Safety professionals understand the hazards that exist when workers are exposed to hot conditions. The most recent OSHA U.S. Heat Fatalities Map shows there were 109 heat-related worker deaths from 2008 to 2014. Employees must be adequately trained and equipped to take proactive measures against heat stress, such as drinking plenty of water, wearing loose and light clothing, or taking regular breaks.

Heat Stress

“Heat stress” is a term that includes several different physical reactions that can occur as the human body attempts to regulate its temperature. These physical reactions range from discomfort to death.

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, but 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 procedural factors affect how safety professionals can address heat-related hazards. The primary concern is to maintain the body’s core temperature at or near the normal level which is approximately 98.6 degrees Fahrenheit.

The risk factors hindering normal body temperature include:

  • Temperature of the work site
  • Relative humidity
  • Personal protective equipment (PPE) that can interfere with the body’s ability to cool itself through sweating
  • Employee workload
  • Employee’s age, drug use, body weight, cardiovascular fitness, and underlying health problems
  • Lack of proper training on heat stress

Signs Of Heat Stress

Early detection is a key factor in preventing heat stress. Properly training employees and supervisors to identify the signs of heat stress can greatly reduce the risk of negative physical responses to heat and prevent heat stress from worsening to heat stroke.

Employees should be trained to watch for the following signs of heat stress:

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

There are several methods of assessing the risk of heat stress for employees. One is to consider the wet bulb globe temperature (WBGT) of a work environment – which factors 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. There are also free tools available, like the U.S. Army’s urine color chart that can be used to gauge the level of worker hydration, and OSHA’s Heat Safety Tool App that features real-time heat index information, precautionary recommendations for specific risk levels, and a guide for identifying signs and symptoms of heat-related illnesses.

Heat Stress Prevention

Workers need to understand the danger of heat stress – the signs, the symptoms and prevention strategies. Supervisors need all the worker training, plus an understanding of the importance of fluid replacement, adjusting procedures for non-acclimatized workers, and how to identify the risk factors of heat stress.

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.


Daily tasks to consider to help employees avoid heat stress.

  • Evaluating work site conditions and assessing heat risks
  • Ensuring water is available and sanitary
  • Actively encouraging workers to drink water regularly
  • 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
  • Utilizing warm-weather PPE

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