According to the Occupational Health and Safety Act, employers must take every reasonable precaution in the circumstances for the protection of a worker.  This applies to the environment in which employees work and as such employers must understand and take action to protect workers from heat stress and extreme heat conditions. Hazardous heat exposure can occur indoors or outdoors and can occur during any season if the conditions are right, not only during heat waves. Some industries whereby workers are prone to heat stress or health-related illness include:

Outdoor Exposure: Agriculture, Construction – especially road, roofing, and other outdoor work, Landscaping, Mail and Package Delivery, Oil and gas well operations

Indoor Exposure:  Bakeries, kitchens, and laundries (sources with indoor heat-generating appliances), Electrical utilities (particularly boiler rooms), Fire Service, Iron and steel mills and foundries, Manufacturing with hot local heat sources, like furnaces (e.g., paper products or concrete), Warehousing

Occupational heat exposure is a combination of many factors.  Body heat results from the equilibrium of heat gain, from internal work and outside addition, and heat loss, primarily from evaporative cooling, that is, sweat evaporation. Contributors include:

  • Physical activity
  • Air temperature
  • Humidity
  • Sunlight
  • Heat sources (e.g., ovens or furnaces, heat-absorbing roofs, and road surfaces)
  • Air movement
  • Clothing that hampers the body's ability to lose excess heat, such as protective gear
  • Individual/personal risk factors, (e.g., pre-existing health conditions and lifestyle)

Heat-related illness is preventable, especially with management commitment to providing the most effective controls. An effective heat-related illness prevention program is incorporated in a broader safety and health program and should align with the OHSA. The following provides some tips on how employers can reduce the risk of heat stress in the workplace.

  1. Design the workplace to reduce heat stress

Engineering Controls such as the ones listed below can be considered:

  • using machines (for example, hoists and lift-tables) to reduce the physical demands of work
  • controlling the heat at its source by using insulating and reflective barriers (for example, insulate furnace walls)
  • exhausting hot air and steam produced by operations
  • using air conditioners to reduce the temperature and humidity
  • using fans if the temperature is below 35°C (if fans are used when the temperature is above 35°C they may recirculate the hot air, which can prevent cooling)
  • Providing cool, shaded work areas and air-conditioned rest areas

2.       Plan to reduce heat stress

The workplace policies and procedures, work schedule and training can help reduce the risk of heat stress. Administrative and work practice controls can include:

  • assessing the demands of all jobs and putting a plan in place for hot days and workplaces
  • increasing the frequency and length of rest breaks
  • scheduling strenuous jobs to cooler times of the day such as in the early morning, late afternoon or night
  • providing cool drinking water near workers
  • reminding workers to drink a cup of water at least every 15 to 20 minutes to stay hydrated
  • cautioning workers to avoid direct sunlight
  • assigning more workers or slowing down the pace of work
  • making sure workers have time to acclimatize to a modified intensity of work
  • training workers to recognize the signs and symptoms of heat stress
  • starting a “buddy system” because people are not likely to notice their own symptoms
  • investigating any heat-related incidents reported by workers
  • making sure workers trained in First Aid are available and on-site
  • creating an emergency response plan to respond to heat-related illnesses
  • advising workers who are pregnant or have a medical condition to consult their physician about working in the heat and make appropriate accommodations

3.       Help workers adjust to hot environments

The more time a worker has to acclimatize to a hot environment, the better their body handles the heat. If workers have health problems or are not in good physical shape, they may need more time to adjust to hot environments.

For workers with no experience in hot conditions, there are two ways to help them tolerate the heat:

  • gradually increase the activity level over one to two weeks
  • gradually increase the amount of time spent in hot working conditions

For workers with experience in hot conditions, but who may have been ill or away from work for 9 or more days, the worker will need to gradually readjust to the heat.
4.       Encourage workers to wear and provide suitable protective clothing

Workers should:

  • wear light and breathable summer clothing (if applicable)
  • cover their head to prevent exposure to direct sunlight
  • wear reflective clothing in a high radiant-heat situation
  • consider air, water or ice-cooled insulated clothing for very hot environments
  • avoid clothing that isn’t breathable, such as chemical protective clothing. If the workers must wear it, they should pay close attention to symptoms that suggest they may be ill due to heat stress.

Supervisors should be constantly monitoring workers for signs that could suggest a risk of illness due to heat stress.

5.       Create a heat stress plan

It is recommended that employers create a heat stress control plan, based on the work environment.

(a)   Process heat

For workplaces that are hot primarily due to process heat (for example, furnaces, bakeries, and smelters), we recommend employers:

  • follow the guidance in the American Conference of Governmental Industrial Hygienists (ACGIH) booklet, Threshold Limit Value (TLVs)
  • set up a heat stress control plan in consultation with the workplace's joint health and safety committee or worker health and safety representative

(b)   Hot weather

A hot weather plan is a simplified heat stress control plan. Employers should create one to use between May 1 and September 30 of each year. Consider using the plan when:

  • the humidex on-site reaches or exceeds 35
  • Environment Canada reports air temperature that exceeds 30°C and a humidex of 40
  • heat waves of 32ºC or more are predicted for three or more days
  • the Ontario Ministry of the Environment, Conservation and Parks issues a smog alert


Where to get help:

If you or someone you know are experiencing the effects of heat-related illness you should: Consult your physician, a healthcare provider or call Telehealth Ontario (1-866-797-0000 or TTY at 1-877-797-0007). Call 911 or your local emergency number immediately if they show signs of heat stroke such as acting strangely/confused, fast pulse, high body temperature, or loss of consciousness.


  1. Centers for Disease Control 2019. National Institute for Occupational Health and Safety (NIOSH) Heat Stress Recommendations. Available at:
  2. Canadian Center for Occupational Health and Safety 2020. Hot Environments – Control Measures. Available at:
  3. Ministry of Labour Training and Skills Development 2019. Managing heat stress at work. Available at: