Heat Stress-Environmental Health & Safety - Carnegie Mellon University

Heat Stress

All of us must be aware of the potential dangers associated with working in hot conditions. Although these conditions are obviously most prevalent in the summer, working in any hot environment, including an unventilated room, can also present some heat-related danger.

Pay attention to the following reminders:

HEAT STROKE 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. Heat stroke is a medical emergency. The primary signs and symptoms of heat stroke are confusion; irrational behavior; loss of consciousness; convulsions; a lack of sweating (usually); hot, dry skin; and an abnormally high body temperature.  If body temperature is too high, it can cause death.

If an individual shows signs of possible heat stroke, professional medical treatment must be obtained immediately. The individual should be placed in a cool area and the outer clothing should be removed. The person's skin should be wetted and air movement around the worker should be increased to improve evaporative cooling until professional methods of cooling are initiated and the seriousness of the condition can be assessed. Fluids should be replaced as soon as possible. The medical outcome of an episode of heat stroke depends on the victim's physical fitness and the timing and effectiveness of first aid treatment.  Regardless of the person's protests, no individual suspected of being ill from heat stroke should be sent home alone or left unattended unless a physician has specifically approved such an order.  

HEAT EXHAUSTION The signs and symptoms of heat exhaustion are headache, nausea, vertigo, weakness, thirst, and giddiness. Fortunately, this condition responds readily to prompt treatment. Heat exhaustion should not be dismissed lightly, however, for several reasons. One is that the fainting associated with heat exhaustion can be dangerous because the victim may be operating machinery when fainting occurs; moreover, the victim may be injured when he or she faints. Also, the signs and symptoms seen in heat exhaustion are similar to those of heat stroke, a medical emergency.  Anyone suffering from heat exhaustion should be removed from the hot environment and given fluid replacement. They should also be encouraged to get adequate rest.

HEAT CRAMPS have been attributed to an electrolyte imbalance caused by sweating. It is important to understand that cramps can be caused by both too much and too little salt, and they appear to be directly related to a lack of water replenishment. Thirst cannot be relied on as a guide to the need for water; instead, water or commercially available carbohydrate-electrolyte replacement liquids (e.g., Gatorade) must be taken every 15 to 20 minutes in hot environments.

HEAT COLLAPSE ("Fainting").  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. This reaction is similar to that of heat exhaustion and does not affect the body's heat balance. However, the onset of heat collapse is rapid and unpredictable. To prevent heat collapse, the worker should gradually become acclimatized to the hot environment.

HEAT RASHES are the most common problem in hot work environments.  Prickly heat is manifested as a rash and usually appears in areas where the clothing is restrictive. As sweating increases, the rash gives rise to a prickling sensation. Prickly heat occurs in skin that is persistently wetted by unevaporated sweat, and heat rash papules may become infected if they are not treated. 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. The use of a program of acclimatization and training for work in hot environments is advisable. The signs and symptoms of heat fatigue include impaired performance of skilled sensorimotor, mental, or vigilance jobs. There is no treatment for heat fatigue except to remove the heat stress before a more serious heat-related condition develops.


  • Ventilation, air cooling, fans, shielding, and insulation are the five major types of engineering controls used to reduce heat stress in hot work environments. Heat reduction can also be achieved by using power assists and tools that reduce the physical demands placed on an individual.
  • The human body can adapt to heat exposure to some extent.  After a period of acclimatization, the same activity will produce fewer cardiovascular demands. The individual will sweat more efficiently (causing better evaporative cooling), and thus will more easily be able to maintain normal body temperatures.
  • Replace fluids.  Cool (50°-60°F) water or any cool liquid (except alcoholic beverages, which actually have an undesirable affect on heat illnesses) should be kept available.  Drink small amounts frequently, e.g., one cup every 20 minutes.  Although some commercial replacement drinks contain salt, this is not necessary for acclimatized individuals because most people add enough salt to their summer diets.     
  • Hot jobs should be scheduled for the cooler part of the day, and routine maintenance and repair work should be scheduled for the cooler seasons of the year, when practical.
  • Anyone who works in conditions that increase the risk of heat stress should work within sight of someone else.
  • Each should monitor the other to ensure that nobody develops symptoms without someone knowing it.
  • Reduce the physical demands of the job, where possible.  Avoid digging, excessive lifting, etc. in the hot part of the day.
  • Have a recovery area where you can go to cool down.  If air conditioning is not available, try to get into a shady or cool area.  Breaks should be more frequent in hot weather.
  • Know the symptoms of heat related illnesses, and know how to respond.
  • Certain prescription drugs can exaggerate the effects of heat.  If you are taking a prescription medication, ask your doctor if it will contribute to the danger of working in the heat, and if so, what precautions you should take.

We can’t do anything about the heat, but we can protect ourselves from its effects.  Following these precautionary steps will make your job a lot safer, and a lot easier.