Pulp and Paper Canada

Heat Stress

May 1, 2008  By Pulp & Paper Canada

There is broad consensus that our climate is changing and that we are experiencing more extreme weather patterns. Scientists have a good understanding of the physical factors that influence our climat…

There is broad consensus that our climate is changing and that we are experiencing more extreme weather patterns. Scientists have a good understanding of the physical factors that influence our climate. Some are due to natural causes and others by greenhouse gases released as a result of human activity. The result: a warmer planet.

While a warmer climate may seem like something desirable, it will actually bring with it more variable and extreme weather patterns. It is predicted that we may see more heat waves, which could lead to more heat stress. Working in the heat and engaging in heavy physical work can affect the body’s cooling system. If the body is unable to cool itself, a worker can experience heat stress. If heat stress is not recognized and treated in it’s early stages, more serious and even fatal conditions may quickly develop.


Heat stress occurs when a combination of hot, humid conditions and physical activity strains, and perhaps overcomes, the body’s natural cooling system. It can cause symptoms ranging from cramps and fainting, to serious heat exhaustion or even heat stroke. Heat stroke is a form of heat stress that rapidly result in death.

Environmental factors that affect heat stress include air temperature, humidity, air movement and sources of radiant heat such as working in the sun or near large, hot objects. Work task factors that affect heat stress are the physical demands of the job and the frequency and length of breaks.

Most people feel comfortable when the air temperature is between 20C and 27C and when relative humidity ranges from 35-60%. When air temperature or humidity is higher, people typically feel uncomfortable. Such situations do not cause harm as long as the body can adjust and cope with the additional heat. Very hot environments can overwhelm the body’s coping mechanisms leading to a variety of serious and possibly fatal conditions.

Heat stress symptoms: rashes, sunburn, cramping, fainting, excessive sweating, headache and dizziness. Learn to recognize the signs and symptoms of heat stress in yourself and co-workers; avoid working alone. Acclimatize your body (gradually expose yourself to heat and work). Drink lots of fluids to replace perspiration. Try to drink a cup of water about every 20 minutes; avoid caffeine, alcohol, and drugs. Avoid working in direct sunlight. Reduce the pace of work. Increase the number of breaks and take breaks in cool or shaded areas. Schedule heavy work for cooler periods. Wear light-coloured and/or light-weight clothing made of breathable fabric. Reduce the physical demands of work by using aides, e. g. hoists etc.

Ways to protect workers: Reduce the temperature and humidity through air cooling mechanisms. Provide air-conditioned rest areas. Increase the frequency and length of rest breaks. Schedule strenuous jobs for cooler times of the day. Provide cool drinking water near workers and remind them to drink a cup approximately every 20 minutes. Assign additional workers or slow down the pace of work. Train workers to recognize the signs and symptoms of heat stress and start a “buddy system” as people are not likely to notice their own symptoms.

A hot weather plan is a simplified heat stress control plan. Criteria for the plans may include weather/environmental indicator triggers such as: Humidex reaching or exceeding 35 Celsius; Environment Canada Humidex advisory (air temperature exceeding 30 Celsius and Humidex exceeding 40 Celsius) or Ontario Ministry of the Environment smog alert Environment Canada weather reports; and/or heat waves (three or more days of temperatures of 32 or more).

What the Law Says: Employers have a duty to take every reasonable precaution under the circumstances for the protection of a worker. This includes developing hot environment policies and procedures to protect workers in hot environments due to hot processes or hot weather. For compliance purposes, authorities recommend the Threshold Limit Values (TLVs) for Heat Stress and Heat Strain published by the American Conference of Governmental Industrial Hygienists (ACGIH). These values are based on preventing un-acclimatized workers’ core temperatures from rising above 38C.


Cindy Hunter is the Program/Communications Specialist for the Pulp and Paper Health and Safety Association.

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