When it comes to heat stress, you know what you need to do to protect workers, right? Eight ounces of cool water an hour, frequent breaks in the shade, planning heavy work for cooler times of day … You’ve got this.

That’s what researchers at the National Institute for Occupational Safety and Health (NIOSH) thought, too—until the Deepwater Horizon disaster led to thousands of workers cleaning up the mess in the heat of a Gulf shore summer.

NIOSH learned some important lessons about heat illness from that experience. As a result, the agency has updated its Criteria for a Recommended Standard: Occupational Exposure to Heat and Hot Environments for the first time since 1986.

Keep reading to find out what’s new in our understanding of heat illness.

Two types of heatstroke

The most significant change to the NIOSH document is a change in the definition of “heatstroke.” At one time, the accepted definition of “heatstroke” included confusion, unconsciousness, and/or convulsions, accompanied by a lack of sweating. In fact, workers were warned that if they stopped sweating, heatstroke was imminent. Unfortunately, this type of heatstroke, now called “classic heatstroke,” isn’t the type that most commonly strikes workers.

NIOSH has recognized that another type of heatstroke, known as “exertional heatstroke,” is more common in workers—and profuse sweating is one of its symptoms. So workers who have been taught that sweating is a positive sign are actually at increased risk.

Exertional heatstroke is caused by the combination of heat exposure and heavy physical exertion. It can lead to a condition called rhabdomyolysis, in which muscle tissue breaks down, releasing large amounts of potassium into the blood. High levels of potassium in the blood can lead to cardiac arrhythmias and seizures. High levels of proteins released by muscle breakdown can cause temporary or permanent kidney damage.

Symptoms of rhabdomyolysis include muscle pain and cramping, swelling, weakness, and decreased range of motion. Fatigue, abdominal pain, back pain, nausea or vomiting, and confusion may also occur. However, many cases occur with very mild symptoms that are mistaken for heat stress. This creates a potentially dangerous situation because these workers don’t receive the intensive medical intervention they require.

Another potential complication of rhabdomyolysis is compartment syndrome, or swelling in a specific type of muscle, usually in the lower extremities, that blocks blood flow. Compartment syndrome is often delayed—it may take several hours to develop—and can lead to permanent loss of function in the affected limb.

Symptoms of compartment syndrome include the “5 Ps”: pain, pallor, pulselessness, paresthesias (sensation of tingling, numbness, or burning, usually felt in the hands, feet, arms, or legs), and paralysis. Pain is the most common and tends to be extremely severe. Workers who experience these symptoms must go to a hospital immediately. Quick surgical intervention is required to treat compartment syndrome.

Both types of heatstroke are accompanied by extremely high body temperature, and both types are a medical emergency that require immediate medical attention. First aid includes cooling the worker as quickly as possible by any means available, including an ice bath, circulating air around the worker, and placing cold packs on the head, neck, armpits, and groin.

For exertional heatstroke, oral hydration is vital—the more the victim drinks, the more potassium and proteins will be flushed from the body. However, in serious cases, it’s impossible for the victim to drink enough fluids to flush out the proteins and potassium; the victim will need intravenous fluids. Emergency medical services should be summoned immediately for all cases of heatstroke, and victims should be transported to a hospital as soon as possible.

Identifying susceptible workers

In addition to the revised definition and symptom description for heatstroke, NIOSH has tweaked the information about factors that make workers susceptible to heat illness, including:

• Age. Older workers are at increased risk of heat illness, and acclimatization is less effective in older workers. NIOSH suggests that working for shorter periods between breaks can help protect these workers.
• Pregnancy. Pregnant women have a higher-than-normal body temperature throughout pregnancy, meaning that it takes more fluids and more effort to cool a pregnant woman once she has overheated. In addition, heat tolerance decreases as pregnancy progresses.
• Obesity. Obese individuals are 3.5 times more likely to suffer heat illness than other workers. Obese workers may require increased supervision and more careful management to prevent heat illness.
• Medication. Both illegal and prescription drugs can affect the body’s fluid balance and thermoregulation. Workers should ask their doctor or pharmacist about the effects of their medication on heat tolerance.
• Alcohol and caffeine. Alcohol significantly reduces heat tolerance and should be avoided. However, recent studies have found that caffeinated fluids have an effect on fluid balance similar to that of water, so that morning cup of coffee shouldn’t increase workers’ risk.