Product Code Database
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, boating, 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 suit configurations, however, all of these are covered as well.
The main difference between dry suits and 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. 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. When this is insufficient, active warming or cooling may be provided by chemical or electrically powered heating accessories.
The essential components are the waterproof shell, the seals, and the watertight entry closure. 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.
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.
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 Diving 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.
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.
Cold shock response is the physiological response of to sudden cold, especially cold water, and is a common cause of death from immersion in very cold water, 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; 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.
Hypothermia is reduced body temperature that happens when a body dissipates more heat than it absorbs and produces, and is a major limitation to swimming or diving in cold water. The reduction in finger dexterity due to pain or numbness decreases general safety and work capacity, which consequently increases the risk of other injuries. 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. The effectiveness of a dry suit in preventing or delaying hypothermia depends on its insulating value.
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.
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. 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.
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.
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 Perspiration, 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.
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.
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. 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.
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. 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, 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.
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.
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.
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 Redox and chemical attack. They are initially relatively expensive, but can be replaced without tools by the user which reduces cost of replacement.
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.
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.
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. 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.
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.
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. A thin polypropylene layer against the skin will keep moisture away from the skin, and may keep the main undersuit clean. 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 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.
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.
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 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" salopettes style trousers with jacket is flexible and puts extra insulation where it is most useful. 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.
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. 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. 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.
Latex rubber ankle seals are sometimes fitted in place of socks and can allow better foot control of and . 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.
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.
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. 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.
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 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.
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.
Adjustable valves can be pre-set or set to suit the undergarments during or after the descent, and in most situations can be left at this setting throughout the dive, but may be closed after surfacing to retain more gas for buoyancy and insulation, An auto-dump valve is a two stage valve to reduce inward leakage of water. The inner valve is generally a mushroom type elastomer non-return valve, with a low opening pressure differential, which will close automatically when there is no suit gas flowing out. This serves to prevent water ingress when the valve is manually opened by pressing down on the outer cover to compress the adjustable spring and open the pressure relief valve. The outer valve is an adjustable pressure relief valve which can be manually opened by pressing it with the hand against the spring preload, or opens automatically when internal pressure overcomes the preload setting. Spring tension is adjusted by screwing the outer cover further down to increase opening pressure difference, and unscrewing to reduce pressure difference. The rotation of the cover has stops at both ends, and clicks every few degrees of turn, so the user can judge the setting. Non-adjustable valves are similar but do not have the adjustment facility and can be more compact. Most dry suit dump valves are manufactured by Apeks and SI Tech and may be relabeled by suit manufacturers, though Northern Divers and Mares manufacture their own valves.The SI Tech valve has a different size gasket to the Apeks glued to the suit, so they are not interchangeable. Maintenance is mostly rinsing in fresh water after a dive, and most minor leaks can be fixed by soaking the valve mechanism and flushing with fresh water.
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. Most, but not all, dry suits from the 1950s and the early 1960s came without dedicated vents; venting was achieved by raising an arm and lifting one of the wrist seals or placing a finger in the neck seal. Several manufacturers back then attached a rubber venting tube closed with a stopper to the chest area of valveless dry suits, enabling the latter to be completely deflated before entering the water or inflated in the water to make the suit buoyant if required. Some mid-twentieth-century divers installed Duckbill valve, also known as spear valves or flutter valves, which were designed to release excess air from the interior of their otherwise valveless dry suits at the head, shoulders or ankles.
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.
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.
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.
Short suits with bicep and thigh cuff seals are also available, and are useful when it is mainly necessary to keep the torso dry.
Immersion suits protect the wearer from cold shock and delay hypothermia by reducing heat loss. Other functions include providing buoyancy and increasing visibility to rescuers. They must allow sufficient freedom of movement to perform necessary actions. There are two basic types: Suits for emergency abandonment, and suits intended to be worn over long work periods where the risk of immersion is relatively high, or there may be no opportunity to put the suit on in the event of an emergency. The size range that must be available for marine abandonment immersion suits is specified by CAN/CGSB-65.16-2005 and other standards, and may include children, small adults, universal, jumbo, and custom sizes. ISO 15027, Canadian General Standards Board (CAN/CGSB-65.16-2005), and Safety of Life at Sea (SOLAS) immersion suit standards, as well as others, apply.
A survival suit for protecting survivors of a helicopter ditching incident is also known as a helicopter transportation suit (HTS). A ditched helicopter may invert immediately after impact, and the suit must facilitate underwater escape, which requires minimal buoyancy until the survivor is outside the ditched helicopter. Once outside, and clear of the wreckage, the suit must provide buoyancy, protection from drowning, and thermal protection while immersed. During normal flight operations the suit must be acceptably comfortable. Except for the underwater egress these requirements are very similar to those for other survival suits.
Helicopter transportation suits are constant wear immersion suits that are required for crew and passengers during operations over cold water. Aircrew and passenger HTS typically differ as pilots must not be encumbered while busy flying, generate more heat due to activity in flight, and are often heated by sunlight through the cockpit glazing.
Lightweight suits of breathable shell fabric which are easy to don, comfortable, strong, seals which can be trimmed to custom fit, and bootees that are easy to don and not bulky in the outer boot are desirable characteristics. Durable materials with reinforcement and padding on the knees, elbows and seat improve the useful life of the suit. High visibility colours and reflective tape which can be seen while wearing a personal flotation device are appropriate for this use case. Adjustable internal suspenders, belts and thigh straps allow better adjustment of fit to the individual, and well drained pockets in convenient locations and relief zippers are useful in the field. Low drag in the water can be valuable in some use cases.
