The Confined Space standard, 1910.146, doesn't specify STLs for heat. However, the standard does call out the following as a definition of permit-required confined space (PRCS) that could include excessive heat and require controls to be put in place before entry:
- Contains or has a potential to contain a hazardous atmosphere (e.g., paint thinner).
- Contains a material that has a potential for engulfing the entrant (e.g., liquid, soil).
- Contains inwardly converging walls or a floor that slopes downward and tapers to a smaller cross-section where an entrant could be trapped or asphyxiated.
- Contains any other recognized serious safety or health hazard (e.g., unsafe temperature, electrical shock, corrosive chemicals).
OSHA highlights in their National Emphasis Program – Outdoor and Indoor Heat-Related Hazards the National Weather Service (NWS) classifications of environmental heat exposure using their heat index as a guide for inspectors. These are:
- Caution (80 – 90 degrees F heat index)
- Extreme Caution (91-103 degrees F heat index)
- Danger (103-124 degrees F heat index)
- Extreme Danger (126 degrees F or higher heat index)
