Mitigating Heat and Cold Stress with FR/AR Clothing
Within the utility industry, employers have long looked to flame-resistant (FR) and arc-rated (AR) garments to help protect workers from injury due to flash fire and arc flash. Because these garments are designed using specially engineered, self-extinguishing fabrics and are certified to rigorous testing standards, they can help prevent or lessen the severity of injury.
Utilizing FR/AR garments as part of a comprehensive personal protective equipment program is also one of the ways employers can meet OSHA’s mandate to provide workers with employment and a place of employment that are free from recognized hazards that are causing or are likely to cause death or serious physical harm.
Questions arise, however, when outside temperatures rise – or plummet. For example, is it possible to maximize protection while also minimizing the risk of heat or cold stress? The answer is yes, but finding the right solution requires an understanding of these interrelated factors:
• How our bodies respond to hot and cold weather conditions.
• How various fibers and fabrics can help keep workers cool.
• How layering can help keep workers warm.
• Balancing protection with comfort in hot and cold weather.
• Effective job site engineering controls.
Mechanisms Behind Heat and Cold Stress
Our bodies are continuously working to maintain a core temperature of approximately 98.6 degrees Fahrenheit. However, when outside temperatures rise, our bodies can overheat, and the excess must be released to avoid heat-related illness. Natural cooling of our bodies happens via four mechanisms:
• Radiation: Heat radiates through the skin and is absorbed by the surrounding, cooler air.
• Conduction: Direct contact with a cooler object, like cool water, cools the body.
• Convection: Air moving across the skin (e.g., from a breeze or fan) cools the body.
• Evaporation: Water in our blood absorbs heat, which then rises to the skin’s surface as sweat and evaporates to cool the body.
Anytime the outside temperature rises, the combination of the radiant heat load and the worker’s exertion level can lead to heat stress. This is the name for multiple heat-related illnesses, including heat rash, heat cramps, heat exhaustion and heat stroke. When acted on early enough, the first three of these can be reversed with hydration, rest and shade. Heat stroke, which can cause permanent disability and even death, requires prompt medical intervention.
Clothing of any type keeps the body’s four natural heat-releasing mechanisms from working efficiently. In addition, once the outside temperature exceeds the body’s internal temperature, the mechanisms are reduced to just one: evaporation. The result can be excessive sweating and subsequent dehydration. Experiencing dehydration can cause a reduction in reaction time, which can be a safety hazard.
Interestingly, sweat plays a leading role in cold weather safety as well. When workers are bundled up and exerting energy, sweat can build up under their clothing. Once their activity level decreases, this moisture cools and the body’s temperature can drop. Cold stress refers to multiple cold-related conditions and illnesses, including chilblains, trench foot, frostbite and hypothermia. All are reversible with dry shelter, warmth and rest, except for hypothermia. Like its heat-related counterpart, heat stroke, hypothermia requires immediate medical attention.
Note that in both hot and cold weather, temperatures don’t have to be extreme for workers to feel the effects of stress. Many of us have experienced becoming chilled soon after working up a sweat, even on a summer day. Understanding your FR/AR clothing and its various features can help mitigate the effects of both heat and cold, no matter how extreme or mild the weather.
Choosing Garments to Keep Workers Cool
Before thinking about the cooling potential of clothing, it’s imperative that you choose FR/AR garments rated to the hazard. Protection is your primary consideration. Look to ASTM F1506 and F1891 for arc flash requirements and NFPA 2112 and ASTM F2733 for flash fire requirements, but keep in mind that these are minimum requirements and ratings. It’s also important to note that single-layer FR/AR clothing is no hotter than non-FR/AR clothing – and it provides protection your workers need.
Next, choose fabrics that assist with cooling, such as the following:
• Open-weave fabrics allow more air to contact the skin (convection).
• Lighter-weight fabrics – if they have an open weave – are less insulating, so they allow for greater release of excess heat (radiation). Note that “lightweight” as a single attribute does not necessarily equate to comfort.
• Moisture-wicking garments move moisture away from the skin to the surface of the fabric (evaporation). Always make sure that moisture wicking is due to a garment’s fiber combination and not because of a finish that will lose effectiveness over time.
Finally, monitor workers carefully when they are using additional PPE layers that may prevent body heat from escaping or sweat from evaporating, such as arc flash suits, rain gear, high-visibility vests, chemical protective wear and soil protective wear (disposable overalls).
