Although OSHA does not have a specific regulation covering heat stress hazards, the "General Duty Clause," Section 5(a)(1) of the Occupational Safety and Health Act, requires each employer to, "furnish to each of his employees employment and a place of employment which are free from recognized hazards that are causing or are likely to cause death or serious physical harm."
To assist employers who have staff who work outdoors or in environments with no air conditioning, OSHA has developed several resources to prevent heat-related injuries, which can be accessed by clicking here.