The following article was sourced from a Wikipedia page at the following address: http://en.wikipedia.org/wiki/Dry_suit
A dry suit or drysuit provides thermal insulation or passive thermal protection to the wearer while immersed in water, and is worn by divers, boaters, water sports enthusiasts, and others who work or play in or near cold water. A dry suit normally protects the whole body except the head, hands, and possibly the feet. In some configurations, however, all of these are covered as well. Dry suits are used typically in these cases:
The main difference between dry suits and wetsuits is that dry suits are designed to prevent water entering. This generally allows better insulation making them more suitable for use in cold water. Dry suits can be uncomfortably hot in warm or hot air, and are typically more expensive and more complex to don. For divers, they add some degree of complexity as the suit must be inflated and deflated with changes in depth in order to minimize "squeeze" on descent or uncontrolled rapid ascent due to over-buoyancy.
Membrane dry suits are made from thin materials, and thus by themselves have little thermal insulation. They are commonly made of vulcanized rubber, or laminated layers of nylon and butyl rubber. Membrane dry suits typically do not stretch, so they need to be made oversized and baggy to allow flexibility at the joints through the wearer's range of motion. This makes membrane dry suits easy to put on and get off, provides a great range of motion for the wearer, and makes them comfortable to wear for long periods, as the wearer does not have to pull against rubber elasticity.
To stay warm in a membrane suit, the wearer must wear an insulating undersuit, today typically made with polyester or other synthetic fibre batting. Polyester and other synthetics are preferred over natural materials, since synthetic materials have better insulating properties when damp or wet from sweat, seepage, or a leak. (Except for wool, which is an effective insulator when damp, albeit bulky.)
Reasonable care must be taken not to puncture or tear membrane dry suits, because buoyancy and insulation depend completely on the gas pockets in the undersuit (whereas a wetsuit normally allows water to enter, and retains its insulation despite it). The dry suit material offers essentially no buoyancy or insulation itself, so if the dry suit leaks or is torn, water can soak the undersuit, with a corresponding loss of buoyancy and insulation.
In warmer waters, some wearers wear specially designed membrane dry suits without an undersuit. These are different in design, materials, and construction from dry suits made for cold water diving.
Membrane dry suits may also be made of a waterproof and breathable material to enable comfortable wear when out of the water for long periods of time. Sailors and boaters who intend to stay out of the water prefer this type of suit.
Neoprene is a type of synthetic rubber. Neoprene can be foamed during manufacture to contain millions of tiny enclosed gas bubbles, forming a buoyant and thermally-insulating material, called "foamed neoprene", "foam-neoprene" or "expanded neoprene". Foamed neoprene may used as the fabric of a drysuit, providing some insulation due to the gas within the material, as in a standard wetsuit. If torn or punctured, leading to flooding, a foam-neoprene suit retains the insulation and buoyancy of the gas bubbles, in the same manner as in a foamed-neoprene wet suit.
Neoprene dry suits are not as easy to put on and remove as are membrane dry suits, largely due to a closer fit which is possible due to the inherent elasticity of the material, and partly due to greater weight. As with wet suits, their buoyancy and thermal protection decreases with depth as the air bubbles in the neoprene are compressed. The air or other gas in the dry fabric undergarments providing insulation under a dry suit is also compressed, but can be restored to an effective volume by inflating the drysuit at depth through an inflator valve, thus preventing "suit squeeze" and compacting of the air-filled dry fabric beneath.
Foam-neoprene also tends to shrink over the years as it outgases and slowly becomes less flexible as it ages. An alternative is crushed or compressed foam neoprene, which is less susceptible to volume changes when under pressure, and shrinks less, while retaining the elasticity which allows freedom of movement.
Foamed-neoprene dry suits provide some insulation by themselves, but even with foam drysuits, thermal under-suits are usually worn. With a thicker foamed neoprene suit, less insulation is needed underneath. The undersuits vary from a standard wet suit (worn dry), to polyester fabrics used in mountaineering and other cold weather uses (these may also be in pieces, including vests and sleeveless vests). Such fabrics also ultimately insulate in the same way as foam, using air in which convection is retarded by the small sizes of the air spaces. However, per volume and weight of fabric, the best-insulating dry polyester fabrics are more effective than foam, because their air pockets are smaller.
