Heat Stress

The Legal Requirements:

Employers have a duty under section 25(2)(h) of the Occupational Health and Safety Act to take every precaution reasonable in 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, the Ministry of Labour recommends 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 unacclimatized workers' core temperatures from rising above 38°C.

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 usually 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

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, the following may be considered:
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 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 each subsequent day.
2. Instead of reducing the exposure times to the job in a hot environment, you can become acclimatized by gradually increasing the physical demands of the job over a week or two.
When there is a potential 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 less than 35°C (e.g. use of fans).

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 about every 20 minutes.
 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 physicians.
 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.
 Outdoors, 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 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.