How do firefighters and scuba divers protect themselves from extreme temperatures?

Answer 1

The primary purpose of a "diving suit" is thermal protection. According to a study done by the University of Michigan, the average temperature of water near the ocean surface is about 17°C (62.6°F). This, coupled with the fact that water is a very good thermal conductor (it conducts heat away from your body about 22 times more efficiently than air) makes hypothermia one of the most significant risks to a Scuba diver. The primary purpose of a diving suit is to prevent this.

There are two general categories of diving suit in common use: the wet suit and the dry suit. The goal of both is the same. They're designed to keep you warm. A wet suit, usually made of neoprene, sometimes sandwiched between two layers of fabric, is open to the surrounding water. It operates by trapping a very thin layer of water between the diver's body and the thermally insulating neoprene. The diver's body quickly heats this thin layer of water, which then serves as a further thermal insulator.

Dry suits are exactly that: dry. Made of a variety of waterproof materials including crushed neoprene and rubber treated fabric, dry suits are fitted with water-tight cuffs and neck seals. Divers typically wear insulating underwear under dry suits. The underwear and the air trapped in the suit insulate the diver from the cold water.

In both cases, diving suits increase a diver's buoyancy by displacing water with either the neoprene suit itself or by the air trapped inside the suit. This is problematic in that it requires supplementary weight to compensate for the buoyancy to make the diver neutrally buoyant. Without supplementary weight, a diving suit wearing diver would not be able to descend in water.

A secondary benefit of both wet and dry diving suits is physical protection of the diver's skin against abrasion and attack by sea life such as jellyfish and coral. Divers diving in warm water often use thin lycra or spandex suits called dive skins. Dive skins provide minimal thermal protection but do provide a measure of physical protection.