Ergonomic hazards can get dicey when conditions turn icy. Here's some advice.
The Complexities of Cold
Cold is relative. Just ask a spouse. The old joke about Floridians firing up their furnaces while, in the same weather, Minnesotans are out gardening in shorts and flip-flops is funny because it's grounded in truth. What is refreshing to one can be uncomfortable to another. Yet, within reason, while what constitutes discomfort clearly varies among individuals, what does not vary is the direct correlation between cold in general and the increased occurrence of injuries and deaths every year during winter.
Depending on which research report you read, the overall mortality rate in temperate, economically developed countries is anywhere from 10 percent to 25 percent higher on an average winter day than on an average summer day. There is no one reason for this consistent seasonal increase. Influenza, pneumonia, and heart attacks spike during the winter, but so do deaths and injuries from falls, accidents, carbon monoxide poisoning, and house fires, and cold weather is indirectly involved in all. Meanwhile, according to the Centers for Disease Control, hypothermia, for which cold is directly responsible, continues to kill between 600 and 700 people every year in this country, despite all that is known about prevention.
Minnesotans notwithstanding, humans are essentially tropical animals and are ill-equipped to deal naturally with even mild cold. For us, as the Welsh poet George Herbert put it, "Every mile is two in winter," and going that extra mile, or failing to, has all kinds of ramifications for outdoor workers. To live and work in cold climates, we must take protective measures and change our behavior. We have to adapt. Those who don't could face a season of discontent, at best.
Climate change can affect any work-related activity. To keep working properly, the human body's core temperature has to stay near its normal 98.6 degrees F/37 degrees Celsius. Separate from skin temperature, the core temperature is the thermal reading of the blood in the brain, and as Cornell University's Dr. Alan Hedge points out, there is little room for negotiation when it begins to fluctuate. "The core temperature range for being relatively OK is very, very narrow," he says. "You're looking at about a plus or minus two-degree range. When you start going over that, then you start getting problems, and when you go below that, you likewise get problems."
Hedge, head of the Human Factors program in the Department of Design & Environmental Analysis, explains that as a body's exposure to cold increases, and as its core temperature gradually decreases, physical and mental functions are adversely affected, creating hazards waiting to happen. "What you see is that as you begin to cool the body down, the body's natural processes start to move blood from the periphery of the body--the hands and the feet--into the core of the body--the central organs and brain--trying to keep those at the ideal temperature. And so your toes and fingers, as well as your nose and ears--the parts that poke out of you--all become susceptible to frostbite because the blood's being taken out of those tissues and shunted toward the center of the body to keep it warm," Hedge says. "At this point you also start to become clumsy; you can't perform manual tasks very well, you can't screw nuts and bolts together as well. Eventually, of course, your hands become so cold that you can't do anything with them--you're still aware, you're still alive, but you can't use your hands to work effectively."
When the body's core temperature reaches 95 degrees F, hypothermia sets in, and, with continued exposure, dexterity and judgment become further impaired. Eventually, the body's natural defenses become depleted. "The mental processes slow way down at that point, and people become very confused," Hedge says. "They can't figure out the fact that they're freezing to death and that they really ought to be moving, and so, often, they just sit down and die."
Dr. David Curry, vice president of Human Performance Sciences & Technology at ITC Experts (Sugar Grove, Ill.), notes that, contrary to popular belief, ambient temperatures do not have to be below freezing for hypothermia to occur. "People have a general appreciation for the fact that when you're working in the cold, it's going to affect your physical activity and performance," he says. "What many people don't have an appreciation for is the cognitive reduction you also have with low temperatures. Actually, you go below about 60 (degrees F) and you start having problems with fine motor work."
A person's rate of work is one of the many elements that figure into how much he or she is affected by conditions. "You want to avoid long periods of inactivity," he says. "When you get right down to it, the harder you're working, the more you're increasing blood flow through the muscles, and the more heat you're pumping out." At the same time, he adds, in cold environments the body is constantly losing heat, through respiration and the skin. When the body is not creating enough heat through blood flow to compensate for the loss, muscles create their own by tensing just slightly, which burns calories and generates heat. Eventually, shivering sets in, which is the muscles' characteristic response to cold, but while this can increase body heat production severalfold within seconds, it also can create a hazard unto itself if power tools or precision tasks are involved.
"Shivering in the workplace is something you never want to see," says Dr. Alvaro Taveira, professor and chair of the Department of Occupational & Environmental Safety & Health at the University of Wisconsin-Whitewater. "The loss or impairment of motion control caused by shivering is definitely problematic."