The combination of neoprene suit and polyester undergarment often reduces the amount of ballast needed to counteract the total buoyancy of the diver, since the total amount of air is usually less than needed for the same insulation in a membrane suit with a thicker undersuit. Notwithstanding the greater insulating power of dry fabrics, membrane suits with undersuits are a combination which usually uses the total volume of insulating air less efficiently (hence uses more air for the same insulation). This is because such suits cause larger volumes of air to be present as large bubbles and spaces, and the phenomena of convection and poor distribution causes such air to be "wasted" in its value as insulator.
A recent innovation is the silicone seal, which is claimed to be as supple as latex, more flexible, yet far more durable. These have not yet been widely adopted but represent a promising development. Silicone seals are hypoallergenic, but can not be glued to the suit, and must be attached using clip-on rings.
Modern dry suits have a waterproof zipper for entry and exit which was originally developed by NASA to hold air inside astronaut space suits. This complex and special zipper is one of the most expensive parts of the suit. The zipper is commonly installed across the back of the shoulders, since this placement compromises overall flexibility the least—but this design normally means the wearer requires assistance in donning and doffing the suit. The other most common zipper placement in modern suits is diagonally across the torso, which allows self-donning. Other designs place the zipper on the side, straight down the middle of the front or back, or on a wide tubular chest entry opening which is folded down and clipped round the waist after sealing the zip.
There are many zipper arrangements in use, because the waterproof-zipper is very rigid, and cannot stretch at all, which can make it difficult for a user to get into and out of the suit. The zipper opening is often quite small, since a large zipper makes the suit stiffer and more difficult to use. Some complex zipper arrangements that wrap around the neck or chest let the suit swing open with a flap or hinge point. Some snug-fitting suits may also use wrap-around expansion zippers that allow the suit to expand or contract to fit different size people.
Dry suits may also be fitted with an extra waterproof zipper "fly" to let the user urinate when out of the water when the suit is worn for long periods.
Before true-waterproof zippers were invented, other methods of keeping the suit waterproof at the entry point had to be devised, with the most common being a long rubber entry tunnel which would be flattened shut, then rolled together from the sides and finally folded and clamped with a metal clip. An early example was the Sladen suit, where the entry tunnel was at the navel. The Louisiana-based dry suit company Aquala still makes a "historical" diving suit of that kind.
Another type of entry featured a rubber tunnel that protruded through a normal cloth zipper. The tunnel would be rolled shut and the zipper closed to hold the roll in place.
Some types did not use a zipper at all. At least one make of old-type British frogman's dry suit was one-piece with a wide neck hole for entry; the bottom of the hood and the edge of the suit's neck hole were held together by a large circular steel clamp around the neck; there was a watertight seal in the bottom of the hood. Two-piece dry suit designs in full length for year-round use and "shorty" styles for summer-season use were also common in the 1950s and early 1960s. Two-piece suits of the period include the American-made Spearfisherman frogman suit, U.S. Divers Seal Suit and the So Lo Marx Skooba Totes suit, the Italian-made Pirelli suit and the UK-made Heinke Delta suit and Siebe-Heinke Dip suit. These suits were sealed at the waist by rolling together the excess material at the bottom of the shirt and the top of the pants. A cummerbund, rail, or surgical tubing was sometimes provided to make the seal more waterproof. A modern version of the two-piece dry suit is manufactured by Customworks of Idaho. Though lacking such features as valves and zippers, these suits still have certain advantages over their modern counterparts. For example, they are cheaper, less bulky, more easily repaired and the footed pants could also double as fishing waders.
Gloves, mitts, and three-finger mitts
If it is not important to have exposed bare hands, permanently attached heavy rubber gloves or mitts can help make getting in and out of the suit much easier since there is no need for the suit to tightly seal around the wrists. Instead, the wearer can slip into the attached gloves as if they were a loose-fitting coat sleeve.
Full-hand diving mitts can be sometimes useful in extreme environments such as ice diving.
