Heat Stress – Guidelines
This document is intended to provide guidance in the development of job specific safe work procedures for the prevention of heat-related disorders.
Development of a heat-related disorder prevention program is the responsibility of individual divisions. Implementation of the program on a day to day basis is the responsibility of the supervisor of the immediate workplace. It is the responsibility of the individual workers to follow guidelines outlined in the program.
Managing Heat Stress
The management of heat stress requires an understanding of the factors that contribute to heat stress and how heat stress may affect a worker. The three factors of climate, work load and clothing combine to dictate the rate of heat gain and the amount of heat loss required to protect the worker. Aspects of the thermal environment that impact heat stress include air temperature, humidity, radiant heat (from the sun or other heat source) and air movement. A worker’s metabolic rate is associated with the physical demands of the work performed; higher work demands increase the metabolic process and result in the internal generation of heat. Clothing material, construction and usage affect the potential heat exchange between the body and the environment and therefore potentially contribute to the risk of heat stress.
In addition to the three factors mentioned above, the potential for a heat-related disorder is also dependent on individual risk factors such as the worker’s age, health, physical condition, use of medication and level of acclimatization. Due to the variance in individual susceptibility, certain individuals may experience effects of heat stress earlier than expected.
Various types of control measures, in different combinations, can be used to manage heat stress.
Engineering controls change the conditions so that the level of heat stress is reduced, ideally below recommended exposure thresholds. Engineering controls are the most effective in reducing excessive heat exposure and include the following.
Reduction in metabolic heat production through reduction in workload
Redesign and/or mechanization of the task to reduce the work time and/or physical effort will reduce the metabolic heat load. For example, power tools, hoists, lift tables or other mechanized devices can be used to reduce manual labour.
Reduction in temperature and humidity
Reductions of air temperature and humidity may be achieved through local or general ventilation. The ventilation systems can be temporary or permanent and may include air conditioning.
Where possible hot air and steam produced by specific operations should be exhausted away from the working environment.
Increase in air motion.At temperatures less than 35°C, increasing air speed can help workers stay cooler by increasing both the convective heat exchange (the exchange between the skin surface and the surrounding air) and the rate of evaporation. In order to be effective, increased air speed (i.e., a fan) must be positioned to directly impact the worker. When the air temperature is greater than 40°C, increasing air motion may actually increase heat stress.
Control of radiant heat. Radiant heat from the sun or any heat source can be reduced through shielding or insulating exterior surfaces.
Whenever possible, canopies should be provided over the work area to provide shading (e.g., ride-on vehicles, lifeguard stations, large unprotected windows). Whenever possible, heat producing equipment should be shielded e.g. furnace or boiler.
Administrative controls attempt to minimize risks through work practices. They are relatively easy to implement, although they may not be the most cost-effective. Administrative controls include the following.
Training is a fundamental health and safety practice for those who may be exposed to a hazard such as heat stress. The Heat Stress Hazards information sheet (Appendix A) should be posted in workplaces where workers are exposed to heat stress.
A training program, offered annually, should include the following components:
- knowledge of the hazards and potential health effects of heat stress
- recognition of predisposing factors, danger signs and symptoms
- awareness of first-aid procedures for heat-related disorders
- employee responsibilities in minimizing heat stress
- possible side effects of certain medications when taken in a hot environment
- use of protective clothing and equipment
Limiting exposure time
Heat stress can be limited by reducing the time a worker is required to work in a hot environment. For example, tasks performed during the hottest time of the day (11am-4pm) may be postponed, partial components of a task may be performed, task variation and rotation may be increased, additional relief workers may be assigned, and so forth.
Routine maintenance and repair work in hot areas should be scheduled for the cooler seasons of the year, whenever possible.
Allowance for recovery time
It is important to provide adequate recovery from heat stress exposures. Appropriate rest breaks for outdoor work should be determined based on the humidex level and type of work performed (refer to Appendix B).
