With tight construction schedules anticipated this winter, contractors should plan to prepare for the challenges of working in cold weather. The importance of these dangerous conditions may not receive as much attention as preparing for hot weather work. Yet the dangers for injury, sickness, and even death are still present.
Cold weather stress is not a common term; thus, contractors must be proactive in recognizing the warning signs that may indicate cold stress conditions. The temperature ranges at which cold stress can occur differ from region to region – yet there is one common element.
Cold stress occurs when working conditions cause a worker’s skin temperature to decline. When the decline is significant, the loss of heat causes the body’s internal core temperature to drop below normal. When the body is unable to maintain an adequate core temperature serious cold-related illnesses and injuries may occur. These can include permanent tissue damage and, in extreme cases, death.
Many contractors wrongly assume cold-stress only occurs in arctic regions. In reality near-freezing temperatures can affect workers on jobsites – even in less extreme climates.
How cold is too cold?
Anyone working in a cool environment may be at risk of cold stress. Whenever temperatures drop below normal and wind speed increases, the body loses heat more rapidly. The resulting cooler conditions force the body to work harder to maintain its core temperature.
Wind chill can be the main instigator of cold stress. It is the temperature your body feels when air temperature and wind speed are combined. For example, when the air temperature is 40°F, and the wind speed is 35 mph, the effect on the exposed skin is as if the air temperature was 28°F. The local Wind Chill Index report provides contractors an indicator of the potential of cold stress.
Other risk factors that contribute to cold stress include: Wetness/dampness, body sweat, dressing improperly, fatigue, predisposing health conditions such as hypertension, hypothyroidism, and diabetes.
Three types of cold stress injuries
In a cold environment, most of the body’s energy is used to keep its internal core temperature warm. Over time in the cold, the body will begin to shift blood flow from the extremities (hands, feet, arms, and legs) and outer skin to the core. This shift allows the exposed skin and the extremities to cool rapidly and increases the risk of cold stress injuries. Safety experts identify three conditions from the switching of blood flow that are associated with cold stress: trench foot, frostbite, and hypothermia.
Trench Foot (or immersion foot) is caused by prolonged exposure to wet and cold temperatures. It can occur at temperatures as high as 60°F if the feet are constantly wet. Non-freezing injury occurs because wet feet lose heat 25-times faster than dry feet. To prevent heat loss, the body constricts the blood vessels to shut down circulation in the feet. The skin tissue begins to die because of a lack of oxygen and nutrients and due to the buildup of toxic products.
Hypothermia occurs when body heat is lost faster than it can be replaced and the normal body temperature (98.6°F) drops to less than 95°F. Hypothermia is most likely at very cold temperatures, but it can occur even at cool temperatures (above 40°F), if a person becomes chilled from rain, sweat, or submersion in cold water. The worker may begin to shiver and stomp the feet in order to generate heat. But should the hyperthermia become severe, the worker may lose coordination, become confused or disoriented, and even stop shivering. A worker could die if help is not received immediately.
Frostbite Frostbite is an injury to the body that is caused by freezing of the skin and underlying tissues. The lower the temperature, the more quickly frostbite will occur. Frostbite typically affects the extremities, particularly the feet and hands. Amputation may be required in severe cases.
How to prevent cold stress
OSHA does not have a specific standard for cold weather work. Yet contractors still have a responsibility to provide workers with safe work sites that prevent cold stress. Effective tools to meet this requirement include encouraging safe work practices through training and enforcement and adopting effective engineering controls in the field.
Engineering controls can start with adopting safe work practices. Since dehydration is still a concern while working in cold weather, contractors should provide plenty of warm sweetened liquids to workers. Schedule heavy work during the warmer parts of the day. Supervisors can assign tasks to pairs so workers can monitor each other for signs of cold stress.
When conditions change suddenly, supervisors should allow workers time to adjust to cold weather conditions by gradually increasing their outdoor workload. This could include more frequent breaks in warm areas, to build up a tolerance for working in the cold environment.
Other engineering controls include the use of portable heaters to warm work stations. When possible, contractors should shield work areas from drafts or wind to reduce wind chill. Large tarps, properly secured can provide some relief from the potential effects of wind chill.
Another engineered control to avoid cold stress is the selection of appropriate clothing. This approach starts with proper fabric. Cotton loses its insulation value when it becomes wet. Wool, silk and most synthetics, on the other hand, retain their insulation even when wet.
Workers in cold conditions should wear at least three layers of loose fitting clothing. Layering provides better insulation as long as it’s not too tight. The inner layer should consist of wool, silk or synthetic to wick moisture away from the body. The middle layer should be of wool or synthetic fabric to provide insulation even when wet. The outer layer should be a material that provides wind and rain protection yet allows some ventilation to prevent overheating.
Remember the key to retaining body heat is to use multiple thin layers and keep clothing, gloves and boots loose-fitting. The body naturally generates heat, which becomes trapped in the air between layers of clothing. Air is a better insulator than your actual gloves. Also, tight clothing restricts circulation which, in turn, prevents your body from effectively generating heat.
Providing workers with the proper type of personal protection equipment designed for the body’s extremities is an important step. Warm hats and hard hat liners reduce the amount of body heat that escapes from the head. Knit masks cover and warm faces and mouths. Insulated gloves protect the hands, while insulated and waterproof boots and toe warming packs and hand warming packs can eliminate foot problems.
Contractors in most regions of North America often face conditions that can lead to cold stress for their workers. This danger can be eliminated with the proper combination of engineered controls, equipment, and training.
Avoiding the flu With winter weather, contractors face an additional challenge – productivity. Late fall, winter and early spring are prime flu seasons. Health experts say that annually as much as 20% of a work force will suffer flu-like systems. For contractors, any absence is a loss of daily production.
Many contractors arrange to offer their crew flu vaccinations during safety meetings. For operations spread over multiple regions, contractors can partner with local healthcare providers or pharmacies to protect against various strains of flu.