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MSJC > Safety > Heat Stress

Heat Stress

Operations involving high air temperatures, radiant heat sources, high humidity, direct physical contact with hot objects, or strenuous physical activities have a high potential for inducing heat stress in employees engaged in such operations.  Outdoor operations conducted in hot weather, particularly those that require workers to wear semi-permeable or impermeable personal protective equipment, are also likely to cause heat stress.

Causal Factors

It is difficult to predict just who will be affected and when, because individual susceptibility varies.  Some factors are listed below:

  • Age
  • Weight
  • Degree of physical fitness
  • Degree of acclimatization
  • Metabolism
  • Use of alcohol or drugs
  • Pre-existing medical conditions (i.e., hypertension)
  • Type of clothing

To evaluate employee heat stress, please see the OSHA Technical Manual, Section III, Chapter 4, Investigation Guidelines.  There are also OSHA regulations that pertain to Heat Stress.

Heat Disorders and Health Effects

  • Heat Stroke.  This condition occurs when the body’s system of temperature regulation fails and body temperature rises to critical levels.  This condition is caused by a combination of highly variable factors, and its occurrence is difficult to predict. 

    Symptoms include: confusion; irrational behavior; loss of consciousness; convulsions; a lack of sweating; hot, dry skin; and an abnormally high body temperature.

    If a worker shows signs of possible heat stroke, professional medical treatment should be obtained immediately.  The worker should be placed in a shady area with their outer clothing removed, skin should be wetted, air movement around them should be increased, and fluids should be replaced as soon as possible.  Regardless of a worker’s protests, no employee suspected of being ill from heat stroke should be sent home or left unattended unless a physician has specifically approved such an order. 

  • Heat Exhaustion.  Fainting is commonly associated with this heat disorder, and is especially problematic if the victim is operating machinery or controlling an operation that should not be left unattended. 

    Signs and symptoms include:  headache, nausea, vertigo, weakness, thirst, and giddiness. 

    This condition responds readily to prompt treatment.  Workers suffering from heat exhaustion should be removed from the hot environment, given fluids, and encouraged to get adequate rest.

  • Heat Cramps.  Performing hard physical labor in a hot environment causes this type of cramps, and have been attributed to an electrolyte imbalance caused by sweating.  Cramps can be caused by both too much and too little salt, and by lack of water replenishment.

    Thirst cannot be relied on as a guide to the need for water; instead, water must be taken every 15 to 20 minutes in hot environments.

  • Heat Collapse.  In heat collapse, the brain does not receive enough oxygen because blood pools in the extremities.  As a result, the exposed individual may lose consciousness.  To prevent heat collapse, the worker should be gradually acclimatized to the hot environment.
  • Heat Rashes.  This is the most common problem in hot work environments.  In most cases, heat rashes will disappear when the affected individual returns to a cool environment.
  • Heat Fatigue.  A factor that predisposes an individual to heat fatigue is lack of acclimatization. 

    Signs and symptoms include: impaired performance of skilled sensorimotor, mental, vigilance jobs.

    There is no treatment except to remove the heat stress before a more serious heat-related condition develops.

Controlling Heat

Engineering Controls

  • Adequate ventilation
  • Air cooling
  • Fans
  • Shielding
  • Insulation
  • Use power assists and tools

Administrative Controls

  • Drink plenty of water
  • Frequent breaks in a cool environment
  • Complete heavy work during cooler parts of the day
  • Wear appropriate clothing
  • Get enough sleep at night

For More Information

The information in the above article is taken from the OSHA Technical Manual, Section III, Chapter 4, Heat Stress which can be located on the web at

This website has OSHA’s Fact Sheet on Protecting Workers in Hot Environments.  This is a quick overview summarizes most of the key points from OSHA’s technical manual.