OSHA has a great free Heat Safety Tool available for both iPhone and Android devices. It allows employers to get current heat stress conditions, or enter their own parameters. It also provides reminders and protective measures you can take to keep employees safe and cool. (Water! Shade!)
Heat Stress Work Site Training Poster
This free poster, available in English and Spanish, covers the symptoms of heat stress, heat stroke, heat stress protective measures, and what to do in the event of a heat emergency. It's a great heat stress awareness tool.