Thermal Regulation, Protective Apparel And Heat Stress

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Whether it’s today’s chemical, biological agent scare or tomorrow’s first responder call, firefighters are among the chosen few who continually play Russian Roulette with their health each time they don their hazardous material suit or turnout gear and head into disaster. Each year governing committees amend standards to improve protective equipment. Yet, in spite of these good intentions, protective fabrics place an immeasurable health risk on the human body. As enigmatic as the term “heat stress” is, so is a “cure-all” solution.

Firefighters, EMTs and other first responders are well versed on the facts and remedies of the minor heat illness occurrences… heat rash, heat cramps, tetany (painful muscle spasms caused by faulty calcium metabolism or diminished parathyroid function), heat syncope (fainting) and heat exhaustion. But, it’s the obscure damage that one serious heat related incident as heat stroke can cause that is shrouded in obscurity. In a 1995 Occupational Medicine article, the Cancer Registry of Norway reported a correlation between the incidence of kidney cancer and both exposure and cumulative exposure to working in hot environments and volatiles some 20 to 35 years before observation. The main findings of this study revealed heat stress and kidney cancer in the group with at least three years of total employment. A quote from this study stated, “increased risk of kidney cancer has been reported from previous studies of workers in aluminum smelters and other hot environments such as foundries and coke ovens”.

Studies published in the American Journal of Medicine suggest that Acute Respiratory Distress Syndrome (ARDS) and a variety of other critical conditions associated with ARDS are also linked to heat stroke. Recently, the Center for Disease Control revealed astounding facts about Chronic Fatigue Syndrome (CFS) that resembles the chronic effects of an individual who survives heat stroke, but it doesn’t end there. Medical research hints a correlation between continual exposure of heat to the body that forces the individual to near exhaustion usually results in mild to serious physiologic and neurologic aftereffects. Typically described as exhaustion and poor stamina, the underlying factor in both a severe heat illness and CFS is their pathology involving our body’s cellular energy “storehouse”.

Research cannot well define the dysfunction of our body’s immune system when it is broached by a disruption caused by severe heat. It does, however, intimate that as our body experiences this severe disruption, our natural killer cells that fight viruses can be suppressed or deficient, compromising our immune system. Commonalities discovered between CFS and sequelae (the medical term for recurrent complications frequently noticed in individuals who recover from a severe heat illness) are:
-overall muscle discomfort, flaccid muscles, headaches and weakness
-sleep disturbances or hypersomnolence (requiring excessive sleep hours and naps)
-spatial disorientation, light headedness and dyslogia (speech impairment, reasoning, memory loss
and/or the ability to concentrate)
-chills and night sweats (a thermoregulatory problem)
-skin sensitivity and sensitivity to heat and cold
-irregular heart beat and recurrent chest and/or abdominal pain
-lowered tolerance to alcohol, irritable bowel and/or diarrhea
-weight fluctuation and menstrual cycle disruption

Our bodies are truly a complex chemical, electrical and biological organism. In the early stages of a severe heat illness, at the cellular level, tremendous hyperactivity and abnormalities are taking place. Excessive heat exposure radically denatures proteins, lipoproteins and phospholipids; it liquifies membranes and provokes electrolyte abnormalities that ultimately leads to cardiovascular collapse, multi-organ failure and finally death. Lipids (one of the principal structural materials of living cells) are transported by the lipoproteins throughout the blood, so disruption of our cells is most definitely not a good thing. As we destroy the lipo-proteins that sheath the myelin in the neurotransmitters (nerve fibers), we impair our communication central processing system. Potassium is essential for muscular contraction and function of the heart, skeletal and smooth internal organ muscles, as well as the osmotic pressure and ionic electrical balance. As heat stress persists, potassium levels peak and wane as muscle damage occurs. As these minerals work together to facilitate one another, abnormal levels of calcium, potassium, magnesium and phosphates could become significant enough to cause hypertension (persistent high blood pressure), cardiac arrhythmias or tachycardia (irregular or elevated heart rate) or be the precursor to mild stroke and require immediate treatment.

As our electrolytes become imbalanced, the onset of vomiting and diarrhea can occur. If excess sweating has occurred, the level of sodium usually measures high unless plenty of water without sodium replenishment was previously ingested. Sodium helps maintain osmotic pressure of extracellular fluid, gastrointestinal absorption of certain sugars and proteins, cell permeability and muscle function. Liver damage is a consistent finding and hypoglycemia (low blood sugar) is very common and may be incited by liver failure.

