Don't Overlook the Hazards of Heat Stress

May 13, 2004
If the dangers of heat stress are well known, why do workers keep getting hurt, or even killed, by the heat?

Heat stress is a common, yet often ignored hazard in the workplace. While it is widely recognized that heat stress can pose a serious health hazard to workers, employers may not realize that working in hot environments also increases safety risks.

Research conducted by the National Institute for Occupational Safety and Health (NIOSH) shows that work in hot environments is linked with lower mental alertness and physical performance, and subsequently, more injuries. Factor in elevated body temperature and physical discomfort and it's easy to see how workers can divert their attention from hazardous tasks and overlook common safety procedures.

Sources of heat stress range from the hot summer sun to the body heat generated inside a hazardous material suit worn during the cleanup of a toxic chemical spill. While often considered a summer or southern states problem, many companies need to take precautions throughout the year regardless of where they are located.

Heat-Related Slips

The safety hazard of heat stress is overlooked partly because the "accidents" that result from it are often not properly recorded, according to Mike Wurm, vice president of engineering at Oconomowoc, Wis.-based Quest Technologies Inc., a manufacturer of industrial hygiene and safety instrumentation. To illustrate the issue, Wurm recounts an episode that occurred at a heat stress meeting in California he attended.

"One guy stood up and said, 'I've been in construction 9 years and no one ever died from heat stress,'" Wurm recalled. "But then someone asked him how many slips and falls his company had during 100-degree days that were recorded as non-heat-related 'accidents.' The fellow sat down and had nothing more to say."

Loren Tapp, M.D., a medical officer at NIOSH, agreed. "If a person trips or breaks an ankle, there's not an emphasis on finding out if the person was heat-stressed," she said. "There needs to be more awareness about that."

Monitoring the Heat

Wurm and Tapp both say that awareness of heat stress is growing. "We see growth in our business," said Wurm. Tapp added, however, that even where the problem is recognized, many companies "have a long way to go as far as training employees to work in heat, surveillance and medical screening."

Medical screening of workers can help identify those who are more vulnerable to heat stress, such as workers who are older, overweight or taking medications that affect their ability to handle exertion in hot weather.

Tapp recommends that employers monitor hot environments by using a wet bulb thermometer, an essential component in obtaining the wet bulb globe temperature (WBGT).

"Use of WBGT is essential, because it allows you to measure not just the air temperature, but humidity in the air, radiant heat and wind velocity," said Tapp. All four factors are crucial in determining the risk of heat stress. The level of work activity, plus the clothes and the condition of the employee, are additional factors that must be considered.

The American Conference of Government Industrial Hygienists (ACGIH) uses WBGT in its threshold limit value (TLV) for heat exposure. Research confirms that WBGT mirrors how hot a person will become in any given environment, according to Thomas Bernard, vice chair of ACGIH's TLV physical agents committee.

"People have looked at bio-physical models of heat exchange, and they find that WBGT behaves much as a human behaves," said Bernard, a professor at the College of Public Health in the University of South Florida. "I've personally done work that has looked at maintaining thermal equilibrium at the upper limits of the heat index, and it tracks WBGT measurements."

Bernard cautioned however, that the critical missing piece from WBGT measurements is how hard somebody is working. "In order to decide if heat stress is of concern, you must know the time-weighted average of the metabolic demands and the time-weighted average of the WBGT, and compare that to the TLV table."

Northern Hazards

An additional reason heat stress may be overlooked is that many people living in the northern part of the U.S. think the issue does not affect them, according to Bernard. A person's ability to withstand the heat is affected by whether the individual has "acclimatized" to high temperatures. That's why sudden hot spells in traditionally cooler areas may pose more acute risks than heat in southern climates.

In addition, many employees are exposed to indoor high-heat environments and northern regions may lack proper ventilation or air conditioning because such precautions are not normally needed. As an example of this phenomenon, Wurm pointed to the number of people who died in France during a heat wave last summer.

"I believe there are plenty of people in northern states who don't believe heat exhaustion and heat strokes are a common problem," Bernard asserted. "But each year, 10 to 15 people die from these causes. It happens more often than we appreciate."

Sidebar: OSHA's Advice About Protecting Workers From Heat

Simple precautions, such as those listed on OSHA's Heat Stress Card, can prevent many heat-related deaths and injuries. Available in both English and Spanish, these laminated, fold-up cards are offered free to employers to distribute to their workers.

The tips on the OSHA cards recommend that you:

  • Encourage workers to drink plenty of water about 1 cup of cool water every 15 to 20 minutes, even if they are not thirsty and to avoid alcohol, coffee, tea and caffeinated soft drinks that dehydrate the body.
  • Help workers adjust to the heat by assigning a lighter workload and longer rest periods for the first 5 to 7 days of intense heat. This process needs to start all over again when a worker returns from vacation or absence from the job.
  • Encourage workers to wear lightweight, light-colored, loose-fitting clothing. Workers should change their clothes if they get completely saturated.
  • Use general ventilation and spot cooling at points of high heat production. Good airflow increases evaporation and cooling of the skin.
  • Train first-aid workers to recognize and treat the signs of heat stress and be sure all workers know who has been trained to provide aid. Also train supervisors to detect early signs of heat-related illness and permit workers to interrupt their work if they become extremely uncomfortable.
  • Consider a worker's physical condition when determining fitness to work in hot environments. Obesity, lack of conditioning, pregnancy and inadequate rest can increase susceptibility to heat stress.
  • Alternate work and rest periods, with rest periods in a cooler area. Shorter, more frequent work-rest cycles are best. Schedule heavy work for cooler times of the day and use appropriate protective clothing.
  • Monitor temperatures, humidity and workers' responses to heat at least hourly.

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