Outdoor and indoor heat exposure can be dangerous. New and returning workers need to build tolerance to heat (acclimatize) and take frequent breaks. Follow the 20% Rule. On the first day, work no more than 20% of the shift’s duration at full intensity in the heat. Increase the duration of time at full intensity by no more than 20% a day until workers are used to working in the heat. Click here to read more about ways to protect yourself and others.