What is OSHA’s New National Emphasis Program on Heat Stress?

Summer is here, and the heat is on. And for the first time ever, OSHA has issued a National Emphasis Program (NEP) to protect workers from the dangers of heat-related illnesses. This means that OSHA is prioritizing this hazard, proactively looking for violations in 70 targeted high-risk industries such as general industry, oil and gas, construction, maritime, and agriculture, to name a few. Inspections will be conducted on both indoor and outdoor worksites on days when the National Weather Service has issued a heat warning or advisory for the targeted area. So, what are the implications of a national emphasis program on heat stress for flame resistant and arc-rated (AR / FR) clothing? Scott Margolin, Tyndale’s Vice President of Technical and Corporate Strategy, answers this question and others we commonly hear on this topic in the video below.


As Scott explains, the three main government organizations that address work-related health hazards – OSHA, the CDC, and the National Institute for Occupational Safety and Health (NIOSH) – all tell us the same thing:

  • No single-layer breathable apparel contributes to heat stress – including long-sleeved, arc-rated (AR) clothing.
  • Long sleeves are actually safer than short sleeved shirts for heat stress because they minimize exposure to the sun, a radiant heat load. And, they of course protect against arc flash and flash fire hazards as well!

How much does task-based clothing adversely affect heat dissipation?

OSHA’s heat stress calculator is a handy tool to help employers determine whether workers’ heat stress factors exceed recommended limits. It calculates these criteria:

  • Environmental heat: A combination of air temperature, humidity, radiant heat from sunlight or other sources, and air movement.
  • Workload: Light, moderate, heavy, or very heavy. Strenuous activity increases metabolic heat, which can raise the body’s core temperature to dangerous levels when combined with environmental heat.
  • Acclimatization status: Whether a worker has been gradually exposed to hot working conditions (acclimatized or unacclimatized).
  • Clothing: Compares clothing types – see chart below – to determine how they impact the wearer and contribute to heat stress.
  • Body weight: Normal or obese.

The Clothing Adjustment Factor (CAF) is the amount that must be added to the environmental heat when determining heat stress. CAFs for the different clothing categories are shown in the table below:

Type of Clothing Clothing Adjustment Factor:
Normal work clothes (e.g., long sleeve shirt and pants) 0
Cloth (woven) coveralls* 0
SMS polypropylene coveralls* 0.9°F (0.5°C)
Polyolefin coveralls* 1.8°F (1°C)
Double layer of clothing 5.4°F (3°C)
Limited-use vapor-barrier coveralls* 19.8°F (11°C)

*Coveralls assume that only undergarments, not a second layer of clothing, are worn underneath.

As the table shows, when wearing a double layer of clothing, such as a 40cal arc flash suit or coveralls over a pant/shirt combo, one must be aware that it has the same effect as adding an additional 5.4°F to the temperature of the worksite. This may not seem like much, but it is enough to push the heat stress into the unsafe range, especially when combined with strenuous work or other factors. However, single-layer AR / FR protective clothing has a CAF of 0 and does not increase the risk of heat stress.

  • FACT: No single-layer breathable apparel – whether AR/FR, long sleeve, or even heavy versus light – is a cause of heat stress.
  • FACT: One of the things that DOES cause heat stress is multiple layer garments – while this includes 40cal arc flash suits, it also includes a coverall over pant/shirt combo.

Since workers in the industries we serve wear AR / FR clothing to stay safe on the job, our best advice is to outfit workers in single-layer breathable AR / FR clothing instead of multi-layer protection – such as coveralls over clothing – which reduces the body’s ability to dissipate heat.

Main causes of heat stress

So, if workers need to wear more than a single layer to deliver necessary arc flash or flash fire protection, employers must take care to ensure that workers are also protected against heat stress. This means being alert to the four primary causes of heat stress and taking the appropriate precautions against them:

  • Dehydration: A lack of hydration reduces sweat, and sweating is how heat is released heat from our bodies. Workers should be sure to drink plenty of water while working.
  • Lack of shade: The sun is a radiant heat load. It’s important for workers to take breaks in the shade and rehydrate with clear liquids while doing so.
  • Lack of rest breaks: While doing physical work, we build up metabolic energy. Periodic breaks are critical to dissipating that energy.
  • Existing medical conditions or medications: Certain illnesses and medications can exacerbate heat stress. Be aware of these risk factors, adjust workloads, and increase breaks accordingly.

OSHA will be out there this summer looking to cite employers proactively, so ensure your workers are properly hydrated – and remain hydrated – and they take rest breaks in the shade or a cool indoor setting as frequently as necessary given the ambient conditions. Stay tuned for an upcoming FR FAQ, which takes a deeper dive into heat-related illnesses and prevention plans businesses can put in place to keep workers safe. For now, here’s the bottom line: There is no reason to put workers in two layers when a one-layer daily wear system protects against the arc flash/flash fire hazard without exposing the worker to heat stress.


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