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Canadian Centre for Occupational Health & Safety
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Extreme Hot or Cold Temperature Conditions
 
bullet Is there a temperature at which work becomes dangerous and should be stopped?
bullet What are the warning signs of heat stroke and hypothermia?
bullet What are the exposure limits for working in hot environments?
bullet What are exposure limits for working in the cold?

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 profuse and prolonged 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.


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.

ASHRAE Standard 55-1992 Thermal Environmental Conditions for Human Occupancy, recommends the following acceptable temperature ranges at relative humidity (RH) of 50% and air speed less than 0.15 m/sec. (30 fpm).

Table 1
Acceptable Temperatures
 Season
Clothing
Temperature
Winter Heavy slacks, long sleeve shirt and/or sweater 20-23.5°C
(68-75°F)
 Summer Light slacks and short sleeveshirt 23-26°C
(73-79°F)

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 "2000 TLVs and BEIs" provides recommended screening criteria for heat stress exposure for workers acclimatized to heat and for workers who are not acclimatized to heat (Table 2). The publications "2000 TLVs and BEIs" 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 2
Screening Criteria for Heat Stress Exposure
(WBGT values in °C)
for 8 hour work day five days per week with conventional breaks
  Acclimatized Unacclimatized
 Work Demands  Light Moderate Heavy Very Heavy Light Moderate Heavy Very Heavy
100% work  29.5 27.5 26    27.5 25 22.5   
75% Work; 25% Rest 30.5 28.5 27.5    29 26.5 24.5   
50% Work; 50% Rest 31.5 29.5 28.5 27.5 30 28 26.5 25
25% Work; 75% Rest 32.5 31 30 29.5 31 29 28 26.5

Source: 2000 TLVs and BEIs - Threshold Limit Values for Chemical Substances and Physical Agents and Biological Exposure Indices. Cincinnati : American Conference of Governmental Industrial Hygienists (ACGIH), 2000 - page 183.

Many Canadian occupational health and safety regulations specify upper and lower temperature limits for work performed inside buildings which are normally heated (see Table 4).

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 3
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

The Treasury Board Secretariat (TBS) of Canada uses humidex as measure of thermal conditions in office accommodations. "An unsatisfactory condition is deemed to exist when the humidex reading exceeds 40°C [inside the building - not based on "weather information" or outdoor air temperatures] or when the air temperature (dry bulb) falls below 17°C. In these cases, operations shall be stopped and employees released from the workplace if relocation is not practicable." Direct comparison between WBGT and humidex is not possible - there are no standard conversion tables or mathematical formulas to do such conversions.

Table 4
Canadian health and safety regulations with respect to
thermal conditions in the workplace
Jurisdiction Regulation Temperature
Canada, Federal Personal 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 stress, cold stress
Treasury Board Guidelines Thermal conditions in office work 20-26°C
Humidex 41°C max.
British Columbia Heat 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 stress and cold stress
Saskatchewan Thermal environment Reasonable and appropriate to nature of work
Manitoba Thermal environment ACGIH TLVs for heat stress, cold stress
Ontario Construction 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.
Quebec Safety in mines:
   Dryhouse temperature
   Occupational exposure limits

22°C min.
WBGT similar to ACGIH TLVs
New Brunswick Enclosed place of employment:  
   Light work while sitting, mental work 20°C min.
   Light work while sitting, work with small
     machine tools
18°C min
   Moderate physical work, standing 16°C
   Heavy physical work 12°C min.
   Work conditions 1991-92 ACGIH TLVs for heat stress and cold stress
Nova Scotia Construction safety regulations: Working chamber 80°F max. (27°C)
ACGIH TLVs for heat stress and cold stress
Prince Edward Island Enclosed workplace:  
Light work while sitting, mental work 20°C min.
Light work while sitting, work with small       machine tools 19°C
Light work, standing 17°C
Moderate work standing 16°C
Heavy work 12°C min.
Occupational exposure limit ACGIH TLVs for heat and cold exposure
Newfoundland Occupational exposure limit ACGIH TLVs for hot and cold environment
Northwest Territories Overnight minimum temperature only, Camp Sanitation Regulation 18°C min
Yukon Territory Thermal environment Heat Stress limits similar to ACGIH TLVs

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 4). No such limits are specified for outdoor work in cold weather.

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 5). 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 "2000 TLVs and BEIs" and "Documentation of TLVs and BEIs" and on the Saskatchewan Labour web page "Cold Conditions Guidelines for Outside Workers".

Table 5
TLVs Work/Warm-up Schedule for Outside Workers based on a Four-Hour Shift*
Air Temperature - Sunny Sky No Noticeable Wind 5 mph Wind 10 mph Wind 15 mph Wind 20 mph Wind
°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

*2000 TLVs and BEIs - Threshold Limit Values for Chemical Substances and Physical Agents and Biological Exposure Indices. Cincinnati : American Conference of Governmental Industrial Hygienists (ACGIH), 2000 - page 176. Adopted from Saskatchewan Labour "Cold Conditions Guidelines for Outside Workers"

Document last updated on August 8, 2001

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