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What Is Heat Illness?

Cal/OSHA investigations (Study 2) that in 2006 18% of the suspected victims of heat illness died, and 42% required hospitalization for more than 24 hours.

Cal/OSHA investigations showed that 52% of the suspected victims of heat illness died, and 32% required hospitalization for more than 24 hours.

What is Heat Illness?

T8CCR 3395(b) Definitions defines “Heat Illness” as the following:

"Heat Illness" means a serious medical condition resulting from the body's inability to cope with a particular heat load, and includes heat cramps, heat exhaustion, heat syncope, and heat stroke (see T8 CCR Section 3395).

Heat Illness – "More to the Story"

What Happens to the Body

Human beings need to maintain their internal body temperature within a very narrow range of a few degrees above or below 98.6° F. People suffer from heat illness when their bodies are not able to get rid of excess heat and properly cool. The body losses it's "heat balance" because it can not shed heat at a fast enough rate.

When the body starts to overheat the blood vessels get bigger and the heart beats faster and harder. More blood flows to the outer layers of the skin from the internal "core" so that the heat can be released into the cooler outside environment. If this process does not cool the body fast enough, or the outside air is warmer than the skin, the brain triggers sweating to cool the body. Sweat glands in the skin draw water from the bloodstream making sweat. The sweat evaporates and releases the heat from the body. During an hour of heavy work in hot weather, the body can easily sweat out one quart of water.

Shifting blood to outer body layers (the "shell") causes less blood to go to the brain, muscles, and other organs (the "core"). Prolonged sweating can deplete the body of water and salt causing dehydration. Because the body looses water and the salts that are needed for the muscles to work, muscle cramping may occur. The physiological strain on the body from heat illness may cause the person to become dehydrated, weak, tired, and confused.

As dehydration gets worse the body can no longer keep its temperature within the normal range, sweating stops and severe heat illness occurs. In heatstroke, the person’s body temperature rises rapidly damaging the brain, muscles and vital organs causing death.


Rapid Onset

Heat illness can develop very rapidly and is not always obvious before it becomes life-threatening. During high heat, heat illness can develop faster and even employees who have been doing their job for sometime are a risk.


Variability in Symptom Recognition and Reporting

The symptoms of heat illness may vary between individuals. Also, employees may not accurately recognize and report the symptoms. As a result victims may be placed at a greater health risk. A person certified to provide first aid should be available at the work site to initially evaluate potential heat illness victims. See Emergency Response Procedures

Victims of heat illness may not report the full range of symptoms they are feeling because they:

  • Choose not to for fear of negative consequences
  • Deny that the symptoms may be serious
  • Have not been trained to identify the symptoms of heat illness
  • Are not physically able to report (e.g., they may have fainted)
  • Are not fully aware of what is happening to their bodies (e.g., they may be delirious or mentally confused)

Types of Heat Illness and Common Signs/Symptoms

Heat illness affects the body, causing employees with mild symptoms to experience weakness, tiredness, and mental confusion, or even exhibit irritable or erratic behavior. Heat illness can also affect employees work performance and increase their risk of having accidents.


Employees should be encouraged never to discount any discomfort or symptoms they are experiencing when working in heat, after work or before the next workday. Heat illness symptoms can occur even after work has stopped. They should immediately report any problems they are experiencing to a supervisor and coworker, or a family member to seek prompt medical attention. Employees and supervisors must be fully trained on the prevention of heat illness before they are assigned to work in locations where they are at risk for heat illness.

Heat illness can be one or more of the following medical conditions including: heat rash, heat cramps, fainting, heat exhaustion, and heatstroke. The following symptoms are commonly associated with the different heat illness medical conditions. Given the variability in recognition and reporting of heat illness symptoms, the information listed below should be used only as a general guideline to train employees and supervisors.

Heat Rash (Prickly Heat) - Heat rash is a skin irritation caused by excessive sweating and clogged pores during hot, humid weather.

General Symptoms:

  • Can cover large parts of the body
  • Looks like a red cluster of pimples or small blisters
  • Often occurs on the neck, chest, groin, under the breasts, or in elbow creases
  • Uncomfortable so it can disrupt sleep and work performance
  • Complicated by infections

Heat Cramps - Heat cramps affect people who sweat a lot during strenuous work activity. Sweating makes the body loose salts and fluids and minerals. If only the fluids are replaced and not the salts and minerals painful muscles cramps may result.

General Symptom:

  • Painful muscle spasms in the stomach, arms, legs, and other body parts may occur after work or at night

Fainting (Heat Syncope) - Employees who stand for long periods or suddenly get up from a sitting or lying position when working in the heat may experience sudden dizziness and fainting. In both cases, the fainting is caused by a lack of adequate blood supply to the brain. Dehydration and lack of acclimatization to work in warm or hot environments can increase the susceptibility to fainting. Victims normally recover consciousness rapidly after they faint.

General Symptoms:

  • Sudden dizziness
  • light-headedness
  • unconsciousness

Heat Exhaustion

Heat exhaustion is the body’s response to an excessive loss of the water and the salt contained in sweat.


Cool skin temperature is not a valid indicator of a normal body temperature. Although the skin feels cool the internal body temperature may be dangerously high and a serious medical condition may exist.

General Symptoms:

  • Heavy sweating
  • Painful muscle cramps
  • Extreme weakness and/or fatigue
  • Nausea and/or vomiting
  • Dizziness and/or headache
  • Body temperature normal or slightly high
  • Fainting
  • Pulse fast and weak
  • Breathing fast and shallow
  • Clammy, pale, cool, and/or moist skin



Heatstroke is usually fatal unless emergency medical treatment is provided promptly.

General Symptoms:

  • No sweating because the body cannot release heat or cool down
  • Mental confusion, delirium, convulsions, dizziness
  • Hot and dry skin (e.g., red, bluish, or mottled)
  • Muscles may twitch uncontrollably
  • Pulse can be rapid and weak
  • Throbbing headache, shallow breathing, seizures and/or fits
  • Unconsciousness and coma
  • Body temperature may range from 102° - 104° F or higher within 10-15 minutes

If the muscles begin to twitch uncontrollably, keep the person from self-injury. Do not place any objects in the mouth.

Monitor body temperature and continue cooling efforts until emergency medical treatment is provided to the victim.