Dry suit

U.S. Navy divers in contamination dry suits preparing to dive
Uses	Environmental protection of underwater divers, boaters and other people who may be immersed in water.
Inventor	Augustus Siebe (1837)[1]: Ch1
Related items	Diving suit, Wetsuit, Survival suit, Hazmat suit

A dry suit or drysuit provides the wearer with environmental protection by way of thermal insulation and exclusion of water,^[2][3][4][5] and is worn by divers, boaters, water sports enthusiasts, and others who work or play in or near cold or contaminated water. A dry suit normally protects the whole body except the head, hands, and possibly the feet. In hazmat configurations, however, all of these are covered as well.^[6]

The main difference between dry suits and wetsuits is that dry suits are designed to prevent water from 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 operational complexity and hazard 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 excessive buoyancy, which requires additional skills for safe use.^[7] Dry suits provide passive thermal protection: Undergarments are worn for thermal insulation against heat transfer to the environment and are chosen to suit expected conditions.^[7] When this is insufficient, active warming or cooling may be provided by chemical or electrically powered heating accessories.^[1]: Ch1

The essential components are the waterproof shell, the seals, and the watertight entry closure.^[1] A number of accessories are commonly fitted, particularly to dry suits used for diving, for safety, comfort and convenience of use. Gas inflation and exhaust equipment are generally used for diving applications, primarily for maintaining the thermal insulation of the undergarments, but also for buoyancy control and to prevent squeeze.^[1]

Function

The dry suit is a form of exposure suit, a garment worn to protect the user from adverse environmental conditions. The two most common purposes are to insulate the wearer against excessive heat loss, and to isolate the wearer from direct contact with a liquid environment during immersion or repeated multi-directional contact with bulk liquids or spray. Most often the liquid is water, usually without significant contaminants, but dry suits also have applications in isolation from hazardous materials and biological contaminants.^[7][6]

Most of the insulation function is provided by passive thermal protection in the form of garments worn under the dry suit, The suit itself has the primary function of keeping the insulating garments dry, and allowing them to be maintained at sufficient loft to provide adequate insulation by adding dry gas to the interior of the suit and releasing excess gas. Active heating systems may also be used but are less popular.^[1]: Ch2

Isolation of the wearer from contact with the environment for purposes other than thermal insulation usually requires the entire surface of the skin to be kept dry and uncontaminated by the ambient environment. This requires that the seal between the breathing apparatus and the suit is also reliably watertight, which is most effectively provided by sealing the suit to a helmet with redundant series exhaust valves, or a return of exhaled gas to the surface by hose, similar to a gas reclaim system, though there are applications where a lesser level of isolation is acceptable.^{[1]: Ch3 [6]: 109}

Dry suits should not leak, but once the suit is sealed, interior humidity rises to 100% and condensation will occur on cold surfaces such as the inside of the suit. A certain amount of dampness is inevitable and common on the inside of the suit after a dive, and is acceptable provided the diver remains warm. Flexing the wrists and large movements of the head may allow water to enter along raised or sunken tendons. This is normal, and to some extent can be avoided or reduced with practice. It can be prevented by attaching the gloves directly to the suit and by sealing the suit to the helmet.^[8]

Heat loss

There are two physiological aspects of heat loss of particular relevance to the diver: Cold shock response and hypothermia.

Cold shock response is the physiological response of organisms to sudden cold, especially cold water, and is a common cause of death from immersion in very cold water,^[9] such as by falling through thin ice. The immediate shock of the cold causes involuntary inhalation, which if underwater can result in drowning. The cold water can also cause heart attack due to vasoconstriction;^[10] the heart has to work harder to pump the same volume of blood throughout the body, and for people with heart disease, this additional workload can cause the heart to go into arrest. This effect is prevented or mitigated by almost any dry suit, as the cold water is kept from direct contact with most of the body and the immediate heat loss is reduced considerably. A person who survives the initial minute of trauma after falling into icy water can survive for at least thirty minutes before succumbing to hypothermia provided they don't drown. However, the ability to perform useful work like staying afloat declines substantially after ten minutes as the body protectively cuts off blood flow to "non-essential" muscles.^[9]

Hypothermia is reduced body temperature that happens when a body dissipates more heat than it absorbs and produces,^[11] and is a major limitation to swimming or diving in cold water.^[12] The reduction in finger dexterity due to pain or numbness decreases general safety and work capacity, which consequently increases the risk of other injuries.^[12][13] Body heat is lost much more quickly in water than in air, so water temperatures that would be quite reasonable as outdoor air temperatures can lead to hypothermia in inadequately protected divers, although it is not often the direct clinical cause of death.^[12] The effectiveness of a dry suit in preventing or delaying hypothermia depends on its insulating value.^[7]

There are two major routes for heat loss. Respiratory and through the skin. The mechanisms of respiratory heat loss are heating the inspired gas and humidifying the inspired gas by latent heat of evaporation. While they are major factors in diver compfort and safety, these are not influenced by the use of a dry suit. The loss of heat through the skin by radiation, conduction, and convection is the aspect which can be controlled by an exposure suit, and the one for which dry suits are effective and appropriate.^[14][7]

Skin will heat up gas and clothing inside a dry suit by radiation and conduction. Convection will transport heated gas within the suit, and may take it to places where it may be transferred through the suit shell more rapidly.^[14] Heat transfer by radiation occurs through a medium that is transparent to infrared radiation of the relevant wavelengths. This is mostly the gas, and the radiation paths are short, multiple, and with small temperature differences, so the effects are relatively small. Heat conduction is kinetic energy transfer by molecular or atomic collision. It has the more important role in heat transfer through a diving suit. Conduction occurs between the diver's skin and the gas and suit materials in contact with it, and through these materials to the shell, through the shell to the surrounding water, where it is rapidly removed by convection. Conduction heat loss is strongly influenced by thermal conductivity of the gas in the suit.^[14]

Convective heat transfer is the consequence of movement of heat carried by a gas or liquid from one place to another, where conduction can occur. It can considerably speed up heat transfer, so thermal protection of the undersuit is improved when it limits convection of the gas within the suit. Convective heat transfer in the suit is strongly influenced by the freedom of the gas in the suit to move around, which is increased when there are large gas spaces, and reduced when the gas is constrained by the loft of the fabric. There is also heat transfer within the suit by evaporation of moisture in contact with the skin, and condensation on the inner surface of the shell. This is reduced by wicking it away from the skin before it evaporates, and preventing condensate on the inside of the shell from wetting the inner layer of the undersuit.^{[citation needed]}

Essential components

The essential components include a shell of watertight material, sufficiently flexible to allow the wearer to function adequately, seals where parts of the body pass through the suit while in use, and a method of sealing the access opening while the suit is worn. An inflation valve with gas supply and dump valve are generally provided on dry suits used for diving, but were not standard on early models, and are not needed when the suit is sealed to the helmet and the helmet space is open to the interior of the suit, or for suits only used for surface activities.^[1]

Shell

The main part of the dry suit is a waterproof shell made from a membrane type material, closed cell foamed neoprene or a hybrid of both. Insulation may be provided in part by the suit shell, but is usually mainly provided by thermal insulation clothing worn under the suit, which relies to a large extent on trapped air for its insulating properties.^[7]

Membrane

Membrane dry suits are made from thin materials which have little thermal insulation. They are commonly made of stockinette fabric coated with vulcanized rubber, laminated layers of nylon and butyl rubber known as trilaminate, or Cordura proofed with an inner layer of polyurethane. With the exception of the rubber-coated stockinette, membrane dry suits typically do not stretch, so they need to be made slightly oversized and baggy to allow flexibility at the joints through the wearer's range of motion and to allow the hands and feet to pass through without difficulty. This makes membrane dry suits easy to put on and take off, provides a good range of motion for the wearer when correctly sized and sufficiently inflated, and makes them relatively comfortable to wear for long periods out of the water compared to a wetsuit or close-fitting neoprene dry suit, as the wearer does not have to pull against rubber elasticity to move or keep joints flexed.^{[1]: Ch4 [16]}

