When we think about workplace heat exposure, images of construction workers under the blazing sun or farmers toiling in fields typically come to mind. However, groundbreaking new research from Harvard's T.H. Chan School of Public Health reveals a sobering truth: heat is silently increasing the risk of injury for workers across virtually every industry—including those working primarily indoors.
A Hidden Crisis in Workers' Compensation
Published in Environmental Health in October 2025, this first-ever nationwide analysis examined 845,014 workplace injuries reported to OSHA in 2023. The findings should alarm every employer, safety professional, and workers' compensation insurer in America.
The research team, led by Dr. Barrak Alahmad, discovered that approximately 28,000 workplace injuries in 2023 can be directly attributed to heat exposure. Yet here's the critical issue for workers' comp: most of these injuries are never classified as "heat-related."
A worker who slips and falls, drops a heavy object, or makes a judgment error on a hot day typically files a claim for a fall injury, a crushing injury, or whatever the immediate cause appears to be. The underlying role of heat—impairing their coordination, attention, reaction time, and decision-making—goes unrecognized and unrecorded.
Why Heat Matters for Every Industry
The study's most striking finding? Heat increases the risk of injury across nearly all major industry sectors, not just traditional outdoor occupations. Industries showing significant heat-related injury increases include:
- Healthcare and Social Assistance (25.8% of all injuries studied)
- Transportation and Warehousing (21.8%)
- Retail Trade (19.1%)
- Manufacturing (18.1%)
Even predominantly indoor workplaces showed elevated injury rates on hotter days. Why? Because heat affects basic human physiology and cognitive function. Research shows that elevated temperatures impair:
- Hand-eye coordination
- Balance and postural stability
- Physical reaction times
- Attention and focus
- Memory and information processing
- Judgment and decision-making
- Muscle function
The Temperature Danger Zone
The research identified a critical threshold: injury risk begins to rise around an 85°F heat index and accelerates sharply above 90°F. The heat index, which combines temperature and humidity, reflects how hot it actually feels to the human body.
Here's what the data shows compared to a comfortable 80°F baseline:
- At 90°F: 3% increase in injury odds
- At 95°F: 6% increase
- At 100°F: 10% increase
- At 105°F: 15% increase
- At 110°F: 20% increase
This means on a 110°F day, a worker is 20% more likely to be injured than on an 80°F day—regardless of whether they work outdoors or in a warehouse, hospital, or retail store.
Heat Standards Work
Perhaps the most important finding for policy and practice is that states with occupational heat rules showed significantly lower increases in heat-related injuries than states without such protections.
At a heat index of 110°F:
- States without heat rules: 22% increase in injury odds
- States with heat rules: 9% increase in injury odds
This represents a roughly 60% reduction in heat-attributable injury risk. As of 2023, the five states with heat standards were California, Colorado, Minnesota, Oregon, and Washington. California's data alone showed a 36% relative reduction in heat injury risk compared to states without regulations.
These regulations typically require:
- Access to water and shade
- Rest breaks during extreme heat
- Acclimatization periods for new or returning workers
- Training on heat illness symptoms
- Written heat illness prevention plans
- Emergency response procedures
Workers' Compensation Implications
This research has profound implications for the workers' compensation system:
1. Underreporting and Misclassification The true cost of heat exposure is hidden in claims data. Traditional "heat illness" claims (heat stroke, heat exhaustion) represent only the tip of the iceberg. The 28,000 estimated heat-attributable injuries dwarf OSHA's official count of 3,288 annual heat injuries.
2. Claims Costs Falls, crushing injuries, lacerations, and other acute trauma caused by heat-impaired performance often result in expensive claims with lost workdays, medical treatment, and sometimes permanent disability. Insurers and employers are paying for heat exposure without recognizing it.
3. Prevention Opportunities Understanding heat's role in diverse injury types opens new prevention strategies. Rather than viewing heat illness as a niche issue affecting only outdoor workers, the industry must recognize heat as a widespread hazard requiring systemic controls.
