Manage Heat Stress with Evaporative Cooling

Heat stress, heat exhaustion or even heat stroke can be caused by the inability of the body to cool itself down by sweating. This overheating can occur when your body temperature and the surrounding air are the same, or when you actually gain heat from the environment because the external temperature is higher than your body temperature. This prevents you from sweating, which inhibits any heat loss. It can also occur in areas where the air is moist and warm, and thus evaporation from the skin is slowed or even prohibited. Individuals who work outdoors doing any kind of physical labor need to make sure that they stay as cool as possible because not only are they subject to the direct heat outdoors but they are producing extra heat from their physical load. In fact, physical work demands four times the energy of work done from a chair. One’s ability to perform well, or even to feel well is affected by an elevated body temperature and dehydration. Higher heat tolerance can be seen in a few groups of people, such as younger individuals, slimmer people more so than overweight ones, and more physically fit ones. Heat illnesses are quite commonly seen in young athletes as well as military recruits.

Signs of heat related illnesses range from headaches, fainting, weakness and clammy skin to cessation of sweating, mental confusion, seizures and convulsions. How can you control heat illnesses? One should try to drink a lot of water all day long and wear a cooling vest. Cool Medics vests work on an evaporative cooling technique once it has been activated in water. When the moisture in the fabric evaporates through the hydrophilic fibers, heat is removed which causes the surrounding area to cool down, transferring the cooling effect to the wearer. This process will cool the wearer down by 20 to 25 degrees, the effects of which can last anywhere from 4 1/2 to 8 hours.

The products are constructed from a patented three-layer fabric that, by combining hydrophilic fibers into a fibrous batting core and a thermally conductive lining, will provide cooling after allowing the product to soak in water for no longer than 5 to 10 seconds. The water activates the cooling process by charging the fibers with moisture and creating an environment for evaporation. Evaporative Cooling works on the premise that when water evaporates from a surface, that surface becomes cooler because heat is expended to change the water from a liquid into a vapor. A nice breeze on a hot day cools us because the current of air makes perspiration evaporate quickly. The effectiveness of the product is based on its ability to absorb heat from the body and release that heat to the outside environment. The water that is absorbed by the batting material provides a heat transfer medium for this effect. Thus, the products are capable of providing evaporative cooling, a principal means for body cooling.

Patients with heat exhaustion are in danger of overheating or contacting heat stroke unless they can get immediate relief from a cooling source. For patients with heat exhaustion, Evaporative Cooling is an initial treatment as it involves stabilization to avoid progression to heat stroke. “Immediate initiation of rapid and effective cooling is crucial in a patient with heatstroke” (Management of Heatstroke and Heat Exhaustion, James L. Glazer). One case series found a trend towards improved survival in patients cooled to a core temperature below 38.9°C within 60 minutes, and another report found improved survival when patients were cooled to the same level within 30 minutes (Cooling methods used in the treatment of exertion heat illness, JE Smith). Although evidence is limited, it would suggest that initial results might be improved when core temperature is reduced as quickly as possible.

In studies with patients with Multiple Sclerosis, who suffer from increased body temperature, decreasing the core temperature of these patients has been shown to reduce the effects of elevated temperature. Reduction of these symptoms have been achieved by different methods of cooling, such as liquid cooling garments. Research of MS patients wearing these types of products was performed by NASA Ames Research Center and Lockheed Martin Engineering & Sciences. Most of the MS patients found relief in the cooling periods including feeling less tired and having more control over their muscular movements after about 1/2 hour of the cooling period. Most also found that these changes lasted for more than an hour after removal of the cooling garment while some subjects even felt better for a period lasting 3-4 hours after being cooled.

Cool Medics products include cooling vests, head coolers and blankets that when immersed in water for a period of no longer than 10 seconds will remain cool for 6 to 8 hours at 98 degrees Fahrenheit. Longer periods of coolness of up to 9 hours will be achieved when indoors and not exposed to the sun. The product can be recharged by simply placing in water for a period of no more than 10 seconds, and thus, recommencing the whole cooling cycle.

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Originally Published in Industrial Hygiene News

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