TSI - Permissible Exposure Limits (PELs) for Heat Stress in Different Occupational Environments

Permissible Exposure Limits (PELs) for heat stress are guidelines that help employers and workers understand safe levels of exposure to high temperatures to prevent heat-related illnesses. These limits vary based on the work environment, the nature of the work, and local regulations. Here’s an overview of heat stress PELs in different occupational environments and the standards set by various organizations.

U.S. Occupational Safety and Health Administration (OSHA)
While OSHA does not have a specific standard for heat stress, it provides guidance under the General Duty Clause of the Occupational Safety and Health Act, which requires employers to provide a workplace free from recognized hazards likely to cause death or serious physical harm.
OSHA recommends using the Wet-Bulb Globe Temperature (WBGT) index to assess heat stress risk. The recommended exposure limits are:

Light Work (e.g., sitting with light manual work):
- WBGT of 86°F (30°C)
Moderate Work (e.g., sustained hand and arm work, walking):
- WBGT of 80.6°F (27°C)
Heavy Work (e.g., heavy lifting, digging):
- WBGT of 77°F (25°C)

These limits are based on continuous work without rest breaks. OSHA also suggests adjusting these limits for different acclimatization levels and providing additional water, rest breaks, and shade.

American Conference of Governmental Industrial Hygienists (ACGIH)
ACGIH provides Threshold Limit Values (TLVs) for heat stress based on WBGT. These TLVs consider work intensity, work-rest cycles, and acclimatization status. According to the ACGIH’s guidelines, the temperature values represent a work and rest process which is explained in the standards. Refer to ACGIH TLVs and BEIs for specific details.

For acclimatized workers:

Work and recovery (TLV)	Light	Moderate	Heavy	Very Heavy
75% to 100%	31.0	28.0	26.0*	23.5*
50% to 75%	31.0	39.0	27.5	25.5*
25% to 50%	32.0	30.0	29.0	28.0
0% to 25%	32.5	31.5	30.5	30.0

Work and recovery (Action Limit)	Light	Moderate	Heavy	Very Heavy
75% to 100%	28.0	25.0	22.5*	20.0*
50% to 75%	28.5	26.0	24.0	22.5*
25% to 50%	29.5	27.0	25.5	24.5
0% to 25%	30.0	29.0	28.0	27.0
*Values not specific by ACGIH have been estimate for continuity.

National Institute for Occupational Safety and Health (NIOSH)
NIOSH provides criteria for a recommended standard for occupational exposure to heat and hot environments. Similar to ACGIH, NIOSH uses WBGT to determine safe exposure limits.

For acclimatized workers:

Light Work: WBGT up to 86°F (30°C)
Moderate Work: WBGT up to 82°F (28°C)
Heavy Work: WBGT up to 77°F (25°C)

For unacclimatized workers, these values are typically reduced by approximately 2-3°F.
International Standards

ISO 7243: The International Organization for Standardization (ISO) provides guidelines through ISO 7243, which outlines WBGT-based limits for heat exposure. The standards are similar to those provided by ACGIH and NIOSH, ensuring global consistency in heat stress management.
Australian and New Zealand Standards: These countries follow guidelines similar to ISO and ACGIH, with slight modifications to suit their specific climates and working conditions.

Industry-Specific Guidelines
Certain industries may have additional guidelines to address unique challenges:

Military: The U.S. military uses the WBGT index extensively and provides specific guidelines for different types of physical training and operational activities.
Athletics: Sports organizations, such as the NCAA, use WBGT to set guidelines for practice and competition in hot conditions, often requiring breaks, hydration, and monitoring.
Agriculture: Guidelines often emphasize the need for rest breaks, hydration, and shade for workers performing physically demanding tasks under direct sunlight.

Conclusion
Understanding and adhering to permissible exposure limits for heat stress is essential for protecting workers in high-risk environments. Organizations like OSHA, ACGIH, and NIOSH provide valuable guidelines to help manage heat stress. By implementing these standards, employers can create safer work environments, reduce the risk of heat-related illnesses, and ensure regulatory compliance.

Find out more about TSI’s QUESTemp Heat Stress Monitors

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Sources

OSHA Technical Manual (OTM) Section III: Chapter 4 - Heat Stress
ACGIH Threshold Limit Values (TLVs) and Biological Exposure Indices (BEIs) Booklet. Available for purchase on the ACGIH website
NIOSH Criteria for a Recommended Standard: Occupational Exposure to Heat and Hot Environments. NIOSH Publication No. 2016-106
ISO 7243:1989 - Hot Environments — Estimation of the Heat Stress on Working Man, Based on the WBGT-Index (Wet Bulb Globe Temperature). Available for purchase on the ISO website

Occupational Health and Safety

Permissible Exposure Limits (PELs) for Heat Stress in Different Occupational Environments

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