The Heat Stress Standard and the Employer's Decision Dilemma

With OSHA's proposed heat rule unfinished but enforcement expanding, the metric an employer chooses to trigger protective action — Heat Index or wet bulb globe temperature — may matter more than the regulation itself.

• By Komi Toviawou
• Oct 15, 2026

On July 26, 2026, Las Vegas reached 111°F while Orlando topped out at 97°F — and by Heat Index, both cities sounded the same alarm. Ask which workforce faced the greater heat danger that afternoon, and the honest answer depends on which metric you consult. That ambiguity sits at the center of the decision facing every safety leader today: the federal heat standard remains unfinished and its future uncertain, yet OSHA is inspecting for heat hazards more actively than at any point in its history.

Where the Rulemaking Stands

The regulatory arc began on October 27, 2021, when OSHA published an Advance Notice of Proposed Rulemaking for Heat Injury and Illness Prevention in Outdoor and Indoor Work Settings (86 Fed. Reg. 59309). On August 30, 2024, the agency published the proposed standard (89 Fed. Reg. 70698), covering general industry, construction, maritime and agriculture. Public comments closed in January 2025; hearings and post-hearing comments concluded on October 30, 2025.

But the path forward remains genuinely uncertain. Legislation introduced in the House in November 2025 (H.R. 6213) would prohibit finalizing or enforcing the proposed standard or any substantially similar one, and it advanced out of committee in July 2026. The Department of Labor's current regulatory agenda projects a supplemental proposal by late 2026 and a final standard in late 2027.

Enforcement, however, is not waiting. On April 10, 2026, OSHA issued a revised National Emphasis Program for outdoor and indoor heat-related hazards, effective immediately for five years, through April 2031. Heat inspections have grown from roughly 200 to about 2,400 per year — approximately 6 percent of all federal OSHA inspections. Under the revised program, inspectors may expand any inspection when heat hazards are evident on heat-priority days and may open heat-focused inspections whenever the National Weather Service issues a heat advisory or warning. The revision also strengthens citation guidance with reorganized appendices for evaluating heat programs.

Hence the dilemma: with no final rule there is no single compliance checklist, yet heat remains fully enforceable today under the OSH Act's General Duty Clause, and the emphasis program materially raises the odds of an inspection. Employers must choose their own guidance — starting with the most consequential choice of all: Heat Index or WBGT.

What the Proposed Standard Would Require

The proposed rule is built on two environmental triggers. The initial heat trigger is an 80°F Heat Index, or a WBGT equal to the NIOSH Recommended Alert Limit. At that point, employers must provide cool drinking water, break areas with shade or air conditioning, and acclimatization protocols for new and returning workers. The first one to two weeks on the job account for a disproportionate share of heat fatalities. At or above the high heat trigger — a 90°F Heat Index, or WBGT at the NIOSH Recommended Exposure Limit, the proposal adds:

• A minimum 15-minute paid rest break at least every two hours
• Observation for signs and symptoms of heat illness, via a buddy system or a supervisor or heat safety coordinator
• A hazard alert before or during the shift
• Two-way communication for lone workers
• Emergency response readiness

While the rule idles, the practical move is a to implement a heat injury and illness prevention plan that meets three tests. First, it must be in writing. Too often the plan lives in one person's head, among the most commonly cited failures, and OSHA can be tolerant on format so long as the plan is actionable. It must also be clear, realistic, and designed around specific work activities. And finally, it must include an emergency response plan and training, with workers and supervisors able to recognize heat illness symptoms and rehearse the response. Employers wanting a check of their program can use OSHA's free On-Site Consultation Program, which is confidential and separate from enforcement.

The rational posture is to act as if the standard were already final. Every element above is already the benchmark inspectors apply under the General Duty Clause and the emphasis program's citation guidance. Building the program now converts regulatory risk into readiness.

Measuring the Right Thing

Here is where many programs quietly fail. The Heat Index is a two-variable comfort regression — temperature and humidity, computed for shade and designed to approximate how hot it feels. Wet Bulb Globe Temperature (WBGT) integrates the four drivers of physiological heat strain: air temperature, humidity, solar radiant load and wind. That is why ACGIH, NIOSH, ISO 7243 and the U.S. military all set work-rest limits in WBGT, not Heat Index.

The difference is not just purely academic. The figure below maps 2,305 National Weather Service airport-station observations for July 26, 2026. By air temperature, the Desert Southwest is the obvious national hot spot at 111°F. Converted to peak-afternoon Heat Index, the emphasis flips east: the corridor plunges into the Danger band, Omaha posts a 117.8°F Heat Index, and Las Vegas's Heat Index lands at 106.3°F, below its own 111°F air temperature, because in dry desert air sweat evaporates efficiently enough that the body outperforms the thermometer.

Estimated WBGT sharpens the picture further: most of the West sits in the low band despite triple-digit air temperatures, while Orlando, 14°F cooler than Las Vegas and carrying a nearly identical Heat Index registered a WBGT two work-rest bands higher, 88.2°F against 81.5°F, under ACGIH screening at a moderate workload. Same alarm, different realities. And in Omaha, the 117.8°F Heat Index met a WBGT at the threshold of the extreme band.

The operational stakes cut both ways. In the dry West, a Heat Index-triggered program stops work the body could safely perform: pure productivity loss. In contrast, where WBGT runs hot relative to Heat Index, the humid Gulf and Southeast, a Heat Index-only program under-alarms exactly where workers are most likely to collapse. At the dry extreme the gap is stark: that same afternoon, Twentynine Palms, California posted a 105°F Heat Index against an estimated WBGT of just 80°F. And everywhere the alarm sounds constantly, alert fatigue sets in. And when the trigger fires all season, crews and supervisors’ habituate. They are numbest on the one afternoon that is genuinely lethal.

The best practice therefore starts with measuring WBGT on site. Forecasts and airport stations screen well, but a globe-equipped measurement at representative work areas is the compliance-grade approach, especially indoors, where no forecast applies. Around that measurement, a successful program tracks a short list of metrics: work-rest compliance against the ACGIH or NIOSH tables at the actual workload; acclimatization status for every new and returning worker; hydration availability; heat-illness near-misses; and the alert-to-action ratio, how often alerts fire versus how often crews act. Alerts that are rare, credible and always acted upon protect both the workforce and the schedule.

The federal standard will arrive, or it won't. Either way, the employers in the strongest position legally and operationally will be the ones who stopped waiting, wrote the plan and started measuring the thing that helps create a balance between productivity and safety.

Data: NWS ASOS observations via Iowa Environmental Mesonet, Iowa State University. 2,305 CONUS stations reporting. Visualization by the author

Methodology: Heat Index = NWS Rothfusz regression (peak-afternoon temperature paired with concurrent/min relative humidity). Estimated WBGT = ISO 7243 outdoor formula (0.7·Tnwb + 0.2·Tg + 0.1·Ta) using Stull (2011) psychrometric wet-bulb plus a clear-sky midday solar-load estimate for globe temperature, evaluated at the 2 p.m. Eastern observation. Thresholds: NWS Heat Index advisory bands; ACGIH 2024 TLV®/Action Limit work-rest screening for the selected workload.

Disclosure: WBGT here is estimated from air temperature, dewpoint, and wind — not measured with a globe thermometer. On-site WBGT instruments remain the compliance-grade measurement; this map is a screening and communication tool. The fixed clear-sky solar assumption can overstate WBGT where it was actually cloudy at 2 p.m., which is conservative in the protective direction.

This article originally appeared in the October 2026 issue of Occupational Health & Safety.