Most heat-related deaths occur in the first few days on the job. Heat acclimatization can help prevent this.

A study of OSHA citations issued between 2012 and 2013 revealed 20 cases of heat-related illness or death of workers [Arbury et al. 2014]. In most of these cases, employers had no program to prevent heat illness, or programs were deficient; and acclimatization was the program element most commonly missing and most clearly associated with worker death.

How Do You Acclimatize to the Heat?

You might have already heard about heat acclimatization, but what is it and why does it actually make your job easier?

Heat acclimatization is a process where your body undergoes physiological changes that allow it better handle the heat— which means that your performance in the heat will improve and you are less likely to suffer from heat-related problems (e.g., heat cramps).

For heat acclimatization to occur, you typically have to increase your core body temperature by 1°C (~1.8°F) for at least 1 hour, repeatedly each day, for 5-14 days in a row (each person will take a different amount of time to acclimatize to the heat).

Physiological Changes that Occur with Heat Acclimatization

After your body is acclimatized to the heat, you will notice lots of different changes.

  1. Sweating: You will start to sweat sooner (at a lower core body temperature) and you will sweat more. This is important because it allows your body to cool off (through evaporative heat loss), which means that your body temperature will stay lower for the same work rate. (See a refresher on heat loss through sweating here). You may also notice that your sweat becomes less salty after you’ve been working in the heat for a while; this is because your body becomes more efficient at reabsorbing the salt in your sweat, which helps you stay better hydrated in the heat.
  2. Heart rate: Your heart rate at rest and during work (or exercise) will be lower after heat acclimatization. This is because you get an increase in plasma volume (the water in your blood) with heat acclimatization, which means that with each heart beat, you can now pump more blood (to get more oxygen to the working muscles). As a result, your heart rate will be lower for the same work rate. This means that you can work for longer in the heat without getting tired. (See a refresher here on heart rate changes with heat stress).
  3. Core and skin temperatures: Due to the improvements in your sweating (and improved ability to get rid of heat), your core and skin temperatures will be lower at rest and during work or exercise (for the same work rate). This, combined with a lower heart rate, means that after heat acclimatization, you can work harder for longer periods of time before needing to take a break because your body is staying cooler.

worker in hot field

Important Tips During Heat Acclimatization:

  • Make sure to drink plenty of fluids before, during, and after the heat acclimatization period (your first two weeks on the job), and replace the water that you’re losing through sweating. This is especially important for helping your body to increase its plasma volume.
  • During heat acclimatization, you can lightly salt your foods as well as drink fluids with more sodium to help you stay hydrated and maintain your body’s electrolyte balance.
  • You can monitor your heart rate at the same time each morning before work (by taking your pulse) during heat acclimatization. You should see a decrease in your resting heart rate over the course of 1-2 weeks, which will indicate that you have likely acclimatized to the heat.
  • You should acclimatize to the environment that you will be working in. The changes that your body makes to a hot, dry environment will be different than those of a hot, humid environment.
  • Be aware of any signs & symptoms of heat injury & illness, and do not push yourself too hard the first week that you are just starting to work in the heat. This process takes time for your body to adjust, and trying to go too hard too fast will only result in serious accidents.
  • If you work in an environment with heavy clothing or PPE, if possible, you should start by wearing the most minimal clothing layer possible on the first 1-2 days, and then slowly adding each additional clothing layer (every 1-2 days) to give your body time to adjust over the course of the 1-2 week heat acclimatization period. As a rule of thumb: you can wear full PPE from day 6 onwards.
  • Lastly, remember that to maintain your heat acclimatization, you’ll need to be exposed to the heat at least once every 5 days. (See here for more info on the decay of heat acclimatization).

Need help figuring all of this out for your workers & work-site? Kenzen can help with our site-specific evaluations, heat safety training, and individualized. recommendations




Pryor, J. Luke, Christopher T. Minson, and Michael S. Ferrara. “Heat acclimation.” Sport and Physical Activity in the Heat. Springer, Cham, 2018. 33-58.

Coco, Aitor, Brenda Jacklitsch, Jon Williams, Jung-Hyun Kim, Kristin Musolin, and Nina Turner. “Criteria for a recommended standard: occupational exposure to heat and hot environments.” control Ccfd, editor (2016).

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