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6 minutes reading time (1112 words)

Thermal Stress: Managing Heat Stroke & Hypothermia

While many analogies are true for the human body, of particular interest is comparing the body to a chemical reaction. All of our bodily functions are forms of chemistry. Respiration, digestion and excretion all have their fundamentals in chemistry, and one of the factors that affect most chemical reactions is temperature. The temperature of the chemical reactants and the surrounding environment can speed up, slow down, or stop a chemical reaction. Our bodies mirror this. The body's core temperature is the temperature of the trunk/chest area. Normal core temperature is 98.6 degrees F. This is the temperature where all of our body's chemical reactions are performing adequately. Our system is at equilibrium, all reactions are under control, and this is referred to as homeostatus. When you move away from 98.6 degrees F., you are entering thermal stress. Remember this is the core temperature—our arms, legs and head (peripherals) will lose temperature or gain it more quickly than our core.

The body has mechanisms to help it remain in homeostasis. As the core temperature rises, the body will begin sweating. As the sweat evaporates, it draws heat with it. The body has other means of reducing temperature that are not so easy to perceive. All the blood vessels near the surface of the skin widen (vasodilatation), allowing more blood flow. This increase in blood flow is similar to a radiator, carrying hot blood to the body's surface to cool off. The respiration rate also rises, carrying hot breath out of the body and allowing cool air in.
Conversely, when the core temperature starts to drop, the body starts shivering. This increases heat generation. Unperceived changes also happen. The blood vessels constrict (vasoconstriction) and the breathing rate will decrease slightly in an effort to decrease heat loss. Both conditions (raising or lowering of core temperature) will also lead to behavior changes. Shirts may start to come off (increasing the skin's surface area to the air and facilitating heat loss) or bulkier clothes may be used (insulating the skin and therefore retaining heat).
Of particular concern is water, which is much better at conducting heat than air. While this can be somewhat of a boon in situations where the core temperature is rising, in the case of cold stress, it will lead to the core temperature dropping very quickly (minutes versus hours). While the worst case for this is total immersion in water, even damp clothing can lead to the core temperature dropping at an accelerated rate.

When the above methods cannot cool off or heat up the body enough, the core temperature starts to change. The two life-threatening thermal stress conditions are heat stroke and hypothermia. Heat stroke occurs when the core temperature rises above 98.6 degrees F. When this happens due to a biological condition, it is referred to as a fever. As the core temperature rises, the body will show a number of symptoms including headache, nausea, vertigo, weakness, thirst and giddiness. At this point, the person is in heat exhaustion. Heat exhaustion is not life threatening, and moving the person to a cooler location and providing water will bring relief.
If the person does not heed the symptoms, the core temperature will continue rising. The above symptoms will continue and worsen to include confusion, irrational behavior, loss of consciousness, convulsions, lack of sweating (usually) and hot, dry skin. At this point the core temperature will be somewhere in the 105.8 degrees F. range and the person is in a life-threatening situation. The body cannot maintain this temperature for an extended period of time. The person needs immediate medical attention. Actions to take while getting the person to medical aid include placing the person in a shady area and removing the outer clothing. Wet the skin and increase air movement to improve evaporative cooling. Fluids should be replaced as soon as possible; however, fluids should not be given to individuals who are unconscious, unresponsive or incoherent.

Once the core body temperature drops below 98.6 degrees, a person is hypothermic. The onset of hypothermia can be acute (a sudden temperature drop, as may be caused by immersion in cold water) or gradual (a drop caused over time, as may be caused by working in cold weather with inadequately insulated clothing). For the cases where hypothermia is gradual, it can be further classified as mild, moderate or severe.
Mild hypothermia has the following symptoms: shivering, numbness in limbs, loss of dexterity, clumsiness and pain from the cold. At this stage the person is still alert. In moderate hypothermia the person shows the same symptoms; however, he or she is losing alertness (becoming lethargic) and the shivering has decreased or stopped. When the person's core temperature has dropped too much (approximately 90 degrees F. or less) he or she is in severe hypothermia and in a critical condition. At this point the shivering has stopped, and the person is unaware, confused, slurring speech and having signs of muscle rigidity.
Mild and moderate hypothermia can be treated by preventing further heat loss (blankets, cover head); giving warm, sweet liquids; applying a gentle heat source; and exercising to generate heat (as appropriate). The person should be checked by a medical professional as soon as possible. For severe hypothermia, the person should be treated as for shock—have external heating sources applied and immediately transport to the hospital. Moderate and severe hypothermia can be difficult to differentiate, in which case the person should be treated for severe shock.

The prevention of either type of thermal stress is similar.
• People should dress for the climate in which they will be working. Light-colored, loose, breathable clothing for warm climates; insulated, layered clothing for the cold weather.
• People should have a re-hab area and work rotations that allow them to warm or cool as needed. A re-hab area can be a shaded area with drinking water available or a car with air-conditioning in warm weather. A heated tent or a car with heat can serve in cold weather.
• People need to stay hydrated. Either weather condition will drain water from the body and this water should be replaced. Once the body is dehydrated, regulating the core temperature becomes more difficult and thermal stress is more likely. This is also why alcohol, caffeine, and some over-the-counter drugs should be avoided. They all adversely affect the body's ability to regulate the heat it produces.

By better understanding thermal stresses and following some simple recommendations, we can ensure that those who have to work in the cold and heat will be able to do so safely. ip

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Saturday, 23 January 2021

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