Risk Assessment for Cold Weather Work
Main health issues
The human body has a core temperature of 37°C. Unconsciousness can occur at 31°C, and death below 26°C. Early indications of being affected by the cold include slower reaction times and a lengthening of the time it takes to complete tasks. Manual dexterity also decreases and more mistakes can be made.
Symptoms of a dangerous decrease in body temperature include:
- persistent, severe shivering
- fatigue, lack of co-ordination, drowsiness or apathy
- hallucinations
- a resistance to help
- skin turning blue and then becoming pale and dry.
If nothing is done to warm up the sufferer at this point, things become very serious and the following occurs:
- shivering stops and muscles turn rigid
- breathing and heart rates slow
- loss of consciousness.
According to the Health and Safety Executive’s (HSE) Construction Industry Advisory Committee, workers are particularly at risk from cold when the ambient temperature is below 10°C. When the air temperature is 10°C, and the wind speed is 20 miles per hour, the effective temperature, so far as the body is concerned, drops to 0°C. A temperature of about -1°C drops to about -9°C with a wind speed of 10 miles per hour.
When the body is exposed to cold temperatures, effects can include dehydration, numbness, shivering, frostbite, immersion foot and hypothermia. In very cold weather, workers can face two major health problems: hypothermia and frostbite.
Frostbite
Frostbite can be caused by exposure to very cold weather, as well as through contact with extremely cold objects, such as metal tools. It commonly affects the face, ears, fingers and toes. When tissue freezes, blood vessels are injured, making the area more susceptible to frostbite in the future.
Frostbite freezes and crystallises the fluids in the body tissues and cellular spaces. This can damage blood vessels, causing blood clotting and lack of oxygen to the affected area and deeper tissues. In severe cases, frostbite can damage tissue to the extent that amputation is required.
Mild frostbite affects the outer skin layer and appears as a blanching or whitening of the skin. These symptoms usually disappear as the affected area warms, although the skin may appear red for several hours.
Deep frostbite is the most serious. Usually, sensation is absent in the affected area and blistering does not occur. The blood vessels, muscles, tendons, nerves and bone may be frozen. This can lead to permanent damage, blood clots and gangrene, which ultimately can lead to amputation and even death if medical attention is not obtained.
Hypothermia
Hypothermia develops when the body can no longer maintain its core temperature. The body first attempts to reduce heat loss by shutting down blood flow to the skin, arms and legs, increasing internal heat production by shivering. While severe cases of hypothermia can be fatal, the effects of even mild hypothermia, such as poor co-ordination, irrational or confused behaviour, can seriously impede workers’ safety.
Older employees and those who are wet, tired, dehydrated or suffering from malnutrition are at greater risk. As alcohol makes blood vessels dilate, providing a larger surface area through which heat can be lost, those who consume alcohol are also more vulnerable.
Other hazards
Workers with cardiovascular problems and those with respiratory diseases or on certain medication need to be especially careful when working in very cold temperatures as the conditions can exacerbate their health problems. Nose and ears, fingers and toes are the body parts that are most likely to be affected by the cold, with the first symptoms often manifested as chilblains (itchy swellings on the skin). Employees may suffer from more colds, attacks of bronchitis and asthma, or painful, stiff joints and fatigue as they use more energy in an attempt to keep warm. Cold workers are also more likely to develop hand-arm vibration syndrome when using pneumatic or vibrating tools.
There is evidence that cold weather conditions can affect manual handling operations.
Risk assessment
According to the HSE, assessment of the risk to workers’ health from working in a cold environment needs to consider both personal and environmental factors. Personal factors include: level of activity, the amount and type of clothing and duration of exposure. Environmental factors include ambient temperature and radiant heat and, if the work is outside, sunlight, wind velocity and the presence of rain or snow.
However, carrying out a risk assessment in winter means taking more than just cold temperatures into account. The most dangerous and rapid heat loss occurs when wind chill comes into play and clothing gets wet, as the body loses 25–30 times more heat when in contact with cold, wet objects compared with dry conditions. Snow and ice on site should also be taken into account.
Controls
As with other health and safety problems, the best method of dealing with the hazards related to cold-weather working is elimination. However, this is not always practical when working outside and so measures are required to reduce exposure. These will include the provision and wearing of appropriate clothing and the best advice suggests that layering clothes is most effective, as these layers can be added to or removed depending on each individual’s metabolism.
There should be an inner layer of clothing that is capable of absorbing moisture and transporting it from the body’s surface, followed by a shirt or sweater, again with insulation and moisture transportation properties. Finally, an outer layer is required that is waterproof, windproof and durable.
Proper insulated headgear should also be provided as up to half the body’s heat can be lost through the head. It is also important to protect the feet and toes through wearing two layers of socks, cotton beneath wool for example, and a pair of well-fitted boots that come above the ankle. Hand protection is vital and mittens are warmer than gloves, although they can limit dexterity. Wearing a pair of gloves under a pair of mittens can help keep fingers warm and the mittens can be removed when extra dexterity is required.
Along with proper clothing, regular breaks being taken in a warm building, with access to warm drinks, is an effective method of ensuring better recovery and efficiency. Food containing plenty of carbohydrates and fats for energy and warmth prior to beginning work can also help. Wet clothing should be removed as quickly as possible as it can cause both accelerated heat loss and impair movement.
Wind speeds should be measured and recorded in order to help assess dangerous cold weather conditions. Work in high winds should be avoided whenever possible. Wind and rain shielding should be provided when an option, and working practices should cover the measures to be taken in poor weather conditions. These might include:
- allowing more time for each task and for the negative effect of protective clothing on performance
- a plan to reduce the cooling effect of sweaty clothing
- regular checks on the health and safety of people working in cold conditions
- preparations for vehicle breakdowns, with warm clothing, gloves and blankets as well as a hot drink and normal emergency supplies
- training workers to recognise the symptoms of overexposure in themselves and their colleagues
- ensuring metal handles are insulated and that controls are capable of being operated with gloves on
- ensuring cold metal surfaces are, where possible, labelled
- shelter, welfare facilities and regular breaks in a heated cabin, including warm water for washing and to help warm up cold hands
- first-aid facilities
- facilities for changing, drying and storing protective clothing
- ensuring that, where fine work is performed with bare hands at 16°C or less for more than 10–20 minutes, measures to keep hands warm, such as warm air jets, are provided.