To stay warm in a membrane suit, the user must wear a thermally insulating undersuit, typically made from synthetic fiber, which is considered preferable to natural materials, since synthetic materials have better insulating properties when damp or wet from sweat, seepage, or a leak. A low capacity for water absorption, retention of loft under mild compression, and quick drying after use are also desirable characteristics.^[7]: 73

Reasonable care must be taken not to puncture or tear membrane dry suits, because buoyancy and insulation depend entirely on the air layer held 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.^[7]: 73

Membrane dry suits for surface use may also be made of a waterproof but breathable material like Gore-Tex to enable comfortable wear without excessive humidity and buildup of condensation. This function does not work underwater. Sailors and boaters who intend to stay out of the water may prefer this type of suit, but the fabric is less tolerant of rough usage, and may develop leaks more easily.^[17]

Membrane suits rely entirely on thermal undergarments for thermal insulation. The thermal undergarments rely on large volumes of trapped air for insulation, and any excess air trapped within the suit is not well constrained from migrating to the high points of the suit when diving. The loose fit necessary to allow reasonable freedom of movement and to make it possible to get in and out of the suit creates baggy air pockets where trapped air accumulates if it is not vented immediately, and some of these air pockets form in the parts of the suit where they are least easily vented by a diver trimmed for efficient horizontal swimming. This combination makes it necessary for the diver to be more vigilant and increases task loading in buoyancy control, and thereby increases risk of overinflation incidents and uncontrolled ascents. These risks are reduced by use of a suit which has the minimum excess volume, which in most cases requires precise custom fitting.^[16] The large and baggy standard diving suits had the option of lacing up the back of the legs to reduce suit volume in the place where it was most hazardous,^[18][19] but this feature is not available on more recent suits, and the nearest functional substitute is gaiters over the lower legs. Bagginess in the torso and arms is less problematic as excess gas in these areas is much easier to vent, and will usually do so automatically if the dump valve is set correctly.^{[1]: 45, 87}

Neoprene

Neoprene is a type of synthetic rubber which can be foamed during manufacture to a high proportion of tiny enclosed gas bubbles, forming a buoyant and thermally-insulating material, called "foamed neoprene", "foam-neoprene" or "expanded neoprene". Wetsuits are made from this material as it is a good insulator, waterproof, and is flexible enough for comfortable wear. The neoprene alone is very flexible and elastic, but not very resistant to tearing, so it is usually skinned with a layer of knitted fabric bonded to each side for strength and abrasion resistance. Foamed neoprene may be used for the shell of a drysuit, providing insulation in proportion to the thickness 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 foam, like a wet suit. Although foamed-neoprene dry suits provide some insulation, thermal under-suits are usually worn in cold water.^[1]: 55

Neoprene dry suits are generally 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 wetsuits, 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 undersuit. Foam-neoprene tends to shrink over the years as it loses gas from the foam and slowly becomes less flexible as it ages.^[1]: 56

An alternative is crushed or compressed foam neoprene, which is less susceptible to volume changes when under pressure. Crushed neoprene is foam neoprene which has been hydrostatically compressed so much that the gas bubbles have been mostly eliminated, this retains the elasticity of foamed neoprene which allows freedom of movement, but does not provide much insulation, and is functionally more like a membrane suit.^[1]: 57

Hybrid

Some suits marketed as hybrid suits combine the features of both types, with a membrane top attached to a neoprene bottom near the waist.^{[20][1]: 33} The neoprene part may also be configured as a "farmer-john" salopette that covers the torso as well as the legs, with membrane sleeves. This style is often used for surface water sports, especially in very cold water. The tighter fitting lower part lets the wearer kick while swimming, and the looser fitting top allows easy arm movement. A close-fitting neoprene torso covering provides additional self-rescue or survival time if the suit leaks.^{[citation needed]} Other manufacturers such as "Waterproof", use the term to refer to a membrane suit with a fitted liner of a relatively compression resistant porous 3-dimensional mesh, which creates a thin but resilient air space between the suit shell and the diver.^[21][22]

