NIOSH Issues Updated Heat Illness Prevention Guidance
NIOSH has released a revised edition of its Heat Stress Guide for Occupational Settings, updating recommended exposure limits (RELs) and providing new guidance for acclimatization programs, engineering controls, and worker monitoring. The previous edition dated from 2016.
What's New in the 2025 Edition
The National Institute for Occupational Safety and Health (NIOSH) periodically updates its recommended exposure limits and occupational health guidance. The 2025 Heat Stress update reflects new research on heat-related illness, climate trends, and effective intervention strategies.
Updated Recommended Exposure Limits
NIOSH updated its RELs for heat stress based on physiological research. The new RELs account for:
- Air temperature and humidity (wet-bulb globe temperature)
- Metabolic work rate (light, moderate, heavy, very heavy)
- Acclimatization status
Key change: lower action limits for unacclimatized workers, particularly in the first 7-14 days on the job.
Acclimatization Requirements
The guidance strongly recommends structured acclimatization programs:
- Day 1: No more than 20% of full heat exposure
- Days 2-7: Increase by 10-20% per day
- New workers and returning workers (absent >3 days) must be treated as unacclimatized
Engineering Controls Prioritized
NIOSH emphasizes the hierarchy of controls. Before relying on PPE or administrative controls:
1. Air conditioning in rest areas and cabs
2. Shade structures and cool rest zones
3. Scheduling hot work for cooler parts of the day
4. Cool water and electrolytes readily available
Federal OSHA Heat Standard Status
OSHA's proposed Heat Illness Prevention Standard for outdoor and indoor workers is still pending as of publication. Several states (California, Washington, Oregon, Minnesota) have state-level heat illness standards in effect.
⚠️ This content is informational only and does not constitute legal advice. For compliance guidance specific to your workplace, consult a qualified EHS professional or attorney.