Dry suit

Dry suit

U.S. Navy divers in contamination dry suits preparing to dive
Uses	Environmental protection of underwater divers
Related items	Diving suit, Wetsuit

A dry suit or drysuit provides the wearer with environmental protection by way of thermal insulation and exclusion of water, 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.

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 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.

Dry suits provide passive thermal protection: They insulate against heat transfer to the environment. When this is insufficient, active warming or cooling may be provided, usually by a hot-water suit, which is a wetsuit with a supply of heated or chilled water from the surface, but it is also possible to provide chemical or electrically powered heating accessories to dry suits.

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.

Components

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. Insulation may be provided in part by the suit shell, but is usually largely provided by thermal insulation clothing worn under the suit, which relies to a large extent on trapped air for its insulating properties. An inflation valve with gas supply and dump valve are generally provided, but were not standard on early models.

Shell

The main part of the dry suit is a waterproof shell made from a membrane type material, foamed neoprene or a hybrid of both.

Membrane

Membrane drysuit in icy water

Membrane dry suits are made from thin materials which have little thermal insulation. To stay warm in a membrane suit, the wearer must wear an insulating undersuit, today typically made with polyester or other synthetic fiber 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.

Neoprene

The neck seal, the zip, the inflator, a wrist seal, and the manual cuff vent of a neoprene dry suit

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.

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. The neoprene part is usually configured as a sleeveless "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 part lets the wearer kick while swimming, and the loose fitting top allows easy arm movement. The torso covering also provides additional self-rescue or survival time if the suit leaks. Other manufacturers such as "Waterproof", use the term to refer to a membrane suit with integral 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.

Seals

Silicone neck seal attached with clamping ring - view inside the suit

Silicone dry suit cuff seals with clip-on clamping rings: above - assembled, below - components

Seals 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 wearer will also get damp due to sweat and condensation. The seals are typically made from latex rubber or foam neoprene, but are also available in silicone rubber. 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.

A recent innovation is the silicone seal, which is claimed to be as supple as latex, more flexible, yet far more durable. These are now 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.

Waterproof entry

Shoulder (rear entry) zipper

Plastic watertight dry suit zipper: tooth and seal edge detail - the watertight seal is made by pressing together the continuous ridge along the middle of the teeth when the zipper is closed.

Front entry zipper

Watertight and airtight dry suit zipper made by TIZIP, Germany: Detail of closed teeth showing interlock above and (not visible) below the seal edge.

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. A later design uses injection moulded plastic teeth, and these are lighter, more flexible and less costly. 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 to close and open the zipper. The other common zipper placement is diagonally across the torso, which allows self-donning. 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) or on a wide tubular chest 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. 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.

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 entry tunnel which would be folded 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 front of the torso. The Louisiana-based dry suit company Aquala makes a "historical" diving suit of that kind. Another type of entry featured a rubber tunnel that protruded through a non-watertight zipper. The tunnel would be rolled shut and the zipper closed to hold the roll in place.

Accessories

Thermal undersuits

Most drysuits do not provide sufficient insulation without suitable undergarments. The type of undergarment selected will depend on the water temperature, type of suit and dive plan. The purpose of the undergarment is to maintain the diver in comfortable thermal balance, where the heat lost is balanced by the heat generated by the diver. More insulation is needed for colder conditions and for less energetic diving activity.

The principle of layering 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 by a trapped layer of air in the garment, and this is largely lost if the air is replaced by water in a flooded suit, so as a general rule, 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.

Some materials have better insulating properties than other 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.

The moisture given off by the human body, 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. Early thermal undersuits for drysuits were commonly made from wool, as it retains its insulating properties better when wet than most other natural fibres.

The fit of the underwear should allow the same range of movement as the suit itself, and together should allow the diver to bend, squat, kneel, climb a ladder, fin and reach all critical parts of the diving equipment. 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 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.

For cold-water use, especially diving under ice, the user will usually wear a thick undersuit in a membrane dry suit. 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 undersuits.

The hydrophobic qualities of Thinsulate help prevent water absorption which helps to maintain the insulating airspace even in the presence of free water. More recently, aerogel material is being added to conventional undergarments to increase the insulating properties of those garments. 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 is not recommended as it absorbs moisture and saturates easily, and will then rapidly conduct heat away from the body. 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" style trousers with jacket is flexible and puts extra insulation where it is most useful.