On the other hand, says Dr. Peter Hancock, head of the University of Central Florida's Institute for Simulation & Training, the cessation of shivering can be a danger sign, as well. "Any time you're in an extreme cold exposure situation and somebody has stopped shivering when they ought to be, that's a real big red flag that this person is in trouble."
Wearing appropriate protective clothing is, of course, one of our primary strategies for avoiding such trouble. Along with building shelters, our strategic use of apparel is the behavioral adaptation that most allows us to adapt to and function in cold climates. Taveira cautions, however, that not planning ahead for a particular day's work can backfire, compounding exposure risks.
"People working in cold often have a tendency to overdress," Taveira says, adding that this tendency leads later in the day to overheating, perspiration, and insulation-counteracting dampness of the clothes themselves. "A good piece of advice if you know you are going to be engaged in strenuous activity in the cold--at a construction site, for example--is to start the day's journey being slightly uncomfortable, just a little bit cold. You need to be dressed for what will become the day's 'cruising' activity, for when you pick up the pace and get into the rhythm of that activity."
Another good strategy is to take a layered approach, says Curry. "The ability to adjust to the environment in real time is often critical in cold temperatures," he says. "When you're starting to work and your body heat is raising your internal temperature, you want to be able to peel off some of those layers, whereas you want to pack them back on when you're standing still. The value you get is not just from the layer of insulation provided by the clothing but from the warm, dead air you're trapping between the layers, which will keep you warmer than just putting on, say, one fur coat. As the temperature fluctuates, you can actually change your level of thermal insulation by adding or shedding the layers."
Hancock adds that no matter what apparel we gird ourselves with, or how strategically we layer, with increased exposure to very cold environments our body is slowly but surely going to bleed heat. "One of the great sources of heat loss is the head," he says. "It's not a bad rule of thumb that about a third of the resting energy of the body is directed at running the brain. But also about a third of the heat loss that you're going to have coming out of the body is coming from the head, so head covering of some sort in cold conditions is absolutely essential."
Often the very equipment workers use for protection can itself become a hazard on the job. Bulky coats and body suits can hamper movement, for example; masks or goggles can fog from workers' increased respiration, which can impair vision. But of all the necessary gear for cold environments, none is more potentially problematic than gloves. Dr. Peter Budnick, president and CEO of Ergoweb Inc. (Park City, Utah), says that the introduction of hand protection into the work environment is often a significant risk factor for the development of musculoskeletal disorders of the hand and wrist because of users' tendency to overcompensate, overgrip, and overexert.
"When I put a glove on my hand to protect me from the cold, I've now changed the grip posture of my hand," says Budnick, who is also president of the Board of Certification in Professional Ergonomics. "In most cases, I'm not getting good tactile feedback, so I don't have the proper closed loop in my musculature system to know how hard I'm gripping. In other words, I'm trying to grip as hard as I can, yet the actual result is probably lower grip strength against whatever I'm grasping because of the intervening bulk of the glove. It depends on the fit and type of the glove, but some research suggests that up to a 40 percent reduction in grip strength is common from glove use, and as far as a risk factor for working in cold environments, that's probably the biggest effect I see."
Work involving exposure not only to cold but also to chemical, biological, radiological, and/or electrical hazards can necessitate the simultaneous use of several pairs of gloves. Springfield, Ohio-based ergonomics consultant Dr. Denise Brooks says she has been involved in work environments requiring workers to wear as many as five or six pairs of gloves at a time. "And if one pair of gloves negatively impacts you, you can suspect with validity that multiple pairs will make the effects worse and worse," she says.
With or without gloves, though, cold's affect on dexterity can lead to other hazards, Brooks adds. "Things just become slippery in the cold. Controls get moist and then frosty. Workers' hands can slip and bump a switch, inadvertently starting or stopping a machine, or their tools can go flying, hurting themselves or others. It's a domino effect. . . . Cold, like heat, is a complex issue, and knowing how to dress is just one piece of minimizing the risks. What we also have to look at are engineering and administrative controls that take into account things like work flow, shift scheduling, and crew complement to mitigate the effects of temperature extremes."
Hancock says that when putting engineering controls in place at a worksite, the basic question that must be asked is, "How can I get my workers out of that stressful environment?" In one form or another, and as far as possible, the answer must involve isolating workers from the stress.
