Avoiding losing body heat

Avoiding losing body heat

Water conducts heat from the diver 25 times[1] better than air, which can lead to hypothermia even in mild water temperatures. Symptoms of hypothermia include impaired judgment and dexterity, which can quickly become deadly in an aquatic environment. In all but the warmest waters, divers need the thermal insulation provided by wetsuits or drysuits.

In the case of a wetsuit, the suit is designed to minimize heat loss. Wetsuits are generally made of neoprene that has small gas cells, generally nitrogen, trapped in it during the manufacturing process. The poor thermal conductivity of this expanded cell neoprene means that wetsuits reduce loss of body heat by conduction to the surrounding water. The neoprene in this case acts as an insulator.

The second way in which wetsuits reduce heat loss is to trap a thin layer of water between the diver's skin and the insulating suit itself. Body heat then heats the trapped water. Provided the wetsuit is reasonably well-sealed at all openings (neck, wrists, legs), this reduces water flow over the surface of the skin, reducing loss of body heat by convection, and therefore keeps the diver warm (this is the principle employed in the use of a "Semi-Dry")

Spring Suit and Steamer.

In the case of a drysuit, it does exactly that: keeps a diver dry. The suit is sealed so that frigid water cannot penetrate the suit. Drysuit undergarments are often worn under a drysuit as well, and help to keep layers of air inside the suit for better thermal insulation. Some divers carry an extra gas bottle dedicated to filling the dry suit. Usually this bottle contains argon gas, because of its better insulation as compared with air.

Drysuits fall into two main categories neoprene and membrane; both systems have their good and bad points but generally their thermal properties can be reduced to:

• Membrane: usually a trilaminate construction; owing to the thinness of the material (around 1 mm), these require an undersuit, usually of high insulation value if diving in cooler water.
• Neoprene: a similar construction to wetsuits; these are often considerably thicker (7-8 mm) and have sufficient insulation to allow a lighter-weight undersuit (or none at all); however on deeper dives the neoprene can compress to as little as 2 mm thus losing a proportion of their insulation. Compressed or crushed neoprene may also be used (where the neoprene is pre-compressed to 2-3 mm) which avoids the variation of insulating properties with depth.