Dry suit
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A dry suit (or drysuit) provides thermal insulation 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. They are typically needed where the water temperature is between -2 and 15°C (28 to 60°F). The dry suit protects the whole human body, except the head, hands, and possibly the feet. It differs from a wetsuit because it is waterproof, and does not allow water to seep in. Dry suits with an integral helmet, boots, and gloves may also be used for personal protection when working in and around hazardous liquids.
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[edit] Parts of a dry suit
[edit] Required
[edit] Shell
The main part of the dry suit is a waterproof shell, made from either a membrane type material, Neoprene foam rubber, or a hybrid of both.
[edit] Membrane
These are made from thin materials, with a consequent poor thermal insulation. Vulcanised rubber, or laminated layers of nylon, butyl rubber and nylon are commonly used. Membrane drysuits typically do not stretch at all, and so need to be made oversize and baggy to permit flexibility at the joints. This makes membrane suits easy to put on and get off, and comfortable to wear for long periods.
To stay warm in a membrane suit, the user must wear an insulating undersuit typicaly made with cotton or polyester fiber batting. Polyester and other synthetics are preferred over cotton since they have better insulating properties when wet from sweat, seepage, or a leak.
Membrane suits can be unreliable because the suit’s buoyancy and insulation depend completely on the gas pockets in the undersuit. The suit material itself offers almost no buoyancy or insulation by itself, and if the suit is compromised, water can completely soak the undersuit, and all buoyancy and insulation is lost.
In warmer waters, some divers are able to wear a membrane drysuit without an undersuit. Surface watersports users may wear their street-clothes inside. Some users wear a wetsuit under the dry suit instead, which also provides additional warmth & safety if the dry suit leaks.
Membrane drysuits may also be constructed with a waterproof and breathable material to enable comfortable wear when of the water for long periods of time. This type of suit is preferred by sailors and boaters who intend to stay out of the water.
[edit] Neoprene
Neoprene is a closed cell foam synthetic rubber, containing millions of tiny air bubbles. These form a buoyant and thermally insulating material that make a neoprene drysuit safer to wear than membrane dry suits. If torn or punctured, a neoprene suit still retains the insulation and buoyancy of the air bubbles when flooded. Being made of a fairly rigid heavy material, they are difficult to get on and off, and their buoyancy and thermal protection decreases with depth as the air bubbles in the Neoprene are compressed. Neoprene also tends to shrink over the years as it outgases and slowly becomes more rigid. An alternative is crushed Neoprene, which is less susceptible to volume changes when under pressure and shrinks less. Neoprene wetsuits fitted with neck, wrist, and ankle seals are also known as semi-dry suits, but the seals on these suits only reduce cold water seepage, so the interior of the suit still gets wet.
[edit] Hybrid
These combine the features of both types, with a membrane top attached to a neoprene bottom near the waist. The neoprene portion is usually configured as a sleeve-less "farmer-john" that covers the torso as well. This style is often used for surface water sports, especially in very cold water. The tight fitting lower allows the wearer to kick while swimming, while the loose fitting top allows easy arm movement. The torso covering also provides additional self-rescue or survival time if the suit leaks.
[edit] Seals
Seals at the wrists and neck prevent water entering the suit. Even so, the user will be damp after a period of time in a drysuit due to sweat and condensation. The seals are either made from latex rubber or Neoprene. Latex seals are supple but easily damaged, and must be removed from the suit and replaced at intervals as short as two years. Neoprene seals last longer, but let more water enter because, being stiffer, they do not seal effectivly in the contours of the wrist and neck. They are also typically sewn together to form a ring, and can leak along the seam.
[edit] Waterproof Entry
Modern dry suits have a waterproof zipper for entry and exit which was originally developed by NASA to hold air inside astronaut space suits. The zipper is commonly installed across the back of the shoulders, but can also be found diagonally across the front of the torso, on the side, or straight down the middle of the front or back.
There are many zipper arrangements in use because the 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 allow the suit to swing open with a flap or hinge point.
Dry suits may also be fitted with an extra waterproof zipper "fly" to allow the user attend to physiological needs when the suit is worn for long periods. Some snug-fitting suits may also use wrap-around expansion zippers that allow the suit to expand or contract to better fit different size people.
Before the invention of waterproof zips, other methods 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. Another type was 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. At least one make of old-type British frogman's drysuit 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.
[edit] Optional
[edit] Thermal Undersuits
For cold-water use, especially diving under ice sheets, the user will usually wear a thick Undersuit in a membrane dry suit. The thicknesses of undersuits vary and can be chosen by the diver according the water temperature. Neoprene dry suits are made from a foam-rubber sheet containing tiny air bubbles, which provide insulation by themselves and generally eliminates the need for an undersuit. A neoprene wetsuit can also be worn under a membrane dry suit for extra protection against condensation and leaks.
[edit] Gloves, Mitts, and 3-Finger Mitts
Drysuits can optionally have wrist seals, permanently attached gloves/mitts, or a third option known as the attachment ring (described below).
