Senin, 18 Juni 2007

Heat Stress

What Is Heat Stress?

Working or playing where it is hot puts stress on your body's cooling system. When heat is combined with other stresses such as hard physical work, loss of fluids, fatigue or some medical conditions, it may lead to heat-related illness, disability and even death.

This can happen to anybody-even the young and fit. In Ontario, heat stress is usually a concern during the summer. This is especially true early in the season, when people are not used to the heat.

Heat exposure may occur in many workplaces. Furnaces, bakeries, smelters, foundries and heavy equipment are significant sources of heat inside workplaces. For outdoor workers, direct sunlight is the main source of heat. In mines, geothermal gradients and equipment contribute to heat exposure. Humidity in workplaces also contributes to heat stress.

How We Cope With Heat

Your body is always generating heat and passing it to the environment. The harder your body is working, the more heat it has to lose. When the environment is hot 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 its 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 to the environment.

Workers on medications or with pre-existing medical conditions may be more susceptible to heat stress. These workers should speak to their personal physicians about work in hot environments.

Controlling Heat Stress


The longer you work hard in the heat, the better your body becomes at adjusting to the heat. If you are not used to working in the heat then you should take a week or two to get used 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.

There are two ways to acclimatize:

1. If you are experienced on the job, 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 can work a full shift the fourth day.

If you are not experienced on the job (if you are, for example, a summer student), 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 each subsequent day.

2. Instead of reducing the exposure times to the hot job, you can become acclimatized by reducing the physical demands of the job for 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 it is hot, consider the following engineering and administrative controls.

Heat Stress Hazards





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.


Too much exposure to the sun.

Red, painful, or blistering and peeling skin.

If the skin blisters, seek medical aid. Use skin lotions (avoid topical anaesthetics) and work in the shade.

Work in the shade; cover skin with clothing; apply skin lotions with a sun protection factor of at least 15. People with fair skin should be especially cautious.

Heat Cramps

Heavy sweating drains a person's body of salt, which cannot be replaced just by drinking water.

Painful cramps in arms, legs or stomach which occur 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 and drink cool salted water (1 tsp. salt per gallon of water) or commercial fluid replacement beverage. If the cramps are severe or don't go away, seek medical aid.

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.


Fluid loss and inadequate water intake.

Sudden fainting after at least two hours of work; cool moist skin; weak pulse.

GET MEDICAL ATTENTION. Assess need for CPR. Move to a cool area; loosen clothing; make 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. 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 AID. This condition can lead to heat stroke, which can kill. Move the person to a cool shaded area; loosen or remove excess clothing; provide cool water to drink; fan and spray with cool water.

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

If a person's body has used up all its water and salt reserves, it will stop sweating. This can cause body temperature to rise. Heat stroke may develop suddenly or may follow from heat exhaustion.

High body temperature (over 41°C) and any one of the following: the person is weak, confused, upset or acting strangely; has hot, dry, red skin; 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.

Modifying Work and the Environment

Heat exposures may be reduced by several methods. Selection of appropriate workplace controls will vary, depending on the type of workplace and other factors. Some measures may include:

Engineering Controls

§ 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 air-conditioned rest areas.

§ Provide cool work areas.

§ Increase air movement if temperature is less than 35°C (fans).

§ Reduce physical demands of work task through mechanical assistance (hoists, lift-tables, etc.).

Administrative 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 every 20 minutes or so.

§ 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.

§ Pregnant workers and workers with a medical condition should discuss working in the heat with their doctor.

§ First Aid responders and an emergency response plan should be in place in the event of a heat-related illness.

§ Investigate any heat-related incidents.

Personal Protective Equipment

§ Light summer clothing should be worn to allow free air movement and sweat evaporation.

§ Outside, wear light-coloured clothing.

§ In a high radiant heat situation, reflective clothing may help.

§ For very hot environments, air, water or ice-cooled insulated clothing should be considered.

§ Vapour barrier clothing, such as chemical protective clothing, greatly increases the amount of heat stress on the body, and extra caution is necessary.

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 Values (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.

