Silent hypothermia and dehydration are some of the conditions divers often encounter. Silent hypothermia, which is the most common form of hypothermia divers experience, predisposes a diver to a dive accident since it causes fatigue and mental dullness during its initial stages. Divers experiencing silent hypothermia may never shiver or feel cold since it involves gradual cooling of the body’s core. Dehydration, meanwhile, occurs as divers try to avoid intake of fluid to lessen the urge to urinate when diving.

“Aw, come on. Don’t be a wuss!” To which we reply: “Better a wuss than a pretzel.”

Amazing, isn’t it? How divers can make a supposedly relaxing, recreational activity so darn competitive. Who surfaced with the most air? Who bagged the most game? Who went deepest? Sometimes the contests are harmless: “You mean you didn’t see the 12-foot moray?” Sometimes motivational: “You mean you haven’t been to Palau?” And sometimes downright dangerous: “You mean you only did two dives a day?”

And if those phrases sound familiar, so will this one often heard at the back of the live-aboard: “You gotta do this night dive! Don’t be a wimp!”

One of the most important skills we learn as divers is to ignore peer pressure and make our own decisions, using good data from our instruments and good sense based on input from our bodies. When is it time to ignore peer pressure and say to your buddies, “Sorry to disappoint, guys, but tonight I’m staying dry. Enjoy your dive”? You might be surprised to learn that it’s not just a matter of how much nitrogen you’ve absorbed.

Self-Test: Bag It or Go For It?

* Are you warm enough? The most common form of hypothermia for divers doesn’t involve blue lips or quivering limbs. It’s called “silent hypothermia,” and it works like this: Even the warmest tropical waters (80F+) are cooler than your body and rob you of heat at the same rate as 42F air. During a full day’s diving, the cooling of your body’s core can be so gradual that your skin never feels cold and you may never shiver. But you still can suffer from the fatigue and mental dullness associated with the initial stages of hypothermia, putting you at increased risk of a dive accident.

* Are you properly hydrated? The most common medical ailment among divers is dehydration. And although we recognize the physical symptoms (nausea, headache, fatigue), we are rarely aware of the cause. We compound the difficulty of staying adequately hydrated in a tropical environment by making two dumb decisions: (1) Deliberately not drinking in order to reduce the urge to pee when diving, which is caused by pressure changes, not the amount of fluids ingested. (2) Substituting diuretics such as coffee, tea and soft drinks – which cause you to lose fluids through urination – for water or replacement drinks. The bottom line: You need up to five quarts more fluid per day than normal while diving in a tropical environment, and if you don’t get it, you risk dehydration – a potentially significant factor in the onset of decompression sickness (DCS).

* Have you off-gassed enough? Dive computers are wonderful instruments, gladly blinking? theoretical no-decompression limits for the next dive while we rest on the surface. But the mathematical models that computers and dive tables use can’t calculate several key factors that can contribute to DCS: difficulty of the dive (currents, cold, activity level); your fitness (on that day, as well as in general); your age; your level of fatigue and hydration. Consider the bottom time your computer gives you as the razor’s edge separating you from DCS, then back off accordingly as you consider the overall picture, not just the mathematical abstraction offered by a silicon chip.

* Are you properly equipped? Dive conditions change throughout the day. A griddle-flat sea can become an ocean of chop – do you need a surface signaling device? The sun sets faster near the equator – will this day dive turn into a night dive while you’re below? The water doesn’t get significantly colder at night, but it sure feels that way, and it’s a lot easier to bump into things – do you have on enough exposure protection?

* Are you well-rested? It’s not enough to know that fatigue leads to mental mistakes and predisposes us to DCS. Breathing under pressure from a machine while swimming in a medium hundreds of times denser than air greatly increases your body’s workload. If you start out fatigued, you could find yourself in an increasingly difficult situation under water.

* Are you motivated enough? In other words, is this something that you really want to do? It’s amazing how attitude and desire can make things a lot easier, or a lot more difficult. You have an obligation to yourself, your family and your dive buddies to make your own decisions, independently, based on your desires and self-evaluation. The ability to draw the line between your desires and someone else’s can often mean the difference between pleasure and misery, between being safe and suddenly realizing that annoying post-dive ache in your shoulder isn’t from carrying your gear bag.

The Cold, Dry Facts Did you know:

* Up to 40 percent of your body’s heat loss occurs through the scalp?

So – Put a lid on it. Covering your head may enable you to reduce rubber elsewhere as well as conserve heat.

* After successive days of diving you accrue a thermal “indebtedness,” making it increasingly difficult to stay adequately warm with the exposure protection you began the week with?

So – Plan on layering. Gradually add a vest, hood and farmer john/jane as the week progresses.

* The ultra-dry air in a scuba cylinder causes twice the amount of fluid loss through respiration as normal? Hot weather increases fluid loss through sweating up to 14 times more than normal.

So – Start drinking early. And don’t stop. Carry a bottle of water with you on the boat.

* Salt pills can cause dehydration? If your body senses excess salt, your kidneys are stimulated to flush it out with urine, drawing from your overall water supply.

So – Drink electrolyte replacements. They have the reverse effect, increasing your body’s ability to absorb fluids.

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