4. Underestimation of Burden The 28,000 figure is likely a significant undercount because:
- The analysis used Bureau of Labor Statistics data, which academic research shows captures only 30-80% of actual workplace injuries
- Only establishments with 100+ employees in high-hazard industries were required to report
- Small businesses (58% of U.S. employment) weren't included
- The study was unable to capture hour-specific exposure or identify workers in air-conditioned environments.
OSHA's own regulatory analysis estimates the true burden could be 6-10 times higher than officially reported.
Climate Change Multiplier
As global temperatures rise and extreme heat events become more frequent and intense, this problem will only worsen. The researchers note that their 2023 analysis provides a baseline, but future years will likely show increased burden as:
- Heat waves become more common
- Geographic areas previously unaffected by extreme heat face new challenges
- Workers in traditionally cooler regions lack acclimatization
- Indoor workplaces without adequate cooling struggle with higher ambient temperatures
Key Takeaways
- Heat affects all workers, not just outdoor laborers—healthcare, retail, warehousing, and manufacturing workers also face an elevated risk of injury on hot days.
- The danger zone starts at an 85°F heat index, and risk accelerates rapidly above 90°F
- Approximately 28,000 U.S. workplace injuries in 2023 were attributable to heat exposure, but most aren't recognized as heat-related
- Heat impairs both physical and cognitive function, increasing risk of falls, errors in judgment, reduced reaction time, and coordination problems.
- Workplace heat standards are effective—states with regulations saw roughly a 60% lower increase in heat-related injuries than unregulated states.
- Workers' compensation systems are paying for heat exposure without recognizing it in claims data and prevention strategies.
- The problem is getting worse—climate change will increase the frequency and severity of occupational heat exposure.
- Prevention measures save lives and money—water, rest breaks, shade, acclimatization, and training reduce injury risk.
What Employers and Insurers Should Do
Immediate Actions:
- Recognize heat as a serious hazard even for indoor operations
- Implement heat safety protocols at 85°F heat index
- Provide easy access to water, rest breaks, and cooling areas
- Train supervisors and workers on heat risks and symptoms
- Establish acclimatization protocols for new workers and after time away
- Monitor local heat index forecasts and adjust work practices accordingly
Strategic Changes:
- Analyze workers' compensation claims data for heat-injury patterns (spikes in injuries on hot days)
- Factor heat exposure into risk assessments and safety audits
- Invest in engineering controls (cooling systems, ventilation, heat-reflective materials)
- Develop written heat illness prevention plans
- Support state and federal heat protection standards
For Workers' Comp Professionals:
- Educate claims adjusters on hidden heat-injury connections
- Review claim patterns for temperature correlations
- Advocate for proper classification of heat-contributory injuries
- Support prevention through safety consultations and premium incentives
- Use this data in underwriting and risk management discussions
About This Research
Study: "A nationwide analysis of heat and workplace injuries in the United States"
Published: Environmental Health, October 2025
Authors: Barrak Alahmad, William Kessler, Yazan Alwadi, Joel Schwartz, Gregory R. Wagner, David Michaels
Institutions: Harvard T.H. Chan School of Public Health, George Washington University Milken Institute School of Public Health
Data Source: 845,014 workplace injuries from OSHA's Injury Tracking Application (2023)
DOI: 10.1186/s12940-025-01231-1
This research represents the first comprehensive national assessment of the impact of heat on workplace injuries across all industries in the United States. As climate change continues to drive more frequent and severe heat events, understanding and addressing this hidden threat becomes increasingly critical for worker safety and the sustainability of workers' compensation systems.
Recommended Citation: Gelman, Jon, Heat: The Silent Worker Threat (10/07/2025) https://workers-compensation.blogspot.com/2025/10/heat-silent-worker-threat.html
Blog: Workers' Compensation
LinkedIn: JonGelman
LinkedIn Group: Injured Workers Law & Advocacy Group
Author: "Workers' Compensation Law" West-Thomson-Reuters
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© 2025 Jon L Gelman. All rights reserved.
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