Hemodynamic reports (the study of the forces involved in blood circulation) reveal in severe dehydration cases, abnormal coagulation occurs altering amino acids and causes cerebral edema (excess fluid in the brain cells or tissues). Prolonged intravascular coagulation or loss of blood to the lungs incites damage to the lung tissues and may predispose people to develop pulmonary problems like ARDS. Once this occurs, individuals require more positive inhalation pressure via mechanical ventilation.

Serious heat damage to the body is often associated with endotoxemia (the presence of endotoxins in the blood and tissues) that form an integral part of the cell wall of certain bacteria and are released when the cell destructs. Blood hemorrhaging in the skin (red bumps) can occur followed by blood in the urine. As dehydration increases, the viscosity of the blood changes (from oxygen rich, easily perfused fluid to a sludge-like substance). Vascular tone and capacity, in turn, alter blood pressure and cardiac output. If left untreated, the heart becomes tired and quits. Neurologic complications vary from mental disorientation to delirium, unconsciousness, convulsions or a comatose state (displaying similar symptoms to that of sustaining a serious head injury). Those individuals may require tomography scans to determine the level of Central Nervous System (CNS) damage.

Nerve damage can be as subtle to recovering heat stroke victims as partial or permanent anhidrosis (cessation of sweating). From thereon, the individual’s ability to maintain thermal equilibrium may be compromised, especially when faced with heat stress conditions. Irreparable damage to the body’s heat-dissipating bodily mechanisms may be noted along with muscle coordination may be weak and affected in some or all quadrants of the body. One’s equilibrium and hand-eye coordination may be off. In some cases, lack of nerve conductivity in the lower limbs may also be noted.

Neurologic disorders during the progression of heat related illnesses are further complicated by release of adrenaline (epinephrine- the most potent stimulant of our sympathetic nervous system). Adrenaline stress is extremely prevalent in high-risk occupations where tension, fear, anger, excitement and life threatening situations occur. Release of adrenaline changes the physiological responses and causes a magnitude of complex reactions including, but not limited to increased blood pressure, heart rate and force of blood vessel contraction, relaxation of bronchiolar and intestinal smooth muscles and other metabolic effects. According to John LoZito, Neurologist, a release of some adrenaline is good, but needless adrenaline incites hyperactivity akin to dropping a fuel drum on a bonfire further increasing susceptibility for more serious maladies: stroke, cardiac stress, etc.

Extreme dehydration causes retention of carcinogens and an imbalance of myoglobin (oxygen carrying proteins) in prominent organs like the bladder and colon. Progressive loss of fluid prevents diluting and flushing of these toxins, predisposes one for constipation and urinary tract infections, as well as bladder and colon cancer. Kidney stones may form more readily as calcium, uric acid and other substances become concentrated and form crystals due to fluid loss. Advanced heat stress damage incites sudden rhabdomolysis and intramuscular necrosis (destroying skeletal muscles and decay of muscle tissue also known as muscle wasting).

Researchers have long purported good fluid intake neutralizes the cavity causing acids, flushes away sugar and inhibits the microorganisms that cause gum disease and other oral hygiene problems. For individuals afflicted with asthma, drying of the nose membranes, throat and lung tissues presumably incite more asthma attacks than with hydrated tissues or humid weather. Dehydration, measuring as little as one percent of one’s body weight in non-heat stress conditions can be the cause for headaches, fatigue, muscle cramps and the overall “blah” feeling. A net water loss of as little as four percent of one’s body weight can cause blood pressure to plummet quickly. These and a host of other disorders make simple nausea and headaches just a walk in the park.

The typical information from organizations like the National Institute of Health, OSHA, NIOSH, CDC, Worksafe Australia and others do not reflect the pathophysiology of how heat stress affects our body at the cellular level. Medical science has just begun to unravel the baneful mysteries of bodily reaction to heat, unfortunately many times after the fact.

