Outdoor Heat Exposure

Updated June 28, 2022

Excessive exposure to heat can cause a range of heat-related illnesses, from less serious heat rash and heat cramps to more serious heat exhaustion and heat stroke. Heat stroke requires immediate medical attention because it can result in serious health effects or death, so take precautions while working in the summer heat.

For people working in hot environments, both air temperature and humidity affect how hot you feel. The higher the heat and humidity, the hotter the weather feels, because sweat is unable to readily evaporate. If the sweat your body produces cannot evaporate, your body cannot easily cool down, and you may be at risk for a heat illness. Certain factors, including personal health conditions, activities being conducted, and weather can increase the risk of a heat-related illness.

Heat exhaustion can also make workers more susceptible to falls, equipment-related injuries, and other on-the-job safety hazards.

University units with personnel who work outdoors must plan, prepare, and train for heat-related illness.


Washington state outdoor heat exposure rules in WAC 296-62-095 apply to UW departments with personnel performing work in an outdoor environment from May 1 through September 30, annually, only when personnel are exposed to outdoor heat at or above an applicable temperature listed in Table 1 below.

In addition to requirements in the permanent rule, as of June 15, 2022 through September 29, 2022, additional temporary requirements go into effect for cool water, shade, cool-down rest periods, and observing and communicating with workers about signs and symptoms of heat illness.

Table 1: Outdoor temperature action levels

Non-breathable clothes, including vapor barrier clothing or PPE such as chemical resistant suits 52 degrees F
Double-layer woven clothes including coveralls, jackets, and sweatshirts 77 degrees F
All other clothing 89 degrees F

Exception: The rules do not apply if incidental exposure occurs when personnel are not required to perform a work activity outdoors for more than 15 minutes in any 60-minute period. The exception may be applied every hour during the work shift.


Heat-related illness and first aid

Heat stroke

  • High body temperature (103°F or higher)
  • Hot, red, dry, or damp skin
  • Fast, strong pulse
  • Headache
  • Dizziness
  • Nausea
  • Confusion
  • Losing consciousness (passing out)
  • Call 9-1-1 right away-heat stroke is a medical emergency
  • Move the person to a cooler place
  • Help lower the person’s temperature with cool cloths or a cool bath
  • Do not give the person anything to drink

Heat exhaustion

  • Heavy sweating
  • Cold, pale, and clammy skin
  • Fast, weak pulse
  • Nausea or vomiting
  • Muscle cramps
  • Tiredness or weakness
  • Dizziness
  • Headache
  • Fainting (passing out)
  • Move to a cool place
  • Loosen your clothes
  • Put cool, wet cloths on your body or take a cool bath
  • Sip water

Get medical help right away if:

  • You are throwing up
  • Your symptoms get worse
  • Your symptoms last longer than 1 hour

Heat cramps

  • Heavy sweating during intense exercise
  • Muscle pain or spasms
  • Stop physical activity and move to a cool place
  • Drink water or a sports drink
  • Wait for cramps to go away before you do any more physical activity

Get medical help right away if:

  • Cramps last longer than 1 hour
  • You’re on a low-sodium diet
  • You have heart problems


  • Painful, red, and warm skin
  • Blisters on the skin
  • Stay out of the sun until your sunburn heals
  • Put cool cloths on sunburned areas or take a cool bath
  • Put moisturizing lotion on sunburned areas
  • Do not break blisters

Heat rash


Red clusters of small blisters that look like pimples on the skin

(usually on the neck, chest, groin, or in elbow creases)

  • Stay in a cool, dry place
  • Keep the rash dry
  • Use powder (like baby powder) to soothe the rash



Prior to outdoor work in temperatures exceeding those listed in Table 1, personnel and supervisors must complete the Outdoor Heat Exposure and Heat-Related Illness training course located on the EH&S Training webpage.

Services available

If you need assistance related to preventing heat related illness, contact EH&S at ehsdept@uw.edu or (206) 543-7388. 

Frequently asked questions

Visit the Washington State L&I website to read frequently asked questions.


The body's gradual temporary adaptation to work in heat that occurs as a person is exposed to it over time; a period of seven to 14 days with a substantial amount of adaptation occurring in the first four to five days. Acclimatization is lost after a week away from working in the heat.



A system where individuals are paired or teamed up into work groups so each employee can be observed by at least one other member of the group to monitor and report signs and symptoms of heat-related illness.

Clothing worn in two layers allowing air to reach the skin; for example, coveralls worn on top of regular work clothes.

Potable water that is suitable to drink and suitably cool in temperature; drinking water packaged as a consumer product and electrolyte-replenishing beverages (i.e., sports drinks) that do not contain caffeine are acceptable. 

The use of devices to reduce exposure and aid cooling (i.e., air conditioning)

An environment where work activities are conducted outside; work environments such as inside vehicle cabs, sheds, and tents or other structures may be considered an outdoor environment if the environmental factors affecting temperature are not managed by engineering controls. Construction activity is considered to be work in an indoor environment when performed inside a structure after the outside walls and roof are erected

A blockage of direct sunlight; one indicator that blockage is sufficient is when objects do not cast a shadow in the area of blocked sunlight. Shade is not adequate when heat in the area of shade defeats the purpose of shade, which is to allow the body to cool. For example, a car sitting in the sun does not provide acceptable shade to a person inside it, unless the car is running with air conditioning. Shade may be provided by any natural or artificial means that does not expose employees to unsafe or unhealthy conditions and that does not deter or discourage access or use.

Clothing that significantly inhibits or completely prevents sweat produced by the body from evaporating into the outside air; such clothing includes encapsulating suits, various forms of chemical resistant suits used for PPE, and other forms of non-breathable clothing.