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Is there a temperature at which work becomes dangerous and should be stopped?

The short answer is yes. Both very cold and very hot temperatures could be dangerous to your health.

Excessive exposure to heat is referred to as heat stress and excessive exposure to cold is referred to as cold stress.

In a very hot environment, the most serious concern is heat stroke. In absence of immediate medical attention, heat stroke could be fatal. Heat stroke fatalities do occur every summer. Heat exhaustion, and fainting (syncope) are less serious types illnesses which are not fatal but interfere with a person's ability to work.

At very cold temperatures, the most serious concern is the risk of hypothermia or dangerous overcooling of the body. Another serious effect of cold exposure is frostbite or freezing of the exposed extremities such as fingers, toes, nose and ear lobes. Hypothermia could be fatal in absence of immediate medical attention.


What are the warning signs of heat stroke and hypothermia?

The victims of heat stroke and hypothermia are unable to notice the symptoms, and therefore, their survival depends on co-workers' ability to identify symptoms and to seek medical help.

While symptoms can vary from person to person, the warning signs of heat stroke can include complaints of sudden and severe fatigue, nausea, dizziness, lightheadedness, and may or may not include sweating. If a co-worker appears to be disorientated or confused (including euphoria), or has unaccountable irritability, malaise or flu-like symptoms, the worker should be moved to a cool location and seek medical advice.

Warning signs of hypothermia can include complaints of nausea, fatigue, dizziness, irritability or euphoria. Workers can also experience pain in their extremities (hands, feet, ears, etc), and severe shivering. Workers should be moved to a heated shelter and seek medical advice when appropriate.

For more information please see our OSH Answers documents on Hot Environments - Health Effects and First Aid and Cold Environments - Health Effects and First Aid.


What are the exposure limits for working in hot environments?

Two types of exposure limits are often used: occupational exposure limits and thermal comfort limits. Occupational exposure limits are to protect industrial workers from heat-related illness. Thermal comfort limits are for office work to ensure productivity and quality of work. Please see the OSH Answers Thermal Comfort for Office Work for more information on indoor temperatures.

The American Conference of Governmental Industrial Hygienists (ACGIH) recommends Threshold Limit Values (TLVs) for working in hot environments. These limits are given in units of WBGT (wet bulb globe temperature) degrees Celsius (°C). The WBGT unit takes into account environmental factors namely, air temperature, humidity and air movement, which contribute to perception of hotness by people. In some workplace situations, solar load (heat from radiant sources) is also considered in determining the WBGT. Some Canadian jurisdictions have adopted these TLVs as occupational exposure limits and others use them as guidelines to control heat stress in the workplace.

The ACGIH publication "2013 TLVs® and BEIs®" (or the most current booklet) provides recommended screening criteria for heat stress exposure for workers (Table 1). The publications "2013 TLVs® and BEIs®" (or most current) and "Documentation of TLVs® and BEIs®" should be consulted for more detailed information on these screening criteria, categories of work demands, guidelines for limiting heat strain and heat strain management.

Table 1
ACGIH Screening Criteria for Heat Stress Exposure (WBGT values in °C)
for 8 hour work day five days per week with conventional breaks
Allocation of Work in a Work/Rest Cycle TLV® Action Limit
Light Moderate Heavy Very Heavy Light Moderate Heavy Very Heavy
75-100% 31.0 28.0 -- -- 28.0 25.0 -- --
50-75% 31.0 29.0 27.5 -- 28.5 26.0 24.0 --
25-50% 32.0 30.0 29.0 28.0 29.5 27.0 25.5 24.5
0-25% 32.5 31.5 30.5 30.0 30.0 29.0 28.0 27.0

Notes:

Table is intended as a screening tool to evaluate if a heat stress situation may exist.

Assumes 8-hour workdays in a 5-day workweek with conventional breaks.

TLVs assume that workers exposed to these conditions are adequately hydrated, are not taking medication, are wearing lightweight clothing, and are in generally good health.

Examples of work loads:

Rest - sitting (quietly or with moderate arm movements)

Light work - sitting or standing to control machines; performing light hand or arm work (e.g. using a table saw); occasional walking; driving

Moderate work - walking about with moderate lifting and pushing or pulling; walking at moderate pace; e.g. scrubbing in a standing position

Heavy work - pick and shovel work, digging, carrying, pushing/pulling heavy loads; walking at fast pace; e.g. carpenter sawing by hand

Very Heavy - very intense activity at fast to maximum pace; e.g. shovelling wet sand

Adapted from: 2013 TLVs® and BEIs® - Threshold Limit Values for Chemical Substances and Physical Agents and Biological Exposure Indices. Cincinnati: American Conference of Governmental Industrial Hygienists (ACGIH), 2013, p.210.

Many Canadian occupational health and safety regulations specify upper and lower temperature limits for work performed inside buildings which are normally heated (see Table 3).

The weather broadcast service of Environment Canada uses the humidex scale to inform the public about hot weather conditions. The humidex scale quantifies human discomfort due to perceived heat taking into account the effect of air temperature and relative humidity. For a given temperature, the humidex increases as the relative humidity (moisture content) of the air becomes higher. The following table gives ranges of humidex for various degrees of thermal effect on people.