Seals

Seals, also known as gaskets,^[23] at the wrists and neck prevent water entering the suit by a close contact fit against the skin around the wrists and neck. The seals are not absolutely watertight, however, and the wearer may experience some seepage during use. The seals are typically made from latex rubber, foam neoprene,^[1]: Ch4 or silicone rubber.^[24] Latex seals are supple but easily damaged and deteriorate with exposure to oils, oxygen, and other materials, so they must be replaced periodically, every two years or more often. Latex also causes an allergic reaction in some users. Neoprene seals last longer and are non-allergenic, but, being less elastic, let more water enter because they do not seal as effectively as latex seals to the contours of wrist and neck. They are also typically glued and sewn together to form a tube, and may leak along that seam.^[1]: Ch4

A more recent innovation is the silicone seal, which is claimed to be as supple as latex, more flexible, yet far more durable. These are available as original equipment on some makes of dry suit. Silicone seals are hypoallergenic, but can not be glued to the suit, and must be attached using clip-on rings. The silicone seals are similar in mechanical strength to latex seals but do not deteriorate as rapidly from oxidation and chemical attack. They are initially relatively expensive, but can be replaced without tools by the user which reduces cost of replacement.^[24][25]

Waterproof entry

Modern dry suits have a watertight zipper for entry and exit. The original bronze-toothed version was developed by NASA to hold air inside space suits. This complex and special zipper is one of the most expensive parts of the suit. Heavy-duty, medium, and lightweight versions are made.^[1]: Ch4 A later design uses injection moulded plastic teeth, and these are lighter, more flexible and less costly.^[26] The zipper is commonly installed across the back of the shoulders, since this placement compromises overall flexibility the least, and usually puts the least stress on the zipper — but this design normally means the wearer requires assistance to close and open the zipper. The other common zipper placement is diagonally across the torso, which allows self-donning.^[1]: 59 Other designs place the zipper straight down the middle of the back (early Poseidon Unisuit), up one side of the front, around the back of the neck and partway back down the front (later model Poseidon Unisuit^[1]: 50) or on a wide tubular chest tunnel entry opening which is folded down and clipped round the waist after sealing the zip (some Typhoon suits). The waterproof-zipper is stiff, and cannot stretch at all, which can make it difficult for a user to get into and out of the suit.^[1]: 43 Dry suits may also be fitted with an extra waterproof "fly", "relief" or "convenience" zipper to let the user urinate when out of the water when the suit is worn for long periods.^[1]: 85

Before truly watertight zippers were invented, other methods of keeping the suit waterproof at the entry point were used, with the most common being a long rubber tunnel entry on the chest or the back, which would be folded shut, then rolled together from the sides and finally folded and clamped with a metal clip or tied with surgical rubber tubing. Sometimes the entry tunnel protruded through a non-watertight zipper, which would be closed over it to hold the roll in place in the pocket so formed.^[1]: 14

The alternatives to tunnel entry were neck entry and the two-piece suit. Neck entry suits were sealed by overlapping the neck opening and the hood over a grooved neck ring, and clamping with a large elastic O-ring. The two piece, or waist entry suits, were sealed by rolling or folding the overlapped rubber skirts of the jacket and trousers together and these were held in place by a separate rubber cummerbund or a ring and rail clamping system much like the neck seal system, but using a grooved rubber belt and elastic loop.^[1]: Ch1

Accessories

Thermal undersuits

Most dry suits do not provide sufficient thermal insulation without suitable undergarments. The type of undergarment selected will depend on the environmental conditions, type of dry suit and the planned activity. The purpose of the undergarment is to maintain the wearer in comfortable thermal balance, where the heat lost is balanced by the heat generated by the user. More insulation is needed for colder conditions and for less energetic activity.^{[1]: Ch2 [27]}

A balance of thermal comfort with freedom of movement, minimal variation in buoyancy with depth, and minimal effects on diver trim is one of the goals of undersuit selection for diving.^[27] For surface applications, thermal comfort with freedom of movement and minimum skin dampness from condensation is the target. Moisture management using wicking textiles is often used.