Managing Heat Stress Induced by Hot Weather

Most workplaces don't have "hot processes" but working in hot weather can pose health risks to their workers. For hot work environments due to 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 reaching or exceeding 35º Celsius

§ Environment Canada Humidex advisory (air temperature exceeding 30º Celsius and Humidex exceeding 40º Celsius) or Ontario Ministry of the Environment smog alert;

§ Environment Canada weather reports; and/or

Heat waves (three or more days of temperatures of 32º or more)

Mercury and Human Health

Mercury and Human Health

The Issue

Although mercury is released naturally from rocks, soil and volcanoes, human activities have boosted levels in the atmosphere. Canadians can be exposed to mercury from many sources, including food and the use of dental amalgam fillings.


Mercury is used in, and released from, a variety of industrial processes and commercial products. Since the 1970s, environmental concerns have resulted in a reduction in the use and processing of mercury around the world.

Mercury exists in three different forms:

  • Elemental mercury – this silvery, shiny, volatile liquid gives off a colourless, odourless vapour at room temperature
  • Inorganic mercury – compounds formed when elemental mercury combines with other elements such as sulphur, chlorine or oxygen to create compounds known as mercury salts
  • Organic mercury – compounds formed when elemental mercury combines with carbon, also known as methyl mercury.

Mercury is a global contaminant because it is toxic, does not break down in the environment and can build up in living things. In its vapour form, mercury can be carried long distances on wind currents, staying in the atmosphere for long periods of time.

Mercury can change from one form to another in the environment. For example, some types of bacteria and fungi can change mercury into its most toxic form, methyl mercury. Methyl mercury tends to accumulate to some degree in all fish, but especially in predatory fish such as shark, swordfish and large tuna, as well as in marine mammals. Predatory freshwater fish such as pike, bass and walleye may also have elevated methyl mercury levels. Since fish is also an excellent source of high-quality protein and omega-3 fatty acids and is low in saturated fat, the benefits and risks of eating fish must be considered carefully.

Sources of Mercury

Mercury comes from a range of natural sources such as volcanoes, soils, undersea vents, mercury-rich geological zones and forest fires, as well as from fresh water lakes, rivers and the oceans. However, human activity has increased the amount of mercury in the environment in several ways, including through a variety of combustion and industrial processes like coal-fired power generation, metal mining and smelting and waste incineration.

Mercury is also leached from flooded soil at new hydroelectric dam sites, or from any flooded area. This process can add to mercury levels in freshwater aquatic food chains in those areas.

Products such as button batteries, fluorescent tube lights, fever thermometers, thermostats, switches and relays, barometers and dental fillings may contain mercury; however, mercury-free alternatives exist in most cases. It is also used as a preservative in some products like cosmetics. When used according to regulated restrictions, mercury in cosmetics is considered safe. Disposing of these products can cause mercury to leach from landfills or be emitted from burning waste, adding to the amount of mercury in the environment.

Because mercury is toxic and has an impact on human and environmental health, even small mercury spills should be considered hazardous and cleaned up with caution. Liquid elemental mercury, commonly found in household thermometers, thermostats and barometers, quickly forms a poisonous, colourless and odourless vapour when spilled. If inhaled, this vapour is rapidly absorbed through the lungs. Children are especially at risk because mercury vapours, which are heavier than air, often linger near the floor where children crawl and play. Your local public health office can give you information on how to clean up small mercury spills.

Health Effects of Mercury Exposure

The health effects of mercury exposure depend on its chemical form (elemental, inorganic or organic), the route of exposure (inhalation, ingestion or skin contact), and the level of exposure. Vapour from liquid elemental mercury and methyl mercury are more easily absorbed than inorganic mercury salts and can, therefore, cause more harm. You should try to reduce your exposure to all forms of mercury whenever possible.

Elemental Mercury
The health effects of elemental mercury depend on the length and type of exposure. For example, if you were to accidentally swallow liquid elemental mercury from a broken fever thermometer, little mercury would be absorbed. However, if you were to inhale the vapour from that mercury spill, it would be more easily absorbed into your body, potentially causing health problems. At higher concentrations, mercury vapour can cause damage to the mouth, respiratory tract and lungs, and can lead to death from respiratory failure. Long-term exposure to low concentrations causes symptoms similar to those of methyl mercury.