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 greatly reduce the thickness needed for the under-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. Crushed neoprene provides the flexibility of neoprene with the consistent buoyancy and insulation of membrane suits. A neoprene wet suit can also be worn under a membrane dry suit for extra protection against condensation and leaks, but it will compress with depth as will any closed cell suit.

Undersuits used for surface watersports are generally thinner than those used for diving, and are commonly made from fleece 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 when the top part of the suit has not yet 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.

Gloves, mitts, and three-finger mitts

Dry glove with attachment ring and liner

Dry suits may have wrist seals, permanently attached gloves or mitts, or removable dry gloves connected by attachment rings.

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.

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

Three-finger mitts are a compromise 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.

Hoods

The dry suit may also have an integrated hood, which seals water out around the wearer's face, and helps keep the wearer'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. 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.

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) "warm neck 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.

Helmets

To provide more protection to the head against impact, to secure the airway, 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.

Boots

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 neoprene or latex socks. 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.

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 or shoe would normally be worn over these socks to protect them from wear and the risk of puncture. The outer boot also provides more warmth than the thin layer of latex. A regular sock (e.g. 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. 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.

Attachment rings

Dry suits with latex seals; Top: quick-change seal (Viking ring); Bottom: glued seal.

Attachment rings allow separate neck seals, gloves, and (less commonly) boots to be joined to the suit with a watertight seal. 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.

More recently, on both commercial and recreational suits, "quick-change" rings have become increasingly common. These are permanently glued to the suit, 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, similar 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 may be incompatible, so the diver must choose accessories that are designed for the ring system on his or her suit.

Inflation valves

Inflation valve on neoprene suit

Dry suits are equipped with an inflation valve and at least one exhaust valve.

The inflation valve allows the diver to compensate for air compression in the suit on descent. Suit 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. Compensating gas is taken either from the breathing gas cylinder, a small, dedicated inflation cylinder or the umbilical. Environmentally sealed suits, which are sealed to the helmet, automatically equalise from the breathing gas.

Exhaust valves

Auto dump valve on neoprene suit

Internal view of automatic dump valve showing underside of rubber mushroom valve

The exhaust valve allows the diver to vent expanding gas from the suit on ascent in order to maintain buoyancy control in the same way that a buoyancy compensator must be vented on ascent to avoid an uncontrolled ascent, missed decompression stops, decompression sickness, arterial gas embolism or pulmonary barotrauma. The manual exhaust vent may incorporate an automatic, adjustable exhaust or supplement a separate automatic over-pressure dump valve on the shoulder. Automatic valves are pre-set and in most situations can be left at this setting throughout the dive.

Suit inflation gas supply

Aluminium cylinder and valve intended for argon at a maximum pressure of 139 bar to be used for the inflation of a dry suit while scuba diving

Normally, the gas used for dry suit inflation 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. 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 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, without adding any bulk or weight. Unfortunately, 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.

Inflation hose

Seatec quick disconnect end fitting commonly used for dry-suit and buoyancy compensator inflation

Low pressure inflation hose with CEJN connector (right) used for some dry suits

There are two types of low-pressure hose commonly used for suit inflation: The standard Seatec style quick release couple, fitted with an internal Schrader valve, as also used on most 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 hoses use incompatible valve nipples, but it is usually possible to swap the fitting on the inflator valve to accept the alternative hose. Both types of BCD and dry suit inflator hoses are supplied with an O-ring sealed 3/8” male UNF thread for connection to a low-pressure first stage port.

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. Divers expecting the need to urinate in dry suits can also use an adult diaper / nappy, which soaks up and retains the urine.

"Bio-seals"

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.

Active heating

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. 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.

Manufacture

Neoprene dry suit glued and stitched seam with inside seam tape detail

Neoprene dry suit seam outside stitching detail

Manufacturing processes mainly depend on the material of the shell. Most suit shells are currently assembled by stitching the seams, which in the case of neoprene suits are first butt-glued, and are then overlock stitched and waterproofed by glued seam tape. DUI use a liquid polyurethane sealing compound over the seams on the inside of the suit instead of tape, and the rubber-coated Viking suits are dipped and heat cured for a seamless waterproof layer. DUI crushed neoprene suit shells are assembled before crushing the bubbles by hydrostatic pressure, then adding seals, zippers and accessories.

