What heat standards apply to indoor manufacturing facilities?

There is currently no federal OSHA standard specifically regulating indoor workplace temperatures. However, several guidelines and enforcement mechanisms apply, and employers should be aware of the current landscape.

NIOSH Recommended Exposure Limits (RELs): NIOSH recommends that no worker be exposed to combinations of metabolic and environmental heat exceeding established limits, assessed using Wet Bulb Globe Temperature (WBGT) — a measure that incorporates temperature, humidity, and air movement. These are recommendations, not enforceable regulations, but they represent the recognized standard of care.

ACGIH Threshold Limit Values (TLVs): The American Conference of Governmental Industrial Hygienists publishes TLVs for heat stress, also based on WBGT measurements, that define exposure limits by workload intensity and acclimatization status. Like NIOSH RELs, ACGIH TLVs are recommendations rather than enforceable regulations — but they are widely referenced by industrial hygienists and safety professionals as benchmarks for acceptable heat exposure.

OSHA General Duty Clause: In the absence of a specific heat standard, OSHA can cite employers under the General Duty Clause for exposing workers to recognized heat hazards. In April 2026, OSHA updated its National Emphasis Program on outdoor and indoor heat-related hazards, directing inspection resources to 55 high-risk industries, including manufacturing, based on heat illness rates and citation history from 2022 to 2025. The updated program includes random inspections on days when the National Weather Service issues heat advisories or warnings.

State standards: Several states have enacted their own heat standards. California's Heat Illness Prevention Standard triggers requirements at 80°F. Maryland, Washington, Minnesota, Oregon and Colorado have also enacted specific occupational heat exposure laws.