Oregon, high heat protections are triggered at a heat index of 90 °F. All the State standards require training for employees and supervisors. All the State standards, except for Minnesota, require employers to provide at least one quart of water per hour for each employee, require some form of emergency response plan, include provisions related to acclimatization for workers, and require access to shaded break areas. Washington and Oregon require that employers provide training in a language that the workers understand. Similarly, California's standard requires that employers create a written heat-illness prevention plan in English as well as in whatever other language is understood by the majority of workers at a given workplace. California also requires close monitoring of new employees for the first fourteen days and monitoring of all employees during a heat wave. Table III-1 below provides an overview of the provisions included in the existing and proposed State standards on heat injury and illness prevention. Table III-2 provides an overview of the additional provisions required when the high heat trigger is met or exceeded. Table III-1—Initial Heat Triggers and Provisions in State Heat Standards Threshold Provision of water Shade or cool-down means Rest breaks if needed Emergency response Acclimatization Training Heat illness prevention plan Observation/ supervision General California: Outdoor 80 °F (Ambient) 1 • • • • • • • Washington: Outdoor 80 °F (Ambient), All other clothing; 52 °F, Non-breathable clothes • • • • • • • (accident prevention) Colorado: Agriculture 80 °F (Ambient) • • • • • • • California (proposal): Indoor 82 °F (Ambient) • • • • • • • Maryland (proposal): Indoor & Outdoor 80 °F (Heat Index) • • • • • • Minnesota: 2 Indoor 86 °F (WBGT), Light work; 80 °F, Moderate work; 77 °F, Heavy work • Oregon: Indoor & Outdoor 80 °F (Heat Index) • • • • • • 1 Some provisions, including water, emergency response, training, and heat illness prevention plan, apply to covered employers regardless of the temperature threshold. 2 Minnesota uses a 2-hour time-weighted average permissible exposure limit rather than a trigger. Table III-2—High Heat Triggers and Additional Provisions in State Heat Standards Threshold Work-rest schedule Observation/supervision Pre-shift meetings Assessment and control measures 1 Additional High Heat Provisions California: Outdoor 2 95 °F (Ambient) • (only agriculture) • • Washington: Outdoor 90 °F (Ambient) • • Colorado: Agriculture 95 °F (Ambient) or other condition 3 • covered in general provisions above • California (proposal): Indoor 87 °F (Ambient or Heat Index) or other conditions 4 • Maryland (proposal): Indoor & Outdoor 90 °F (Heat Index) • • Oregon: Indoor & Outdoor 90 °F (Heat Index) • • 1 Assessment and control measures include measuring temperature and heat index, identifying and evaluating all other environmental risk factors for heat illness, and using specified control measures to minimize the risk of heat illness. 2 High heat procedures apply in agriculture; construction; landscaping; oil and gas extraction; transportation or delivery of agricultural products, construction materials or other heavy materials, except for employment that consists of operating an air-conditioned vehicle and does not include loading or unloading. 3 Other conditions include unhealthy air quality, shifts over 12 hours, heavy clothing or gear required, or the employee is new or returning from absence. 4 Other conditions include wearing clothing that restricts heat removal, or working in a high radiant heat area, when the ambient temperature is at or above 82 °F. IV. Health Effects A. Introduction I. Health Effects of Occupational Heat Exposure Exposure to workplace heat can be seriously detrimental to workers' health and safety and, in some cases, can be fatal. Workplace heat contributes to heat stress, which is a person's total heat load (NIOSH, 2016) from the following sources combined: (1) heat from the environment, including heat generated by equipment or machinery; (2) metabolic heat generated through body movement, which is proportional to one's relative level of exertion (Sawka et al., 1993; Astrand 1960); and (3) heat retained due to clothing or personal protective equipment (PPE), which is highly dependent on the breathability of the clothing and PPE worn (Bernard et al., 2017). Heat is routinely an occupation-specific risk because, for example, workers may experience greater heat stress than non-workers, particularly when they are required to work through shifts with prolonged heat exposure, complete tasks that require physical exertion, and/or their employers do not take adequate steps to protect them from exposure to hazardous heat. In addition, many work operations require the use of PPE. PPE can increase heat stress and can reduce workers' heat tolerance by decreasing the body's ability to cool down. Workers may also face pressure, or incentivization through pay structures ( e.g., piece-rate, bonuses), to work through hazardous heat. Pressure to produce results and be seen as a good worker can have a direct impact on worker self-care choices that impact health (Wadsworth et al., 2019). Pay structures and production quotas intended to motivate workers may also compromise worker safety (Iglesias-Rios et al., 2023). These pressures can increase their risk of heat-related injury and illness (Billikopf and Norton, 1992; Johansson et al., 2010; Spector et al., 2015; Pan et al., 2021). The body's response to heat stress is called heat strain (NIOSH, 2016). As the heat stress a person experiences increases, the body attempts to cool itself by releasing heat into the surrounding environment. If the body begins to acquire heat faster than it can release it, the body will store heat. As stored heat accumulates, the body can show signs of excessive heat strain, such as increased core temperature and heart rate, as well as symptoms of heat strain, such as sweating, dizziness, or nausea. Two large meta-analyses (n=2,409 and n=11,582) 1 have confirmed that occupational heat exposure is associated with both signs and symptoms of heat strain (Ioannou et al., 2022; Flouris et al., 2018). In one, the authors found a high prevalence of heat strain (35%) among workers in hot conditions, defined by the authors as WBGT greater than 26 °C (78.8 °F); they also found that workers in hot conditions were four times more likely to experience signs and symptoms of heat strain than workers in more moderate conditions (Flouris et al., 2018). 