Hazards of use

Overheating before a dive

Dressing into a dry suit is usually more time-consuming than a wet suit, and may require the assistance of another person to check the neck seal and close the zipper. In situations where the air is warm but the water cold, a prolonged time on the deck of a boat donning a dry suit and other gear can present a risk of overheating to the diver. Wetting the outside of the suit, and seating the diver in shade and a breeze, are the usual solutions to this problem.

Suit squeeze

During descent the air in the suit is compressed and unless more is added, the folds may be pressed together so tightly by water pressure that they pinch the skin, which is painful and may cause local bruising. The suit may also become so tight that movement is restricted, particularly in a membrane suit. This problem is managed by suit inflation from a low pressure gas supply.

Over-inflation

See also: Scuba skills § Management of a dry suit blowup

During ascent, the air added during descent must be removed again, in order to prevent over-inflation, excessive buoyancy, and potential uncontrolled ascent, with possibly fatal consequences. Most modern dry suits are equipped with adjustable spring-loaded automatic exhaust valves, which can assist with this problem by automatically dumping excess gas when properly set and when the valve is higher than the excess gas in the suit.

Suit flooding

Damage to the lower part of the suit can cause a sudden inrush of very cold water for winter users, or an inrush of contaminated water or chemicals for hazmat divers. Damage to the upper part of the suit can cause a sudden venting of the air, resulting in a loss of buoyancy and possible uncontrolled descent, followed by flooding with water and loss of thermal insulation, and possible exposure to hazardous materials if the water is contaminated.

A flooded suit may contain so much water that the diver cannot climb out of the water because of the weight and inertia. In this case it may be necessary to cut a small slit in the lower part of the leg to let water drain out as the diver rises out of the water. This will take some time, and agility will be seriously compromised. The damage should not be difficult to repair if the slit is cut with reasonable care. Ankle dump valves will also serve to drain a flooded suit once enough of the diver is above the water.

Decompression risk from loss of heat during a dive

Experimental work by the US Navy Experimental Diving Unit shows that getting cold during decompression after being warm during the working part of the dive may be the worst case body temperature profile for decompression risk. Active heating systems that fail during the dive, and suit flooding have the potential to cause this scenario. Divers should be aware of the possible effects of thermal stress on decompression outcome, and the use of active heating should be considered in the context of this risk. Decompression computer algorithms that are claimed to take temperature into consideration are generally taking ambient temperature measurements, which has no reliable correlation to actual body temperature of the diver, and are in those cases of little relevance. Pollock (2015) suggests that active diver heating should be minimised to safely complete dive tasks during ingassing and increased during decompression with due attention to avoiding heat stress and dehydration,

Diving without a buoyancy compensator

Dry suits are not designed to be used as buoyancy compensator devices (BCD) and cannot offer the same degree of safety and control as a BCD. However, the fact that it is possible to control buoyancy using a dry suit has led some divers to attempt to control their buoyancy with the dry suit alone and dive without the dedicated BCD normally worn by scuba divers. Although it is possible to dive like this, the risks are higher than when using a buoyancy compensator for the following reasons:

Carotid-sinus reflex

An over-tight neck seal can put pressure on the carotid artery, causing a reflex which slows the heart, resulting in poor oxygen delivery to the brain, light-headedness and eventual unconsciousness. For this reason, neck seals should be stretched or trimmed to the correct size.

Accidental body-inversion hazards

Underwater

If there is more air in the dry suit than is needed to counteract "squeeze" on the undersuit, that excess air creates a "bubble" which moves to the highest point of the suit; in an upright diver this is the shoulders. In such cases, divers wearing loose baggy suits need to keep their legs at level or below their waist. Otherwise the bubble quickly moves to the highest point, and if the legs are above the waist, the bubble moves into the legs and feet, causing the legs to rise, and "inverting" the diver's body into a head-down position.

The movement of 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 through 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.

Surface

Surface dry suit users can face a similar inversion problem. The problem is more acute when not wearing a personal flotation device (life vest) over the dry suit. For surface dry suit users, an inversion can be critical since the wearer may be held upside down and unable to breathe, however, as the user is unlikely to be wearing weights it should be easy to return to a horizontal position.

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. Excess air can be "burped" out of the neck or cuff seal if there is no dump valve. The zip should be closed with as little tension as reasonably practicable across the opening.

History

Early years

Siebe's improved design in 1873, from the Illustrated London News. The helmet's basic features can be seen: A helmet, supplied with air from the surface, and a waterproof suit. The corselet of the helmet is clamped onto the suit with wingnuts over a rubber flange.

