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Acclimatization Elements of Your Written Program and Effective Work Practices

What is in T8CCR 3395?

T8CCR 3395(b) Definitions states the following:

  • “Acclimatization” means temporary adaptation of the body to work in the heat that occurs gradually when a person is exposed to it. Acclimatization peaks in most people within four to fourteen days of regular work for at least two hours per day in the heat.

T8CCR 3395 (g) Acclimatization states the following:

  • (1) All employees shall be closely observed by a supervisor or designee during a heat wave. For purposes of this section only, "heat wave" means any day in which the predicted high temperature for the day will be at least 80 degrees Fahrenheit and at least ten degrees Fahrenheit higher than the average high daily temperature in the preceding five days.
  • (2) An employee who has been newly assigned to a high heat area shall be closely observed by a supervisor or designee for the first 14 days of the employee's employment.

T8CCR 3395(h)(1)(D) states the following:

  • (1) Employee training. Effective training in the following topics shall be provided to each supervisory and non-supervisory employee before the employee begins work that should reasonably be anticipated to result in exposure to the risk of heat illness:
  • (D) The concept, importance, and methods of acclimatization pursuant to the employer's procedures under subsection (i)(4).

T8CCR 3395 (i)(4) states the following:

  • (i) Heat Illness Prevention Plan. The employer's shall establish, implement, and maintain, an effective heat illness prevention plan. The plan shall be in writing in both English and the language understood by the majority of the employees and shall be made available at the worksite to employees and to representatives of the Division upon request. The Heat Illness Prevention Plan may be included as part of the employer's Illness and Injury Prevention Program required by section 3203, and shall, at a minimum, contain:
  • (4) Acclimatization methods and procedures in accordance with subsection (g).

Guidance, Best Practices and Warnings

Acclimatization is a process in which the body adjusts to increased heat exposure. The body needs time to adapt when working in hotter environments. Employees are more like to develop heat illness if not allowed or encouraged to take it easy when a heat wave strikes or when starting a job that newly exposes them to heat. Acclimatization is fully achieved in most people within 4 to 14 days of regular work following at least 2 hours per day in the heat.

Cal/OSHA investigations showed that in 2005:

  • 46% of the reported cases of heat illness occurred on the employee’s first day on the job.
  • 80% of the reported cases of heat illness occurred within the first four days of employment.

In fully acclimatized individuals, sweating starts faster and the sweat carries less salt and other minerals out of the body. As a result, by sweating more efficiently the body cools down faster. Also there is less demand on the heart and cardiovascular system. For the reasons given above, being fully acclimatized can decrease the risk of heat illness and unsafe acts.

In general, physically fit individuals become acclimatized about 50% faster than those individuals who are not physically fit. Overweight individuals may retain more body heat and therefore may be more prone to developing heat illness.

During heat waves and with new employees, employers must be extra-vigilant. A supervisor or designee must closely observe employees.

Best Practices

To minimize the risk of heat illness, encourage employees to report to their supervisors if they have:

  • Returned to work after an absence
  • Recently been working in cool climate and are just now starting work in a warm or hot climate
  • Had a change in their work activities, locations or conditions

Any of the above mentioned circumstances may mean that employees are not acclimatized to working in warm or hot environments, and are at greater risk for heat illness.

Make Sure Employees Are Trained, Monitored and Watched Closely.

Remember that employees who are not acclimatized to working in the heat are at greater risk for developing heat illness. Unacclimatized employees should not work alone. It is important to:

  • Train employees and supervisors on the importance of acclimatization
  • Train employees and supervisors to quickly recognize and report any conditions associated with lack of acclimatization, such as employee not having continuously worked enough hours under hot conditions.
  • Train employees and supervisors on the importance of recognizing and quickly reporting heat illness symptoms.
  • Have supervisors and coworkers use a "buddy system" to watch each other closely, and for discomfort or signs of heat illness. Watch new employees even more closely.
  • Finding ways to lessen the intensity of employees' work during a heat wave and during the 14-day break-in periods of new employees.
  • Set-up a system to account for the whereabouts of your crew at appropriate intervals throughout the work shift and at the end of the work shift (e.g., keep a log of employees on your work crews including their names, supervisors, work locations, and hours worked on a given day, etc.)


During high heat or a heat wave even previously acclimatized employees are at risk for heat illness because the body has not had enough time to adjust to a sudden, abnormally high temperature or other extreme conditions.

Best Practices

Options for Acclimatizing Employees to Work in Warm or Hot Environments include One or More of the Following:

Have Employees Pace Themselves

  • If they are not accustomed to working in warm or hot environments, they should start work slowly and pick up the pace gradually.

Reduce Physical Demands

  • Assign employees to less physically demanding tasks during their first 14 days of working in a warm or hot environment.
  • Schedule and provide frequent breaks. Supply sufficient amounts of drinking water

Start an Acclimatization Program

  • These programs have employees work for progressively longer periods in warm or hot conditions where they are at risk for heat illness.
  • One such program is suggested by NIOSH (1986):
    For employees who have previous experience at worksites where they are at risk for heat illness
    Day # Hours Worked in Hot Work Environment

    For employees new to worksites where they are at risk for heat illness

    Day # Hours Worked in Hot Work Environment
    11.6 (96 minutes)
    23.2 (192 minutes)
    34.8 (288 minutes)
    46.4 (384 minutes)
    58.0 (480 minutes)


The acclimatization schedule by NIOSH, as shown above, is only an example program. Depending on the environmental and personal risk factors present, you may need to extend the time employees spend in your acclimatization program. This means that for some employees it may take up to 14 days of working in the heat for them to become fully acclimatized. Throughout this time period you should gradually increase employee’s time working in the heat.


Consult with Your Physician Before Replacing Salts and Minerals

For un-acclimatized employees, or those on a restricted salt diet, additional salting of food with the approval of their physician may be required to replace the salt and minerals lost in sweating. Acclimatized employees generally loose relatively little salt in their sweat, therefore salt and mineral supplements are normally not required.

April 2015