The principle of layered clothing can be used to provide a wider range of insulation possibilities from a relatively small range of underwear items, however this can only be done before entering the water. Most dry suit underwear insulates mainly by a trapped layer of gas in the garment, and this is largely lost if the gas is replaced by water in a flooded suit, so as an approximation, insulation is proportional to the combined thickness of the undergarments. The layering principle shows that the option of two layers of undergarment in two thicknesses allows three levels of insulation to be selected. Thin only, thick only, and both layers.^[1]: Ch2

Some materials have better insulating properties than others when wet, and will keep the diver warmer if the suit leaks or floods. The best dry suit undergarment is the thinnest material that will provide the required insulation, by trapping air in the smallest spaces. These will require less air in the suit and thus less excess buoyancy for which weighting will be required.^[1]: Ch2

The moisture given off by the human skin, even when not exercising and sweating, will condense against the inside of the dry suit, and the way this condensate is handled by the underwear material will influence the comfort of the diver. If the underwear soaks up this moisture it will feel cold and clammy, particularly if this layer is against the skin. Materials which wick the moisture away from the skin and do not soak up the condensate will be more comfortable.^[1] A thin polypropylene layer against the skin will keep moisture away from the skin, and may keep the main undersuit clean.^[8] Early thermal undersuits for drysuits were commonly made from wool, as it retains its insulating properties better when wet than most other natural fibres.^[28]: Ch2

The fit of the underwear should allow the same range of movement as the suit itself, and together should allow the wearer to bend, squat, kneel, climb a ladder, fin and reach all critical parts of equipment worn on the body. Underwear which is flexible and stretches, particularly at the joints, will allow the diver more freedom of movement, and is less likely to chafe, and for diving use, materials which resist compaction under light pressure will maintain a more even thickness in use, which will provide better insulation for the same overall volume.^[7]: 76

For cold-water use, especially diving under ice, the user will usually wear a thick undersuit. The thickness of undersuits varies and can be chosen by the wearer according to the water temperature. Thinsulate is one of the preferred fabrics for diving undersuits.^[29][30]

The hydrophobic qualities of Thinsulate help prevent water absorption which helps to maintain the insulating airspace even in the presence of free water.^[1] More recently, aerogel material is being added to conventional undergarments to increase the insulating properties of those garments.^[31] Polar fleece is a good insulator with good stretch, is lightweight, and dries quickly if it gets wet. It is also hypoallergenic and comfortable against the skin. Polyester liners can add to the insulation and will wick perspiration away from the skin. Cotton absorbs moisture and saturates easily, and will then rapidly conduct heat away from the body, so it is not used. Most dry-suit underwear is full length, either as a one piece or jacket and trousers, but a vest may be added for extra insulation on the torso, and a "Farmer John" salopette style trousers with jacket is flexible and puts extra insulation where it is most useful.^[1]

The dry suit manufacturer "Waterproof" has introduced an unusual style of suit liner for diving drysuits which is made of a compression resistant but light and flexible coarse nylon mesh, and attached to the inside of the trilaminate drysuit shell when in use, which maintains an air gap between the undersuit and the inner surface of the shell, and which keeps condensate that forms on the inside of the shell from contact with the undersuit, so the undersuit is more likely to remain dry.^[32]

Neoprene dry suits are made from a foam-rubber sheet containing tiny air bubbles, which provide insulation by themselves, and can eliminate the need for an under-suit, or reduce the thickness needed for the under-suit fabric, but the bubbles in the neoprene are compressed and the insulation of the suit decreases with depth in the same way as for a wetsuit.^[7]: 55 Crushed neoprene provides the flexibility of neoprene with the consistent buoyancy and insulation of membrane suits, but is heavy like other neoprene suits and provides less insulation in shallow water than regular foamed neoprene.^{[7]: 57 [16]} A neoprene wet suit can also be worn under a membrane dry suit for insulation and extra protection against condensation and leaks, but it will compress with depth, as will any flexible closed cell material.

