Is there a minimum temperature at which work becomes dangerous and should be stopped?
The short answer is yes.
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 hypothermia?
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 Cold Environments - Health Effects and First Aid.
What are exposure limits for working in the cold when outdoors?
In some cases, legislation does provide a range of acceptable temperatures for specific circumstances. The Threshold Limit Values® (TLVs®) for cold stress as published by the American Conference of Governmental Industrial Hygienists (ACGIH) have been formally adopted as occupational exposure limits in some jurisdictions, while jurisdictions use the TLVs® as guidelines. See the OSH Answers Temperature Conditions - Legislation for a list of legislation from each jurisdiction.
The ACGIH has adopted the guidelines developed by the Saskatchewan Labour for working outdoors in cold weather conditions. 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. For more information see the webpage from the Occupational Health and Safety Division of the Government of Saskatchewan on Working Outdoors.
|Table 1 |
TLVs Work/Warm-up Schedule for Outside Workers based on a Four-Hour Shift*
|Air Temperature - Sunny Sky||No Noticeable Wind||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|
- Applies to moderate to heavy physical work in any 4 hour period. Warm-up breaks should be in a warm environment for 10 minutes. If there is limited physical activity, apply the schedule one step lower (more protective).
- Use estimates for wind speed if accurate information is not available (e.g., an 8 km/h (5 mph) wind will move a light flag, a 16 km/h (10 mph) wind will fully extend the flag, a 24 km/hr (15 mph) wind will raise a newspaper sheet, and a 32 km/h (20 mph) wind will produce blowing and drifting snow)
- Additional considerations are required if only the wind chill cooling rate if available.
- Guidelines apply to workers wearing dry clothing.
Source: 2017 TLVs® and BEIs® - Threshold Limit Values for Chemical Substances and Physical Agents and Biological Exposure Indices. Cincinnati: American Conference of Governmental Industrial Hygienists (ACGIH), 2017, pages 217-218.
What are exposure limits for working in the cold when in a building or indoors?
Some Canadian jurisdictions specify a minimum temperature for indoor work environments in buildings that are normally heated. See the OSH Answers on Temperature Conditions - Legislation for a list of legislation.
What should be done when it is very cold or windy outside?
Employers have a duty to take every reasonable precaution to make sure the workplace is safe for the worker. This duty includes taking effective measures to protect workers from cold stress disorders if it is not reasonably practicable to control indoor conditions adequately, or when the work is done outdoors.
General recommendations include to:
- Dress in layers of warm clothing, with an outer layer that is wind-resistant.
- Cover all exposed skin.
- Wear a hat, mittens or insulated gloves, a scarf, neck tube or face mask, and insulated, waterproof footwear.
- Stay dry (including taking steps to prevent excess sweating).
- Keep active.
- Maintain a work/break schedule. Breaks should be taken in a warm area, with protection from drafts.
- When very cold, consider cancelling outdoor activities.
Please see the OSH Answers document Cold Environment - Working in Cold for more information.
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