1 In the Health Effects section, OSHA refers to statistics that were reported by authors when describing results from their research studies. These include the sample size (n), the odds ratio (OR), the confidence interval (CI), and the p-value (p). These statistics provide information about effect size, error, and statistical significance. II. Literature Review for Health Effects Section OSHA conducted a non-systematic review of the medical and scientific literature to identify evidence on the relationship between heat exposure and illnesses and death. OSHA's literature review focused on meta-analyses, systematic reviews, and studies cited in NIOSH's Criteria for a Recommended Standard: Occupational Exposure to Heat and Hot Environments, published in 2016. OSHA separately searched for additional meta-analyses and systematic reviews that were not cited in the NIOSH Criteria document, including those that were published after the document was released ( i.e., 2016 and on). OSHA also reviewed sentinel epidemiological evidence including observational, experimental, and randomized controlled studies. OSHA primarily reviewed epidemiological studies focusing on worker populations, athletes, and military members, but also included studies in non-worker populations where appropriate. For example, when there was limited occupation-specific research or data for some heat-related health effects, OSHA sometimes considered general population studies as they relate to understanding physiological mechanisms of heat-related illness, severity of an illness, and prognosis. In addition to the evidence of heat-related illnesses and deaths, OSHA reviewed a large body of evidence that evaluated the association of occupational heat exposure with workplace injuries such as falls, collisions, and other accidents. OSHA also reviewed evidence regarding individual factors such as age, medication use, and certain medical conditions that may affect one's risk for heat-related health effects. III. Summary The best available evidence in the scientific and medical literature, as summarized in this Health Effects section, demonstrates that occupational heat exposure can result in death; illnesses, including heat stroke, heat exhaustion, heat syncope, rhabdomyolysis, heat cramps, hyponatremia, heat edema, and heat rash; and heat-related injuries, including falls, collisions, and other workplace accidents. B. General Mechanisms of Heat-Related Health Effects This section briefly describes the mechanisms of heat-related health effects, i.e., how the body's physiological responses to heat exposure can lead to the heat-related health effects identified in OSHA's literature review. More detailed information about the mechanisms underpinning each specific heat-related health effect is described in the relevant subsections that follow. As explained above, occupational heat exposure contributes to heat stress. The resulting bodily responses are collectively referred to as heat strain (Cramer and Jay, 2016). The bodily responses included in heat strain serve to decrease stored heat by increasing heat loss to the environment to maintain a stable body temperature (NIOSH, 2016). When the brain recognizes that the body is storing heat, it activates the autonomic nervous system to initiate cooling (Kellogg et al., 1995; Wyss et al., 1974). Blood is shunted towards the skin and vasodilation begins, meaning that the blood vessels near the skin's surface become wider, thereby increasing blood flow near the surface of the skin (Kamijo et al., 2005; Hough and Ballantyne, 1899). The autonomic nervous system also triggers the body's sweat response, in which sweat glands release water to wet the skin (Roddie et al., 1957; Grant and Holling, 1938). These processes allow the body to cool in four ways: (1) radiation, i.e., when heat is released directly into the surrounding air; (2) convection, i.e., when there is air movement that moves heat away from the body; (3) evaporation, i.e., when sweat on the skin diffuses into surrounding air (as clothing/PPE permits) and (4) conduction, i.e., when heat is directly transferred through contact with a cooler surface ( e.g., wearing an ice-containing vest (Cramer and Jay, 2016; Leon and Kenefick, 2012)). Importantly, the extent of heat release through radiation, convection, and evaporation depends on environmental conditions such as the speed of air flow, temperature, and relative humidity (Clifford et al., 1959; Brebner et al., 1958). For example, when relative humidity is high, sweat is less likely to evaporate off the skin, which significantly reduces the cooling effect of evaporation. Additionally, when sweat remains on the skin and irritates the sweat glands, it can cause a condition known as heat rash, whereby itchy red clusters of pimples or blisters develop on the skin (DiBeneditto and Worobec, 1985; Sulzberger and Griffin, 1968). While the purpose of the sweat response is to cool the body, in doing so, it can deplete the body's stores of water and electrolytes ( e.g., sodium [Na], potassium [K], chloride [Cl], calcium [Ca], and magnesium [Mg]) that are essential for normal bodily function (Shirreffs and Maughan, 1997). The condition resulting from abnormally low sodium levels is known as hyponatremia. When stores of electrolytes are depleted, painful muscle spasms known as heat cramps can occur (Kamijo and Nose, 2006). Additionally, depletion of the body's stored water causes dehydration, which is known to reduce the body's circulating blood volume (Trangmar and Gonzalez-Alonso, 2017; Dill and Costill, 1974). During vasodilation that happens as the body attempts to cool, blood can pool in areas of the body that are most subject to gravity, and fluid can seep from blood vessels causing noticeable swelling under the skin (known as heat edema). Upright standing would further encourage blood to pool in the legs, and thus, the heart has an even lower blood volume available for circulation (Smit et al., 1999). A large reduction in circulating blood volume will lead to (1) a continued rise in core body temperature, and (2) reduced blood flow to the brain, muscles, and organs. A rise in core body temperature and reduced blood flow to the brain can cause neurological disturbances, such as loss of consciousness, which are characteristic of heat stroke and heat syncope (Wilson et al., 2006; Van Lieshout et al., 2003). A rise in core body temperature and reduced blood flow to muscles can also cause extreme muscle fatigue (to the point of collapse) and muscle cell damage during exertion, which are