According to the Health and Safety Executive, cold weather and shorter periods of daylight mean there is more potential for accidents to happen. Mike Everley investigates the health and safety issues that should be taken into account when carrying out risk assessments for outside work at this time of year.

Those working outdoors in cold conditions face several health and safety problems, including threats to health and an increased risk of slip injuries.


The Health and Safety at Work, etc Act 1974 requires employers to provide their employees with, among other things, a safe and healthy working environment. The Management of Health and Safety at Work Regulations 1999 require employers to assess the risk to health and safety of their employees arising out of their work activity. Workplace temperatures are covered by the Workplace (Health, Safety and Welfare) Regulations 1992, which place a legal obligation on employers to provide a “reasonable” temperature. However, because there is no legal minimum outdoor working temperature, employers need to rely on thermal risk assessments.

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 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.

Factors that influence how severe frostbite can be include: the length of time an employee is exposed to the cold, the temperature outside, the wind chill factor, the amount of humidity in the air, dampness of clothing, high altitudes and whether the person has ingested alcohol or other drugs. These can cause further constriction of the blood vessels, which prevents warm blood from reaching affected areas. Older employees, those with circulation problems, anyone with a previous history of frostbite and those who ingest alcohol, use nicotine or take beta-blocker medications are at greater risk, as are employees who have had a recent injury or blood loss.

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.

Superficial frostbite can result in blistering, with the skin feeling numb, waxy and frozen, and looking greyish-yellow, greyish-blue or white.

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 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.

Symptoms start with shivering, which is the body’s attempt to obtain heat from rapid muscular shaking. When the body’s temperature drops to below 35°C, shivering stops and dizziness and disorientation begin. At this stage, the body only maintains heat around its vital organs: brain, heart and lungs, shutting down circulation to the arms and legs. The heart rate becomes slow, intermittent and weak, and the blood vessels widen. This makes a person feel hot before they slip into unconsciousness. Ultimately, the heart stops.

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. Employees may also select excessive weights and lifting frequencies as a strategy for keeping warm.

Of particular interest in manual handling studies are the effects of cold on the hands. The extremities are anatomically and physiologically susceptible to cooling as they have a small muscle mass and a large surface-area-to-volume ratio, and the hands are affected immediately by the reduction in blood flow caused by vasoconstriction. Physiological amputation is a phenomenon that occurs as a result of a declining internal temperature. It is a result of severe vasoconstriction of the blood flow to the extremities in order to conserve the heat flow to the core.

In those exposed to an environmental air temperature of 8°C, the effect of the blood flow to the hand was identical to that of a completely occluded hand. This has obvious implications for manual dexterity and is of particular interest when risk assessing manual handling tasks. A gradual loss of manual dexterity is experienced with the decline in temperature of various physiological structures including skin, muscle, receptor, nerve and joint temperatures. More details can be found in the HSE publication The Effects of Thermal Environments on the Risks Associated with Manual Handling (RR337).

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.

ISO 15743:2008 Ergonomics of the Thermal Environment — Cold Workplaces. Risk Assessment and Management, provides practical instructions for risk analysis and management in cold working conditions. It describes:

  • a model and methods for risk assessment practices in cold work

  • a model and method for occupational healthcare professionals to identify individuals with symptoms that increase their cold sensitivity, plus optimal guidance and instructions for individual cold protection

  • informative guidelines on how to apply different international thermal standards and other validated scientific methods when assessing cold-related risks

  • a model and methods for cold-risk-management practices

  • practical examples of working in cold conditions.


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.

Key cold weather tips for employees

  • Always dress properly for cold weather. Put on warm clothes before you go outside. Carry extra dry clothing if you are likely to get wet.

  • Keep your skin dry. Wet skin freezes quicker than dry skin.

  • Drink plenty of water to prevent dehydration.

  • If possible, do outdoor work during the warmest part of the day.

  • Avoid sitting still outdoors for long periods of time. Take adequate breaks from the cold.

  • Do not touch metal or wear metal jewellery outdoors in the cold. Metal conducts cold, thus increasing your chances of frostbite.

  • Avoid alcohol, cigarettes and too much coffee and other drinks with caffeine. Smoking decreases circulation and alcohol increases the rate at which your body cools. Caffeine also decreases circulation, its diuretic effect speeds dehydration and its stimulant effect can hasten hypothermia.

  • Stay in good physical shape.

Last reviewed 18 December 2017