Dru Sahai, ROH, M.Sc.(A) Project Coordinator
Construction Safety Association of Ontario
Working in cold environments can involve health risks
Cold stress or hypothermia can affect construction 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 construction 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.
Construction workplaces exposed to cold, wet, and/or windy conditions include
Knowing this information can help construction workers avoid hypothermia and frostbite.
The body tries to maintain an internal (core) temperature of approximately 37ºC (98.6ºF). 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 involves the combined effect of air temperature and air movement. Wind-chill cooling rate is defined as heat loss (expressed in watts per meter 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 compares the effects of air temperatures with and without wind. For example, when the air temperature is -28.9šC (-20šF) there is little danger of flesh freezing with no wind, increased danger with a wind of 8 km/h, and extreme danger with a wind of 32 km/h or more. When air speed and temperature produce a chill temperature of -32šC (-25.6šF), continuous skin exposure should not be permitted. Unprotected skin will freeze only at temperatures below -1šC (30.2šF), regardless of wind speed.
Chart 1: Wind-Chill Dangers
Adapted from TLVs® and BEIs®: Threshold Limit Values® for Chemical Substances and Physical Agents and Biological Exposure Indices®, American Conference of Governmental Industrial Hygienists, 1999.
When weather information is not available, the following signs may help to estimate wind speeds in the field:
HYPOTHERMIA--signs and symptoms
When the body can no longer maintain core temperature by constricting blood vessels, it shivers to increase heat production. Maximum severe shivering develops when the body temperature has fallen to 35ºC (95ºF).
The most critical aspect of hypothermia is the body's failure to maintain its deep core temperature. Lower body temperatures present the following signs and symptoms:
In addition, acute exertion in cold can constrict blood vessels in the heart. This is particularly important for older workers or workers with coronary disease, who may have an increased risk of heart attack.
Early signs of hypothermia include
The next stage includes
In severe cases, hypothermia resembles death. Patients must be treated as though they are alive.
Symptoms of severe hypothermia include
Stop further cooling of the body and provide heat to begin rewarming.
FROSTBITE--signs and symptoms
Frostbite is a common injury caused by exposure to severe cold or by contact with extremely cold objects.
Frostbite occurs more readily from touching cold metal objects than from exposure to cold air. That's because heat is rapidly transferred from skin to metal.
The body parts most commonly affected by frostbite are face, ears, fingers, and toes. When tissue freezes, blood vessels are damaged. This reduces blood flow and may cause gangrene.
Frostbite symptoms vary, are not always painful, but often include a sharp, prickling sensation.
The first indication of frostbite is skin that looks waxy and feels numb. Once tissues become hard, the case is a severe medical emergency.
Severe frostbite results in blistering that usually takes about ten days to subside. Once damaged, tissues will always be more susceptible to frostbite in future.
Various medical conditions can increase the risk of cold injury:
Check with your health practitioner to learn whether medications you are taking may have adverse effects in a cold environment.
The best protection against cold-related health risks is to be aware and be prepared. Workers should recognize the signs and symptoms of overexposure in themselves and others. Pain in the extremities may be the first warning sign. Any worker shivering severely should come in out of the cold.
Select protective clothing to suit the cold, the job, and the level of physical activity.
For work performed continuously in the cold, allow rest and warm-up breaks. Heated shelters such as trailers should be available nearby. Encourage workers to use these shelters at regular intervals depending on wind-chill factor.
Workers showing signs of shivering, frostbite, fatigue, drowsiness, irritability, or euphoria should immediately return to the shelter.
Workers entering the shelter should remove their outer layer of clothing and loosen other clothing to let sweat evaporate. In some cases, a change of clothing may be necessary.
Ontario has no legislated exposure limits for work in cold environments. Table 1 was developed by the Saskatchewan Department of Labor and adopted by the American Conference of Governmental Industrial Hygienists (ACGIH). It indicates Threshold Limit Values (TLVs) for properly clothed personnel working at temperatures below freezing.
Before working in extreme cold, workers should be instructed in safety and health procedures.
Training should cover
Adapted from Occupational Health and Safety Division, Saskatchewan Department of Labour
a) Schedule applies to any 4-hour work period of moderate-to-heavy work with warm-up periods of ten minutes in a warm location and with an extended break (e.g., lunch) at the end of the 4-hour work period in a warm location. For light-to-moderate work (limited physical movement) apply the schedule one step lower. For example, at -35ºC (-30ºF) with no noticeable wind (Step 4), a worker at a job with little physical movement should have a maximum work period of 40 minutes with 4 breaks in a 4-hour period (Step 5).
b) TLVs apply only for workers in dry clothing.