characteristic of heat exhaustion and rhabdomyolysis, respectively (Torres et al., 2015; Nybo et al., 2014). Finally, a rise in core body temperature and reduced blood flow to organs can damage multiple vital organs (such as the heart, liver, and kidneys), which is often observed in heat stroke (Crandall et al., 2008; O'Donnell and Clowes, 1972). Heat stroke and rhabdomyolysis can lead to death if not treated properly and promptly. C. Identifying Cases of Heat-Related Health Effects In its review of the scientific and medical literature on the health effects of occupational heat exposure, OSHA found several studies that relied upon coding systems, in which medical providers or other public health professionals identify fatalities and non-fatal cases of various illnesses and injuries, including heat-related illnesses and injuries (HRIs). The medical and scientific communities use data from these coding systems to study the incidence and prevalence of illnesses and injuries, including HRIs. In both this Health Effects section and Section V., Risk Assessment, OSHA relied on several studies that make use of data from these coding systems. A brief summary of each of the major coding systems is provided below. I. International Statistical Classification of Diseases and Related Health Problems (ICD) Codes The International Statistical Classification of Diseases and Related Health Problems (ICD) System is under the purview of the World Health Organization (WHO), an international agency that, as the leading authority on health and disease, regularly publishes evidence-based guidelines to advance clinical practice and public health policy. The ICD System harmonizes the diagnosis of disease across many countries, and ICD codes are used routinely in the U.S. healthcare system by medical personnel to record diagnoses in patients' medical records, as well as to identify cause of death. These codes are utilized as part of a standardized system for recording diagnoses, as well as organizing and collecting data into public health surveillance systems. Each ICD code is a series of letters and/or numbers that corresponds to a highly specific medical diagnosis. Healthcare providers may record multiple ICD codes if an individual presents with multiple diagnoses. The ICD system has multiple codes that medical personnel can use when diagnosing HRIs. The ICD system was first developed in the 18th century and was adopted under the purview of the World Health Organization (WHO) in 1948 (Hirsch et al., 2016). Since then, the ICD system has been revised 11 times—ICD-11 was released in 2022. However, because the ICD-11 system has not yet been implemented in the United States, many of the epidemiological studies cited throughout this Health Effects section used the ICD-9 and ICD-10 systems to survey heat-related deaths and HRIs. Table IV-1 provides a list of heat-related ICD-9 and ICD-10 codes. Table IV—1—ICD-9 and ICD-10 Codes for Heat-Related Health Effects * ICD-9 code ICD-10 code equivalent 992 Effects of heat and light T67 Effects of heat and light. 992.0 Heatstroke and sunstroke T67.0 Heatstroke and sunstroke. 992.1 Heat syncope T67.1 Heat syncope. 992.2 Heat cramps T67.2 Heat cramp. 992.3 Heat exhaustion, anhydrotic T67.3 Heat exhaustion, anhydrotic. 992.4 Heat exhaustion due to salt depletion T67.4 Heat exhaustion due to salt depletion. 992.5 Heat exhaustion, unspecified T67.5 Heat exhaustion, unspecified. 992.6 Heat fatigue, transient T67.6 Heat fatigue, transient. 992.7 Heat edema T67.7 Heat edema. 992.8 Other effects of heat and light T67.8 Other effects of heat and light. 992.9 Effects of heat and light, unspecified T67.9 Effects of heat and light, unspecified. E900 Accident caused by excessive heat NA. E900.0 Accident caused by excessive heat due to weather conditions X30 Exposure to excessive natural heat. E900.1 Accidents due to excessive heat of man-made origin W92 Exposure to excessive heat of man-made origin. E900.9 Accidents due to excessive heat of unspecified origin X30 Exposure to excessive natural heat. Note: The above heat-related codes exclude X32 Exposure to sunlight and W89 Exposure to man-made radiation, among others. * These ICD codes are specific to heat as indicated by the names of the codes. There are additional codes that can be associated with diagnosed heat illness but may not be specific to heat-related illness which are not included here but may be included in text where relevant ( e.g., M62.82 for rhabdomyolysis and E87.1 for hypo-osmolality and hyponatremia). Various surveillance systems exist to track documentation of ICD codes. For example, the CDC leverages ICD-10 codes to collect nearly real-time data on heat-related deaths and HRIs through the National Syndromic Surveillance System (NSSP). The CDC also uses ICD-10 codes to collect annual data on heat-related deaths and HRIs, then reports these data via the National Vital Statistics System (NVSS) and National Center for Health Statistics (NCHS). Additionally, all branches of the U.S. Armed Forces ( i.e., Army, Navy, Air Force, and Marine Corps) use ICD-10 codes to document HRIs among service members in the Defense Medical Surveillance System (DMSS). The US Army also uses ICD-10 codes to document HRIs in the Total Army Injury and Health Outcomes Database (TAIHOD) (Bell et al., 2004). II. Occupational Illness and Injury Classification System (OIICS) Codes The U.S. Bureau of Labor Statistics (BLS) is a Federal agency, housed in the Department of Labor, that collects and analyzes data on the U.S. economy and workforce. In 1992, BLS developed the Occupational Illness and Injury Classification System (OIICS) to harmonize reporting of injuries and illnesses that affect U.S. workers. The OIICS is similar to the ICD system. Each OIICS code is a series of numbers that specifies a diagnosis (referred to as the nature of an illness or injury, or a “nature code”) and event(s) leading to an illness or injury (referred to as an “event code”). OIICS was updated in 2010 (Version 2.0), and again in 2022 (Version 3.0); Version 3.0 is the most up to date version ( https://www.bls.gov/iif/definitions/occupational-injuries-and-illnesses-classification-manual.htm; BLS, 2023e). The OIICS system has multiple codes that can be used when identifying occupational HRIs. Table IV-2 provides a list of heat-related OIICS codes (nature and event codes). Table IV—2—OIICS Codes (Version 3.0) for Heat-Related Health Effects † Nature Codes: 172 Effects of heat and light. 1720 Effects of heat—unspecified. 1721 Heat stroke, syncope. 