Heat Stress

• Issued: April 2008
• Revised: May 2012
• Content last reviewed: May 2012
• PDF Version [ 84 Kb / 8 pages | Download Adobe Reader ]
• See also: Heat Stress

Disclaimer: This resource has been prepared to help the workplace parties understand some of their obligations under the Occupational Health and Safety Act (OHSA) and regulations. It is not legal advice. It is not intended to replace the OHSA or the regulations. FOR FURTHER INFORMATION PLEASE SEE FULL DISCLAIMER

How We Cope With Heat

Your body is always generating heat and passing it into the environment. The harder your body works, the more heat it has to lose. When the environment is hot and/or humid or has a source of radiant heat (for example, a furnace or the sun), your body must work harder to get rid of heat.

If the air is moving (for example, from fans) and it is cooler than your body, it is easier for your body to pass heat into the environment.

Workers on medication or with pre-existing medical conditions may be more susceptible to heat stress as some medication and/or medical conditions may impair the body’s response to heat. Such workers should speak to their personal physicians to see if their medication(s) and/or health condition(s) affect their ability to work in hot environments.

Heat-Stress–Related Disorders

A summary of heat-stress-related disorders, causes, symptoms, treatment and prevention is presented in the table below.

Controlling Heat Stress

Acclimatization

The longer you work in a hot environment, the better your body becomes at adjusting to the heat. This is called acclimatization. If you are ill or away from work for a week or so you can lose your acclimatization.

To become acclimatized, consider the following:

1. If you are experienced on the job, you should limit your time in hot working conditions to 50 per cent of the shift on the first day, 60 per cent of the shift on the second day, and 80 per cent of the shift on the third day. You should be able to work a full shift the fourth day.
2. If you are not experienced on the job (for example, if you are a new employee), you should start off spending 20 per cent of the time in hot working conditions on the first day and increase your time by 20 per cent of your shift each subsequent day. You should be able to work a full shift in hot working conditions the fifth day.
3. Instead of progressively increasing the exposure times on the job in a hot environment, you can become acclimatized by gradually increasing the physical demands of the job over a week or two.

If you have health problems or are not in good physical condition, you may need longer periods of acclimatization. Hot spells in Ontario seldom last long enough to allow acclimatization. However, exposure to workplace heat sources may permit acclimatization.

When there is a potential for exposure to heat stress, control measures must be taken to prevent heat exposure in the workplace. These include engineering controls, administrative controls and protective clothing. Selection of appropriate workplace controls will vary, depending on the type of workplace and other factors. Some measures may include:

Engineering Controls

• Reduce physical demands of work task through mechanical assistance (hoists, lift–tables, etc.)
• Control the heat at its source through the use of insulating and reflective barriers (e.g. insulate furnace walls)
• Exhaust hot air and steam produced by operations
• Reduce the temperature and humidity through air cooling
• Provide cool, shaded work areas
• Provide air–conditioned rest areas
• Increase air movement if temperature is below 35°C (e.g. use fans).

Administrative and Work Practice Controls

• The employer should:
  • Assess the demands of all jobs and have monitoring and control strategies in place for hot days and hot workplaces
  • Increase the frequency and length of rest breaks
  • Schedule strenuous jobs to cooler times of the day
  • Provide cool drinking water near workers and remind them to drink a cup about every 20 minutes, or more frequently, to stay hydrated
  • Caution workers to avoid direct sunlight
  • Assign additional workers or slow down the pace of work
  • Make sure everyone is properly acclimatized
  • Train workers to recognize the signs and symptoms of heat stress and start a buddy system since people are not likely to notice their own symptoms
  • Investigate any heat–related incidents
• First Aid responders should be available and an emergency response plan should be in place in the event of a heat related illness.
• Pregnant workers and workers with a medical condition – or those taking certain medications – should discuss with their physicians about working in the heat

Protective Clothing

• Light summer clothing should be worn to allow free air movement and sweat evaporation
• If working outdoors, wear light-coloured clothing, preferably long-sleeve shirt and pants, and cover the head to prevent exposure to direct sunlight
• In a high radiant heat situation, wearing reflective clothing to shield radiant heat may help
• For very hot environments, consider air, water or ice–cooled insulated clothing
• Vapour barrier clothing, such as chemical protective clothing, greatly increases the amount of heat stress on the body. Extra caution is necessary such as heat strain (physiological) monitoring

Managing Heat Stress from Process Heat

For an environment that is hot primarily due to process heat (furnaces, bakeries, smelters, etc.), the employer should follow the guidance of the American Conference of Governmental Industrial Hygienists (ACGIH) as outlined in its booklet and documentation for the recommended Threshold Limit Value (TLVs), and set up a heat stress control plan in consultation with the workplace's joint health and safety committee or worker health and safety representative.

Further information on the ACGIH TLVs, and on the development of heat stress control plans, can be found at the following websites:

ACGIH
http://www.acgih.org/home.htm (documents available for purchase)

U.S. Occupational Safety and Health Administration (OSHA)
http://www.osha.gov/dts/osta/otm/otm_iii/otm_iii_4.html (documents available for free)

Managing Heat Stress Caused by Hot Weather

Most workplaces do not have hot processes; however working in hot weather can pose health risks to their workers. For work in hot weather, a hot weather plan is appropriate. A hot weather plan is a simplified heat stress control plan. A hot weather plan should establish the implementation criteria, or triggers, to put the plan into effect. The criteria may include weather⁄environmental indicator triggers such as:

• Humidex (local or specific site) reaching or exceeding 35
• Environment Canada humidex advisory (air temperature exceeding 30°C and humidex exceeding 40);
• Environment Canada weather reports;
• Heat waves (three or more days of temperatures of 32ºC or more); and⁄or
• Ontario Ministry of the Environment smog alert.

Generally, plans related to hot weather should be in place between May 1 and September 30 of each year.

The following websites have information on humidex, weather reports and smog alerts:

Environment Canada - Weather and Meteorology
http://www.msc.ec.gc.ca

Environment Canada Weather Office
http://www.weatheroffice.ec.gc.ca/canada_e.html

Air Quality Ontario Smog Advisories
http://www.airqualityontario.com

Occupational Health Clinics for Ontario Workers (OHCOW) - humidex-based heat response plan
http://www.ohcow.on.ca/menuweb/hhrplan.pdf [100 Kb]

Other Resources

Additional information on methods to monitor and manage workplace heat exposures:

WSIB Prevent Heat Stress

• Information and tools on heat stress awareness, monitoring and control measures can be found on the WSIB website, such as the Heat Stress Awareness Toolkit: a guidebook [1.1 Mb], a poster [235 Kb], and a tool [302 Kb] to determine humidex guidelines.

Health and Safety Ontario (HSO)

• Health and safety information, training materials and consulting services are offered by the HSO Partners in Prevention.
• The Infrastructure Health and Safety Association (IHSA) has a website that provides links to resources on heat stress prevention at construction sites. These include a Heat Stress kit, resources, and e-learning and video.

These links to external websites are offered for convenience only; they do not constitute an endorsement of the websites or their contents. The Ministry of Labour takes no responsibility for the views, contents or accuracy of the information presented by external websites.

Remember that while complying with occupational health and safety laws, you must also obey applicable environmental laws.

For further information or assistance, please call the Ministry of Labour Health & Safety Contact Centre.