Heat Stress Fact Sheet

This year, record hot temperatures are causing increased cases of heat-related illness in the general population and workforce. Make sure you know what to do to prevent, recognize and treat heat illness.

Understanding Heat Stress

A comfortable air temperature for most people is around 68°F to 73°F. If the air temperature is much warmer, people generally begin to feel uncomfortable, which is not a hazard as long as the body is able to regulate and manage hot temperatures.

But many factors affect your body’s ability to cope with heat, including air temperature, air movement, humidity, radiant heat, and physical exertion. The combination of these factors determines total heat load on the body and are known as, “heat stress.”

What Causes Heat Illness?

Very hot environments begin to overwhelm and affect the body’s internal temperature. To compensate, the body attempts to regulate heat gain, by sweating and pumping more blood to the skin to “throw off” heat. The evaporation of perspiration is a vital tool for cooling the body. When it is very hot, heat gain surpasses the body’s ability to lose heat. Temperature in the body rises, resulting in heat illness.

Factors that Increase Your Risk

Periods of extreme heat coupled with humidity are exceedingly dangerous for those exposed, because evaporation is hindered by moisture content in the air. In fact, evaporation may cease completely when relative humidity is at or above 90 percent. Therefore, the body cannot effectively cool via perspiration when it’s very humid, making people prone to heat illness at a quicker rate.

Limited air movement further inhibits the cooling of evaporation and increases the risk of heat illness. When physical exertion, heavy clothing, pre-existing medical conditions, high humidity, radiant heat or poor levels of hydration are included in this situation, individuals can easily and quickly succumb to the effects of heat.

What Can You Do to Prevent Heat Illness?

  • Schedule frequent rest periods with water breaks in shaded or air conditioned areas.
  • Routinely check on others who are at risk of heat stress due to health issues or chronic exposure to high temperatures.
  • Know the signs and symptoms of heat illnesses and monitor yourself and others
  • Block out direct sun and other heat sources with a light-weight visor or hat, shaded area or tent.
  • Drink plenty of fluids. The CDC recommends 8 ounces of water every 15 to 20 minutes of exposure. Drink frequently and BEFORE you are thirsty. Thirst mechanisms are not reliable to determine levels of water to consume.
  • Pre-hydrate before heat exposure by consuming two 16 ounce bottles of water and then continue drinking during exposure.
  • Avoid beverages containing alcohol or caffeine. Do not smoke or use nicotine.
  • Wear lightweight, light-colored, loose-fitting clothes.
  • Pay attention to the heat index (or the combination of heat and humidity) and avoid heavy work or extended exposure during high heat index periods.
  • Plan for heat and take ample water with you when it is hot
  • Never work alone when exposed to high heat.
  • Radiant or reflective heat adds to the burden of heat stress. Limit your exposure and guard against radiant/reflective heat sources, such as heat emanating from equipment or reflecting off pavement.
  • Consider using personal protective equipment (PPE)  to reduce the stress of heat. Excellent options are vests that incorporate removable ice packs or specially designed bands that hold water and stay cool for hours.
  • Employers should develop a heat stress program which includes a policy that limits certain types of work in extreme heat and incorporates protective measures, such as hydration, rest breaks, employee training and first aid procedures.

You should know that poor physical condition, some health problems (such as high blood pressure or diabetes), pregnancy, colds and flu, and certain medications can amplify your personal risk. Those who have had previous heat illness are also subject to increased risk in heat.

Inform your employer and get medical clearance to work in hot temperatures if you have any known medical conditions that may pose a heat-related health risk.

What to Do If a Person Becomes Ill from Heat

  • Signs of heat illness can include: Dizziness, light-headedness, irritability, cramps, heavy sweating, extreme weakness or fatigue, confusion, nausea, clammy or moist skin and pale or flushed complexion, slightly elevated body temperature, fast and shallow breathing. In some instances there may be an absence of sweating, as well.
  • At the first indication of heat illness (displaying any symptoms or signs), move the individual to a cooler/shaded area. Seek medical attention.
  • While waiting on medical care, remove outer clothing. Mist, fan or apply ice (ice bags or ice towels).
  • If the victim is able to drink, provide cool drinking water. Do not leave the victim unattended. Watch the individual and talk to them to monitor symptoms.
  • IF THE INDIVIDUAL IS NOT ALERT, FAINTS or seems CONFUSED, this may be heat stroke, which is a true, life threatening medical emergency. CALL 911 IMMEDIATELY!! While waiting on professional care, use aggressive and continuous methods to cool the victim with ice, splashes or misting of water, fanning if humidity is high, to increase evaporation.
  • Heat Stroke can transpire slowly, over time OR may occur suddenly, without warning. Do NOT wait to call 911 if the victim is not responding to treatment promptly, (within five to ten minutes) OR worsens OR exhibits signs of confusion, fainting or seems disoriented. Heat Stroke cannot be treated only by a first aid team. The victim suffering from heat stroke will need rapid care of medical professionals and a fully equipped treatment facility.
  • NOTE: As in the tragic case of this young firefighter recruit, body temperature of heat stress victims may rise above 106-108 degrees, which can cause irreversible organ damage. Death may be imminent without aggressive cooling and prompt treatment!!!

Do not allow anyone who has exhibited heat illness symptoms to return to hot conditions or perform physical exertion the same day, even if the symptoms are very mild.

You can also print this info out in a PDF format here:

Heat Stress Fact Sheet PDF

Helpful Resources:




NOTE: The use of this material does not constitute medical or legal advice and is intended for educational purposes only. © The Safety Training Solution 2011



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