Choosing Garments to Keep Workers Warm
When selecting garments to keep workers warm, you should again choose those rated to the hazard. Look to ASTM F1506 and F1891 for arc flash requirements and NFPA 2112 and ASTM F2733 for flash fire requirements.
Next, workers should layer up for maximum heat retention. At a minimum, this includes:
• A moisture-wicking base layer to pull perspiration and dampness away from the skin.
• A moisture-absorbing middle layer that traps sweat and insulates even when wet.
• A water-resistant, wind-blocking outer layer that protects workers from the elements and traps warm air inside.
Layering offers workers more control over their comfort in both hot and cold environments. Since layers may be donned and doffed throughout the workday, it’s vital that every garment in your system is fully rated to the hazard and has the necessary FR/AR properties.
In cold environments, it’s important to always cover extremities, as follows:
• Wear appropriately rated hats, balaclavas, shrouds, neck shades and/or gaiters to prevent body heat from escaping the head, face and neck.
• Choose proper footwear for the conditions.
• When feasible, chemical hand and foot warmers can provide extra, targeted heat.
Finally, be sure that anything worn over your FR/AR garments is tested to the hazard as well or your whole system could be compromised. For example, look for rainwear tested to ASTM F1891 and ASTM F2733.
Additional Clothing Selection Tips
Whether you’re dealing with heat or cold, here are some additional recommendations that can help your crews work more safely:
• Choose loose clothing. Doing so allows for better airflow in the heat and better insulation in the cold.
• Look for purposefully designed clothing. Garments designed with movement in mind will help your crews accomplish tasks more efficiently, no matter the weather.
• Select clothing that protects skin from direct and indirect exposure to heat and cold, and make sure workers wear garments properly.
• Head protection should incorporate shade and/or insulation as needed for the conditions.
• To ensure you’re choosing garments that are comfortable and functional as well as protective, always conduct wear trials prior to purchase or rental.
A Word on FR/AR Base Layers
Moisture-wicking FR/AR base layers not only provide additional protection against thermal energy, but they also allow for greater moisture management by moving sweat away from the skin and into the middle and outer clothing layers.
While industry standards for both arc flash and flash fire protection do allow for all-natural, non-meltable base layers, if these garments are flammable, the arc rating of the outermost FR/AR layer must be sufficient to prevent break-open. If the outer layer is not equal to or greater than the hazard, then all base layers must also be arc-rated.
Job Site Best Practices
In a 2018 interview with National Public Radio (see www.npr.org/2018/08/27/642237217/as-planet-warms-advocates-urge-u-s-to-set-rules-to-protect-workers-from-heat), occupational physician Ronda McCarthy, M.D., MPH, FACOEM, said she “sees a dramatic decrease in workers compensation costs” when employers “voluntarily adopt many of the measures recommended by NIOSH.”
She advised employers and workers to look to NIOSH for suggested heat standards and also recommended the OSHA-NIOSH Heat Safety Tool app (see www.cdc.gov/niosh/topics/heatstress/heatapp.html). This mobile app provides the current heat index, hourly forecasts, first aid information and more.
Further, the following practices should be considered as part of the workday routine when temperatures are extreme:
• Keep workers hydrated. Provide warm or cool sweetened liquids throughout the day. Avoid serving caffeine and alcohol.
• Schedule plenty of rest breaks. Along with hydration, this is by far the most effective way to avoid heat and cold stress.
• Use relief workers or assign extra workers for long, demanding jobs.
• If possible, schedule the most strenuous work during the mildest parts of the day.
• Provide warming/cooling tents where workers can rest.
• Encourage workers to change out of damp or wet garments before becoming chilled.
• Adopt acclimatization programs, exposure limits and rest/work cycles.
• Train workers to know the symptoms of heat and cold stress. Monitor one another and call 911 in emergencies.
An Effective Solution
There’s no single magic bullet for simultaneously protecting workers from arc flash and flash fire hazards and the risks of heat and cold stress. PPE alone is not enough, and neither are weather-related engineering controls. However, when combined, and with proper education and training, you can create quite a safe, effective solution.
About the Author: Derek Sang is the technical training manager at Bulwark Protection. Reach him at firstname.lastname@example.org.
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