Ambient pressure diving suits are a form of exposure protection used in scuba diving or free diving. They protect divers from the cold and provide some defence from stinging animals and from abrasive and sharp objects and animals underwater, but they do not protect dividers from the pressure of the surrounding water.
Unlike atmospheric diving suits, ambient pressure diving suits provide no protection to the diver from barotrauma or decompression sickness.The suits are often made from neoprene, heavy-duty fabric coated with rubber, or PVC. A side effect of diving suits is that they also provide buoyancy, which the diver must control underwater.
There are main four types of ambient pressure diving suits:
Wet suits are used typically when diving in water temperatures between 10 and 25 o C (50 to 80 o F). A modern wetsuit is mostly made from thin neoprene, which provides limited thermal protection, and lined with a nylon fabric to make it easy to put on and take off.
A wetsuit allows a small amount of water into the suit, but traps this thin layer of water between the skin and the neoprene, which body heat then warms up. The neoprene itself insulates the warm layer against the cold of the surrounding water. A close fit is essential to ensure the suit efficiently works, as too loose a fit will simply allow the warm layer to flush away and be replaced by cold water.
There is some controversy over who invented the wetsuit. Most say it was Jack O'Neill who started using neoprene, which he found lining the floor of an airliner, to make a simple vest. He went on to found the successful wetsuit manufacturer, O'Neill. On the other hand, Bob and Bill Meistrell, a couple of kids from Manhattan Beach, California, claim to have started experimenting with neoprene around 1953. Their company would later be named Body Glove.
Wetsuits come in different thicknesses depending on the conditions for which it is intended. The thicker the suit, the warmer it will keep the wearer. A thick suit is stiff, so mobility is restricted. A wetsuit is normally described in terms of its thickness. For instance, a wetsuit with a torso thickness of 5mm and a limb thickness of 3mm will be described as a "5/3" Different types of wetsuit are available, from a "shorty" (short arms, short legs) to a "long john" (full length arm and legs).
Wet suits are cheap and simple. They lose buoyancy and thermal protection as they compress at depth. Wetsuits are also commonly worn for water sport activities other than diving, such as wind surfing.
Dry suits are used typically when diving in water temperatures between 0 and 15 o C (32 to 60 o F). Seals at the wrists and neck prevent water entering the suit. Even so, the diver will be damp after a dive in a dry suit due to sweat and condensation. The seals are either made from latex rubber or neoprene. Latex seals survive for a maximum of two years but are supple. Neoprene seals last longer but allow more water to enter because, being stiffer, they do not make effective seals in the contours of the wrist and neck.
The suit has an air inflation valve, which allows the diver to control the buoyancy of the suit by injecting gas from the diving regulator to avoid squeeze during descent. It also has an air vent valve, which allows the diver to vent off higher pressure gas from the suit during the ascent. Vent valves can be automatic, operating as pressure relief valves, or manual, where the diver must raise the valve to vent. Automatic vents are generally located at the shoulder and manual vents are located at the wrist. The typical dry suit has built-in boots. It has a zipper, for entry and exit, across the back of the shoulders or diagonally across the front of the torso.
There are two types of dry suit:
Membrane dry suits are constructed from materials with low thermal insulation such as vulcanised rubber or a trilaminate of nylon, butyl rubber and nylon. So the diver must wear an insulating under suit. Membrane dry suits are comfortable to put on, get off and wear. They can be unreliable because the suitís buoyancy and insulation depends on the air trapped in the under suit: if the suits is punctured the buoyancy and insulation is lost. Neoprene dry suits are constructed from neoprene, a buoyant and thermally insulating material. This built-in buoyancy and thermal protection makes them safer to wear than membrane dry suits when punctured because they maintain some of those properties when flooded. Being made of a fairly rigid and heavy material, they are, however, difficult to get on and off and their buoyancy and thermal protection decreases with depth as the neoprene is compressed. Neoprene also tends to shrink over a period of years. An alternative is crushed neoprene, which is less susceptible to volume changes when under pressure and shrinks less.
Semi-dry suits are used typically when diving in water temperatures between 10 and 20 o C (50 to 70 o F). Seals at the wrists and neck limit the volume of water entering and leaving the suit. The diver gets wet in a semi-dry suit but the water that enters is soon warmed up and does not leave the suit readily, so the diver remains warm. The trapped layer of water does not add to the suit's insulating ability. Any residual water circulation past the seals still causes heat loss. But semi-dry suits are cheap and simple compared to dry suits. They are constructed from thick neoprene, which provides good thermal protection. They lose buoyancy and thermal protection as the trapped gas bubbles in the neoprene compress at depth. Semi-dry suits can come in various configurations including a single piece or two pieces, composed of 'long johns' and a separate 'jacket'. Semi dry suits do not usually include boots so a separate pair of insulating boots are worn
Dive Skins and Jeans
Skins are used typically when diving in water temperatures above 25 o C, 77 o F. They are made from Lycra and provide little thermal protection but simply protect the skin from stings and abrasion. Lycra became popular approximately 20 years ago, and is styled after women's nylon stockings. Aussie lifeguards wore nylons to protect against jellyfish stings when on rescues. The down side of lycra is that it can shred when contacting an abrasive surface, and that it can be costly.
The original dive skins were a neoprene jacket and tight jeans and known as a 'Top and Levis'. Jeans have a negative buoyancy of approximately 8 oz. Some divers believe them to be excellent diving skins. They offer minimal thermal protection but good protection against sun, abrasion, and stings. They can be purchased slim fit or tapered and will shrink to fit. Jeans can also be tucked into dive boots or cuffed to prevent drag underwater. With street clothes and a t-shirt or dive top one has the basics for a safe and fun dive. However, jeans provide very poor thermal characteristics out of the water. Wet jeans stay very wet and very cold in even moderate climates. So modern dive skins may be preferable in all but the warmest conditions.
Atmospheric diving suits
An Atmospheric Diving Suit or ADS is a person-shaped, articulated submersible that provides the "diver" with a environment at one atmosphere of pressure at any depth. They can be used for very deep dives, 600 metres / 2000 feet, for many hours without the normal hazards of depth, such as the decompression sickness or nitrogen narcosis.
They look like suits of armour, with elaborate pressure joints to allow articulation while resisting the large difference between the inside and outside pressure. They are often constructed from aluminium, weigh around 250 kg/500 pounds and have propellers allowing them to move in water. Often they are lowered from a support vessel, which supplies breathing gas, electric power and communications to the suit through an umbilical cable. The suit may incorporate a rebreather-type breathing system in the event of an emergency where the umbilical supply fails