If it's 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 diver can just 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 like the science-fiction Vulcan salute. This provides slightly better hand-grasping dexterity while still permitting heavy insulation around the hands.
[edit] Hoods
The dry suit may also have an integrated hood, which seals water out around the diver's face, and helps keep the diver's head warm. The integrated hood is often latex rubber that fits tightly around the head, but can also be made from neoprene or membrane to allow an insulating cap to be worn under the hood. Separate (non integral) neoprene hoods for use with a dry suit are different from wetsuit hoods, because they cannot be tucked inside the suit at the collar, as this would compromise the neck seal.
[edit] Helmets
When a diver needs to be underwater for long periods of time day after day, a snug-fitting elastic hood can cause uncomfortable pressure sores on the ears, face, and jaw. To alleviate this and to permit easy surface communication, a hard metal or plastic diving helmet may be worn with the drysuit. This can be separate from the drysuit with its own watertight neckseal, or it can be permanently attached with a neckring, and air from the helmet can enter into the suit.
[edit] Boots
Most commercial diving dry suits have heavy built-in boots. Sport diving suits may have boots or thin sheet-rubber booties, while surface dry suits may have booties or ankle seals to allow better foot control of skis and boards. Surface dry suits may be used with separate non-waterproof neoprene booties for foot warmth, and aqua-shoes for protection while using personal watercraft.
For a commercial environment where the option of interchangable boots for different sizes of feet is desired, the legs of the dry suit can also be outfitted with attachment rings (described below).
[edit] Weight boots
For commercial drysuit divers who must work on the ocean bottom or on an underwater platform (such as under an oil rig), the drysuit may be fitted with heavy metal boots to keep the diver firmly weighted down. This allows the suit to be comfortably inflated like a balloon as the diver works, without concern that the diver may float uncontrollably to the surface. For these divers they cannot swim freely, and may need to ride an underwater cable elevator down to the work area.
[edit] Attachment Rings
These are typically only seen on professional and commercial diving suits. They allow separate neck seals, gloves, and boots to be joined to the suit with a watertight seal. The 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.
The support ring can optionally be slipped into the sleeve of a regular drysuit 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 two small halves that can be directly installed up close around the neck/wrists/ankles.
Attachment rings permit a commercial diver to change their suit to best perform the task at hand. Wrist seals can still be used with an attachment ring suit; they are simply mounted onto the ring like a pair of gloves.
[edit] Valves
A typical diving drysuit has an air exhaust valve, which lets the diver vent off higher pressure gas from the suit during the ascent. This is necessary because when the divers ascends, the air in the suit expands, balloons out the suit, and hinders movement. The air in a ballooned suit can overcome the diver's neutral buoyancy, and can cause a sudden uncontrolled ascent to the surface, resulting in decompression sickness and loss of consciousness if the diver does not immediately descend and undergo decompression.
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. Some older drysuits have no vents, but the diver must pull one of the wrist or neck seals open to vent the drysuit. Surface dry suits are not inflated, and must be vented to remove most of the gas inside.
Because the air inside the suit is compressed as the diver descends, a modern diving drysuit 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.
Some old-type frogman's drysuits had a small "jack cylinder" to be inflated from, or the frogman (who was using an oxygen rebreather and so limited to about 30 feet (10 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. Pure argon cannot be used as a breathing gas. Alternatively, some trimix divers inflate their suits from a decompression cylinder containing a nitrox blend.
In surface dry suits, the wearer normally never dives deeply underwater, and is not concerned about neutral buoyancy, so there are no air valves on a surface drysuit.
[edit] The P-Valve
For commercial divers that may spend many hours in a suit underwater, it is not practical to have to climb back onboard the ship in order to open a waterproof relief zipper and urinate. The P-valve is essentially a urinal that is built into the suit, which allows a diver to relieve themselves at any time without having to get out of the water, and while also still keeping the diver dry and clean inside the suit.
Before putting on the drysuit, the diver puts on a condom catheter, which is similar in design to a condom except built more heavily, with a cuff to prevent slipping off, and with a drain tube molded into the end. After putting it on, the diver attaches the end of the tube to a drain hose in the crotch of the suit. The drain hose leads to a vent opening just above the knee, and may also have a one-way valve to prevent ocean water from flowing back in if the hose were to become disconnected.
[edit] Uses of dry suits
[edit] Surface
[edit] Boating
Dry suits are often worn for boating, especially sailing, and with 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. Dry suits only intended for temporary immersion protection are less rugged than diving dry suits. They are usually made of a breathable membrane material to allow sweat to 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.
[edit] Water Sports
Dry suits are used for windsurfing, kitesurfing, 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 fall 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.
