OSHA - NIOSH Infosheet on Protecting Workers from Heat Illness
"At times, workers may be required to work in hot environments for long periods. When the human body is unable to maintain a normal temperature, heat-related illnesses can occur and may result in death. This fact sheet provides information to employers on measures they should take to prevent heat-related illnesses and death."
A variety of resources to prevent heat illness can be found at: https://www.osha.gov/heat/index.html