Table 2
Humidex and Thermal Comfort
Humidex Range
(°C)
Degrees of Comfort
20 - 29 Comfortable
30 - 39 Varying degrees of discomfort
40 - 45 Uncomfortable
46 and Over Many types of labour must be restricted

 

Table 3
Canadian health and safety regulations with respect to
thermal conditions in the workplace
JurisdictionRegulationTemperature
Canada, FederalPersonal service food preparation area
Materials handling: operators' compartment
First aid room
18°C min./29°C max.
27°C max.
21°C - 24°C
ACGIH TLVs for heat and cold exposure
National Joint Council (Public Service Canada)Occupational Health and Safety Directive20-26°C
Humidex 40°C max. (as measured at workstation)
British ColumbiaHeat Stress Regulations
Indoor Air Quality Regulation, ASHRAE 55-1992 Standard
Limits in WBGT units similar to ACGIH TLV
Summer Indoor
Winter Indoor
23.3 - 27.2°C or 74 - 81°F
20.5 - 24.4°C or 69 - 76°F
Alberta(Guidelines only)Similar to ACGIH TLVs for heat and cold exposure
SaskatchewanThermal environmentReasonable and appropriate to nature of work
ManitobaThermal environmentACGIH TLVs for heat and cold exposure
OntarioConstruction projects:  
   Change room for underground workers
   Work chamber
   Medical locks
27°C min.
38°C max.
18°C min./27°C max.
Enclosed workplace, Industrial Establishment
Regulations
18°C min.
QuebecSafety in mines:
   Dryhouse temperature
   Occupational exposure limits

22°C min.
WBGT similar to ACGIH TLVs
New BrunswickEnclosed place of employment: 
   Light work while sitting, mental work20°C min.
   Light work while sitting, work with small
     machine tools
18°C min
   Moderate physical work, standing16°C
   Heavy physical work12°C min.
   Work conditions1997 ACGIH TLVs for heat and cold exposure
Nova ScotiaWorkplace Health and Safety Regulation ACGIH TLVs for heat and cold exposure
Prince Edward IslandEnclosed workplace: 
Light work while sitting, mental work20°C min.
Light work while sitting, work with small       machine tools19°C
Light work, standing17°C
Moderate work standing16°C
Heavy work12°C min.
Occupational exposure limitACGIH TLVs for heat and cold exposure
Newfoundland and LabradorOccupational exposure limitACGIH TLVs for heat and cold exposure
Northwest TerritoriesOvernight minimum temperature only, Camp Sanitation Regulation18°C min
NunavutOvernight minimum temperature only, Camp Sanitation Regulation18°C min
Yukon TerritoryThermal environmentSimilar to ACGIH TLVs for heat and cold exposure

What are exposure limits for working in the cold?

Some Canadian occupational health and safety regulations specify a minimum temperature for indoor work environments in buildings that are normally heated (see Table 3). As indicated in Table 3, some jurisdictions have adopted the ACGIH TLVs for both heat and cold exposure for outdoor work.

The ACGIH has adopted the guidelines developed by the Saskatchewan Labour for working outdoors in cold weather conditions. These guidelines recommend protective clothing and limits on exposure time (Table 4). The recommended exposure times are based on the wind chill factor, a scale based on air temperature and wind speed. The work-break schedule applies to any four-hour period with moderate or heavy activity. The warm-up break periods are of 10 minute duration in a warm location. The schedule assumes that "normal breaks" are taken once every two hours. At the end of a 4-hour period, an extended break (e.g. lunch break) in a warm location is recommended. More information is available in the ACGIH publications "2013 TLVs® and BEIs®" (or most current) and "Documentation of TLVs® and BEIs®" and on the Saskatchewan Labour web page Cold Conditions Guidelines for Outside Workers.

Table 4
TLVs Work/Warm-up Schedule for Outside Workers based on a Four-Hour Shift*
Air Temperature - Sunny Sky No Noticeable Wind Wind
8 km/h
(5 mph)
Wind
16 km/h
(10 mph)
Wind
24 km/h
(15 mph)
Wind
32 km/h
(20 mph)
°C (approx) °F (approx) Max. work Period No. of Breaks** Max. Work Period No. of Breaks Max. Work Period No. of Breaks Max. Work Period No. of Breaks Max. Work Period No. of Breaks
-26° to -28° -15° to -19° (Norm breaks) 1 (Norm breaks) 1 75 min. 2 55 min. 3 40 min. 4
-29° to -31° -20°to -24° (Norm breaks) 1 75 min. 2 55 min. 3 40 min. 4 30 min. 5
-32° to -34° -25°to -29° 75 min. 2 55 min. 3 40 min. 4 30 min. 5 Non-emergency work should cease
-35° to -37° -30° to -34° 55 min. 3 40 min. 4 30 min. 5 Non-emergency work should cease
-38° to -39° -35° to -39° 40 min. 4 30 min. 5 Non-emergency work should cease
-40° to -42° -40°to -44° 30 min. 5 Non-emergency work should cease
-43° & below -45° & below Non-emergency work should cease

*2013 TLVs® and BEIs® - Threshold Limit Values for Chemical Substances and Physical Agents and Biological Exposure Indices. Cincinnati: American Conference of Governmental Industrial Hygienists (ACGIH), 2013, page 202.

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Document last updated on November 19, 2013

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