SHARP Investigates Heat-related Illness in Washington State's Workers

Safety & Health Assessment & Research for Prevention (SHARP) — Research for Safe Work

Hot weather can kill. Workers can be protected if they know how to prevent heat-related illness and if they are familiar with the signs, symptoms and appropriate first aid procedures for serious heat illnesses.

High temperatures and high humidity conditions in combination with other risk factors can limit the body's ability to cool. When the body retains more heat than it can release, protective mechanisms can be overwhelmed resulting in heat-related illness (HRI).

HRI ranges from relatively harmless conditions such as heat edema (swelling) and heat cramps to more serious illness such as heat syncope (fainting) and heat exhaustion. The most serious and often fatal form of HRI is heat stroke.

SHARP has reviewed the workers compensation claim incidence of HRI among Washington State workers. The study analyzed ten years of workers compensation data from 1995 to 2004.

The SHARP study found that:

  • Industry sectors accounting for the most number of claims were:
    • Construction with 150 claims (34%).
    • Public Administration with 71 claims (16%).
    • Manufacturing with 43 claims (10%).
    • Agriculture, Forestry, Fishing and Hunting with 31 claims (7%).
  • Workers in Eastern Washington were at higher risk of HRI. Only 22% of Washington residents live in Eastern Washington. However, 47% of the HRI workers compensation claims occurred there.
  • Individual case files indicated several risk factors known to contribute to HRI. These included medical conditions and medication use known to affect the body's ability to cope with high heat.

SHARP also reviewed the literature regarding HRI. An executive summary of SHARP's Report: Heat-related Illness in Washington State, State Fund Workers' Compensation Claims, 1995-2004 is available online or by calling the SHARP program at 1-888-667-4277.

Protect yourself and your employees from heat-related illness

The following are effective ways to anticipate, prevent, identify and provide first-aid treatment for serious heat-related illness.

1. Anticipate - Understand the mechanisms of heat stress and heat strain

Heat Stress is the amount of heat in a person's body originating from both exposure to environmental heat AND metabolic sources (how hard you are working). During increased exertion up to 80% of the energy from muscular activity is converted to metabolic heat. When a person is working hard, even in high heat conditions, this is by far the largest source in generating stored body heat. Keep this in mind and pace yourself appropriately.

Heat Strain is the body's physiological response to heat stress. Normal responses include:

  • Increased sweating.
  • Expansion of the blood vessels (vasodilatation).
  • Slightly increased heart rate and core temperature.

Evaporation of perspiration is the body's key cooling mechanism. In fact, under heat stress conditions, up to 80% of the heat lost from the body is through this natural process. If the evaporative cooling rate cannot keep pace with the rate that heat is generated and stored in the body, heat strain becomes excessive and heat-related disorders are more likely to occur.

Environmental conditions of high humidity and low air movement decrease the evaporative cooling process (think of the deep-south in summer). Clothing that does not allow the passage of air and water vapor (like working hard in a plastic rain suit) can also impair the body's cooling mechanisms. Special care and attention is required in these situations.

2. Prevent - Control of heat stress and heat strain

Specific recommendations for the control of thermal stress are available through the American Conference of Governmental Industrial Hygienist's 2006 TLV booklet (see reference at end of document). Washington State currently has rules requiring protective heat stress controls for those occupationally exposed to heat stress conditions (WAC 296‑62‑09013 (; WAC 296‑305‑07017 (; WAC 296‑307‑10020 ( While these regulations address the issue in general terms, they offer limited guidance in specifying what actions to take. In addition to practices documented here the use of general controls is also encouraged.

