Illness from exposure to heat is preventable; however, every year thousands become sick from occupational heat exposure.

For most outdoor fatalities, 50% to 70% occur in the first few days of working in warm or hot environments. Why? Because the body needs to build up a tolerance to the heat gradually and over time. This process is called acclimatization.

Lack of acclimatization can pose a serious risk factor for those new to the job.

Protection Strategies

Employers should establish a culture of acclimatization to protect new workers from heat-related illness by doing the following:

  • Schedule new workers to work shorter amounts of time working in the heat, separated by breaks, in heat stress conditions
  • Give new workers more frequent rest breaks.
  • Train new workers about heat stress, symptoms of heat-related illness, and the importance of rest and water.
  • Monitor new workers closely for any symptoms of heat-related illness.
  • Use a buddy system and don’t allow new workers to work alone.
  • If new workers talk about or show any symptoms, allow them to stop working. Initiate first aid. Never leave someone alone who is experiencing symptoms!

Initial Two Weeks

Implement protection strategies for 1 to 2 weeks. After that, your “new” workers should be acclimatized and able to safely work a normal schedule.

Rule of 20 percent
To prevent heat-related illnesses, new workers should work shorter workdays in the heat during their first two weeks. OSHA and NIOSH recommend the “Rule of 20 percent” for building heat tolerance.

• 20 percent First Day: New workers should work only 20 percent of the normal duration on their first day.

• 20 percent Each Additional Day: Increase work duration by 20 percent on subsequent days until the worker is performing a normal schedule.

By following the Rule of 20 Percent, new workers will be working a full schedule by the end of their first week. This should protect most workers who are physically fit and have no medical problems. Others may require more time.

Other Strategies
To become acclimatized to heat, workers should perform job tasks that are similar in intensity to their expected work. For example, if a new worker has been hired to lay bricks outdoors in hot weather, then he should lay bricks during his first week. Doing light work may not acclimatize a worker to the demands of their job.

Remember, to help workers build heat tolerance, reduce the duration of the work but not the intensity of the work.

New Workers, as Defined by OSHA

“Workers who are new to working in warm environments” include:

1. New, temporary, or existing employees who start new work activities:

• in warm weather or hot environments
• while wearing additional clothing (e.g., chemical protective clothing)
• with increased physical activity

2. Workers returning to work environments with potential exposure to heat hazards after an absence of one week or more for example returning from any kind of extended leave.

3. Workers who continue working through seasonal changes when temperatures first begin to increase in the spring or early summer.

4. Workers who work on days when the weather is significantly warmer than on previous days (i.e., heat wave).

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