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Learn more about heat stress

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Understanding heat stress

Heat stress occurs when the body absorbs more heat than it can release, causing a rise in core body temperature. The body normally cools itself through sweating and increased blood flow to the skin. However, in hot or humid environments, during physically demanding work, or when workers wear certain types of protective clothing, these natural cooling mechanisms may not be effective. When the body cannot cool itself adequately, heat stress and heat related illness can develop.

Heat stress can affect both indoor and outdoor workers. Sources of heat exposure may include direct sunlight, hot weather, heat-generating equipment or processes, radiant heat from hot surfaces, high humidity, and strenuous physical work.

If heat stress is not identified and controlled early, it can progress from mild symptoms (such as excessive sweating and fatigue) to more serious conditions, including heat exhaustion and heat stroke, which can be life-threatening and require immediate medical attention. Some workers may have an increased risk of heat-related illness due to personal risk factors such as lack of acclimatization, dehydration, or health and medical conditions or medications.

Employer responsibilities

Employers are responsible for assessing the risk of heat stress and implementing effective controls to protect workers. There is no single air temperature at which work becomes unsafe; instead, heat risk must be evaluated based on multiple factors such as temperature, humidity, workload, clothing, and duration of exposure. See “Evaluate current conditions for heat stress risk” on the homepage for more information on assessing the risk.

When workers are at risk, employers must develop and implement a heat stress exposure control plan that follows the hierarchy of controls and includes education, supervision, safe work practices, and ongoing monitoring.

Controls and general actions to minimize heat stress

Educate and train workers

Employers must provide adequate training and education to all workers at risk of heat stress, their immediate co-workers, and their supervisors. Training should include the following information:

  • How heat stress develops
  • Personal factors
  • How to prevent heat stress
  • How to recognize signs and symptoms for different stages of heat stress
  • What workers should do if they, or their co-workers, develop a heat-related illness

Provide drinking water

The body naturally sweats to cool itself. Sweating can use up a significant amount of fluid, which must be replaced continuously throughout the workday. If fluid is not regularly replaced, workers will become dehydrated, increasing their risk of heat stress.

Employers are required to provide an adequate supply of cool drinking water, close to the work area for workers exposed to heat.

  • Workers should drink about two glasses (about 0.5 litres) of water before starting work in a hot environment and one glass every 20 minutes throughout the workday.
  • In very hot environments, or where sweating is profuse, even more water may be required.
  • Suitable drinks include tap water, mineral water, and fruit juice.
  • Cooled drinks between 10 °C and 15 °C are adequate. Fluids do not need to be iced.
  • Eating fresh fruit also helps to replace lost fluids.

Workers must not wait until they are thirsty to replace fluids.

Engineering controls

If elimination is not practicable, engineering controls are the most effective and preferred means to reduce excessive heat exposure. The following are some examples of engineering controls:

For indoor workplaces:

  • Automate tasks to reduce worker exposure to heat or reduce workload.
  • Cover or insulate hot surfaces to reduce radiant heat.
  • Install shielding between workers and radiant heat sources.
  • Provide air conditioning or increased ventilation to remove hot air.
  • Provide fans for spot cooling (Caution: Fans may interfere with local exhaust ventilation and may not be effective at high temperatures).
  • Where humidity is high, use dehumidifiers or reduce sources of moisture (e.g., cover water baths, drains, leaky steam valves).

For outdoor workplaces:

  • Use power tools or other equipment to reduce workload.
  • Install and maintain air conditioning in equipment cabs.
  • Provide shade to workers (e.g., erect canopies or tarps).
  • Provide temporary cooling spaces (e.g., tents or trailers with portable air conditioning).
  • Provide a misting station where humidity is low and where safe to do so.
  • Provide fans for spot cooling (Caution: Fans may not be effective at high temperatures or may interfere with contaminant control).

Administrative controls

If engineering controls are not practicable or sufficient to reduce risk to workers, administrative controls must be implemented. The following are some examples of administrative controls:

  • Determine and implement appropriate work-recovery cycles to allow adequate time for workers to cool down.
  • Schedule work to minimize heat exposure.
  • Assign workers to work in pairs or groups and provide adequate supervision to monitor for signs and symptoms of heat stress.
  • Provide adequate supervision.
  • Determine acclimatization status of workers and implement a plan to acclimatize workers.
  • If appropriate, have workers wear light-coloured, loose-fitting clothing made of breathable fabric.
  • Post heat stress warning signs where heat exposure limits may be exceeded.

Personal protective clothing and equipment

Specialized heat-protective clothing

  • May be required in extremely hot environments when the risk of heat stress is not adequately controlled by other methods
  • May be used in moderately hot environments to allow longer work periods between recovery periods
  • Should be worn only by properly trained workers following manufacturer's instructions

A proper assessment of all heat sources is required to determine if any specialized clothing would be effective in reducing heat stress.

The clothing's effectiveness must be monitored through physiological measurements.

Precautions such as close supervision should be maintained until the effectiveness of the clothing is known.

Temperature-controlled clothing

Examples of temperature-controlled clothing include:

  • Air- or water-cooled suits
  • Ice-cooled waistcoats

There may be practical limitations on the use of such equipment.

Anti-radiant heat or reflective clothing

This clothing:

  • May be necessary where there is excessive radiant heat from hot surfaces
  • May include aprons, jackets, or suits
  • Provides little or no protection from high air temperatures unless the clothing is also temperature controlled

Additional resources

Employers can find additional guidance, tools, and requirements in the following WorkSafeBC resources:

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Have questions about heat stress? Call us at 604.276.3100 (or toll-free at 1.888.621.7233).

Have a technical issue with this tool? Call us toll free at 1.888.855.2477 or email ehelp@worksafebc.com