Three-finger mitts are a midpoint between gloves and mittens. In the three-finger mitts, the fingers are arranged with the index finger in a separate pocket to the other three fingers. This provides slightly better hand-grasping dexterity while still permitting heavy insulation around the hands.
Separate (non integral) hoods are of two types: one which extends only to the base of the neck, and the other a standard wetsuit hood with a large flange. Hoods are never tucked into the neck seal as they would be tucked into a wetsuit, as this would compromise the watertight integrity of the seal. Some suits are designed with a second (non-watertight) collar around the neck seal, which allows the flange of a standard wetsuit hood to tuck in around the outside of the seal. This can keep the neck significantly warmer, since the seal itself provides little insulation.
Surface dry suits may have socks or ankle seals fitted. Socks are normally made from latex rubber or from a breathable material similar to the rest of the suit. An outer boot would normally be worn over these socks to prevent them from wear and the risk of puncture. The outer boot also provides more warmth than the thin layer of latex. A regular sock (eg. a woollen sock) would normally be worn inside the drysuit sock for comfort. Latex rubber ankle seals are sometimes fitted in place of socks and can allow better foot control of water skis and surfboards.
For a commercial environment where the option of interchangeable boots for different sizes of feet is desired, the legs of the dry suit can also be fitted with attachment rings (described below). Some commercial divers order their suits without boots and install rubber work boots such as those used by miners or firefighters.
Attachment rings allow separate neck seals, gloves, and (less commonly) boots to be joined to the suit with a watertight seal. In the older style, attachment ring system uses a support ring inside the suit and a clamping band outside the suit to tightly hold the suit and the separate hood/boot/glove together. They were also used with the neck seals of some old British frogman-type dry suits (see above).
The support ring can optionally be slipped into the sleeve of a regular dry suit that has wrist seals, to temporarily put watertight rubber gloves on the suit, or the wrist seals can be removed and the inner support ring is permanently attached inside the sleeve. The support ring may be a large one-piece unit that can be slipped over the head/hands/feet, or it may be split into halves that can be directly installed up close around the neck/wrists/ankles.
More recently, on both commercial and recreational suits, "quick-change" rings have become increasingly common. These are permanently glued to the suit and accessories, either during manufacture or as a retrofit. These systems form a watertight seal between the suit and components using soft rings on both pieces that comprise a series of interlocking channels, identical in principle to a common food storage bag. Quick-change rings allow a diver to easily replace a damaged seal on the surface with no tools or adhesives, or to change attachments depending on conditions–for example, choosing between dry gloves and standard wrist seals. Different manufacturers' ring systems are generally incompatible, so the diver must choose accessories that are designed for the ring system on his or her suit.
Exhaust valves can be automatic, operating as pressure relief valves, or manual, where the diver must actuate the valve to vent. Most modern suits have an adjustable exhaust on the shoulder which can be set to release at varying pressures, closed completely, (manual operation only) or operated manually at any setting. In most situations, the diver can leave the valve "open" throughout the dive so that it releases with a moderate amount of pressure, and needs only to raise his arm while in a vertical position in order to vent the suit. With this technique, the suit will vent as needed automatically as the diver ascends. Automatic vents are generally at the shoulder, and manual vents are at the wrist. Some older dry suits have no vents, but the diver must lift one of the wrist seals or the neck seal open to vent the dry suit. Surface dry suits do not normally have exhaust valves, but the wearer may vent excess air by crouching down, "hugging" his legs, and slipping a finger under the neck seal.
Because the air inside the suit is compressed as the diver descends, a modern diving dry suit also has a gas inflation valve, which lets the diver control the buoyancy of the suit by injecting gas from a diving cylinder to avoid the suit from being squeezed tightly and painfully onto the diver's body during descent. The sensation is similar to being pinched, but all over the body. Suit squeeze can also hinder the diver's movement and make swimming more difficult. Suit squeeze also compresses insulating garments and thus reduces thermal protection.
Some old-type frogman's dry suits had a small "jack cylinder" from which they could be inflated. Otherwise the frogman (who was using an oxygen rebreather, and so limited to about 30 feet (9.1 m) depth), had to put up with the suit squeeze.