Suspenders

Some dry suits are provided with internally attached suspenders (British English: braces), which when hooked over the shoulders, will hold the trouser section up while the top part of the suit has not been fully dressed into by the diver, this is also convenient if the suit is partly removed between dives for comfort. The suspenders also help to keep the trousers fully lifted if the torso of a membrane suit is a little long to provide enough space for the diver to bend the torso comfortably when in use. If the crotch hangs too low it encumbers the legs when finning, and increases the risk of the feet pulling out of the boots in an inversion.^[1]: Ch4

Hoods

The dry suit may also have an integral hood, which seals water out around the wearer's face, and helps keep the wearer's head warm. The integral hood is often latex rubber that fits tightly around the head, but can also be made mainly from neoprene or membrane to allow an insulating cap to be worn under the hood. Care must be taken to avoid the hood making an airtight seal around either of the ears, as this could cause an eardrum bursting outwards at depth.^[1]: 106 Separate hoods are generally neoprene wetsuit hoods with a flare at the bottom opening, worn over the neck seal. Some suits are made with an external "warm neck collar" around the base of the neck seal, which allows the flare of the hood to tuck in over the outside of the seal and under the collar. This can keep the neck significantly warmer, since the seal itself provides little insulation.^[1]: Ch9

Helmets

To provide more protection to the head against impact, to secure the airway, to fully isolate the diver from the water, and to permit easy communication with the surface and between divers, a rigid metal or fibre-reinforced plastic diving helmet may be worn with the dry suit. This can be separate from the dry suit with its own watertight neck seal, or it can be clamped onto a neck ring attached to the suit, so that air can flow between the helmet and the suit.^[6]

Boots or socks

Most commercial diving dry suits have heavy duty integral boots. Sport diving suits may have lightweight integral boots or soft neoprene booties. Rock boots or heavy working boots may also be worn over integral socks of latex or neoprene or the same material as the rest of the suit. Boots which are stiff at the ankle make finning inefficient and are unsuitable for many diving applications where mobility is important. If the suit will be used by a diver who needs to fin efficiently on some dives and to walk on sharp surfaces on other dives, it is more effective to wear boots suited to the dive over a dry suit with integral socks.^{[7]: 49 [1]: 44}

Latex rubber ankle seals are sometimes fitted in place of socks and can allow better foot control of water skis and surfboards.^[1]: 55 Survival suits may have neoprene socks of the same material as the suit, with tougher soles and ankle ties to keep them on the feet, as the "one-size fits all" socks must be too big for most users if they are to accommodate the few with larger feet.^[33][34]

Gloves, mitts, and three-finger mitts

Dry suits may have wrist seals, permanently attached gloves or mitts, or removable dry gloves connected by attachment rings.^[1]: 84

Neoprene wetsuit gloves are pulled over the top of wrist seals. They are wet gloves and vary considerably in effectiveness depending on construction and fit. As they are not watertight they do not fail catastrophically when damaged, and are reasonably tough.^[8]

Permanently attached gloves or mitts are unusual, It is more common for them to be connected by attachment rings. Either way, the absence of a wrist seal makes getting in and out of the suit much easier since there is no need for the suit to tightly seal around the wrists. It may be necessary to use a wrist strap to prevent loose gloves pulling off the hands when filled with air. Dry gloves can also be fitted over a wrist seal, which prevents leakage into the sleeves if the gloves are penetrated.^[6]: 81 Rubber or rubber coated stretch fabric dry gloves are the most effective at insulation while they remain dry inside, Insulation is provided by liner gloves worn underneath, which may be chosen to suit insulation and dexterity requirements.^[8]

Full-hand diving mitts can be sometimes useful in extreme environments such as ice diving, but significantly reduce dexterity and grip.^[1]: 84 Dry gloves and mitts usually allow a dry insulating glove to be worn underneath.^[6]: 82

Three-finger mitts are a compromise between gloves and full 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.^[1]: 84

Attachment rings

Attachment rings allow separate neck seals, gloves, and (less commonly) boots to be clipped to the suit with a watertight seal. On both commercial and recreational suits, "quick-change" rings have become common. These are glued to the suit, either during manufacture or as a retrofit. These systems form a watertight seal between the suit and components. 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 may be incompatible.^[1]: 41

