Wednesday, January 22, 2014

SAFETY: COLD STRESS dangers and risk factors

COLD STRESS
Contents
- Core temperature
- Wind chill
- Hypothermia
- Frostbite
- Risk factors
- Controls
- Exposure limits

Cold stress or hypothermia can affect workers who are not protected against cold. The cold may result naturally from weather conditions or be created artificially, as in refrigerated environments.

Cold is a physical hazard in many workplaces. When the body is unable to warm itself, serious cold-related illnesses and injuries may occur, leading to permanent tissue damage and even death.

Workplaces exposed to cold, wet, and/or windy conditions include
- roofs
- open or unheated cabs
- bridges or other projects near large bodies of water
- large steel structures that retain cold or are exposed to cold
- high buildings open to the wind
- refrigerated rooms, vessels, and containers.

This section provides information on
- effects of overexposure to cold
- factors that can worsen these effects
- control measures.

Knowing this information can help construction workers avoid hypothermia and frostbite.

Core Temperature
The body tries to maintain an internal (core) temperature of approximately 37°C (98.6°F). This is  done by reducing heat loss and increasing heat production.

Under cold conditions, blood vessels in skin, arms, and legs constrict, decreasing blood flow to extremities. This minimizes cooling of the blood and keeps critical internal organs warm. At very low temperatures, however, reducing blood flow to the extremities can result in lower skin temperature and higher risk of frostbite.

Wind Chill
Wind chill involves the combined effect of air temperature and air movement. The wind-chill cooling rate is definedas heat loss (expressed in watts per metre squared) resulting from the effects of air temperature and wind velocity upon exposed skin.
The higher the wind speed and the lower the temperature in the work environment, the greater the insulation value of the protective clothing required.

Chart 1 provides equivalents between air temperatures with and without wind. For example, -12.2°C with a wind of 48 km/h is equivalent to -45°C with no wind. When air speed and temperature produce an equivalent chill temperature of -32°C (-25.6°F), continuous skin exposure should not be permitted. Unprotected skin will freeze only at temperatures below -1°C (30.2°F), regardless of wind speed.

When weather information is not available, the following signs may help to estimate wind speeds in the field:
- 8 km/h (5 mph) light flag just moves
- 16 km/h (10 mph) light flag is fully extended by the wind
- 24 km/h (15 mph) raises a newspaper sheet off the ground
- 32 km/h (20 mph) wind capable of blowing snow.


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