| Heat Stress
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Acclimatization occurs in 5 to 10 days of heat exposure as the body:
You can acclimatize by gradually increasing work time in the heat, taking care to replace fluids, and resting as needed. You maintain acclimatization with periodic work or exercise in a hot environment.
On the Job
The heat stress chart illustrates how temperature and humidity combine to create moderate or high heat stress conditions.
Be alert for heat stress when radiant heat from the sun or nearby flames is high, the air is still, or when you're working hard, creating lots of metabolic heat.
Some organizations use the WBGT Heat Stress Index. The index uses dry bulb, wet bulb, and black globe temperatures. The temperatures are weighted to indicate the impact of each measure on the worker:
Heat stress indexes do not take into account the effects of long hours of hard work, dehydration, or the impact of personal protective clothing and equipment.
When heat stress conditions exist, you must modify the way you work or exercise. Pace yourself. There are individual differences in fitness, acclimatization, and heat tolerance. Push too hard and you'll be a candidate for a heat disorder.
Most important, maintain hydration by replacing lost fluids.
Studies on wildland firefighters indicate that fire suppression activities generate about 7.5 kilocalories of heat each minute worked, or over 400 kilocalories for each hour. Additional heat (about 180 kilocalories per hour) comes from the environment and the fire. The total heat load amounts to 580 kilocalories per hour (400 + 180 = 580).