The Effects of Medication and Drugs:
The picture becomes more complicated when diet pills, diuretics, over-the-counter cold and flu remedies, and pain medication have been ingested on individuals succumbing to a heat stress illness. Antihistamines, decongestants and remedies containing alcohol act to dry up the mucous membranes and decrease sweat gland secretion, causing further dehydration. Caffeine and herbal stimulants incite the bladder and heart rate, while sleep aids can dull the senses and motor skills and can linger in the body for as long as 24 hours. Individuals diagnosed with diabetes, hypoglycemia or anemia and other undetected maladies (atherosclerosis and other vascular diseases) negatively alter the equation for maintaining thermal regulation. Age, malnutrition, impaired health, adiposity (excess body fat), prior fatigue, lack of proper sleep, or previous or repeated episodes of heat-related illnesses all play a vital role in predisposing individuals to the negative effects of heat stress. Individuals with a previous head injury or nerve damage, underactive thyroid, hypertension or smoke heavily are potentially more susceptible to heat stress.

During the past decade, I have collected data from innumerable sources: pathology and medical reports, insurance and government labor statistics, Department of Defense (DOD) and University sponsored epidemiological studies on Gulf War soldiers, and a myriad of information from institutes around the world. All have revealed astonishing facts. The most notable fact is best stated by my long-time mentor, John LoZito, Neurologist who tutored me for several years… “what heat stresses and negative pressures your body tolerates today are not necessarily the same levels that your bodily functioning mechanisms will tolerate tomorrow… or the day thereafter.”

More than two decades ago, I was a small business owner. Every day I dressed in expensive clothing, sat behind an over-sized desk and dealt with the general public from a nice air-conditioned office. Each week I faithfully attended Rotary Club meetings and networked with other business associates at all the right social events. I was a member of the Better Business Council, taught a business course at a junior college and donated more than my share of hours of community service. And one night I changed from the dress ensembles to Levi’s and tee-shirts and joined my soul mate in a research and development venture to solve heat stress problems for the U.S. Armed Forces. The project initially sounded reasonable. Create a passive means of keeping ground soldiers cool, especially in desert warfare conditions, without using electricity and encumbering mechanical devices like pumps and batteries that were prone to fail at critical times. The end result must be a man portable device with temperatures that would be tolerated by the body without negative physiologic reaction.

We examined a variety of patented devices, amassed data from previous test contingents – case studies on battlefield soldiers, firefighters, miners, roughnecks, helicopter pilots, off-shore powerboat and super bike motorcycle racers, and a host of other subjects who were required to wear protective apparel under normal work conditions, many while conducting high metabolic activity in high heat indexes. We evaluated numerous laboratory test results of a variety of ice / gel, evaporative, vortex and water circulative technologies. Aside from the usual shortcomings of too cold of temperature to allow heat abstraction from an exothermic body or mechanical devices that failed at critical times, we elected to explore exotherm type, constant temperature phase-change technology. Little did we realize what a huge undertaking this project would become. During the three and a half years of research and development, I was fortunate to have been tutored by some terrific medical doctors. I spent an inordinate amount of time in sports rehabilitation facilities like Alabama Sports Medicine (where athletes earning seven figures go for major surgery), HealthSouth, and Atlantic Orthopaedic. My thirst for knowledge on this subject was not limited to humans. I also visited armed forces working dog kennels and Churchill Downs horse track in an attempt to better understand optimum healing temperatures.

According to the United States Sports Academy the perfect temperature for optimum healing in prolonged cryotherapy for return to function is 50 degrees F (10 degrees C). Devices that could maintain that temperature would not cause negative physiologic reaction, vasoconstriction, soft tissue damage, cold shock or frostbite. Rather, this temperature also thwarted the onset of histamine production, swelling and fluid retention to the affected tissue. Hence, this lead to a starting point for understanding how to reduce heat stress in humans by first understanding of how our bodies reacted to temperature variation. Further, I learned about the negative affects/effects prolonged heat exposure has to individuals afflicted with heat intolerant diseases like Multiple Sclerosis, Ichthyosis and other neurological and related skin disorders that thwart an individual’s ability to sweat or regulate their temperature naturally.

Today’s Achilles Heel:
The serious heat related ailment is described as either Classic or Exertional Heat Stroke (EHS). The latter, common among firefighters and people who conduct high metabolic activity, is highly morbid. Classic Heat Stroke (CHS) is common among sedentary or elderly people, obese, chronically ill, or individuals with advanced heart disease who are exposed to high ambient temperatures, but aren’t necessarily exercising in this environment. On the other hand, EHS is accelerated when personal protective equipment (PPE) alters the equation of balancing heat gain against heat loss in an incubative environment like firefighting, mining, smelting etc. EHS victims can display the same acute symptoms of classic heat stroke, but many may continue to sweat. Terms like micro-environmental temperature zone (MTZ), moisture vapor transfer rate (MVTR), intense temperature differential (ITD), sweat fog, work tolerance time (WTT), and latent heat of vaporization all work in concert against you when wearing impermeable chemical suits, turnout gear and a variety of protective fabrics with little or no porosity. Synonymous with HazMat suits, MTZ is defined as the continual rise in the temperature of the latent heat trapped inside the encapsulated apparel when caloric activity occurs and vaporization of moisture is not attainable, creating a thermal burden-the rainforest effect.

