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How to Maintain a Heat Acclimatization Program

January 15, 2021

A fundamental method for protecting workers is through the implementation of various controls to diminish occupational hazard exposures. Following the hierarchy of controls has historically been a good method for determining the types of controls to use and at what stage those controls should be implemented. 

OSHA hierarchy of controls


For instance, one common occupational hazard comes from hot work environments. Knowing how to acclimate your workforce to heat is an administrative control that can help your team operate in hot environments. 

When working in hot conditions the body needs time to enact some physiological defences. The idea of building up a tolerance to heat gradually over time is known as heat acclimatization and the lack of a properly executed heat acclimatization program can be a major risk to the safety of your team. 

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

In this article we’ll:

  • 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

What is heat acclimatization and why is it important?

Heat acclimatization is the name given to the collection of the 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 more quickly cool the body
  • Increased worker comfort during physical tasks in heat

Because the majority of heat related injuries occur in the first few days on the job, it's important to bring newly onboarded workers through a program that helps their bodies adjust to the type of heat they will be working in. Additionally, a program that installs guard rails to protect against ‘just this one time’ or ‘real quick’ worker placements can assist with the overall safety and creates a culture that doesn’t cut corners. 

Heat acclimatization occurs over a 7-14 day period with a methodical, incremental approach where 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, more methodical approach will achieve the best results in a workforce. 

Keys to a successful acclimatization plan

When building and implementing an acclimatization plan make sure to remember that on the first day of work the body temperature, heart rate and general discomfort will be the highest. With each following day of exposure, these responses should decrease and sweat production (watch out for dehydration!) will increase. 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:

  1. Timeliness

    Don’t rush it. When thinking of heat acclimatization, slow and steady wins the race. Workers being onboarded to a hot job should begin their heat acclimatization plan on Day 1.

  2. Duration

    Gradually increase work times in hot conditions over a period of 7 to 14 days. Less strenuous activities and more experienced workers might tend toward the shorter range where more strenuous and less accustomed workers toward the longer range. When in question a more conservative approach should be used. 

  3. Intensity

    Heat acclimatization of the human body will only reach the level of work demanded for it. Just standing in a hot place is not sufficient. 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 towards... 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.

  4. 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 really the key to any proper program.  

What does an acclimatization schedule look like?

Full acclimatization for a worker may take up to 2 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 that has endured prolonged absence, start with a workload of about 20% on the first day. Increase the workload by no more than 20% in each subsequent day. 

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

Sample first week on the job

Example workload schedule for starting heat acclimation plan


Sample workload for heat waves

Example workload schedule for acclimating to heat waves


How fast can the body lose its tolerance to heat? 

The acquisition of heat acclimatization has become better documented in scientific literature, but the idea around heat acquisition decay (HAD) or how quickly heat acclimatization is lost remains less well known. The available literature suggests that each day of heat acclimatization takes 2 days to lose.

Generally speaking it is preferred, not detrimental, for a worker to experience 1-2 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 1 week of working 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 2 to 3 days.

What to watch out for with an acclimatized workforce:

  • Dehydration
  • Workers with a higher degree of heat acclimatization sweat more quickly and with a higher volume. Because of this, there will be an increased demand for 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. 

What are some other good resources?

There’s an increasing number of really good resources around the topic. The Center for Disease Control and Prevention is always a great place to get started. As is OSHA and its Technical Manual (OTM).

Though the University of Connecticut’s Korey Stringer Institute is geared primarily toward secondary school athletics the information translates well. 

And for our friends in Canada the Canadian Centre for Occupational Health and Safety (CCOHS) can get you started with an overall understanding and they use exposure guidelines recommended by American Conference of Governmental Industrial Hygienists (ACGIH).

Thanks for reading our article! For questions or feedback please feel free to email

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