Normally, the gas used for dry suit inflation for diving is air from the primary breathing cylinder. When divers breathe helium-based gas mixes such as trimix, they often avoid inflating their suits with the helium-based gas due to its high thermal conductivity. They often carry a separate cylinder for this purpose; generally it contains air, although sometimes argon, which has lower thermal conductivity, is used. Using argon increases the insulation value of a given suit by approximately 20%, without adding any additional bulk or weight. To gain the full benefit, the user must purge the suit of air several times before each dive. Argon cylinders should always be clearly marked so that a diver does not accidentally attach a breathing regulator; this is a potential hazard especially for technical divers, who often carry several independent cylinders and regulators. Breathing pure argon will result in rapid unconsciousness. Alternatively, some trimix divers inflate their suits from a decompression cylinder containing a nitrox blend (all such decompression blends, including pure oxygen, have essentially the same thermal conductivity as air).
In surface dry suits, the wearer normally never dives deeply underwater, and is not concerned about suit squeeze or neutral buoyancy, so there are no air valves on a surface dry suit.
Before putting on the dry suit, the male diver puts on a condom catheter, which is similar to a condom except that it is made of thicker material with a cuff or adhesive ring to prevent it from slipping off, and its end connects to a built-on drain tube. After putting it on, he attaches the end of the tube to a drain hose in the crotch of the suit. This drain hose leads to a vent opening just above a knee, and may also have a one-way valve (P-valve) to prevent ocean water from flowing back in if the hose gets disconnected. The female diver puts on an external catching device in the form of a wide-rimmed, low-profile, elongated cup. The rim is affixed onto the skin surrounding the labia with medical grade glue. The cup's drain hose connects to the drain hose.
Risks involved with the utilization of the P-valve can include urinary tract infection, pneumaturia and genital squeeze.
Divers intending to urinate in dry suits sometimes wear an adult diaper / nappy, which soaks up and retains the urine.
Dry suits are often worn for boating, especially sailing, and on personal water craft in the winter months. The primary uses are for protection from spray, and in case of accidental short-term immersion in cold water if the user falls overboard. These dry suits, which are only intended for temporary immersion, are less rugged than diving dry suits. They are usually made of a breathable membrane material to let sweat permeate, keeping the wearer dry and comfortable all day. Membrane type surface dry suits only keep the user dry, and have little thermal insulating properties. Most users will wear a thin thermal undersuit, or street clothes, for warmth; but wearing ordinary fabrics can be dangerous if the suit leaks in cold water because they will lose all insulating properties.
Dry suits are used for windsurfing, kitesurfing, kayaking, water skiing and other surface water sports where the user is frequently immersed in cold water. These suits are often made from very lightweight material for high flexibility. Membrane type suits are commonly used in the spring and autumn with moderate water temperatures, but Neoprene and hybrid dry suits for surface sports are preferred in cold water. These provide greater thermal protection in the event of a leak. The ability to swim for self-rescue in these types of suits is important to water sports users that do not use a boat. A neoprene bottom also is less likely to allow trapped air to collect in the legs, causing the wearer to tend to float head down in the water.
A warm undersuit made of synthetic fabric designed to wick moisture from sweat generated by physical exertion away from the user’s skin.
A dry suit made with a waterproof breathable membrane to let moisture permeate out of the suit.
A durable outer shell, designed to protect the dry suit, and to carry tools and survival gear. The outer shell may also be equipped with an inflatable bladder to give the wearer additional flotation and freeboard when immersed.
DONNING AND DIVING HAZARDS
Hyperthermia on deck before a dive
Latex is subject to rubber perishing, or "dry rot," where ozone normally present in the air deteriorates the material over time, regardless of use. A latex seal is generally expected to last 1–2 years. The useful life can be extended by coating the seals with a special protective compound, and (in suits with removable seals) detaching the seals when not in use and keeping them in airtight containers. They should also be kept in a cool, dark environment.
Latex seals are somewhat elastic, but can be easily torn if overstretched. Powdered talc can help the seals slide on easier.