1722 Heat exhaustion, fatigue. 1729 Effects of heat—not elsewhere classified. 2893 Prickly heat, heat rash, and other disorders of the sweat glands including “miliaria rubra”. Event Codes: 53 Exposure to temperature extremes. 530 Exposure to temperature extremes—unspecified. 531 Exposure to environmental heat. 5310 Exposure to environmental heat—unspecified. 5311 Exposure to environmental heat—indoor. 5312 Exposure to environmental heat—outdoor. † Some of the data OSHA relies on uses older versions of OIICS codes (Versions 1 and 2) but the major categories for heat-related incidents did not change significantly between versions. Through a combination of survey staff and a specialized automated coding system, BLS applies OIICS codes to data collected through their worker safety and health surveillance systems, the Census of Fatal Occupational Injuries (CFOI) and the Survey of Occupational Injuries and Illnesses (SOII), to identify and document occupational heat-related deaths and occupational HRIs, respectively. Researchers have also relied on this system for identifying occupational HRIs ( e.g., Spector et al., 2016). However, BLS data does not currently specify discrete codes for all HRIs described in this health effects section. The CFOI is a cooperative program between the Federal Government and the States that relies on various administrative records, including death certificates, to accurately produce counts of fatal work injuries (BLS, 2012). The CFOI examines all cases marked “At work” on the death certificate, and the CFOI database relies on the death certificate (among other sources) to ascertain the cause(s) of death. Further details about BLS reporting using OIICS codes, as well as rates of HRIs, can be found in Section V., Risk Assessment. III. Limitations A limitation to relying on these coding systems to identify heat-related fatalities and HRIs is underreporting. Numerous studies have found that HRIs are likely vastly underreported (see Section V., Risk Assessment). Reasons for the likely underreporting include underreporting of illness and injuries by workers to their employers (Kyung et al., 2023), underreporting of injuries and illnesses by employers to BLS and OSHA (Wuellner and Phipps, 2018; Fagan and Hodgson, 2017), underutilization of workers' compensation insurance (Fan et al., 2006; Bonauto et al., 2010), influence of structural factors and work culture on workers perceptions about seeking help (Wadsworth et al., 2019; Iglesias-Rios, 2023), and difficulties with determining heat-related causes of death ( e.g., Luber et al., 2006; Pradhan et al., 2019). As a result, there are likely many heat-related fatalities and cases of HRIs that are not captured in these coding systems. For a more detailed discussion of underreporting, see Section V., Risk Assessment. IV. Summary As demonstrated by these coding systems, in which medical providers or other public health professionals assign one or more codes to identify a heat-related fatality or HRI, it is well accepted in the medical and scientific communities that heat exposure, including occupational heat exposure, can result in death and HRIs. Indeed, in its review of the best available scientific and medical literature on the health effects of occupational heat exposure, OSHA identified several studies that relied upon data from these coding systems to determine the incidence or prevalence of heat-related deaths and HRIs in workers. OSHA relies on these studies in both this Health Effects section and Section V., Risk Assessment, of this preamble to the proposed rule. D. Heat-Related Deaths I. Introduction Heat is the deadliest weather phenomenon in the United States (NWS, 2022). Heat as a cause of death is widely recognized in the medical and scientific communities. Studies investigating relationships between heat and mortality have long demonstrated positive associations between heat exposure and increased all-cause mortality ( e.g., Weinberger et al., 2020; Basu and Samet, 2002; Whitman et al., 1997). As explained below, the connection between heat exposure, the body's physiological responses, and death ( i.e., heat-related death mechanisms) is clearly established. Exposure to occupational heat can be fatal. According to BLS's CFOI, occupational heat exposure has killed 1,042 U.S. workers between 1992-2022 (BLS, 2024c). II. Physiological Mechanisms Death caused by exposure to heat can occur in occupational settings if the worker's body is not able to adequately cool in response to heat exposure or if treatment for symptoms of heat-related illness is not provided promptly. Nearly all body systems can be negatively affected by heat exposure. Mora et al. (2017) systematically reviewed mechanistic studies on heat-related deaths and identified five harmful physiological mechanisms triggered by heat exposure that can lead to death: ischemia (inadequate blood flow), heat cytotoxicity (damage to and breakdown of cells), inflammatory response (inflammation that disrupts cell and organ function), disseminated intravascular coagulation (widespread dysfunction of blood clotting mechanisms), and rhabdomyolysis (breakdown of muscle tissue). These mechanisms, with the exception of rhabdomyolysis, are associated with the development of heat stroke. Rhabdomyolysis, which is a potentially fatal illness resulting from the breakdown of muscle tissue, can also occur in conjunction with or in the absence of heat stroke. For a more detailed discussion on rhabdomyolysis, see Section IV.H., Rhabdomyolysis. Mora et al. (2017) also identified seven vital organs that can be critically impacted by heat exposure—the brain, heart, kidneys, lungs, pancreas, intestines, and liver. Across the five identified mechanisms and seven vital organs, Mora et al. (2017) found medical evidence for twenty-seven pathways whereby physiological mechanisms triggered by heat exposure could lead to organ failure and fatality. The most common cause of heat-related occupational deaths is heat stroke. Heat stroke is a potentially fatal dysregulation of multiple physiological processes and organ systems resulting in widespread organ damage. Heat stroke is typically marked by significant elevation in core body temperature and cognitive impairment due to central nervous system damage. The physiological mechanisms involved in the development and progression of heat stroke are discussed in more detail in Section IV.E., Heat Stroke. III. Determining Heat as a Cause of Death The identification of deaths caused by heat exposure can take place in a few different