Heat Illness is a serious problem not just in the desert. Humidity must be accounted for when trying to determine heat illness. Check out this Employers Guide on Heat index provided by OSHA. Here in Arizona many employers forget that there are exposure limits on the amount of time an employee can be exposed to heated environments.
Don’t risk losing a valuable employee due to heat stroke, please read this article. Just click on the picture and you will be taken to the DOL website.