Silicone seals are similar in strength and elasticity to latex, but do not perish in the same way.
Neoprene seals are a less popular alternative. They are less watertight than latex, but are much more resistant to dry-rot although they cannot be repaired as easily by the user.
Waterproof zippers need the two rows of open teeth to be reasonably lined up in front of the pull, for the zipper to slide without excessive effort. (Because of their construction waterproof zippers need two or three times as much pull as regular zippers to close.) It is best to hold the opening together as the zipper is pulled shut to prevent misalignment which can permanently damage the sealing edge.
Damage to the upper part of the suit can cause a sudden venting of the air, resulting in a total loss of thermal insulation in membrane suits and sudden uncontrolled descent, followed by water/chemicals seeping in.
Extra buoyancy risks related to excess air
Diving without a BCD
Dry suits are generally more easily damaged and prone to failure. The provided buoyancy is less reliable than buoyancy compensators, and dry suits can flood when punctured. Wrist and neck seals can vent easily without the diver wanting them to vent; a trivial problem during normal diving but more serious in an emergency or with an incapacitated diver. If the diver is over-weighted, the suit may contain additional air to offset the extra weight; migration of this air, particularly to the legs when the diver is not upright, can cause the diver to "invert" to a legs-up position that makes venting the drysuit difficult (see more on this problem, in the following section below).
The air bladders of buoyancy compensator are generally more robust and reliable than dry suits. They are designed for life-saving both at the surface and underwater. They provide buoyancy only at the top of the body, where it usefully keeps the diver upright. In addition, the vent valves of a BCD are more secure, requiring the diver to press a button to release buoyancy.
Accidental body-inversion hazards
The movement of a such a large bubble to the legs can be a problem for a number of reasons: It balloons the legs, and it may inflate thin rubber booties enough to cause fins to pop off; a diver without fins has more restricted ability to move and become upright, and also loses the ability to kick downward to maintain depth, so that the bubble expansion problem does not grow worse. Movement of gas into the legs and feet may also cause special difficulties in drysuits that have air exhaust values only at the shoulders or wrists, because the air in the legs and booties cannot be evacuated while the diver is inverted, and such a diver may be moving toward the surface, causing the problem of expanding air in the suit to grow worse with each meter of lost depth. (Some low-quality buoyancy control devices also cannot vent air, when inverted). If the diver is positively buoyant and rising, the buoyancy of the dry suit becomes uncontrollable after rising though a certain fraction of depth, and there is then an increased risk of a rapid ascent which grows more rapid, as the distance to the surface decrease. The final result of such a run-away inversion is a diver rising all the way to the surface, feet first, in an uncontrolled ascent that is too rapid for decompression safety.
When the suit is being used correctly, the bubble inside it is relatively small, and its movement is not important. The bubble may be large for a variety of reasons: if a diver has ascended without venting the suit; if the valve supplying gas to dry suit fails in the open position; or if the diver is over-weighted, and extra air has been added to the suit at some point to make the diver neutrally buoyant. The size of the bubble can be minimised by being correctly weighted and venting excess gas from the suit on ascent. Some divers ensure that the bubble remains at the top of their body by using the buoyancy compensator to counteract any excess weighting, keeping only the minimum gas necessary to avoid squeeze inside the drysuit.
The recommended solution in all such "inversion accidents," is for the wearer to bend at the knees and powerfully flap the arms to do a backward or forward roll to the upright position and then vent the suit, if needed, by manually opening the neck seal (sometimes called "burping the suit") by breaking the seal-neck contact with a finger.
It is not a problem for close-fitting neoprene suits, or hybrid suits with neoprene bottoms, which prevent air from easily moving into the legs of the suit. Wearers of baggy surface dry suits can mitigate the problem by venting out as much excess air as possible before entering the water. This is typically done by crouching down and leaning forward, wrapping the arms around the knees, and then having an assistant zip the suit shut while it is stretched out tightly. Excess air can also be "burped" out of the neck seal.
Gaiters and ankle weights
To read more about dry suits, please click on the following link: http://en.wikipedia.org/wiki/Dry_suit