The University of Iowa

Heat Stress

What is Heat Stress?

Heat stress occurs when the body cannot get rid of excess heat. When this happens, the body's core temperature rises and the heart rate increases. As the body continues to store heat, the person begins to lose concentration and has difficulty focusing on a task, may become irritable or sick, and often loses the desire to drink. The next stage is most often fainting and even death if the person is not cooled down.

Factors that contribute to heat stress are high air temperatures, radiant heat sources, high humidity, direct physical contact with hot objects, and strenuous physical activities.

The Occupational Safety and Health Administration (OSHA) has developed a Heat Stress National Emphasis Program (NEP). The purpose of the program is to protect workers from the increasing threat of heat-related illness in both indoor and outdoor work locations. In conjunction with this, EHS has developed resources to help UI departments put in place an effective Heat Stress Prevention Program. The NEP requires departments establish a program if they have employees that work in outdoor locations, or have indoor employees that are exposed to work temperatures that exceed 80°F. Occupational Safety staff will be contacting several departments to evaluate the risk for heat stress and helping to establish a program, where required.

Contact information and areas of expertise can be found on the Contact Us page.


Heat Stress Prevention Program 


  • Heat Stress - W552OS 
    • This course covers the signs, symptoms and treatment of heat-related illnesses and how to prevent them from happening.
    • Audience: All employees that work outdoors, their supervisors, and their departmental safety person should take this course on a yearly basis. All employees that work inside and are exposed to a Wet Bulb Globe Temperature Effective (WBGTE) above 75°F, their supervisors, and their departmental safety person should also take this course on a yearly basis. 

For further training and registration information, go to EHS Safety Training. 

Heat Rash

Also known as prickly heat, is skin irritation caused by sweat that does not evaporate from the skin. Heat rash is the most common problem in hot work environments.


  • Clusters of red bumps on skin
  • Often appears on neck, upper chest, folds of skin

First Aid

  • Try to work in a cooler, less humid environment when possible
  • Keep the affected area dry

Heat Cramps

Are caused by the loss of body salts and fluid during sweating. Low salt levels in muscles cause painful cramps. Tired muscles—those used for performing the work—are usually the ones most affected by cramps. Cramps may occur during or after working hours.


  • Muscle spasms
  • Pain

First Aid

  • Have worker rest in shady, cool area
  • Worker should drink water or other cool beverages
  • Wait a few hours before allowing worker to return to strenuous work
  • Have worker seek medical attention if cramps don't go away

Heat Exhaustion

Is the body's response to loss of water and salt from heavy sweating? 


  • Cool, moist skin
  • Heavy sweating
  • Headache
  • Nausea or vomiting
  • Dizziness
  • Light headedness
  • Weakness
  • Thirst
  • Irritability
  • Fast heartbeat

First Aid

  • Have worker sit or lie down in a cool, shady area
  • Give worker plenty of water or other cool beverages to drink
  • Cool worker with cold compresses/ice packs
  • Call 911 if signs or symptoms worsen or do not improve within 60 minutes.
  • Do not return to work that day

Heat Stroke

The most serious form of heat-related illness happens when the body becomes unable to regulate its core temperature. Sweating stops and the body can no longer rid itself of excess heat.


  • Confusion
  • Fainting
  • Seizures
  • Excessive sweating or red, hot, dry skin
  • Very high body temperature


  • Call 911
    • Then
      • Place worker in shady, cool area 
      • Loosen clothing, remove outer clothing
      • Fan air on worker; cold packs in armpits
      • Wet worker with cool water; apply ice packs, cool compresses, or ice if available
      • Provide fluids (preferably water) as soon as possible 
      • Stay with worker until help arrives 

General Controls

  • Monitor the heat index or wet bulb globe temperature throughout the day.
  • Allow time for employees to adjust to hot jobs when possible. It often takes two to three weeks for an employee to become acclimated to a hot environment.
  • Adjust the work schedule, if possible. Assign heavier work on cooler days or during the cooler part of the day.
  • Establish a schedule for work and rest periods during hot days.
  • Train workers to recognize signs and symptoms of heat stress disorders and be prepared to give first aid if necessary.
  • Drink at least one cup of fluids for every 20 minutes of work in the heat.

Job Specific Controls

  • Use adequate fans for ventilation and cooling, especially when wearing personal protective equipment (PPE).
  • Wear light-colored, loose clothing or clothing designed to cool the person down.
  • Keep shaded from direct heat where possible (e.g., wear a hat in direct sunshine).
  • Reduce the workload. Increase the use of equipment on hot days to reduce physical labor.
  • Monitor the employees heart rate while working, core body temperature, recovery heart rate, and weight loss during the shift. Consult with EHS and Employee Health before implementing.  

To determine if it is too hot a heat hazard assessment (HHA) needs to be conducted. This can be done using either the wet bulb globe temperature (WBGT) or the heat index. EHS recommends using the WBGT as it is more accurate, and the method OSHA uses in issuing citations.  

If you are working outside you can use the WBGT from the Kinnick Weather station and use WBGT HHA Worksheet to complete the HHA. An Excel version of the WBGT HHA is also available that will automatically update with the current WBGT, if the spreadsheet is downloaded to your computer, and color code based on the risk. If you are working inside you will need to use a WBGT meter along with 1 of the worksheets. 

The heat index HHA can only be used for outside locations. The easiest way to complete the heat index HHA is to use the OSHA NIOSH Heat safety tool app for Android or IOS. If you do not have the app you can use the HI HHA Worksheet to complete the assessment.