According to OSHA, recent studies have shown that almost half of heat-related deaths occur on a worker’s very first day on the job and over 70 percent occur during the worker’s first week. These types of tragedies can be avoided if employers take actions to protect new workers. OSHA interprets a new work term as one in which workers are new to working in warm environments. This includes the following groups: (1) new, temporary, or existing employees who start new work activities in warm or hot environments while wearing additional clothing and are performing increased physical activity; (2) workers returning to work environments in which they are potentially exposed to heat hazards after an absence of one week or more; (3) workers who continue working through seasonal changes when temperatures first begin to increase, such as in the spring or early summer; and (4) workers who work on days when the weather is significantly warmer than on previous days, such as during a heat wave. In any of these groups, workers may not be used to the heat load; this increases their risk of developing heat-related illness.
A worker’s body can prepare for warmer work conditions through acclimatization. Acclimatization refers to when the body gradually adapts to and tolerates higher levels of heat stress. A worker’s body needs time to adapt to working in hot conditions in order to develop heat tolerance. Heat tolerance is the physiological ability to endure heat and regulate body temperature at an average or above-average rate. As workers go through the acclimatization process, their heat tolerance can increase. This increase is impacted by their physical conditioning and personal risk factors.
When a non-acclimatized worker sweats, it contains a high level of salt. During acclimatization, the body produces more sweat, which results in more evaporative cooling. The worker’s sweat will now contain less salt, and the worker will be less likely to develop an electrolyte imbalance and heat cramps. The acclimatized worker’s body will become more efficient at getting rid of heat and will have a slower heart rate and a slower increase in body temperature. More blood will flow to the skin, resulting in more efficient cooling.
OSHA and NIOSH recommend following the Rule of 20 Percent for new workers who are exposed to hot work environments. On the first day, a new worker should be exposed for only 20 percent of their work shift. In the days that follow, exposure time can be increased by an additional 20 percent per day until the worker is acclimated to the conditions. Workers should perform tasks similar in intensity to their expected workload during this time.
OSHA also provides recommendations for modification to the Rule of 20 Percent for new workers who have recently worked in a hot environment. All new workers assigned to a high-heat area must be closely monitored during the first 14 days of employment.
Workers can maintain their acclimatization even if they are away from the job for a few days, such as when they go home for the weekend. However, if they are absent for a week or more, then the likelihood of heat-related illness occurring increases, and the need to gradually re-acclimate to the hot environment becomes more important.
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