How to Maintain a Heat Acclimatization Program

Heat acclimatization is important for any work environment with significant heat exposure and risks. Heat acclimatization is building a tolerance to heat gradually over time. Knowing how to acclimate your workforce to the heat is an administrative control that can help your team operate in hot environments.

A fundamental way to protect workers from occupational hazard exposures such as potential heat illness and injury is by implementing a method from the hierarchy of controls. The hierarchy of controls is an inverted pyramid that lists the most effective methods from top to bottom to eliminate or decrease the hazards in a particular work environment. Using any of the methods in the pyramid leads to overall inherently safer practices and a reduction in the risk of illness or injury.

This hierarchy also helps determine which methods and how they should be implemented, depending on the work environment and situation. When working in hot conditions, the body needs time to enact some physiological defenses. Implementing a heat acclimatization program is important to avoid the risk of heat illness and injury for your team and to ensure their safety.

The majority of heat-related deaths occur in the first few days on the job. Proper heat acclimatization training can help prevent this. Continue reading to:

  • Learn what heat acclimatization is and what it means to the workforce
  • Set up some heat acclimatization guidelines
  • Understand how to maintain heat acclimatization in the workforce

Heat Acclimatization: Why is it Important?

The majority of heat-related injuries occur in the first few days on the job. It’s important to educate new workers about heat acclimatization and other safety measures to implement in the work environment. (photo courtesy Adobe Stock Images)

Heat acclimatization refers to beneficial biological adaptations that help reduce physiological heat strain (the overall physiological response resulting from heat stress) in hot environments.

Benefits for heat acclimatization include:

  • Decreased heat strain on the heart, brain and other vital organs
  • Improved sweating (quicker onset, higher volume) to cool the body more quickly
  • Increased worker comfort during physical tasks in the heat

Because the majority of heat-related injuries occur in the first few days on the job, it’s important to educate new workers about heat acclimatization and other safety measures to implement in their work environment. Ensuring this education is part of each new employee orientation and onboarding will help mitigate risks and promote a culture that doesn’t cut corners.

Heat acclimatization occurs over a seven-14 day period with an incremental approach. The environment and exposures are sufficiently stressful to invoke profuse sweating and elevated body temperatures but not to a point of heat exhaustion. Generally speaking, a slower approach will achieve the best results.

Successful Heat Acclimatization Plan

When building and implementing an acclimatization plan, remember that body temperature, heart rate and general discomfort will be the highest on the first day of work. With each following day of exposure, these responses should decrease, and sweat production will increase. It will also be important to ensure workers are properly hydrated throughout the process. The goal for the end of the program is for the worker to find it possible to perform the work with less distress.

When introducing an acclimatization plan for your organization make sure to think about a few key areas:

  • Timeliness: When thinking of heat acclimatization, don’t rush the process. Workers being onboarded to a hot job should begin their heat acclimatization plan on Day 1.
  • Duration: Gradually increase work times in hot conditions for seven-14 days. Less strenuous activities and more experienced workers might tend toward the shorter range, whereas more strenuous and less accustomed workers toward the longer range. When in question, a more conservative approach should be used.
  • Intensity: While on the acclimatization plan, the level of work should increase in difficulty to meet the rigors of the daily post-acclimatization work. Think of it this way: If the job in demand will include laying bricks in the South Florida sun all day, then that workers’ acclimatization schedule should be striving toward laying bricks in the South Florida sun all day. Light or brief physical work will only acclimatize the worker to light and brief physical work.
  • Rest: Rest during an acclimatization schedule is just as important as the work. The gradual build-up of getting the body to a point is the key to any proper program.

A fundamental way to protect workers from occupational hazard exposures is by implementing a method from the hierarchy of controls—including heat acclimatization. (photo credit NIOSH)

What does an acclimatization schedule look like?

Full acclimatization for a worker may take up to two weeks, depending on individual factors. Certain medications, medical conditions or even additional environmental factors can all have an impact.

For a new worker or one returning from a prolonged absence, start with a workload of about 20% on the first day. Increase the workload by no more than 20% on each subsequent day.

When there is an expectation of a rapid change leading to increased environmental heat conditions, such as a heat wave, even experienced workers should begin excessive heat days on a graduated schedule.

How fast can the body lose its tolerance to heat?

Heat acclimatization has become better documented in scientific literature, but the idea of how quickly heat acclimatization is lost, also known as heat acclimation decay (HAD), remains less well-known. The available literature suggests that each day of heat acclimatization takes two days to lose.

Generally speaking, it is preferred, not detrimental, for a worker to experience one-two days in a cooler environment. Although heat acclimatization can be sustained after a few days, most workers will see a decrease in beneficial effects after about one week away from heat.

It takes somewhere around a month away from hot work for most people’s heat tolerance to return to baseline. In the cases where a worker is away from hot work for a prolonged period (about one week), it can often be regained in two-three days.

What to watch out for with an acclimatized workforce:

  • Dehydration: Due to increased sweating among those with a higher degree of heat acclimatization, dehydration is a concern due to the loss of liquid.
  • Rapid heat increases: Sudden higher levels of heat in a work environment, like a heat wave, can still be dangerous because acclimatization only matches the level of heat stress exposure.
  • Health considerations: Workers that have underlying health considerations or are less physically fit may require longer acclimatization periods to bring up to standard.

[Editors Note: This article first appeared as a blog post on Go to for the original.]

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