Heat and Sun Exposure


Workers who [task] may face hazards from [hazard name].  Working in high temperatures, with high humidity, direct sun exposure, no breeze or wind, in an enclosed area, or in impervious personal protective equipment, may lead to heat-related illnesses and, in severe cases, death.  In addition, dehydration and other heat-related symptoms can lead to fatigue and increase the risk of injury.

Risk Description:


Thousands of workers become ill each year from working in high temperatures, and some die.  Heat-related health problems range from the pain and discomfort caused by heat rash and heat cramps to much more serious conditions including heat exhaustion and heat stroke.  

  • Heat stroke is the most serious heat-related illness.  It occurs when the body is unable to control its temperature and cool down naturally.  Workers experiencing heat stroke may stop sweating.  Symptoms may include one or more of the following:  a body temperature of 104 degrees Fahrenheit or more; red, hot, dry skin; confusion; dizziness; hallucinations; chills; slurred speech; convulsions; and/or fainting.  Heat stroke is life threatening and requires immediate medical attention.
  • Heat exhaustion occurs when the body has lost an excessive amount of water and salt.  Symptoms of heat exhaustion may include one or more of the following: dizziness, headache, sudden weakness, cramps, nausea, vomiting, thirst, heavy sweating, a fast heart beat, fast and shallow breathing, clammy skin, muscle cramps, a pale or flushed complexion, and/or a temperature of 100.4 degrees or higher.
  • Heat syncope is light-headedness, fainting or dizziness.  It is brought on by dehydration and by not being acclimated to a hot work environment.
  • Heat cramps are muscle pains caused by loss of fluids and salt due to sweating.    
  • Heat rash, sometimes called ‘prickley heat,’ is a painful rash that results from sweating.  The rash appears as clusters of red pimples or small blisters on the neck, upper chest, groin, under the breasts, and in elbow creases – wherever sweat accumulates.

Assessment Info:

Identifying situations that could require workers to perform tasks in high-heat conditions should be an integral part of the site safety planning process. 


To determine if workers are at risk of heat-related illnesses consider the following:

  • What is the air temperature and humidity level the workers will be exposed to?
  • Will workers be exposed to direct sun or be working in an enclosed area?
  • Is there shade or a place to cool down readily available?
  • Is water readily available?
  • Does the equipment used by the workers contribute to their heat exposure?
  • Does the required personal protective equipment have the potential to raise a worker’s body temperature?
  • Is there equipment that can be used, or other work that can be performed, to reduce physical demands during high-heat periods?

It is important to note that temperature measured with a normal dry bulb thermometer does not fully measure the risk of heat stress.   The American Conference of Governmental Industrial Hygienists (ACGIH) recommends work-rest cycles based on a "wet bulb globe temperature" ("WBGT).  The WBGT approach measures the combined effects of the air temperature, air speed, humidity, and radiant heat as a 2-hour time-weighted average.  This assumes lightly clothed acclimatized workers. The level of work activity is also taken into consideration.  For example an individual working in a high temperature, performing “heavy work” would be at risk of heat stress sooner than if performing “moderate work.”  ACGIH defines the levels of risk as follows:

  • "Heavy work" (350 to 500 kilocalories per hour), for example: “Intense arm and trunk work, carrying, shoveling, manual sawing; pushing and pulling heavy loads; and walking at a fast pace.” Two hour average less than 77 WBGT, °F (MnOSHA); 78.8 (ACGIH Acclimatized and 100% work); 72.5 (ACGIH unacclimatized & 100% work).
  • "Moderate work" (200 to 350 kcal/hr), for example: “Sustained moderate hand and arm work, moderate arm and leg work, moderate arm and trunk work, or light pushing and pulling.  Normal walking.”  Two hour average less than 80 WBGT, °F (MnOSHA); 81.5 (ACGIH Acclimatized and 100% work); 77 (ACGIH unacclimatized & 100% work).
  • "Light work" (up to 200 kcal/hr), for example: “Sitting with light manual work with hands or hands and arms, and driving, or standing with some light arm work and occasional walking.”  Two hour average less than 85 WBGT, °F (MnOSHA); 85.5 (ACGIH Acclimatized and 100% work); 81.5 (ACGIH unacclimatized & 100% work)

The National Oceanic and Atmospheric Administration (NOAA) uses the term “heat index,” which only considers temperature and humidity, and is generally the basis for community excessive heat warnings.  It does not consider work load or radiant heat sources. (http://www.weather.gov/om/heat/index.shtml)

Regulations & Standards:


There is no Federal OSHA standard specifically for working in high temperatures; however, hazardous work activities or exposures that are not covered by a specific standard are covered by the general duty clause, which requires each employer to provide a safe and healthful workplace.

OSHA has a national “Campaign to Prevent Heat Illness in Outdoor Workers” with information and materials targeted for workers, contractors and the general public. The goal is to raise awareness and reduce the number of heat-related illnesses and deaths. (http://www.osha.gov/SLTC/heatillness/index.html)

Federal OSHA Standards are enforced by the U.S. Department of Labor in 26 states. There are currently 22 states and jurisdictions operating complete state plans (covering both the private sector and state and local government employees), and 5 - Connecticut, Illinois, New Jersey, New York and the Virgin Islands that cover public employees only. If you are working in one of those states or jurisdictions you should ensure that you are complying with their requirements

Cal OSHA has the “California Heat Illness Prevention Standard (GISO 3395),” which “applies to all outdoor places of employment.” (http://www.dir.ca.gov/title8/3395.html; http://www.dir.ca.gov/dosh/etools/08-006/index.htm; http://www.dir.ca.gov/dosh/etools/08-006/WhatIs.htm)  Cal OSHA requires shade be provided when the temperature reaches 85 degrees Fahrenheit, but a worker may show signs of a heat-related illness at a lower temperature.   

Minnesota OSHA has a more limited heat stress prevention regulation which only applies to indoor work spaces.  (http://www.dli.mn.gov/OSHA/PDF/heat_stress_guide.pdf )  Minnesota Rules 5205.0110, subpart 2a and Appendix A (revised 1997), is the Minnesota OSHA standard for heat exposure. The standard is based on the wet bulb globe temperature (WBGT) and level of work activity.  If the heat stress limit is approached or exceeded the following rules also apply:  Employee Right-to-Know requirements specified in Minnesota Rules 5206.0700, subparts 1 and 3, “Training Program for Harmful Physical Agents;” and Minnesota Rules 5206.1100 “Labeling Harmful Physical Agents and Label Content.”                    

NIOSH has criteria for a recommended standard for “Exposures to Hot Environments,” which was revised in 1986 (http://www.cdc.gov/niosh/86-113.html.)

The international Standards Organization (ISO) provides guidance on heat stress (ISO 7933:2004 Ergonomics of the Thermal Environment).

Select Solution:

Engineering control

Administrative control

Personal Protective Equipment