The truly hot weather is just around the corner. Are you doing the right things to get workers ready for extreme heat? Using an acclimatization schedule will help avoid dangerous work-related heat illness.

“Acclimatization” is the process of adapting to environmental extremes and it’s a necessary component of heat stress prevention. Intensity, frequency, duration and quantity of previous heat exposures greatly influences the physiological strain and resistance to heat.

These factors are essential for employers and workers to consider.

For example:

Nancy: Age 34: Was born and raised in Wisconsin and was physically active in track as a youth. Although she is physically fit, Nancy hasn’t been involved in outdoor sports since high school. She has recently relocated to Arizona.

Mike: Age 36: Was raised in New Mexico and moved to Arizona two months ago. He runs in 5 and 10K races often and coaches Little League.

Although both individuals are approximately the same age and in excellent physical condition, Mike would likely be better adapted to hot working conditions due to his long-term and frequent exposures to physical activity in extreme heat. Nancy, on the other hand, has no history of working or being physically active in extreme heat. It’s likely she’d have a harder time adjusting to the physical burden of heat.

Through a carefully planned process of acclimatization, most workers can adapt to the conditions. After a period of one to two weeks of gradual exposure, the worker will tolerate heat better and be less prone to heat related illnesses.  However, even workers with previous work experience in heat need gradual introduction. Every year, prior to the onset of extreme heat, employers should use an acclimatization schedule to assist workers adjust to climate changes.

Acclimatization is more than “feeling better” in heat.

There are remarkable physical changes made by the body when it has adapted to heat.

For example, when acclimatization is properly achieved:

• Blood is redirected to the skin’s surface to speed cooling
• The heart becomes more efficient
• Sweating is more profuse and begins earlier, which speeds evaporation and cooling
• Thermal comfort improves
• Physical performance is enhanced
• Core body temperature is lower
• Sweating releases less salts and electrolytes
• Thirst mechanisms and fluid balance improve

But when workers are not allowed to slowly adjust to heat, serious and sometimes fatal consequences can transpire.  A significant percentage of workplace heat stroke cases occur in the first week of exposure due to lack of adequate adjustment to hot working conditions.

Employers should integrate an acclimatization schedule into the heat stress program, to allow for workers that have had previous exposure to hot working environments and also those with no previous job experience in heat.

Acclimatization Schedule

 According to NIOSH, for workers with previous experience in hot working environments, the regimen should be 50% exposure on day one, 60% on day two, 80% on day three, and 100% on day four.

For workers new to work in heat extremes, the regimen should be 20% exposure on day one, with a 20% increase in exposure each additional day.

Physically fit workers tend to acclimatize 50 percent faster than those who are in poor physical condition. Acclimatization can also be adversely affected by illness. Hence, workers who are sick, dehydrated, or taking certain medications, may not adapt well to the heat, even with gradual exposure.

If the individual is exposed to a significantly different environment—such as an air-conditioned home over a long weekend—some acclimatization can be lost. NIOSH notes that reductions in adaptation can occur in as little as 3 to 4 days.  A single unseasonably hot day, preceded by several cooler days may also cause heat stress in workers due to poor acclimatization. If you have a worker who has suffered a recent heat illness, it is recommended that you use an acclimatization schedule to help them adjust to the hot working environment. (Of course, pending a doctor’s release to work).

CDC Report: http://www.cdc.gov/niosh/face/stateface/ca/97ca010.html

NIOSH: Control of Heat Stress: http://www.cdc.gov/niosh/pdfs/86-113d.pdf

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