Heat-related illnesses are preventable, yet excessive heat remains a serious workplace hazard. Employees may be exposed while working outdoors in Florida’s heat or indoors in foundries, bakeries, manufacturing facilities, and other hot or humid environments.
Heavy physical activity, elevated temperatures, humidity, limited air movement, and clothing or personal protective equipment that retains body heat can all increase the risk of heat illness. Hazardous conditions can occur at any time of year—not only during summer or an officially declared heat wave.
Why New Workers Face Greater Risk
Workers who are new to a hot environment or returning after an extended absence are particularly vulnerable because their bodies may not be accustomed to the conditions.
According to the Occupational Safety and Health Administration (OSHA), nearly half of heat-related worker fatalities occur on a worker’s first day on the job or first day back after an extended absence. More than 70% of heat-related worker fatalities occur during a worker’s first week. Employers can help protect these workers by gradually introducing them to hot conditions rather than immediately assigning a full schedule of work in the heat.
Building Heat Tolerance Through Acclimatization
Acclimatization is the process through which the body gradually adapts to working in a hot environment. As a worker becomes acclimatized:
- The body produces more sweat, improving evaporative cooling.
- Sweat contains less salt, reducing electrolyte loss.
- Heart rate and body temperature rise more slowly during work.
- Blood flow to the skin increases, helping the body release heat more efficiently.
The time required to acclimatize varies. Physical condition, medical conditions, medications, previous heat exposure, and the demands of the job may all affect how quickly a worker adapts.
New workers may also need time to develop the physical conditioning required to perform strenuous tasks safely.
| Unacclimatized Workers | Acclimatized Workers |
|---|---|
| Sweat less efficiently | Sweat more efficiently |
| Lose more salt through perspiration | Retain electrolytes more effectively |
| Experience faster increases in heart rate and body temperature | Maintain lower heart rates and body temperatures during comparable work |
| Have greater difficulty releasing excess body heat | Release heat more effectively through increased blood flow to the skin |
Note: In addition to the heat-specific acclimatization factors listed above, new workers
may lack sufficient physical fitness for the work.
Follow the Rule of 20 Percent
OSHA and the National Institute for Occupational Safety and Health (NIOSH) recommend gradually increasing a new worker’s exposure to heat.
- Day 1: Limit work in the heat to 20% of the usual duration.
- Each additional day: Increase the duration of work in the heat by no more than 20% of the usual duration until the worker reaches a normal schedule.
For an eight-hour workday in hot conditions, 20% equals 1 hour and 36 minutes on the first day. The remainder of the shift should be spent away from heat stress, such as performing tasks in a cooler environment.
During the acclimatization period, employers should provide appropriate rest breaks and closely monitor workers for signs and symptoms of heat illness. Although the schedule may reach a full workday by the end of the first week, complete acclimatization can take longer. Some workers may require up to 14 days to adapt. When uncertain, employers should allow more time.
Workers should perform tasks similar in intensity to their expected assignments during these limited periods of heat exposure. Light work alone may not adequately prepare the body for a physically demanding job.
Remember: Gradually increase the duration of work in the heat while maintaining appropriate rest breaks and other protective measures. Acclimatization does not eliminate the risk of heat illness.
Support New and Returning Workers
Acclimatization is only one part of an effective heat illness prevention program. Employers should also:
- Provide cool drinking water
- Encourage workers to hydrate regularly
- Schedule appropriate rest breaks
- Provide access to shade or cooled recovery areas
- Train workers to recognize and report symptoms
- Monitor new and returning workers closely
- Establish procedures for responding to heat-related emergencies
Planning for heat exposure before work begins can help employers prevent serious illnesses and fatalities. Giving workers sufficient time to adapt is one of the most important steps an organization can take.
Additional Resource: Explore OSHA’s Heat Exposure resources for guidance on recognizing heat hazards, protecting new workers, and preventing heat-related illness in indoor and outdoor workplaces.
The USF SafetyFlorida Consultation Program provides confidential occupational safety and health consultation services at no cost to eligible Florida employers. Request a consultation or call 866-273-1105 for assistance evaluating workplace hazards and strengthening your prevention efforts.