ways. Healthcare professionals may identify heat-related deaths in medical settings. For example, a heat-related death may be identified if an individual experiencing heat stroke presents to an emergency room and then later dies. The heat-related nature of the death should be documented by the healthcare professional in the chief complaint field during medical history taking and selection of relevant ICD diagnosis codes. The ICD system allows for identification of heat as either an underlying cause of death or a significant contributing condition. The ICD-10 instruction manual defines underlying cause as “(a) the disease or injury which initiated the train of morbid events leading directly to death, or (b) the circumstances of the accident or violence which produced the fatal injury” (WHO, 2016, p. 31). A significant contributing condition is defined as a condition that “contributed to the fatal outcome, but was not related to the disease or condition directly causing death” (WHO, 2004, p. 24). Medical examiners or coroners can also identify heat as a cause of death or significant condition contributing to death during death investigations, which should be noted on the deceased individual's death certificate. The National Association of Medical Examiners (NAME), a professional organization for medical examiners, forensic pathologists, and medicolegal affiliates and administrators, defines “heat-related death” as “a death in which exposure to high ambient temperature either caused the death or significantly contributed to it” (Donoghue et al., 1997). This definition was developed in an effort to standardize the way in which heat-related deaths were identified and documented on death certificates. According to the NAME definition, cause is ascertained based on circumstances of the death, investigative reports of high environmental temperature ( e.g., a known heat wave), or a pre-death temperature ≥105 °F. Cause is also indicated in cases where the person may have a lower body temperature due to attempted cooling measures, but where the individual had a history of mental status changes and specific toxicological findings of elevated muscle and liver enzymes. Heat may be designated as a “significant contributing condition” if: (1) “antemortem body temperature cannot be established but the environmental temperature at the time of collapse was high”; and/or (2) heat stress exacerbated a pre-existing disease, in which case heat and the pre-existing disease would be listed as the cause and significant contributing condition, respectively, or vice versa. Importantly, Donoghue et al. note “The diagnosis of heat-related death is based principally on investigative information; autopsy findings are nonspecific.” (Donoghue et al., 1997). While this definition is the official definition of this professional organization, other definitions or processes for determining whether or not a death is heat-related may be used. Additionally, there are processes in place to identify and document deaths that are work-related. Death certificates include a field that can be checked for “injury at work” (Russell and Conroy, 1991). Further, work-related fatalities due to heat are identified and documented through the CFOI (for more details, see Section IV.C., Overview of ICD and OIICS Codes for Heat-Related Health Effects). IV. Occupational Heat-Related Deaths Occupational heat exposure has led to worker fatalities in both indoor and outdoor work settings and across a variety of industries, occupations, and job tasks (Petitti et al., 2013; Arbury et al., 2014; Gubernot et al., 2015; NIOSH, 2016; Harduar Morano and Watkins, 2017). BLS's CFOI identified 1,042 U.S. worker deaths due to heat exposure between 1992 and 2022, with an average of 34 fatalities per year during that period (BLS, 2024c). Between 2011 and 2022, BLS reports 479 worker deaths (BLS, 2024c). During the latest three years for which BLS reports data (2020-2022), there was an average of 45 work-related deaths due to exposure to environmental heat per year (BLS, 2024c). However, for the reasons explained in Section V., Risk Assessment, these statistics likely do not capture the true magnitude and prevalence of heat-related fatalities because of underreporting. There are numerous case studies documenting the circumstances under which occupational heat exposure led to death among workers. For example, in three NIOSH Fatality Assessment and Control Evaluations (FACE) investigations of worker fatalities, workers died of heat stroke after not receiving prompt treatment upon symptom onset (NIOSH, 2004; NIOSH, 2007; NIOSH, 2015). Another case report of a farmworker who died due to heat stroke indicates that confusion the worker experienced as a result of heat exposure may have played a role in his ability to seek help (Luginbuhl et al., 2008). Additional case reports show workers have collapsed and later died while working alone, such as in mail delivery (Shaikh, 2023), and that worker distress has been interpreted as drug use as opposed to symptoms of heat illness (Alsharif, 2023). V. Summary OSHA's review of the scientific and medical literature indicates that occupational heat exposure can and does cause death. The physiological mechanisms by which heat exposure can result in death are clearly established in the literature, and heat exposure being a cause of death is widely recognized in the medical and scientific communities. Indeed, occupational surveillance data demonstrates that numerous work-related deaths from occupational heat exposure occur every year. E. Heat Stroke I. Introduction Among HRIs, the most serious and deadly illness from occupational heat exposure is heat stroke. NIOSH (2016) defines heat stroke as “an acute medical emergency caused by exposure to heat from an excessive rise in body temperature [above 41.1 °C (106 °F)] and failure of the [body's] temperature-regulating mechanism.” When this happens, an individual's central nervous system is affected, which can result in a sudden and sustained loss of consciousness preceded by symptoms including vertigo, nausea, headache, cerebral dysfunction, bizarre behavior, and excessive body temperature (NIOSH 2016). Because progression of symptoms varies and involves central nervous system function, it may be difficult for individuals, or those they are with, to know when they are experiencing serious heat illness or to understand that they need urgent medical care (Alsharif, 2023). If not treated promptly, early symptoms of heat stroke may progress to seizures, coma, and death (Bouchama