[edit] Working
Crew members who must work on the decks of commercial ships wear a type of dry suit also known as an immersion survival work suit. Single engine aircraft ferry pilots flying between North America and Europe, and helicopter pilots that must fly over the open ocean, must wear a survival suit in the cockpit, so they can continue to fly the aircraft, then exit immediately if the aircraft is ditched in cold water after an engine failure. These suits are also used on shore when working on docks, bridges, or other areas where cold water immersion is a safety risk. They are usually a three-part system consisting of:
- 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 allow moisture to 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.
[edit] Survival
Immersion survival suits are dry suits carried for use by ship and aircraft crew who will be immersed in cold water if the craft must be abandoned. Unlike immersion survival work suits, these are not intended to be worn all the time, and are only to be used in an energency. Survival suits will typically be a one-piece design made of fire-retardant neoprene, and optimized with quick donning features.
[edit] Rescue
Dry suits are also worn by rescue personnel who must enter, or may accidentally enter, cold water. Features of dry suits designed for rescue may be a hybrid of the immersion survival and work suits, since the wearer is not expected to be working in the suit for an extended time. They may also be optimized for a specific task such as ice rescue, or helicopter rescue swimmer.
[edit] Underwater
[edit] Sport Diving
These drysuits are made in both membrane and neoprene, and primarily differ from surface drysuits in that they have inflation and deflation air valves to maintain neutral buoyancy, and are slightly more durable.
[edit] Commercial/Military Diving
These tend to be much heavier and even more durable than sport drysuits because they will endure a harsh and abrasive environment, especially if being used for heavy labor work such as underwater welding. Some commercial drysuits are rated for hazardous-environment diving, and when combined with a full-face helmet can completely isolate and protect the diver from hazardous environments such as sewage pits and chemical storage tanks.
[edit] Drysuit Donning and Diving Hazards
Drysuits pose their own unique problems compared to wetsuit diving, due to the complex construction and since the diver needs to constantly manage and adjust the air volume inside the suit.
[edit] Seal Damage
- Latex seals are easily pierced by sharp objects. Gripping the seal with long fingernails to pull it on or off can cut through the material, while long toenails can damage thin rubber booties when the foot is pushed inside tight-fitting fins.
- Latex seals are elastic to a point, but can be easily torn if overstretched. Powdered talc can help the seals slide on more easily.
[edit] Zipper Damage
Waterproof zippers require the two rows of open teeth to be reasonably lined up in front of the pull, for the zipper to slide easily. It is best to hold the opening together as the zipper is pulled shut to prevent misalignment that can permanently damage the sealing edge. For this reason zippers across the back of the shoulders or down the back of the suit are almost impossible for one person to close properly by themselves, and yanking harder to try and force the unreachable zipper closed often just results in misalignment and permanent zipper damage.
[edit] Suit Damage
- Damage to the lower part of the suit can cause a sudden inrush of very cold water for winter divers, or an inrush of hazardous chemicals for commercial inspection divers.
- Damage to the upper part of the suit can cause a sudden outrush of the air, resulting in a total loss of thermal insulation in membrane suits and sudden uncontrolled descent, followed by water/chemicals seeping in.
[edit] Diving Without a BCD
Since the drysuit can contain air, some divers do without the usual buoancy control vest that is commonly worn by wetsuit divers. Although this can be done, it is against the manufacturer's recommendations and poses its own unique hazards, which are not plainly obvious until the situation is already getting out of control. This non-BCD methodology is more common among divers using neoprene drysuits.
- During descent, air must be added to maintain constant volume (prevent suit squeeze) and thus loss of neutral buoyancy, and potential uncontrolled descent.
- During ascent, air must be remove to prevent ballooning, loss of neutral buoyancy, and potential uncontrolled ascent. A drysuit can be equipped with an automatic spring-loaded exhaust valve, which can assist with this problem.
[edit] Inversion Hazards
- Drysuit divers wearing loose baggy suits need to keep their legs at level or below their waist. When inverted with the legs above the waist, all the air in the suit can suddenly rush up into the legs, ballooning them out. Thin rubber booties can also inflate and cause the fins to pop off, losing them in the water.
- Surface drysuit users can face the exact same problem, when they do not wear a Coast-Guard approved life vest either under or over their drysuit. It is not so much a problem for close fitting neoprene suits, but wearers of baggy surface drysuits can help alleviate the problem by venting out as much excess air as possible before entering the water. This is done by crouching down and leaning forward, wrapping their arms around their knees, and then zipping the suit shut while the suit is stretched out tightly.
For an inexperienced diver, ballooning of the legs can cause a loss of control that may to lead to panic and an inability to flip upright again. The solution is not difficult: bend the knees, reach up and grab the legs, and do a somersault to flip upright again.
For surface drysuit users, the situation can be much more critical if no one is nearby to assist, since they may be held upside down and unable to breath, and may also have water run down into their nose while inverted.
Some baggy suits have elastic "gaiters" that can be pulled snug around the legs to help prevent this inversion event from happening, while many surface drysuits are of the combo variety with close-fitting neoprene pants and a loose top, to prevent air from easily moving into the legs of the suit.