Italian frogman of the Decima Flottiglia

Royal Navy divers in Sladen suits during the Second World War

British navy frogman in dry suit c1945

In the 1830s, the Deane brothers asked Augustus Siebe to improve their diving helmet design. Expanding on improvements already made by another engineer, George Edwards, Siebe produced his own design; a helmet clamped to a full length watertight canvas diving suit. The real breakthrough of the equipment was sealing the helmet to the suit, and using a non-return valve in the helmet to exhaust the air, which meant that the suit and helmet could not flood no matter how the diver moved.

Siebe introduced various modifications on his diving dress design to accommodate the requirements of the salvage team on the wreck of HMS Royal George, including making the helmet be detachable from the corselet; his improved design gave rise to the typical standard diving dress which revolutionised underwater civil engineering, underwater salvage, commercial diving and naval diving.

In France in the 1860s, Rouquayrol and Denayrouze developed a single stage demand regulator with a small low pressure reservoir, to make more economical use of surface supplied air pumped by manpower. This was originally used without any form of mask or helmet, but vision was poor, and the "pig-snout" copper mask was developed in 1866 to provide a clearer view through a glass faceplate on a copper mask clamped to the neck opening of the suit. This was soon improved to become a three-bolt helmet supported by a corselet (1867). Later versions were fitted for free-flow air supply.

The earliest suits were made of waterproofed canvas invented by Charles Mackintosh. From the late 1800s and throughout most of the 20th century, most suits consisted of a solid sheet of rubber between layers of tan twill. Their thick vulcanized rubber collar is clamped to the corselet making the joint waterproof. The inner collar (bib) was made of the same material as the suit and pulled up inside the corselet and around the diver's neck. The space between the bib and corselet would trap most condensation and minor leakage in the helmet, keeping the diver dry. The sleeves could be fitted with integral gloves or rubber wrist seals and the suit legs ended in integral socks.

The Pirelli dry suit was designed in the 1930s and used by Italian frogmen during World War II. It became available for recreational divers after the war and was patented (US Pat. No. 2,570,019) in 1951 for Pirelli by Eugenio Wolk, listed as the inventor. This two piece suit was made from thin and elastic rubber, optionally bonded to a knit fabric reinforcement liner except at the sealing areas at the neck, wrists and waist. The waist seal was achieved by overlapping the jacket and trousers and folding the overlap down more than once before securing it in place over a profiled heavy rubber waistband using an elastic belt which pulls the rolled part into a groove in the waistband. Neck and cuff seals were the forerunners of the latex seals still used for this application. The patent claims this to be the first application of thin and flexible form-fitting rubber for the manufacture of dry suits, and also patents the waist seal system. The suits were intended to be worn over woolen underwear for thermal protection. There was no facility to inject air during a dive. These suits were available in four sizes and five styles, three of which were full length two-piece suits with integral boots, one of which was lined with cloth, and two of which had an optional integral hood on the jacket. The other two models were a two-piece with short sleeves and legs, and a one piece short trouser unit with suspenders which sealed on the chest and thighs.

British frogmen of World War II and for some time afterwards used a similar one or two piece rubberized knit fabric suit by Siebe Gorman. They produced the one-piece front-entry Sladen suit with integral rubber helmet, developed by the British Admiralty for use with manned torpedoes, and in the late 1950s also the Essjee two-piece swim suit, based on the Sladen suit. The Essjee suit consisted of a jacket with rubber hood and lightweight wrist cuffs, and trousers shod with moulded rubber soles. The two parts were sealed by rolling the overlapped rubber skirts of the jacket and trousers together and these were held in place by a separate rubber cummerbund. Soft sponge-rubber pads inside the hood covered the ears and allowed them to be equalised. There was space under the suit for plenty of woollen underclothes. The suit was available in proofed gabardine or rubberised stockinette, with the cloth on the outside and the rubber inside, to protect the rubber from sunlight while in use.

Waterwear of Newport Beach, California, produced the natural gum-rubber Seal suit for US Divers from 1953 or earlier. Several versions were available, including one piece and two piece suits. The one piece suits were available with long or short legs and sleeves, and with front, neck or back entry. 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 suit shirt and pants were also available separately and could be sealed together at the waist by a system similar to the neck entry suit.