A major chemical corporation and the University of Central Florida conducted a 90-day test in a laboratory on how garments interfered with the body’s cooling mechanisms. Different garments in weight and porosity were worn by subjects walking on a treadmill until their core temperature reached 101 degrees F. The conclusions – simple cotton clothing can inhibit the MVTR by as much as 20 percent, while fire retardant clothing (contingent upon its porosity, denier weight, color and chemical additive) increases the thermal burden and decreases the MVTR. Researchers continually strive to increase safety while reducing health risks associated with the wearing of protective fabrics.

While testing on treadmills may result in good data in controlled environments, walking on a treadmill in controlled conditions does not emulate the exacting metabolic stress on the body when lifting heavy objects in real life situations, further complicated by wearing protective apparel. A study of threshold limit values in the workplace reveal that even wearing the lightest of garments, heat stress threshold action limits (where individuals core temperature rises to 38 degrees C before requiring treatment) are exceeded in most U.S. cities each summer. The heat wave of July 1999 (in the chemical valley) in Sarnia, Ontario lasted for several days. Two workers lost their lives due to heat stroke while wearing protective coveralls as required by their occupation. Both individuals were in their middle ages and had previous exposure to this type of environment throughout theirworking career.

Balancing heat stress while complying with safety regulations is a dual edged sword. In July of 1998, at the Dothan, Alabama Fire Academy training grounds, I measured the intense temperature differential inside ten firefighters HazMat suits conducting routine chemical spill exercises on a hot 96 degree F day with 82 percent relative humidity. The asphalt temperature averaged 126 degrees F at 0930 hours to 132 degrees F at 1200 hours. The average ITD measured at least 20 degrees warmer than normal skin temperature inside their suits, creating an incubative environment for heat stress.

I define incubative environments as surrounding temperatures that breed heat stress in confined areas where moving air to assist in sweat evaporation, shade and other cooling means are not attainable. One such test I conducted was with the shuttle rescue Black Hawk helicopter crew stationed at Patrick Air Force Base, Florida. These pilots have little means of recirculating cool air while flying nap of the earth at low altitudes. They must wear fire retardant flight suits, further reducing the MVTR as well as a full head helmet, trapping more heat that the body’s radiator wants to dissipate. I suspected it would be a highly incubative environment and was interested in determining the ITD these pilots might experience on a normal mission.

The helicopter faced south to gain maximum UV exposure for the six-hour test. At 0800, I placed a sunscreen in the window and a thermometer on the floor shaded from direct sun. At 0900 hours, I took a digital reading of the outside air temperature (OAT) as 92 degrees F. At 0900, the inside thermometer shaded from direct sun measured 99 degrees F. At 1300 hours, the shaded thermometer read 108 degrees F. I removed the sunscreen and moved the thermometer to the seat exposed to direct sun. At 1303 hours, three minutes after removal of the sunscreen, the thermometer measured 115 degrees F. At 1306 hours, the thermometer measured 129 degrees F. Later that afternoon, after 30 minutes of flying into direct sunlight at an altitude of 1000 feet, the sustained cockpit temperature measured 109 degrees F where the OAT at that altitude measured 94 degrees F.

A few years ago, I attended a special military conference held at the U.S. Marine Corps Chemical Biological Incident Response Force (CBIRF) Headquarters at Indian Head, Maryland. The purpose of the conference was to acquaint the military with off-the-shelf solutions to the age-old problem of heat stress. Hence, I briefed key Marine Corps individuals about the most suitable solution- a myriad of HTF exotherm type cooling devices that had been scientifically proven to increase WTT by 22%, while maintaining normal body vitals, as possible solutions to heat stress for some in-field applications. After the bombing of Khobar towers in 1996, the joint armed forces employ more working canines on perimeter security patrol. Desert conditions pose an extreme health hazard to working dogs, as they do not have the bodily means to expel heat readily like humans. After a technology briefing and demonstration of the HTF exotherm technology, I was approached by an engineer from a company who was promoting their new ingestible, non-soluble “thermosensor” being tested by the Navy Seals. When swallowed, this device would directly transmit thermosensory information to the Corpsman when one’s core temperature reached 39 degrees C.