General controls for heat stress include:

  • Provide pre-season heat stress/strain training. At a minimum, conduct a tailgate safety meeting to review heat-related disorders, symptoms and prevention methods, and first aid measures.
  • Supply adequate water and encourage employees to drink regularly, even when not thirsty (a cup about every 20 minutes is recommended).
  • Avoid alcohol or drinks with caffeine before or during work as they can cause dehydration. Get enough sleep at night.
  • Start the work as early in the day as practical and schedule the heaviest work during the cooler parts of the day.
  • Wear light-weight, loose-fitting, light-colored, breathable (e.g. cotton) clothing and a hat. Change clothes if they become completely saturated with sweat.
  • Take regular breaks in the shade. Loosen or remove clothing that restricts evaporative cooling.
  • Use fans and air movers to help the cooling process.
  • Acclimatization allows a person to better cope with the effects of heat stress. Significant acclimatization takes place within five of the last seven days. Full acclimatization occurs within about three weeks of regular exposure to heat stress conditions.
  • Age and/or obesity may reduce an individual's capacity for coping with heat stress. Conduct activities within your limits.
  • Medical conditions, medications and some illicit drugs may interfere with a person's ability to acclimatize and cope in hot conditions. Those persons with heart or kidney disease, diabetes or high blood pressure, persons on a low sodium diet and those taking medications for these or other conditions may wish to seek medical advice before exposure to heat stress conditions.
  • Keep an eye on co-workers for symptoms of heat-related illness. This is especially important for non-acclimatized workers, those returning from vacations and for all workers during heat wave events. A "Buddy System" may accomplish this.
  • Allow self-limitation of heat exposures and encourage self-reporting of symptoms. Never dismiss a person's reported symptoms. Allow the person to self-regulate. Have them rest, cool and recover and monitor them closely for symptoms of heat-related illness.

3. Identify - Know the symptoms of serious heat illness

The two major heat-related illnesses are heat exhaustion and heat stroke. Heat exhaustion if untreated may progress to deadly heat stroke.

If workers show symptoms or complain of being overheated or not feeling well always take this seriously and have them take a break and cool down. Stay with them. If symptoms worsen or the worker does not recover within about 15 minutes, call 911 and have them transported and medically evaluated. Do not delay transport.

Symptoms of heat exhaustion or heat stroke
Heat Exhaustion Heat Stroke
Heavy sweating Sweating may or may not be present
Exhaustion, weakness Red or flushed, hot dry skin
Fainting/Light headedness Confusion/bizarre behavior
Paleness Convulsions before or during cooling
Headache Collapse
Clumsiness, dizziness Any symptom of heat exhaustion but more severe
Nausea or vomiting Panting/rapid breathing
Irritability Rapid weak pulse
  Note: May resemble a heart attack

4. First aid treatment for heat exhaustion or heat stroke

Heat exhaustion
  • Move the victim to a cool shaded area to rest; do not leave him or her alone.
  • Loosen and remove heavy clothing that restricts evaporative cooling.
  • Give cool water to drink, about a cup every 15 minutes.
  • Fan the person, spray with cool water, or apply a wet cloth to his or her skin to increase evaporative cooling.
  • Recovery should be rapid. Call 911 if he or she does not feel better in a few minutes.
  • Do not further expose the person to heat that day. Have them rest and continue to drink cool water or electrolyte drinks.
Heat stroke (medical emergency)
  • Get medical help immediately, call 911 and transport as soon as possible.
  • Move the victim to a cool shaded area and remove clothing that restricts evaporative cooling.
  • Seconds count! Cool the victim rapidly using whatever methods you can and continue cooling until medical help arrives. Examples of cooling methods:
    • Immerse the victim in a tub of cool water.
    • Place the person in a cool shower.
    • Spray the victim with cool water from a garden hose.
    • Sponge the person with cool water.
    • If the humidity is low, wrap the victim in a cool, wet sheet and fan him or her vigorously.
  • If emergency medical personnel are delayed, call the hospital emergency room for further instruction.
  • Do not give the victim water to drink until instructed by medical personnel.


American Conference of Governmental Industrial Hygienists (2006), 2006 TLVs & BEIs, Based on the Documentation of the Threshold Limit Values for Chemical Substances and Physical Agents & Biological Exposure Indices. Also known as, "the TLV booklet."

Additional information

Safety and Health Topic: Heat Stress( by the National Institute for Occupational Safety and Health (NIOSH).

References on Heat Stress Physiology and Control ( by the University of California at Berkeley.

Heat Stress( by the Occupational Safety and Health Administration (OSHA).

Educational videos on heat stress at L&I's Video Library.

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