Inorganic Mercury Compounds
Inorganic mercury can cause kidney failure and gastrointestinal damage. Mercury salts are irritating, and can cause blisters and ulcers on the lips and tongue. Rashes, excessive sweating, irritability, muscle twitching, weakness and high blood pressure are other symptoms of elevated exposures.

Organic Mercury Compounds (Methyl mercury)
Mercury can change from one form to another in the environment. Methyl mercury tends to accumulate to some degree in all fish, but especially in the predatory fish noted above. Methyl mercury is absorbed through the intestines and distributed throughout the body. It readily enters the brain, where it may remain for a long period of time. In a pregnant woman, it can also cross the placenta into the fetus, building up in the fetal brain and other tissues. Methyl mercury can also be passed to the infant through breast milk.

A child's developing nervous system is particularly sensitive to methyl mercury. Depending on the level of exposure, the effects can include a decrease in I.Q., delays in walking and talking, lack of coordination, blindness and seizures. In adults, extreme exposure can lead to health effects such as personality changes, tremors, changes in vision, deafness, loss of muscle coordination and sensation, memory loss, intellectual impairment, and even death.

The Risks of Mercury Poisoning

In general, Canadians are not at risk from mercury poisoning. However, people exposed to elevated levels of mercury may experience health problems ranging from rashes to birth defects, even death in cases of extreme poisoning.

People who consume large amounts of fish, marine mammals and wild game as part of their daily diet increase their risk. The developing fetus and children of women who have consumed large amounts of fish and marine mammals during pregnancy are the most susceptible to health problems. Children, who tend to put things in their mouths, may increase their intake of mercury through soil and contaminated objects.

In regions such as the Arctic, the traditional diet may include large quantities of fish and/or marine mammals at certain times of the year. However, this traditional diet has many nutritional and socio-cultural benefits, which must be weighed against the potential risks.

If you are concerned about mercury exposure, samples of hair, blood and urine can be taken in a doctor's office or health clinic and tested.

Minimizing Your Risk

Elemental mercury from dental fillings doesn't generally pose a health risk. There is, however, a fairly small number of people who are hypersensitive to mercury. While Health Canada does not recommend that you replace existing mercury dental fillings, it does suggest that when the fillings need to be repaired, you may want to consider using a product that does not contain mercury.

Pregnant women, people allergic to mercury and those with impaired kidney function should avoid mercury fillings. Do not have mercury fillings removed when you are pregnant because the removal may expose you to mercury vapour. When appropriate, the primary teeth of children should be filled with non-mercury materials.

Predatory fish such as shark, swordfish, fresh and frozen tuna (not canned), have higher levels of mercury and should be consumed only occasionally. The health benefits of eating fish outweigh the risk of exposure to mercury if Health Canada consumption guidelines are followed. If you are an adult, limit your intake of these fish to no more than one meal per week. Pregnant women, women of child-bearing age and young children should be especially careful and limit their intake of these fish to no more than one meal a month.

For information on sport fish caught in local waters, check with your provincial or territorial authority on any advisory that may have been issued for that area.

The Government of Canada's Role

The Government of Canada issues retail fish consumption advisories, while the provincial and territorial agencies issue advisories on sport fish. The Canadian Food Inspection Agency enforces a guideline for mercury in fish. It applies to all fish except shark, swordfish, and fresh and frozen tuna, for which meal limits are recommended.

The Government of Canada is working in a number of areas to reduce the use and release of mercury into the environment. In 2000, the Canadian Council of Ministers of the Environment developed several Canada-wide standards to reduce mercury release to the environment. Standards have been, or are being, developed for certain mercury-containing products and for mercury emissions from selected industries. The Government has also helped set up the Northern Contaminants Program and the National First Nations Environmental Contaminants Program. Canada also has Cosmetic Regulations. These regulations contain restrictions for mercury; it is only permitted as a preservative ingredient in cosmetics intended for use in the area of the eye.

Although Canada will continue to reduce mercury releases, efforts must also be made elsewhere. Much of the mercury deposited on our lakes and soil comes from other countries. Canada is taking an active role in regional and international efforts to reduce mercury in the environment globally. The Government is working with the USA and Mexico through the North American Commission for Environmental Co-operation to address mercury issues under the North American Regional Action Plan on Mercury.