et al., 2022). Thus, heat stroke is often referred to as a life-threatening form of hyperthermia ( i.e., elevated core body temperature) because it can cause damage to multiple organs such as the liver and kidneys. Of note, the term “stroke” in “heat stroke” is a misnomer in that it does not involve a blockage or hemorrhage of blood flow to the brain. There are two types of heat stroke: classic heat stroke (CHS) and exertional heat stroke (EHS). CHS can occur without any activity or physical exertion, whereas EHS occurs as a result of physical activity. CHS typically occurs in environmental conditions where ambient temperature and humidity are high and is most often reported during heat waves (Bouchama et al., 2022). It is most likely to affect young children and the elderly (Laitano et al., 2019). Studies have found that EHS can occur with any amount of physical exertion, even within the first 60 minutes of exertion (Epstein and Yanovich, 2019; Garcia et al., 2022). Additionally, EHS can occur in healthy individuals who would otherwise be considered low risk performing physical activity, regardless of hot or cool environmental conditions (Periard et al., 2022; Epstein et al., 1999). Cases of heat stroke can be identified in a few ways. Medical personnel who make a formal diagnosis of heat stroke record the corresponding ICD code in the patient's medical record. Medical examiners also identify heat stroke as a cause of death or significant condition contributing to death and note it on the deceased individual's death certificate. II. Physiological Mechanisms Heat stroke happens when the body is under severe heat stress and is unable to dissipate excessive heat to keep the body temperature at 37 °C (98.6 °F), resulting in an elevated core body temperature (Epstein and Yanovich, 2019). The hallmark characteristics of heat stroke are: (1) central nervous system (CNS) dysfunction, including encephalopathy ( i.e., brain dysfunction manifesting as irrational behavior, confusion, coma, or convulsions); and (2) damage to multiple organs, including the kidneys, liver, heart, pancreas, gastrointestinal tract, as well as the circulatory system. There are three accepted mechanisms through which heat exposure can cause CNS dysfunction and/or multi-organ damage (Bouchama et al., 2022; Garcia et al., 2022; Iba et al., 2022). All three mechanisms share a common origin: heat exposure contributes to excessive heat stress, which results in hyperthermia. One mechanism of heat stroke is reduced cerebral blood velocity (CBV) (an indicator of blood flow to the brain) that results in orthostatic intolerance ( i.e., the inability to remain upright without symptoms) (Wilson et al., 2006). As individuals experience whole body heating, CBV is reduced and cerebral vascular resistance (the ratio of carbon dioxide stimulus to cerebral blood flow) increases. These changes ultimately contribute to reduced cerebral perfusion (flow of blood from the circulatory system to cerebral tissue) and blood flow, as well as orthostatic intolerance (Wilson et al., 2006). Another mechanism is damage to the vascular endothelium. Hyperthermia can damage or kill cells in the lining of blood vessels, known as the vascular endothelium. The body responds to vascular endothelium damage through a process called disseminated intravascular coagulation (DIC). DIC is characterized by two processes: (1) tiny clots form in the tissues of multiple organs, and (2) bleeding occurs at the sites of those tiny clots. DIC is extremely damaging and results in injury to organs (Bouchama and Knochel, 2002). Namely, DIC limits the delivery of oxygen and nutrients to several organs including the brain, heart, kidneys, and liver. Thus, DIC can result in both CNS dysfunction and multi-organ damage. Additionally, damage to the vascular endothelium makes it more permeable and creates an imbalance in the substances that control blood clotting, which promotes abnormal and increased blood clotting (Bouchama and Knochel, 2002; Wang et al., 2022). A third mechanism is damage to the cells in the lining of the gut, known as the gut epithelium. Hyperthermia can alter the cell membranes' permeability (Roti Roti et al., 2008), or directly cause cells to die (Bynum et al., 1978). In either case, cells in the gut epithelium will leak endotoxins into the blood, a process known as endotoxemia. When these endotoxins circulate throughout the body, the immune system aggressively responds by activating cells to fight infection and inflammation, known as systemic inflammatory response syndrome (SIRS) (Leon and Helwig, 2010). The presence of endotoxins, as well as the body's aggressive immune response, can cause serious multi-organ damage (Epstein and Yanovich, 2019; Wang et al., 2022). In particular, the liver is usually one of the first organs to be damaged and is often what causes a heat stroke death (Wang et al., 2022). III. Occupational Heat Stroke Heat stroke is life-threatening and can severely impair workers' safety and health (Lucas et al., 2014). A study of work-related HRIs in Florida using hospital data reported that, during the warm seasons from May through October between 2005 through 2012, heat stroke was the primary diagnosis in 91% (21 of 23) of deaths. In total, they reported 160 cases of work-related heat stroke (Harduar Morano and Watkins, 2017). Analyses of heat stroke among military members indicate that roughly 73% of EHS patients require hospitalization for at least two days (Carter et al., 2007). IV. Treatment and Recovery Heat stroke is a serious medical emergency that requires immediate rest, cooling, and usually hospitalization. Prognosis for heat stroke is highly dependent on how quickly heat stroke is recognized and how quickly an affected worker can be cooled. When an affected person can be diagnosed early and cooled rapidly, the prognosis is generally good. For example, rapid cooling within one hour of presentation of symptoms of CHS was found to reduce the mortality rate from 33% to 15% (Vicario et al., 1986). For EHS, cooling the body below 104 °F within 30 minutes of collapse is associated with very good outcomes (Casa et al., 2012; Casa et al., 2015). The authors also reported that they were unaware of any cases of fatalities among EHS victims where it was recorded that the body was cooled below 104 °F within 30 minutes of collapse (Casa et al., 2012). Comparably, others have found that the risk of morbidity and mortality from heat stroke increases as treatment is delayed (Demartini et al., 2015; Schlader et al., 