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How to Recognize and Prevent Occupational Heat Stress

Jul 29, 2018

Man at work enduring heat stressIt’s tougher to beat the heat on job sites than at backyard barbecues this summer. Not only are shifts traditionally longer, but workers may be insufficiently trained and ill-equipped by their employers to take preventive measures against heat stress, such as finding shade, drinking lots of water, wearing loose and light clothing, or taking regular breaks.

Occupational safety and health (OSH) professionals know that exposure to hot conditions presents a real threat to workers, and there’s a lot of work to do in this area. According to a recent U.S. Heat Fatalities Map from the Occupational Safety and Health Administration (OSHA), there were 109 heat-related occupational fatalities between 2008 and 2014. Donald J. Garvey, CSP, CIH, ARM, a construction technical specialist for 3M’s Personal Safety Division, says agriculture and construction workers typically run the highest risk of heat-related problems. In his Professional Safety article, “Fire and Ice: Protecting Workers in Extreme Temperatures,” Garvey notes that construction in particular is an industry where fast-track projects must continue even in adverse weather conditions.

Heat Stress

“Heat stress” is a term that encompasses many different physical reactions that result from a body’s attempt to regulate its temperature in response to the environment. These physical reactions range from uncomfortable to fatal, and tend to exacerbate other workplace risks, Garvey says.

“All of these types of issues can help create safety hazards for both the worker and their co-workers.”

Common symptoms of heat stress include heat rash due to sweating and clogged pores, heat cramps due to the loss of electrolytes from sweat, and heat exhaustion. These issues might not seem particularly threatening on the surface. However, Garvey says they often lead to worker irritability, low morale, absenteeism and shortcuts in procedures.

On the other end of the spectrum, heat stroke is a true medical emergency. Heat stroke occurs when the body becomes unable to regulate its temperature, and the condition can be fatal.

Risk Factors

Certain environmental, physical and operational variables affect the ease with which OSH professionals can address heat-related hazards.

“The primary concern is to maintain the body’s core temperature at or near the normal level,” Garvey says, “which is approximately 98.6 degrees Fahrenheit, or 37 degrees Celsius.”

According to Garvey, the risk factors inhibiting this objective include:

  • The temperature of the work site
  • The environment’s relative humidity
  • Personal protective equipment (PPE) that interferes with the body’s ability to sweat effectively
  • An employee’s workload (the body produces heat during muscular exertion)
  • An employee’s age, drug use, body weight, cardiovascular fitness, underlying health problems and existing burns (these may damage or destroy sweat glands)
  • A lack of worker and supervisor training on heat stress

First Signs

There are several technical methods of assessing the risk of heat stress for a general employee population. One is to examine the wet bulb globe temperature (WBGT) of a work environment – which considers the temperature, humidity, air movement and radiant heat sources – compared with the occupational exposure limits (OELs) recommended by organizations such as the National Institute for Occupational Safety and Health (NIOSH).

Another method is to utilize the free National Weather Service Heat Index, which can help determine the likelihood of heat stress using relative humidity and temperature data. Garvey says this system may be simpler than using the WBGT, but these heat stress index values are based on shaded conditions and full winds, and do not consider the added effects of strenuous workloads, heavy clothing or specialized PPE.

Observational indicators of heat stress may be less scientific, but it is still worthwhile for workers and frontline supervisors to learn how to keep a watchful eye. Not only are they easier to use in assessing individuals, but they can be identified more quickly and yield a faster response. There are free and helpful tools available to assist these efforts. For example, the U.S. Army has a urine color chart that can be used to gauge the level of worker hydration. OSHA and NIOSH also have a Heat Safety Tool App that features real-time heat index information, precautionary recommendations based on weather conditions, and a guide for identifying signs and symptoms of heat-related illnesses.

As part of regular training practices, Garvey says workers and supervisors should also learn to watch for the following signs of heat stress:

  • Sudden, severe nausea or headaches
  • Increased incidents or absenteeism
  • Chronic fatigue
  • A lack of alertness

“Employers must use measurements, along with the observation of workers and their professional judgment, to help ensure workers remain safe.”

Methods for Prevention

Mitigating heat exposure risks begins with a high-quality training program.

“The workers need to understand the danger of heat stress – the signs, the symptoms and prevention,” Garvey says. “The supervisors need all the worker training, plus they need to understand the need for fluid replacement, know how to adjust expectations for non-acclimatized workers and learn the importance of removing workers at the first signs of heat illness.”

Once team members have been properly trained, they should be well-equipped for the day-to-day work of protecting themselves from hot temperatures. For supervisors, maintaining worker acclimatization is one of the most important things to cover. “Acclimatization” refers to the beneficial physiological adaptations that occur as a result of frequent exposure to hot environments. These adaptations take from seven to 10 days to develop, Garvey says, and include more efficient sweating, stabilized circulation and the ability to work with a lower heart rate.

According to NIOSH, workers can maintain their acclimatization over a weekend, but they may need supervisors to help them gradually reacclimate to environmental conditions if they are absent for a week or more. OSHA recommends that new workers and those returning from a break should begin with 20 percent of their usual workload on their first day, increasing by no more than 20 percent on each subsequent day. In the case of a rapid temperature change, OSHA says an appropriate acclimatization program might require even experienced workers to start with 50 percent of their normal workload, increase to 60 percent on the second day, 80 percent on the third day and 100 percent on the fourth day.

Garvey says other important daily tasks for heat stress prevention might include:

  • Evaluating work site conditions and assessing heat risks
  • Ensuring that water is available and water coolers are sanitary
  • Actively encouraging workers to take regular drinks of water
  • Scheduling hot or physically demanding jobs for the coolest parts of the day
  • Implementing mandatory work/rest schedules
  • Creating a “buddy system” for workers to watch out for each other
  • Installing shade canopies
  • Providing air-conditioned trailers or break rooms for spot cooling
  • Utilizing vented, full-brim hard hats and other types of warm-weather PPE


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