The engineer purported that this device could be the answer to reducing heat stress in the field. So I asked him the proverbial question. “Let’s say you’re on a covert operation in Central America where the heat index averages 100 degrees F and higher. You’re carrying only 40 pounds of weapons, radios and extra gear. You must keep your camouflage BDUs on for protection against insect bites, snakes and the like. The heat and humidity, coupled with simple walking in the jungle will increase your core temperature quickly, by one or more degrees. What will this thermosensor device accomplish if remedies can’t be implemented the moment the alarm signals?” He replied that they conducted testing in a laboratory on treadmills. “Why the treadmill?” I asked. “Well, because it measures cardiovascular output.”

In turn I asked, “have you ever watched a decon team wearing MOPP2/4 gear or JS-List Overgarments during a chem/bio warfare exercise lift the dead weight of an apparently unconscious 180 pound person lying on the ground and carry that individual to a decontamination tent some 40 yards away… and then do this hurriedly thirty or more times representing a bio-chemical agent incident?” Ah, no. “Are you aware of the exponential increase in metabolic energy required to lift an object versus just walking to increase one’s heart rate?” Not really. “Do you know what bodily heat is trapped inside this chemical suit in a heat index of 95 degrees F when this individual is carrying people and breathing filtered air?” “No, but the sensor tells the individual to immediately hydrate.” “Wouldn’t he also have to be decontaminated first before breaking the veil and exposing himself to the environment which delays rehydrating?” He walked away in silence.

OSHA and other organizations purport utilizing measuring devices like Wet Bulb Globe Temperature (WBGT) and other heat stress monitoring equipment as a good means of knowing the environment you’re facing. However, WBGT and other devices cannot measure the decrement in mental and physical performance that results in a lower margin of safety and increased potential of errors of pilots and other personnel when placed in incubative situations. Just as each of us are unique as our DNA, so will our WTT vary from day to day and task to task, especially so when protective apparel and nonporous fabrics are introduced in the equation.

Aboard the submarine tender the U.S.S. Frank Cable, due to heat radiating off the engines and equipment in their boiler/engine rooms and adjacent operational rooms, the sustained room temperature averages 96 degrees F to 99 degrees F on most days. The safety director at Electric Boat, builders of the Wolf Class submarine, report that their welders, plumbers and electricians were the top three job classifications to report recurrent heat stress illnesses. They predominantly worked in confined spaces the size of a Magnetic Resonance Imaging tube wearing fire retardant coveralls. During industrial training week in July 1996 at Texas A&M Firefighting Academy, I gained great empathy for the firefighters from Canada that were not acclimated to Texas heat and humidity. All seven first aid tents were kept busy ferrying heat stress cases to a more suitable location for treatment.

During February of 1998, I conducted six heat stress awareness seminars around Australia beginning in Perth, working my way around the continent to Sydney. During that time, I was invited to tour the world’s largest deep copper mine in northwestern Queensland, in the heart of the outback. Mount Isa Mine mines four minerals in close proximity – copper, silver, lead and zinc where approximately 35,000 tons of ore are produced daily in this labyrinth whose tunnels extend well in excess of 500 km and at a depth well over 1760 meters. After completing a medical questionnaire, I rode the double-decker lift with 180 workers to the primary sub-level for my briefing. The first oral instruction was to advise me that the best temperature, as good as it gets, averages 41 degrees C year-round…. the kind of environment that incubates heat related illnesses. The previous day, during my on-site heat stress seminar, MIM ventilation coordinator Tony Nixon, reported 28 heat stress casualties occurred during January, almost one per day. To better comprehend work tolerance time, environmental temperatures, air current and other workplace variables, I had to experience it for myself. Although MIM boasts 19 shafts, 14 dedicated to ventilation, the temperature of the air blowing in the shafts was slightly warmer than average skin temperature so excess heat gained by convection was inevitable.

Donned in high denier coveralls and 18 pounds of equipment, I set out to explore the darkness over one mile down. Accompanied by a safety coordinator, we walked and rode in transport vehicles to expose me to a multitude of work situations. Occasionally, I would put on the filter mask to avoid breathing diesel fumes and fine particulate dust. The temperature was unforgiving. Near the stoking areas, the radiant heat approached 60 degrees C. Workers averaged 12 to 15 minutes in this sector, returning red-faced, drenched in sweat, fatigued and dehydrated. Had I not been wearing the HTF exotherm cooling solution of the armed forces research project, I too would have succumbed to heat stress after over four and one-half hours in that environment.

