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.
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 (such as a furnace or the sun), your body must work harder to get rid of heat.
If the air is moving (for example, by 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 because 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.
A summary of heat-stress-related disorders, causes, symptoms, treatment and prevention is presented in the table below.
|Heat rash||Hot humid environment; plugged sweat glands.||Red bumpy rash with severe itching.||Change into dry clothes and avoid hot environments. Rinse skin with cool water.||Wash regularly to keep skin clean and dry.|
|Heat cramps||Heavy sweating from strenuous physical activity drains a person’s body of fluid and salt, which cannot be replaced just by drinking water. Heat cramps occur from salt imbalance resulting from failure to replace salt lost from heavy sweating.||Painful cramps occur commonly in the most worked muscles (arms, legs or stomach); this can happen suddenly at work or later at home.
Heat cramps are serious because they can be a warning of other more dangerous heat-induced illnesses.
|Move to a cool area; loosen clothing, gently massage and stretch affected muscles and drink cool salted water (1½ to 2½ mL salt in 1 litre of water) or balanced commercial fluid electrolyte replacement beverage. If the cramps are severe or don’t go away after salt and fluid replacement, seek medical aid. Salt tablets are not recommended.||Reduce activity levels and⁄or heat exposure. Drink fluids regularly. Workers should check on each other to help spot the symptoms that often precede heat stroke.|
|Fainting||Fluid loss, inadequate water intake and standing still, resulting in decreased blood flow to brain. Usually occurs in unacclimatized persons.||Sudden fainting after at least two hours of work; cool moist skin; weak pulse.||GET MEDICAL ATTENTION. Assess need for cardiopulmonary resuscitation (CPR). Move to a cool area; loosen clothing; have the person lie down; and if the person is conscious, offer sips of cool water. Fainting may also be due to other illnesses.||Reduce activity levels and⁄or heat exposure. Drink fluids regularly. Move around and avoid standing in one place for too long. Workers should check on each other to help spot the symptoms that often precede heat stroke.|
|Heat exhaustion||Fluid loss and inadequate salt and water intake causes a person's body's cooling system to start to break down.||Heavy sweating; cool moist skin; body temperature over 38°C; weak pulse; normal or low blood pressure; person is tired and weak, and has nausea and vomiting; is very thirsty; or is panting or breathing rapidly; vision may be blurred.||GET MEDICAL ATTENTION. This condition can lead to heat stroke, which can cause death quickly. Move the person to a cool shaded area; loosen or remove excess clothing; provide cool water to drink; fan and spray with cool water. Do not leave affected person alone.||Reduce activity levels and⁄or heat exposure. Drink fluids regularly. Workers should check on each other to help spot the symptoms that often precede heat stroke.|
|Heat stroke||There are two types of heat stroke:
||High body temperature (over 40°C) and any one of the following: the person is weak, confused, upset or acting strangely; has hot, dry, red skin (classic heat stroke) or profusely sweating (exertional heat stroke); a fast pulse; headache or dizziness. In later stages, a person may pass out and have convulsions.||CALL AMBULANCE. This condition can kill a person quickly. Remove excess clothing; fan and spray the person with cool water; offer sips of cool water if the person is conscious.||Reduce activity levels and/or heat exposure. Drink fluids regularly. Workers should check on each other to help spot the symptoms that often precede heat stroke.|
The longer you work in a hot environment, the better your body acclimatizes to the heat. If you are ill or away from work for a week or so you can lose your acclimatization.
To become acclimatized, consider the following progressive approaches:
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:
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 (documents available for purchase)
U.S. Occupational Safety and Health Administration (OSHA - documents available for free)
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:
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:
Health Canada – Climate Change and Health
Information on extreme heat and human health for the public and health care providers can be found on the Health Canada website.
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: 1-877-202-0008.
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