2022). Schlader et al. (2022) found that a delay in cooling can result in tissue damage, multi-organ dysfunction, and eventually death. Similarly, Zeller et al. (2011) found in their retrospective cohort study that patients who did not receive early or immediate cooling had worse outcomes, such as more severe forms of disease or death, although their study design does not allow for conclusions regarding causality (Zeller et al., 2011). Khogali and Weiner's (1980) case study report on 18 cases of heat stroke found that 72% of the patients took between 30-90 minutes to cool, whereas the other 28% were resistant to cooling, taking two to five hours to reach 38 °C (100.4 °F). This means that there is variation in how individuals respond to heat stroke treatment and that some individuals will respond quicker to treatment than others. Prompt treatment is likely even more critical for the individuals who take longer to cool. Data from the general population also demonstrate the serious nature of heat stroke. One analysis of nationwide data estimated that nearly 55% of emergency department visits for heat stroke required hospitalization and roughly 3.5% of patients died in the emergency department or at the hospital (Wu et al., 2014). This study also found that heat stroke medical emergencies are more severe than other non-heat-related emergencies, with a 2.6-fold increase in admission rate and a 4.8-fold increase in case fatality compared to those other conditions (Wu et al., 2014). Complete recovery for individuals who are affected by heat stroke may require time away from work. Some research suggests the length of recovery time and the need for time away from work is based on how long a person was at or above the critical core body temperature of 41 °C (105.8 °F), and how long it takes for biomarkers in blood to normalize (McDermott et al., 2007). Relevant biomarkers include those for acute liver dysfunction, myolysis (the breakdown of muscle tissue), and other organ system biomarkers (Ward et al., 2020; Schlader et al., 2022). Guidelines for military personnel and athletes suggest that it may be weeks or months before a worker who has suffered heat stroke can safely return to work or perform the same level of work they did before suffering heat stroke. U.S. military members have clear return-to-work protocols post-heat stroke where members are assigned grades of functional capacity in six areas: physical capacity or stamina, upper extremities, lower extremities, hearing and ears, eyes, and psychiatric functioning (O'Connor et al., 2007). For example, when a soldier/airman experiences heat stroke, they automatically receive a reduced function capacity grade status in physical capacity. This also results in an automatic referral to a medical examination board. Soldiers and airmen are not cleared to return to duty until their laboratory results normalize, and even then, their status remains a trial of duty. If the individual has not exhibited any heat intolerance after three months, they are returned to a normal work schedule. However, maximal exertion and significant heat exposure remains prohibited for these individuals. If a military member experiences any heat intolerance during the period of restriction, or subsequent resumption to normal duty, a referral to the physical examination board for a hearing regarding their health status is required (O'Connor et al., 2007). The U.S. Navy has its own set of guidelines, which does not distinguish between heat exhaustion and heat stroke, but uses laboratory tests, especially liver function tests, to determine when sailors are allowed to return to duty. For those who have suffered heat stroke, full return to duty is usually not granted until somewhere between two days to three weeks later (O'Connor et al., 2007). In 2023, the American College of Sports Medicine (ACSM) published their consensus statement which provides evidence-based strategies to reduce and eliminate HRIs, including a return to activity protocol for athletes recovering from EHS (Roberts et al., 2023). Of note, ACSM names athletes (whether elite, recreational, or tactical) and occupational laborers as groups who are active and regularly perform exertional activities that could lead to EHS. Specifically, ACSM recommendations include refraining from exercise for at least seven days following release from the initial medical care for EHS treatment. Once all laboratory results and vital signs have normalized, ACSM recommends an individual can exercise in cool environments and gradually increase duration, intensity, and heat exposure over a two to four-week period to initiate environmental acclimatization (Roberts et al., 2023). If the affected athlete does not return to pre-EHS activity levels within four to six weeks, further medical evaluation is needed. ACSM recommends a full return to activity between two to four weeks after the individual has demonstrated exercise acclimatization and heat tolerance with no abnormal symptoms or test results during the re-acclimatization period (Roberts et al., 2023). Similarly, the National Athletic Trainer's Association proposes that individuals who experience EHS should complete a 7 to 21-day rest period, be asymptomatic, have normal blood-work values, and obtain a physician's clearance prior to beginning a gradual return to activity (Casa et al., 2015). In the military setting it is accepted that returning to work too early and/or without adequate work restrictions can result in incomplete recovery from heat stroke, which may necessitate a prolonged restricted work status (McDermott et al., 2007). About 10-20% of people who have had heat stroke have been shown to experience heat intolerance roughly two months after having the heat stroke (Binkley et al., 2002). In some instances, this has lasted for five years and has increased the risk for another heat stroke (Binkley et al., 2002; McDermott et al., 2007). Similarly, a case study report of EHS cases amongst the U.S. Army found that in one of the ten cases examined, the person was heat intolerant for 11.5 months post-EHS (Armstrong et al., 1989). Only a limited number of studies have focused on the long-term effects of heat stroke. This includes research by Wallace et al. (2007), whose retrospective review of military service members found that those who suffered an EHS event earlier in life were more likely to die due to cardiovascular disease and ischemic heart disease. Similarly, Wang et al. (2019) report that prior exertional heat illness was associated with a higher prevalence