Actually, no. In legislation, there is no single value for the maximum temperature to which you can be exposed at work, nor is there a single value above which work should stop. Of course, some temperature and relative humidity combinations cause discomfort. However, in some situations, exposure to excessive heat can lead to heat stress that could lead to heat exhaustion, fainting, heat stroke, and other conditions which should be addressed.
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:
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.
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. This reference is by the National Joint Council in Part II - Permanent Structures and Safe Occupancy of the Workplace (Use and Occupancy of Buildings). It applies to federal employees only. 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 those cases, operations shall be stopped and employees released from the workplace if relocation is not practicable." [Section 2.2(b) Environmental Conditions].
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:
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.
Please see the OSH Answers document Working in Hot Environments - Health Effects.
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.
Document last updated on July 20, 2011