Some styles of cuff ring allow dry gloves to be clipped on over a wrist seal. A seal breaker strand is worn under the cuff seal to allow the interior of the glove to equalise with the sleeve of the dry suit. If the glove is damaged underwater, the strand can be removed to prevent further water leakage into the suit.^[35]

Suit inflation

Dry suits for diving are usually equipped with an inflation valve (or inlet valve) and at least one exhaust valve (or dump valve, or outlet valve).^[1]: Ch5 Survival suits and other dry suits designed for wear on the surface have no inflation or dump valves as suit squeeze and achieving neutral buoyancy are not relevant.The inflation valve allows the diver to compensate for gas compression in the suit on descent. Suit gas compression squeezes the suit uncomfortably onto the diver's body, especially where the suit folds, it hinders the diver's freedom of movement, reduces thermal insulation through compression of insulating garments and interferes with buoyancy control.^[1]: Ch5 Environmentally sealed suits, which are sealed to the helmet, automatically equalise from the breathing gas, and will also inflate from the breathing gas if inverted.^[1]: Ch3

Suit inflation gas supply

Compensating gas is supplied from a breathing gas cylinder, a small, dedicated suit inflation cylinder, or the umbilical of a surface-supplied diver. Normally, the gas used for dry suit inflation on scuba is air from the primary breathing cylinder. Helium-based gas mixes such as trimix or heliox are avoided for suit inflation because of helium's high thermal conductivity.^[36] Nitrox blends from a decompression cylinder have essentially the same thermal conductivity as air but oxygen rich mixes introduce a fire hazard when out of the water. Using a small (1-2 litre), dedicated cylinder for suit inflation avoids these complications; usually this will contain air but argon may be used instead. Argon has a low thermal conductivity, which improves insulation by approximately 20% compared to air,^{[1]: 24 [14][8]} without adding any further bulk or weight. However, the accidental breathing of pure argon results in rapid unconsciousness and probable death. Consequently, argon cylinders must be clearly marked to prevent the accidental attachment of a breathing regulator or have valves that cannot accept a breathing regulator. To gain the full benefit of argon the suit must be flushed with argon before the dive to remove the air.^[37][38]

Inflation valve

An inflation valve is fitted to diving dry suits to admit gas to compensate for compression during descent. This is not necessary when the suit is sealed directly to a diving helmet, as the demand valve will automatically feed gas into the suit if the internal pressure difference drops. The spring-loaded push-button inflation valve is usually mounted over the chest for easy access, and is manually operated by the diver during descent to maintain the loft of the undergarments for insulation and to prevent discomfort from suit squeeze. Descent rate may also be adjusted by controlling suit volume and thereby buoyancy. Gas is supplied to the valve through a low-pressure hose, which can be connected and disconnected under pressure and underwater .^[1]: Ch5

Inflation hose

There are two types of low-pressure hose connections commonly used for suit inflation. These are the standard Seatec style quick release coupler, fitted with an internal Schrader valve, as also used on most diving buoyancy compensators, and the CEJN connector which allows a higher flow rate due to a larger bore through the non-return valve in the connector. This valve can allow a dangerously fast inflation rate if it jams open, and is also more likely to free-flow when disconnected. These hose connectors use incompatible valve fittings, but it is usually possible to swap the fitting on the inflator valve to accept the alternative hose end fitting. Both types of BCD and dry suit low pressure inflator hoses are supplied with a standard fitting for connection to a scuba regulator first stage low-pressure port.^{[39][1]: Ch5}

Exhaust valves

The exhaust valve (or dump valve, often an auto-dump valve) allows the diver to vent expanding gas from the suit during ascent to maintain buoyancy control in the same way that a buoyancy compensator must be vented during ascent to avoid an uncontrolled (or runaway) buoyant ascent, missed decompression stops, decompression sickness, arterial gas embolism or pulmonary barotrauma. Configurations may vary but adjustable over-pressure automatic vents (auto-dump valves) are generally on the sleeve at the left shoulder, clear of the harness or buoyancy compensator, and non-adjustable over-pressure vents at the wrist, where they can be raised quicklyto dump, and occasionally at the ankle, to automatically dump in the event of an inversion. Adjustable valves can be pre-set and in most situations can be left at this setting throughout the dive, but may be closed after surfacing to retain more gas,^[40][41][1]