of acute ischemic stroke, acute myocardial infarction, and an almost three-fold higher prevalence of chronic kidney disease. Other research in mice support these claims and indicate that epigenetic effects post-EHS result in immunosuppression and an altered heat shock protein response as well as development of metabolic disorders that could negatively impact long-term cardiovascular health (Murray et al., 2020; Laitano et al., 2020). V. Summary OSHA's review of the scientific and medical literature indicates that occupational heat exposure can cause heat stroke, a medical emergency. The physiological mechanisms by which heat exposure can result in heat stroke are well-established in the literature, and heat exposure as a cause of heat stroke is well-recognized in the medical and scientific communities. The best available research demonstrates that heat stroke must be treated as soon as possible and that prolonged time between experiencing heat stroke and seeking treatment increases the likelihood of death and may result in long-term health effects. F. Heat Exhaustion I. Introduction NIOSH defines heat exhaustion as “[a] heat-related illness characterized by elevation of core body temperature above 38 °C (100.4 °F) and abnormal performance of one or more organ systems, without injury to the central nervous system” (NIOSH, 2016). Heat exhaustion can progress to heat stroke if not treated properly and promptly, and may require time away from work for a full recovery. Signs and symptoms of heat exhaustion typically include profuse sweating, changes in mental status, dizziness, nausea, headache, irritability, weakness, decreased urine output and elevated core body temperature up to 40 °C (104 °F) (NIOSH, 2016; Kenny et al., 2018). Collapse may or may not occur. Significant injury to the central nervous system, and significant inflammatory response do not occur during heat exhaustion. However, there appears to be a fine line between heat exhaustion and heat stroke. Kenny et al. 2018 state that it can be difficult to clinically differentiate between heat exhaustion and early heat stroke. NIOSH also states that heat exhaustion “may signal impending heat stroke” (NIOSH, 2016). Armstrong et al. (2007) recommend that rectal temperature be taken to distinguish between heat exhaustion and heat stroke. II. Physiological Mechanisms Heat exhaustion occurs when heat stress results in elevated body temperature between 98.6 °F and 104 °F (37 °C and 40 °C) and physiological changes occur (Kenny et al., 2018). Under these significant heat stress conditions, heavy sweating occurs, tissue perfusion is reduced, and inflammatory mediators are released. Electrolyte imbalances can occur due to fluid and electrolyte losses through sweating paired with inadequate replenishment. Voluntary and involuntary dehydration can exacerbate this process (Hendrie et al., 1997; Brake and Bates, 2003). “Voluntary dehydration,” as used by Brake and Bates, refers to the circumstance where a dehydrated worker does not adequately rehydrate, despite the availability of water. Upon review of several studies, Kenny et al. (2018) report that dehydration among workers is common, even when water is readily available. There is also evidence that even when water intake increases, as sweat rate and dehydration increase, intake may not be adequate to fully replace losses (Hendrie et al., 1997). Brake and Bates (2003) summarized various hypothesized reasons for voluntary and involuntary dehydration. One hypothesized reason for voluntary dehydration is a delayed or decreased thirst response (Brake and Bates, 2003). Other reasons include mechanisms that affect fluid retention, such as the dependence of fluid retention on solutes such as sodium, which may be in imbalance under heat stress (Brake and Bates, 2003). Lack of adequate hydration could also be due to workplace pressures or concerns about sanitation (Rao, 2007; Iglesias-Rios, 2023). The combination of heat stress, upright posture, and low vascular fluid volume (hypovolemia) can further dysregulate the circulatory system and affect clotting mechanisms (Kenny et al., 2018). Heat stress reduces blood flow to the abdominal organs, kidneys, muscles, and brain and increases blood flow to the skin to aid in cooling. These changes in the circulatory system and blood flow to the brain can potentially lead to dizziness or faintness upon standing (orthostatic intolerance), or collapse. Other factors that affect the development of heat exhaustion include individual health status, preparedness (such as acclimatization level), individual characteristics, knowledge, access to fluids, environmental factors, personal protective equipment use and work pacing and intensity (Kenny, 2018). III. Occupational Heat Exhaustion Heat exhaustion is one of the more common heat-related illnesses (Armstrong et al., 2007; Harduar Morano and Watkins, 2017; Lewandowski and Shaman, 2022). In their study of heat-illness hospitalizations in Florida during May to October from 2005-2012, Harduar Morano and Watkins (2017) reported that there were 2,659 cases of work-related heat exhaustion that resulted in emergency department visits or hospitalization, versus 181 cases of work-related heat stroke that resulted in emergency department visits, hospitalization, or death. Similar results have been reported in studies of heat-related illness among the United States Armed Forces and miners showing the frequency of heat exhaustion (Dickinson, 1994; Armed Forces Health Surveillance Division, 2022b; Lewandowski and Shaman, 2022; Donoghue et al., 2000; Donoghue, 2004). While in some studies heat exhaustion is not specifically diagnosed, several qualitative studies describe self-reported symptoms in workers that may be indicative of heat exhaustion ( e.g., Mirabelli et al., 2010; Fleischer et al., 2013; Kearney et al., 2016; Mutic et al., 2018). These symptoms included headache, nausea, vomiting, feeling faint, and heavy sweating. IV. Treatment and Recovery Heat exhaustion may require treatment beyond basic first aid to prevent progression to heat stroke (Kenny et al., 2018). In cases where the degree of severity of heat illness is unclear, the individual should be treated as if they have heat stroke (Armstrong, 1989). For a worker experiencing heat exhaustion, NIOSH recommends the following steps to ensure t [Text truncated at 120,000 characters. The full text is on the page linked above.] --- Source: Frix Law Library, https://www.frixlaw.com/law-library/documents/fr%3A2024-14824. Public record. Not legal advice.