When you become chilled underwater, you lose functionality, strength, and the ability to concentrate on anything other than your own discomfort. In extreme cases, being cold can lead to hypothermia, which is a harmful drop in body temperature to below 95 Fahrenheit (35 C). It can lead to impaired judgment, uncontrollable shivering and, in extreme cases, unconsciousness and death. In addition, loss of body heat is associated with an increased risk of decompression sickness, because when you’re cold, your body constricts its blood vessels in an attempt to conserve heat. In a diving scenario, this means blood off-gasses nitrogen slower than your dive computer or RDP anticipates. Despite the safety risks of becoming cold underwater, however, it will have happened to most of us at some point; it’s an inevitable byproduct in a sport that involves constant contact with water. Water conducts heat away from the body 25 times faster than air, meaning that even in tropical climates we are susceptible to cold, especially in situations involving repetitive dives over a series of consecutive days.
To prevent hypothermia, a heightened vulnerability to decompression sickness, or even a general decline in physical and mental capability while underwater, divers must take every precaution to maintain their body heat. In some colder climates, the only way to do this is by wearing a drysuit, but in many places, a wetsuit in good condition, with the right accessories, and with good pre- and post-dive procedures, is sufficient. It’s important to remember that varying factors, including weight, gender, age and metabolism affect the level of insulation each person needs to keep warm. Exposure protection also differs in varying situations; for example, if you plan to dive deeper than normal, you may need a thicker wetsuit than you would usually wear.
There are a few basic tips for maintaining body temperature that are pertinent to everyone and all situations. The obvious place to start is with finding the right wetsuit. Out of all their gear, many divers buy their wetsuit first because rental suits so rarely do the job properly. If your wetsuit is going to keep you warm, it must fit you, and not the countless others who have worn it before you. When buying a suit, the most important factor is the fit; the seals around your neck, ankles and wrists should be snug, and there shouldn’t be vast expanses of loose neoprene in the small of your back, your groin, your armpits, or at the back of your knees. When you try a wetsuit on in the store, it should be as tight as possible while still allowing you to breathe, especially because dry neoprene expands slightly when wet. It’s difficult for many people to find an off-the-rack wetsuit that fits perfectly; if that’s the case, consider a custom-made suit. The luxury of having a suit that keeps you warm while underwater will be well worth the extra cost. When choosing a suit, it’s also important to consider the seal mechanisms; semi-dry suits, for example, have second seals around the wrists and ankles to minimize flushing. The flushing of water in and out of your suit is critical to heat loss, as it replaces the warmer water trapped against your skin with cold water, which conducts more heat away from your body.
If you already have a wetsuit, make sure to maintain it properly by replacing broken seals and seams. Even the best suit in the world won’t keep you warm as soon as these areas are compromised. Also ensure that you wear the right amount of neoprene for the water you’re diving in; while a shorty wetsuit might be appropriate for very warm water, in general a thin, full-length suit will offer more warmth than a thick half suit. The more skin that’s exposed, the more skin will be in direct contact with water and the more heat will be conducted away from the body. This principle also explains why dive accessories like hoods, gloves and booties are so useful when it comes to keeping warm underwater. Consider a hood, in particular, if your wetsuit isn’t doing the job on its own, for two reasons: First, because you lose 20 to 40 percent of your body heat through your head, and second, because many hoods have an attached neck flap or yoke that minimizes flushing via your neck seal. Some divers find that a hood increases feelings of claustrophobia underwater; if this applies to you, ensure that your hood fits tightly around your head, but then make an incision in the chin/throat area to allow for easier breathing. Gloves and booties also minimize contact between skin and water, as well as reinforcing ankle and wrist seals.
Although your suit and accessories are keys to keeping warm, how you conduct yourself before and after a dive is also a big part of fighting the cold. Maintain as much of your body heat as possible while you’re on the surface — don’t start a dive cold, and warm up as soon as you can thereafter. Water draws heat from your body as long as you’re wet, not just while you’re underwater; the water’s evaporation from your skin also causes heat loss. Windy surface conditions exacerbate this process, so oilskins, rain jackets or any other kind of windbreaker are a good idea on surface intervals. Getting dry is the best way to get warm after a dive — remove your wet wetsuit, towel off and get dressed. Warm drinks are also a good way to recover from a chill, though remember that if you’re planning to dive again that day, you must stick to tea, coffee or cocoa: no matter how warming sherry or brandy may be, diving and alcohol should never mix. Even when diving in a hot country, bring warm clothes to change into after your dive, and never underestimate the chilling power of water.
Finally, a good way to minimize heat loss underwater is to keep shallow. Not only is water often colder at depth, but increased pressure also compresses the thickness of your wetsuit and reduces its ability to insulate. If your dive means that going deep is unavoidable, wear thicker neoprene than you normally would to counter the effects of pressure on your suit. Regardless of your depth, if either you or your buddy displays symptoms of hypothermia, including excessive shivering, end the dive immediately and seek warmth upon surfacing. Above all, remember that it is possible to dive comfortably in almost any climate with sufficient preparation and equipment.