What are Heat Stress Causes, Symptoms, and Solutions?

As reported in a recent blog, OSHA has issued a National Emphasis Program (NEP) to protect workers from the dangers of heat-related illnesses. This summer, OSHA is proactively looking for violations in 70 targeted high-risk industries when a heat warning or advisory has been issued in the area. This initiative is part of a larger effort to protect workers from extreme heat and rising temperatures due to climate change. According to Secretary of Labor Marty Walsh, the three-year average of workplace deaths caused by heat has doubled since the early 1990s. OSHA’s NEP fact sheet on heat hazards indicates that over 3,500 worker injuries and illnesses are related to heat each year.

Watch the video below as our Vice President of Corporate Strategy and Technical, Scott Margolin, explains the causes and symptoms of heat stress and provides essential information on how companies can protect workers against this potentially deadly hazard:


What causes heat stress?

When the heat index – which combines the relative humidity with the actual air temperature to provide a “feels like” temperature – is 80°F or higher, serious occupational heat-related illnesses become more frequent. In workplaces where workers perform strenuous labor or work in direct sunlight or areas where other heat sources are present, the risk of heat stress increases. As Scott explains, heat stress is primarily caused by poor hydration, a lack of shade, and insufficient rest breaks. Certain illnesses, medications, and dehydration from alcohol consumption can exacerbate the problem, as does the absence of worker acclimatization and wearing heavy or bulky equipment.

Does PPE contribute to heat stress?

Multiple-layer garments or non-breathable PPE adversely affects the body’s ability to dissipate heat, increasing the risk of heat stress. PPE that is either non-breathable like rainwear or Tyvek®, a brand of synthetic high-density polyethylene fibers, or multiple layers like a 40-calorie arc flash suit or task-based coveralls worn over top of street clothing does contribute to heat stress. However, single-layer, breathable PPE, such as daily-wear arc-rated, flame resistant (AR / FR) clothing, does not contribute to heat stress. Even long-sleeved shirts, lightweight or relatively heavy-weight, arc-rated, flame resistant (AR / FR) garments do not cause heat stress since they are worn in a single layer and are composed of breathable fabric.

What are the symptoms of heat stress?

Heat illness can begin with relatively minor symptoms but can quickly progress to more dangerous reactions, such as:

  • Heat cramps – muscle spasms or pain usually in the legs, arms, or trunk.
  • Heat exhaustion – symptoms include fatigue, irritability, thirst, nausea or vomiting, dizziness or lightheadedness, heavy sweating, elevated body temperature, or fast heart rate.
  • Heat stroke – is a medical emergency that can potentially lead to death. Signs include confusion, slurred speech, unconsciousness, seizures, heavy sweating or hot, dry skin, a very high body temperature (reaching 104°F or higher), and a rapid heart rate.

Why are heat-related illnesses so dangerous?

OSHA’s NEP was issued because heat-related illnesses can quickly become fatal. Heat-related fatalities are usually the result of exertional heat stroke due to physical activity in hot environments. These deaths may be underreported due to improper diagnosis. In some cases, a death attributed to a heart attack may have a root cause of exertional heat stroke.

How can companies protect their workers against heat stress?

Businesses are encouraged to be proactive about heat-related dangers by developing a heat-illness prevention plan to keep workers safe during heat priority days when the heat index is expected to be 80°F or more. The NEP outlines measures employers should include in their heat-illness prevention plan, such as:

  • Access to water – The National Institute for Occupational Safety and Health (NIOSH) recommends that workers drink a cup of water every 15-20 minutes to stay hydrated while involved in moderate work activities in hot conditions.
  • A cool place to rest – If indoors, use air conditioning and fans to improve ventilation and use reflective shields and insulation to block radiant heat.
  • Shade from the sun – for outdoor work sites.
  • Adequate training – to prevent illnesses and deaths.
  • Acclimatization procedures – to gradually increase the exposure time of new or returning employees to hot environmental conditions. Begin the acclimatization process with no more than 20% exposure to heat on day 1, then increase exposure by no more than 20% on each subsequent day.

Other effective measures employers can add to their heat-illness prevention plan include:

  • Administrative controls – such as scheduling work during cooler times of day, cross-training workers, or setting up a buddy system to ensure workers are monitored for symptoms of heat stress.
  • Implementing an occupational medical monitoring program – to identify workers who have increased risk factors for heat illness due to medical conditions.

Finally, companies must consider how protective clothing may contribute to heat stress. A single-layer breathable coverall is often worn over top of regular “street clothing,” resulting in a double-layer system where a single layer would suffice. This double layer has the same effect as adding an additional 5.4°F to the temperature of the worksite. Switching from double-layer task-based protective clothing to single-layer breathable daily wear for AR / FR clothing enables workers to stay cooler on the job and significantly lowers the risk of heat stress.

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