Chapter 4- Diving Physiology Diving Physiology 131 is preferred, taking extreme care to avoid jostling and jarring. Protect against further heat loss with warm layers over the diver and between the diver and the ground or transport litter. Prevention: Wear well-fitting, good quality exposure suits. For moderate temperature diving, wear a good quality, comfortable wetsuit that is not so big that cold water can circulate, nor too small. For colder waters, use a drysuit, and learn how to use it well. Check wind, current, and air and water temperature conditions before your dive. Get out of the water when you are cold, go to a warm place, and drink warm nonalcoholic drinks. Pack your clothes in waterproof bags so you do not put on wet clothes after your dives. Remember wind chill after you get out of the water, and shelter yourself from wind on the boat ride back to shore or your next destination. Wear a hat. Make sure you regularly eat enough to allow your body to generate heat and do exercise that warms you. Get regular exercise so that you are in good physical shape and have muscle mass for warmth. Get enough sleep. It is not the case that wearing a coat indoors if you are chilly will necessarily make you colder once outside or underwater. It often is important to help you build heat stores that you will need when you are out losing heat in the cold. Some immersions in cold water are unexpected. Dive boats must have personal flotation devices (PFDs) other than diving equipment, one for each person onboard. There are five main classes of PFDs. Only Type I and Type II PFD will keep your head out of water and be self-righting if you become unconscious. Seat cushions or Type V flotation devices that require you to hold on are not satisfactory in cold water. Chilling will decrease your grip ability. The colder and rougher the water, the more your life depends on your PFD. Remain still and assume the heat escape lessening position (H.E.L.P. position), in which you draw your knees up to your chest and hold with crossed arms. Practice using your PFD and H.E.L.P. position ahead of time (figure 4-19). A group of people may huddle together in the water to reduce heat loss, prevent separation, and provide morale until rescue. In the huddle position, everyone wraps their arms around each other and pulls into a tight circle, remaining as still as possible. Overheating Any upward variation of body temperature is frequently, but mistakenly called hyperthermia. Your body temperature normally rises during the day, reaching a high in the afternoon, for example, and is not hyperthermia. Your core temperature can rise 3-5 degrees during exercise, an effect that makes your body and joints better prepared for exercise. If germs get out of hand in your body (if germs had hands), your brain tells your temperature center to heat your body enough to kill the germs. The resulting fever is a normal, desirable, if not sometimes uncomfortable, body event. But just as chilling is dangerous, so is increase of body heat far above normal limits. You produce body heat through metabolism, through chemical processes, and by moving around - all part of the processes of being alive. Producing heat is not a problem, but a benefit that allows you to function as a warm-blooded animal. You just need to lose enough to match production to keep your internal environment in its normal healthy range. Overheating results when you produce more heat than you lose. You are not likely to have heat problems underwater during ordinary diving. You may overheat if you work hard in warm water. Military divers in the Persian Gulf had to wear cooling vests to avoid overheating. The most common way to overheat is when you wear a full exposure suit while preparing for your dive on a hot, humid day. You are at increased risk of overheating if you are overweight, impaired by alcohol or recreational drugs, out of shape, very old, or not used to the heat. When air temperature and humidity are high, with little or no breeze, your normal heat loss avenues are reduced or blocked. Your body temperature rises. If you continue sweating, working, and overheating, you can lose so much body water that your blood pressure drops and your circulation is impaired. You do not have enough water to sweat well. Heat exhaustion, also called heat prostration, can occur. If your temperature regulating mechanisms fail, the
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