By the mid-1950s, C.E. Heinke & Co. Ltd., an established manufacturer of Standard diving equipment, had diversified into recreational underwater swimming equipment, including the Delta dry suit, made from natural rubber on a stockinette base. The basic Delta was a two piece suit made up of a jacket with neck seal and trousers with ankle seals which could be worn over woolen undergarments. The full suit included integral hood and feet. The overlapped and rolled waist seal was held in place by a cummerbund.

For a few years after C.E. Heinke & Co. Ltd. was taken over by Siebe-Gorman and Company in 1961, dry suits were marketed under the Siebe-Heinke label. The Siebe-Heinke Dip Suit for recreational diving, swimming, yachting and fishing, was advertised in Lillywhites’ 1964 underwater catalogue. The standard Dip Suit was a set of seamless black dipped-latex jacket with neck and cuff seals, and trousers with separate yellow latex waist-seal cummerbund. A yellow hood and black protective over-bootees were optional extras. Small, medium and large sizes were available. The Siebe-Heinke Frogman dry suit for professional and recreational use was introduced in 1963. It was available in stockinette proofed with black rubber, or proofed fawn twill. The suit consisted of a set of booted trousers with reinforced soles or optional ankle seals, and a jacket with cuff seals and an option between a neck seal or integral hood. The two parts were connected by a rolled waist seal held in place by a rubber cummerbund. Sizes available were small, medium, large short and large.

In 1955, Healthways retailed Carib drysuits, made of 3-ply translucent gum rubber, and available in long and short versions. Entry was by a front chute with rubber band closure. The full version included an integral hood and covered the feet. In 1957, they added the Aqua King and Aqua Flite dry suits to their product range. The Aqua King suit was a full-length waist entry suit, comprising hood, long sleeved shirt, booted pants and waistline sealing ring, and was made of seamless latex rubber. All these suits were available in small medium and large sizes.

Yellow Skooba-"totes" dry suit manufactured by So Lo Marx Rubber Company of Loveland, Ohio, in late 1950s or early 1960s.

Introduction of the watertight zipper and variable volume dry suit

Development of space-suits led to the pressure-tight zipper, first manufactured by B.F. Goodrich, and first used on a dry suit by Bev Morgan in 1956. The suit was in expanded neoprene and had an oral inflator and latex seals. This was followed by the Unisuit, by Poseidon Industri AB of Sweden, also in neoprene, and which included a low pressure inflator valve and exhaust valves. The zipper ran from mid-back to mid-chest via the crotch. This design became the industry standard for a while and use was widespread. Overpressure valves were installed in the ankles, wrists and neck of dry suits to remove excessive air introduced through the face mask to prevent discomfort created by squeeze, which also increased the insulation capacity of the undergarments. These were called constant volume dry suits. Also in Sweden, Stig Insulán and Jorn Stubdal developed a vulcanised rubber drysuit, and Insulán patented the semi-automatic variable volume drysuit exhaust valve in 1971. When combined with the low pressure inflator valve, it gave the diver precise and trouble-free buoyancy control in the variable volume dry suit. Since then, plastic watertight zippers have been developed and are in widespread use on new suits and for replacement of damaged zippers, though the original metal zippers are still available both as original equipment and for replacements.

Training

See also: Diver training

Several diver training agencies offer skills training and certification to safely dive in a dry suit. These skills are often part of a professional diver's basic training.

Training in the use of a dry suit generally involves a theory class on the characteristics and types of dry suit, and the advantages and hazards associated with their use. There may be content on selection of a suit and assessing fit. Practical training will generally include inspection of the suit, how to put it on and take it off, how to determine correct weighting in conjunction with the rest of the diving equipment, routine maintenance and cleaning, basic skills of buoyancy control, and recovery from common problems which if not promptly corrected, could develop into emergencies. A small number of confined water and open water dives will be done to learn and practice the skills, but the ability to use a dry suit competently develops with practice. The prerequisite is usually an entry level diving certification, but in some regions where the water is very cold, and with some agencies, entry level training may be done in dry suits as an option.

See also

• Diving suit – Garment or device designed to protect a diver from the underwater environment
• Human factors in diving equipment design – Influence of the interaction between the user and the equipment on design
• List of water sports
• Sailing – Propulsion of a vehicle by wind power
• Tuilik – Watertight jacket used when paddling a kayak
• Wetsuit – Garment for thermal insulation from water