"As an ergonomist, if you can't actually make the task at hand a telerobotics task, where someone's sitting in a nice office in Houston doing something on the moon, well, then, when you get there you try to provide your workers with as much support as you can," Hancock says. "You try to create for them a microclimate, insofar as possible; you make sure they have all the necessary equipment and things we expect, all the padded gear, the outer-Gore-Tex-type fabrics, all the insulation you can. It doesn't stop them from being exposed to the stress, it doesn't isolate them completely, but it tries to help support that.
"A second and very effective strategy is to create some sort of warming facility where people can go for recovery intervals and thus minimize exposure time. Our data on repeated exposures is a little less solid than our data on one-time, long-term exposures, but it does seem to be better if you can provide this sort of 'oasis' or rest station, some kind of warming hut. But if you can't isolate them from the cold, at least try to make sure you're isolating them from the wind. If you can put up a windbreak and shelter the working environment, you're not going to get that otherwise just stunning reaction from the cold."
"Every mile is two in winter." -- George Herbert, 1593-1633.
Curry agrees that wind chill is the great equalizer for outdoor workers. "Cold is one thing. Cold and wet is something different. Cold and wet with wind is even worse," he says, adding that warming huts, while a boon to cold workers, must be maintained with thermal balance in mind. "Obviously you don't want to take a worker out of zero-degree temperature and shove him into an 80-degree room. You don't want to create a thermal shock effect; you want your people to move in and out while trying to maintain a fairly balanced skin temperature. The real problem area you get into is when you're cycling between warm and cold temperatures for those who are working inside part of the time and outside part of the time. When you go into a heated environment from outside in such conditions, you're obviously too hot and can start to sweat. When you go back outside, that sweat can start to freeze on the body, and that's the last thing you want to do."
According to M. Franz Schneider, CEO of Humantech Inc. (Ann Arbor, Mich.), one of the essential understandings workers must have is that, no matter what preventive measures they take, their bodies will have to pay a price for working in the cold, and the cost is the production and expenditure of incremental energy. Echoing George Herbert, Schneider says, "Any physiological workload that a task has in ideal conditions has more of a physiological workload in less-than-ideal conditions.
"I can go out and lift a box every day of my life, but then if one day I lift it with four inches of heavy, wet snow on it? It's not the same. And meanwhile I'm wearing protective equipment that decreases the efficiency of my lever systems? And I'm a little bit discombobulated because I'm in a hurry, trying to get out of the cold? This isn't the same box anymore. There's a whole different gorilla sitting inside that box. So I think that's what you look for, is that cold has these multiple effects. It's a risk factor with many variables."
Raynaud's: A Perennial Condition
"If you have an old injury--a strain, sprain, or broken bone from some previous time in your life, or any of the usual musculoskeletal disorders like carpal tunnel--it will react negatively to cold," says Denise Brooks, Ph.D., a Springfield, Ohio-based ergonomics consultant. "Often, these negative impacts are for life."
Raynaud's disease is one such perennial disorder. It's a condition in which blood vessels in some areas of the body--usually fingers and toes--appear to overreact to cold temperatures or stress. Doctors don't completely understand the cause of Raynaud's attacks, but they suspect prior injuries to the hands or feet, such as wrist fracture, frostbite, or carpal tunnel syndrome itself can lead to it. Workers who operate vibrating tools can develop a type of Raynaud's called vibration-induced white finger.
During an attack, arteries narrow, limiting blood circulation to the affected areas causing them to feel numb and cool, usually also resulting in a sequence of skin discolorations and a prickly or stinging feeling upon warming or relief of the stress. Cold temperatures are most likely to provoke an attack, but in some cases emotional stress alone can cause an episode. For most people the disease is more a nuisance than a disability, but in severe cases--which are rare--blood circulation can permanently diminish, causing deformities and, rarer still, amputations.
Doctors' suggested preventive and self-care measures for Raynaud's sufferers include:
• Dress warmly outdoors.
• Take precautions indoors. Consider wearing socks to bed during winter; consider wearing gloves when taking food out of the freezer.
• Don't smoke. Nicotine causes skin temperature to drop by constricting blood vessels, which may lead to an attack; inhaling secondhand smoke also can aggravate Raynaud's.
• Exercise. It can increase circulation, among other health benefits.
• Control stress. Because stress may trigger an attack, learning to recognize and avoid stressful situations may help to control the number of attacks.
• Take care of your hands and feet. Guard them from injury; avoid wearing tight wristbands, rings, or footwear that compresses blood vessels in your hands and feet.
• Avoid workplace triggers. Avoiding tools that vibrate thehand may reduce the frequency of attacks.
For more information, visit www.mayoclinic.com.