The Physiological Benefits of HTF (Heat Transfer Formula Exotherm) Cooling:
Based on substantial medical research, the unique Heat Transfer Formula (HTF) temperature of 55 degrees F for specific use in personal body cooling has unequivocally proven its effectiveness in greatly reducing the symptoms and effects associated with heat related illnesses. Primarily, this optimum temperature does not cause vasoconstriction or the “thermal shock syndrome” generally felt when exposed to the cold temperatures of ice and gel. Thermogenesis (rapid heat production through shivering) is not incited when this optimum temperature is held in close contact (thermal communication) with the body. Rather, this temperature allows for quick acclimatization, accompanied by a comfortable cool sensation felt on the peripheral skin areas, further inducing heat abstraction from the torso.

First acting as a heat sink, this 55 degree F temperature abstracts excess body heat gained through metabolic activity and/or micro-environmental temperatures created when donning personal protective apparel. The blood carried throughout the peripheral vessels and surrounding soft tissues expel the latent heat and become cooler as more and more heat is abstracted from the surface area. Consequently, recirculating cooler blood back throughout the venous return thwarts additional concomitant hyperactivity among the body’s vitals required to meet the demands of thermal regulation. As cooler blood continually irrigates the cardiovascular system, less metabolic energy is required, slowing the activity of essential body vitals (blood pressure, heart rate, pulmonary output of increased oxygen demands) as well as the latent heat of vaporization (sweating). As sweating wanes, cellular metabolic activity is reduced and less electrolyte fluids and precious minerals are forfeited resulting in a prolonged endurance factor. Since no vascular constriction is occurring, proper oxygen flow is maintained for optimum muscle function, brain activity and CNS functions.

Akin to the radiator of an engine, the optimum temperature of 55 degrees F is the cooler receptor absorbing heat from the medium closest in proximity (the human body). In this example, as the body’s engine cools, less heat needs to be expelled and less stress is placed on the engine itself. Clearly, the engine and its ancillary bodily functions operate more smoothly. As more hyperactive heat is exacted by the body’s cooling mechanisms when attaining thermal equilibrium, an individual’s vigilance and senses remain more acute. Individuals can focus more clearly on the task at hand, not being physiologically and psychologically distracted by the uncomfortable reactions their body is experiencing as a result of trying to attain or maintain thermal equilibrium.

According to John LoZito, Neurologist, utilizing the optimum temperature of 55 degrees F in as a body management device “helps maintain the body’s ‘vitals’… the first technology I’ve seen to work in harmony with physiology to cool both the mind and body. I find this technology especially effective in high risk occupations where ‘adrenaline stress’ adds further negative pressures to the already stressed individual.”

Former Miami Dolphins trainer, Dr. Gary Berns states, “this technology uses safe, comfortable temperatures that work in direct correlation to our body’s physiological, neurological and metabolic systems. As the body cooling device absorbs the excess heat from the chest cavity or extremity, the blood flow begins to cool. As the blood cools, the sympathetic system slows down the metabolism. We then vasodilate and decrease the sympathetic outflow and turn our body into a more calm, relaxed state further reducing body vitals, i.e. blood pressure and heart rate etc. Cooling the blood flow at its source with a higher temperature medium keeps the body from adversely reacting – fighting vasoconstriction by pumping more blood through the arterial system.”

To further substantiate the effectiveness of “optimum temperature” body cooling, the U. S. Air Force Operations Test & Evaluation Center (AFOTEC), now located at Kirtland AFB New Mexico, in conjunction with Alamo Medical Research Institute conducted an extensive 10-day instrumented evaluation of this HTF Exotherm type cooling device. This technology was studied to determine the utility of these one-of-a-kind Heat Transfer Formula Exotherm Type body cooling devices for sole source inclusion for procurement worldwide. Ten male firefighters with medical clearance for unrestricted duty from San Antonio, Texas volunteered to participate in this study. Laboratory testing was conducted to baseline test participants’ physical condition to quantitatively evaluate the physiological benefits of wearing the HTF constant temperature body cooling vests in high heat, high exertion environments versus not wearing a body cooling device.

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