Initiation of a ‘Buddy’System. Individuals are less likely to notice their own symptoms; a buddy system approach reduces the risk of signs and symptoms going unnoticed. Workers should also buddy-up when travelling to remote locations or when entering extremely hot environments.
Decrease in metabolic heat production through reduction in workload
Metabolic heat may be decreased by reducing the work pace, work duration or the physical exertion required to perform the task. This can be achieved by increasing the frequency and duration of rest breaks, alternating or substituting heavy tasks with light tasks, increasing assigned staff so that more workers share the loads, and so forth.
A gradual period of acclimatization to work in hot weather is recommended for new and other non-acclimatized workers. It generally takes 1 to 2 weeks to become accustomed to working in hot environments. This may happen gradually as spring temperatures warm into summer, however, sudden exposure to work in hot temperatures does not allow for adequate acclimatization and increases an individual’s risk of heat-related disorders. There are two ways to acclimatize, one can either gradually increase exposures to work in hot environments, or one can reduce the physical demands of the job for one to two weeks. If a worker has health problems or is not in good physical condition, longer periods of acclimatization may be required.
Reduce use of heat generating devices
Where possible, eliminate the use of heat or steam generating devices. For examples, kitchen staff could implement a ‘heat stress menu’ that does not (or minimally) uses ovens.
During the selection of clothing, heat stress prevention should be balanced with other health and safety risks requiring protective clothing. For example, for outdoor workers, a balance must be achieved between heat stress prevention guidelines recommending minimal, light-weight and light-coloured clothing and the ultraviolet hazard prevention guidelines recommending maximum skin coverage and tightly-woven, dark clothing.
Personal prevention strategies
Personal prevention strategies are those actions individuals can take to lower their risk of heat-related disorders. Many of these strategies should be considered both prior to and during exposure to heat related hazards. Although they are the responsibility of individual workers, management should minimize, to the extent possible, any barriers to the practice of personal prevention strategies. Strategies include the following:
Individual workers should interrupt heat stress exposure once extreme discomfort or the initial symptoms of a heat-related disorder are detected. Individuals should be required to report to their supervisor heat stress-related symptoms in themselves or their co-workers. Note: Self-monitoring is not always sufficient, because individuals are less likely to notice their own symptoms. When possible, the buddy system should be used (see Administrative Controls)
Thermal regulation depends on sweating and the necessary loss of water. Therefore, water should be replaced at frequent intervals to maintain acceptable hydration. If drinking is restricted or impossible (e.g. wearing a respirator), allowances for pre- and post-exposure hydration should be considered. Workers should drink approximately 1 cup of cool water (10°-16°C) every 20 minutes. Fluid replenishment should occur throughout the day and not only during the workshift. Caffeinated and carbohydrate-rich beverages should be avoided.
Salt lost during sweating can be replaced through the use of table salt at mealtimes. The use of salt tablets in drinking water is not recommended.
Lifestyle and diet
On hot days, workers should eat ‘light’ foods such as fruits and vegetables, and avoid heavy foods such as proteins which increase body heat. Practicing a generally accepted healthy lifestyle (getting adequate sleep, limiting non-work exposures to heat stress, exercising, not abusing alcohol or drugs, eating a well-balanced diet) greatly reduces the risk of heat-related disorders.
Pregnant workers and those with medical conditions should inform their physician of occupational exposures to heat stress and discuss prescribed recommendations with their supervisor. Older workers should be particularly cautious due to a decreased ability to sweat with age.
Many conditions predispose individuals to heat stroke. An appropriate history and physical examination is an excellent prevention measure. People taking certain medications may have inhibited sweat mechanisms and should consult their pharmacists. Certain antibiotics will cause photosensitivity and exposure to strong sun-rays should be avoided.
Occupational Health and Safety Co-ordinating Committee (OHSCC), April 30, 2001
Executive Management team (EMT), June 15, 2001
June 15, 2001
Reviewed by OHSCC
September 29, 2009