Occupational exposure limits or guidelines for exposure to high temperatures actually depend on a number of factors, not just the temperature. These other factors include:
Are there any general guidelines about temperature?For non-office workplace situations, occupational health and safety agencies generally use the Threshold Limit Values for Heat Stress published by the American Conference of Governmental Industrial Hygienists (ACGIH). The units of heat stress exposure are expressed as Wet Bulb Globe Temperature (WBGT) values in C. The WBGT measurement takes into account air temperature, air movement, radiant heat and humidity. There are direct-reading WBGT meters that are commercially available. These are also called "heat-stress indicators". The WBGT measurements can then be related to the physical demands of the job. Only qualified professionals, whether they are in-house staff, consultants, or from the local occupational health and safety regulatory agency, should perform the measurement.
Unfortunately, direct comparison between WBGT and humidex is not possible - there are no standard conversion tables or mathematical formulas to do such conversions. More information about WBGT is available in the OSH Answers document "Working in Hot Environments - Control Measures"
In addition, while there is no maximum temperature, legislation does provide a range of acceptable temperatures for various circumstances. See "Working in Extreme Hot or Cold Temperature Conditions" for more information.
Are there any general guidelines about maximum temperature conditions in offices?The OSH Answers document Thermal Comfort for Office Work discusses 'comfortable' temperature and humidity conditions for work is done mainly while seated or does not involve much physical activity. Table 4 under the heading What are the exposure limits for working in hot environments? summarizes limits or guidelines for workplace thermal conditions in the Canadian health and safety regulations.
When the humidex rating is in the 40 - 45°C range, most people would it uncomfortable. However, many kinds of work must be restricted when the humidex is above 45°C.
Only one jurisdiction that we know of that has a directive about the temperature and humidity conditions when employees should be relocated or released from the office workplace. The Use and Occupancy of Buildings Directive published by the Treasury Board of Canada Secretariat applies to federal employees (as defined in the Public Service Staff Relations Act). It states, in part, that if the humidex reading exceeds 40°C [measured inside the building - not based on weather reports or outdoor air temperatures], it is considered to be an unsatisfactory condition. "In these cases, operations shall be stopped and employees released from the workplace if relocation is not practicable." [Section 17.3 Environmental conditions, Use and Occupancy of Buildings Directive.
What should be done when it is very hot and/or humid?Employers have a duty to take every reasonable precaution to ensure the workplace is safe for the worker. This duty includes taking effective measures to protect workers from heat stress disorders if it is not reasonably practicable to control indoor conditions adequately, or where work is done outdoors.
Certain steps can be taken to reduce discomfort. These include:
- using fans or air conditioning
- wearing light, loose fitting clothing
- taking more frequent rest breaks
- drinking cold beverages (ones that do not have caffeine or alcohol)
- allowing flexibility to permit less physically demanding activities during peak temperature periods.
- using screens or umbrellas to create shade.
More information about ways to control heat stress is available in the OSH Answers document "Working in Hot Environments - Control Measures"
Please note: An employee always has the right to refuse unsafe work. If they believe that the degree of heat stress being experienced may be hazardous to the health and safety to themselves or a co-worker, then a work refusal could be initiated.
Where can I find more information about health effects of working in the heat?Please see the OSH Answers document "Working in Hot Environments - Health Effects".
Where can I find more information about humidex?Humidex information is available in the "Humidex Rating and Work" document.
Additional information on humidity and thermal comfort is in "Thermal Comfort for Office Work".
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