Environmentally sealed suits used for diving in contaminated water have a watertight seal to the helmet, rely on the helmet exhaust valve to release air from the suit, and may not have a separate exhaust valve on the suit itself. This is common for free-flow helmets and was part of the standard diving dress system. Older, now obsolete, dry suits had no dedicated vents; venting was achieved by raising an arm and lifting one of the wrist seals or placing a finger in the neck seal. Surface-use dry suits do not normally have exhaust valves, but the wearer may vent excess air by crouching down and hugging the legs while slipping a finger under the neck seal.^[1]: Ch1

During ascent, the diver has several things to monitor and do, so an adjustable automatic exhaust valve which provides hands-free operation helps reduce this task loading.^[41]

Zipper and seal protection

Some suits are provided with a flap which can be closed over the outside of the zipper to protect it from being damaged by contact with the diver's equipment or the environment. these flaps may be held in place by velcro or a non-watertight outer zipper. These flaps are almost always fitted to zippers fitted diagonally across the front of the suit, and less often to rear entry cross shoulder zippers.^{[1]: 105 [23]}

Cuff and collar extensions to the shell may be fitted to protect the seals from abrasion and tears. This is particularly useful on suits used for activities like rescue, where the environment may be rough on the suit.^[23]

The P-valve

For commercial divers or technical divers who may spend many hours in a dry suit underwater, it is not practical to have to climb back on board the ship in order to open a waterproof relief zipper and urinate. The P-valve is a urinal built into the suit, which enables a diver to urinate at any time without having to get out of the water, while keeping him or her dry and clean inside the suit. Risks involved with the use of the P-valve can include urinary tract infection, pneumaturia and genital squeeze.^[42] Divers expecting the need to urinate in dry suits can also use an adult diaper / nappy, which soaks up and retains the urine.^[7][42] Watertight relief zippers may be fitted which allow urination when out of the water without removing the suit.^[1]: Ch7 but these are a potential source of leaks and an additional expense.^[8]

Cargo pocketsedit

Pockets are a convenient storage for small items of equipment and tools that may be needed on a dive, or on surface dry suits, during work. They are often used by scuba divers who use back inflation buoyancy control devices without integral pockets, and are often simply glued to the suit in the position chosen by the diver. Various styles and capacities are used. The usual positions are on the thighs. Forward position is more ambidextrously accessible, but can make boarding a small boat over the gunwale difficult or impossible, the sides of the thighs is more streamlined and better for boat entry, but makes it difficult to reach into the pocket with the opposite hand. Chest pockets are also sometimes used.^[1]: Ch7 Pockets may alternatively be mounted on shorts, a tunic, or protective overalls worn over the dry suit, or be integral parts of the buoyancy compensator. They usually cause additional drag underwater, and should drain rapidly while climbing out of the water.^[8][23]

"Bio-seals"edit

To reduce the contact with latex seals in divers with a latex allergy, a soft elastomer band called a "Bio-seal" can be worn under the latex contact area. These may also reduce friction with the seal and improve watertightness.^[43]

Active heatingedit

For applications where passive heating is insufficient, active heating can be used. One of the earliest systems was the tube suit, a set of underwear with a complicated labyrinth of tubes which carried heated water supplied from the surface or the lockout submersible through an additional hose in the diver's umbilical.^[1] Other active heating systems use electrical heating elements in an undersuit layer, or internal pockets containing hot-packs, sealed plastic bags containing materials which emit latent heat during a phase change.^[1]: 23

Associated equipmentedit

Some equipment may require modification to suit use with a dry suit. This is particularly relevant for weighting systems and buoyancy control devices.^[8]

Weighting systemsedit

Zdroj:https://en.wikipedia.org?pojem=Dry_suit
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