Skip to main content

Heat Related Illness

| Chaizong Lor

Heat Related Illness

General Information:

Heat related illnesses are caused by the body’s inability to cool itself. The way our body cools down is by sweating but in extreme temperatures or when someone is doing physical activities in the heat, sweating is not enough to keep the body cool. There are 3 types of heat illnesses: heat stroke, heat exhaustion, and heat cramps. Heat cramps are the first stage of heat illnesses, heat exhaustion is next, and heat stroke is the most dangerous.

Heat Cramps are painful muscle spasms. They occur when a worker drinks a lot of water but does not replace salts lost from sweating. Tired muscles – those used for performing the work – are usually the most likely to have cramps. The symptoms include heavy sweating during exercise and muscle cramping.  The treatment is to drink an electrolyte solution (sports drink) such as Gatorade. If the cramps are severe or not relieved by drinking a sports drink, seek medical attention as appropriate.

Heat Exhaustion Symptoms are when your body cannot keep blood flowing both to vital organs and to the skin for cooling.  The symptoms include heavy sweating, cold, pale skin, weak pulse, nausea, tiredness, dizziness, headache, and fainting. The treatment is to takes at least 30 minutes to cool down in an air conditioned or shaded are to prevent the body from getting to the level of heat exhaustion. If it is not treated quickly, it can lead to heat stroke.

Heat Stroke is the most serious health problem for people working in the heat but is not very common. It is caused by the failure of the body to regulate its core   temperature. Sweating stops and the body cannot get rid of excess heat. Victims will die unless they receive proper medical treatment promptly. The symptoms include high body temperature, hot, red, dry skin, fast, strong pulse, headache, dizziness, nausea, confusion, and losing consciousness. The treatment, if a co-worker shows symptoms of heat stroke, you must take the following actions seriously:

  • Call 911 or get the worker to a hospital quickly.
  •      Take steps to cool the workers down (i.e., put them in a tub of cool water or give them a cool shower, spray them with a hose, or wrap them in a cool, wet sheet and fan rapidly).
  •      If the worker is unconscious, do not give them anything to drink.

Preventing Heat Related Illness

In most cases, heat stress can be prevented or, at least, the risk of developing heat stress can be reduced.

Engineering Controls

Several engineering controls can help reduce heat exposure. These include:

  •          General and local exhaust ventilation in areas of high heat.
  •          Shielding of radiant heat sources, such as furnaces or hot machinery.
  •          Elimination of steam leaks.
  •          Use of cooling fans or personal cooling devices, such as cooling vests.
  •          Use of power tools to reduce manual labor.

Work Practices

  •      Clothing:  Wear loose-fitting, lightweight clothing, such as cotton, to allow sweat to evaporate. Light colors absorb less heat than darker colors. When working outside, wear a lightweight hat with a good brim to keep the sun off your head and face.
  •      Drinking Drink plenty of liquids, especially if your urine is dark yellow, to replace the fluids you lose from sweating – as much as one quart per hour may be necessary. Water and/or sports drinks are recommended. Since caffeine is a diuretic (makes you urinate more), beverages such as cola, iced tea and coffee should be avoided. Thirst is not a reliable sign that your body needs fluids. When doing heavy work, it is better to sip rather than gulp the liquids.
  •     Work Schedule: If possible, heavy work should be scheduled during the cooler parts of the day. Otherwise, alternate heavy work in the heat with lighter work or work in cooler areas. When the temperature humidity index is between 84 and 93 (Warning Zone), try to minimize the amount of time working in the heat such that approximately half of each hour is spent doing heavy work in the heat. When the temperature humidity index is 94 or higher (Danger Zone), this should be further minimized to approximately one quarter of each hour spent doing heavy work in the extreme heat.
  •     Acclimatization:  New employees and workers returning from an absence of two weeks or more should have 5 days to get used to the heat. Begin with 50% of the normal workload and time exposure on the first day and gradually build up to 100% on the fifth day.
  • Body Weighing: Workers may be at greater risk of heat stress if they lose more than 1.5% of their body weight in a single day from sweating.

Personal Protective Equipment

When work must proceed in hot conditions at UW-Eau Claire, personal cooling systems may help reduce the risk of heat stress. There are several systems available through health and safety catalogs, including the following:

  •     Heat reflective clothing may alleviate the problem of radiant heat sources, such as furnaces. However, if the worker is fully covered, he or she will have trouble evaporating sweat.
  •     Ice vests or cooling vests remove heat from the skin. They are relatively inexpensive and allow freedom of movement.
  •     Liquid cooling systems also remove heat from the skin. Cool liquid flows in the suit around the body and carries the heat away.


Employees and supervisors need to be trained to be able to detect early signs of heat stress. Employees must understand the need to replace fluids & salt from sweat and recognize the signs of dehydration, fainting, heat cramps, heat exhaustion, and heat stroke.

Supervisors should watch for signs of heat stress and allow workers to interrupt their work if they are extremely uncomfortable. Supervisors should also ensure that work schedules allow appropriate rest periods and ensure liquids are available. They should use appropriate engineering controls, personal protective equipment, and work practices to reduce the risk of heat stress incidents.