Polyurethane coated nylon and trilaminate suits are usually assembled using double stitched seams for strength, which are then taped on the inside for watertightness.
Vulcanised rubber dry suits are made from a rubber coated knitted fabric, stitched together along the seams to hold them together during the vulcanising process. Once the suit has been assembled, it is stretched over an aluminium mandrel in the shape and size of the finished suit. When the suit is on the mandrel, the seams are taped with strips of the same rubber, but without the liner cloth, then bonded together with heat and pressure in an autoclave, which vulcanises the rubber of the suit and seam tape into a homogeneous layer which is very reliably watertight. Any customising of the suit is done after this process, and requires cutting and gluing and taping of additional seams, which are generally not as reliable and strong as the original structure The thickness of the rubber layer can be varied and patches added for abrasion resistance. Vulcanised rubber suits can also be made using rubber coated fabric that has already been vulcanised, assembled in much the same way as trilaminate suits, and the seams taped after assembly. This is more versatile for customising, but the seam quality is not as reliable as the method of vulcanising the assembled suit and seam tape together. The combination of high stretch rubber over stretchy knitted fabric makes these suits very flexible and elastic, so a baggy cut is not needed. However, the mandrels are expensive, so a limited number of standard sizes are available.
Seals, zippers, boots, pockets, and other accessories, are usually glued on to the shell after assembly, and joins and edges may be reinforced by seam tape in high stress areas or to improve watertightness. Some abrasion reinforcement and logos are bonded or stitched to the suit or printed onto the component panels before or after assembly.
Latex is subject to rubber perishing, or "dry rot", where ozone normally present in the air deteriorates the material over time, regardless of use. A latex seal is generally expected to last 1–2 years. The useful life can be extended by detaching removable seals when not in use and keeping them in airtight containers in a cool, dark environment. Silicone seals are similar in strength and elasticity to latex, but are more chemical resistant and do not perish in the same way. Latex and silicone seals are highly elastic, but can be easily torn if overstretched or nicked on an edge to form a stress raiser. Powdered talc can help the seals slide on easier.
Neoprene seals are a tougher and more tear resistant alternative, though they must be correctly sized for the user, as they cannot be adjusted much. These are much more resistant to perishing than latex, and the knit fabric backing helps redistribute concentrated loads and thereby reduces the risk of major tears. Minor tears are usually repairable. A lubricating liquid such as dishwashing liquid or KY jelly can be used to facilitate for donning and removing neoprene wrist seals.
Metal zipper failure modes include: worn out backing rubber, where the slider wears through the outer layer of the zipper, exposing the reinforcing fabric, loose or lost teeth, kinked or torn side tape between teeth, and worn out teeth on the interlocking area. Fraying of the reinforcing fabric along the cut edge can be tolerated as long as frayed fibres do not get between the sealing surfaces, thereby causing a leak, cause the slider to jam, or hook on snags and cause more serious damage.
Temperatures above the ice may be considerably lower than water temperature, which is limited by freezing point of the water, and may be further exacerbated by wind chill. This can be a limiting factor on the endurance of the surface team if inadequately insulated and sheltered, and can have an impact on the divers on exiting the water in wet exposure suits.
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.
The movement of a large bubble to the legs can be a problem for a number of reasons: It inflates the legs, and may inflate thin rubber booties enough to cause fins to pop off, or cause the boots to pop off the feet, with the fins still in place on the boots. A diver without fins has reduced ability to maneuver back to a head up trim, and also loses the ability to kick downward to maintain depth, so that the bubble expansion problem does not get worse. Gas in the legs and feet of the suit usually cannot be evacuated while the diver is inverted, as most suits do not have ankle dump valves, and the inverted diver may start to float toward the surface, causing the problem of expanding air in the suit to grow worse in proportion to the decrease in depth. If the diver is positively buoyant and rising, the buoyancy of the dry suit will become uncontrollable, and ascent rate will accelerate. 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 used correctly, the excess gas 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 ascends without venting the suit; if the valve supplying gas the suit fails in the open position; or if the diver is over-weighted, and extra gas has been added to the suit to make the diver neutrally buoyant. The size of the bubble can be minimised by being correctly weighted, using the buoyancy compensator to adjust for weight changes due to gas consumption, keeping the exhaust valve high, and venting excess gas from the suit on ascent. It is a recommended practice to ensure that the bubble remains small and at the top of the body by using the buoyancy compensator to counteract any excess weighting, keeping only the minimum gas necessary to maintain undergarment loft inside the drysuit. Suits that fit correctly and are not excessively stretchy also help.
The recommended procedure in all such inversion incidents, is for the diver to bend at the knees and powerfully swing the arms to do a backward or forward roll to the upright position without delay, to allow the gas to flow to the shoulders and arms, allowing the automatic dump valve to operate, 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. If finning downwards is not immediately effective, it will not become effective later as the gas continues to expand.
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.
On 14 June 1834, Leonard Norcross of Dixfield, Maine was awarded a patent for a dry suit made of rubber with an attached metal helmet. This was not the first American patent for a diving suit – it was the third patent of that year for an underwater suit, but Norcross' invention was the first to specify rubber as the waterproofing material.
In France in the 1860s, Benoît Rouquayrol and Auguste 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 Waterproofing. 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 twill was available in heavy, medium, and light grades, with the heavy having the best resistance to abrasion and puncture against rough surfaces like barnacles, rocks and the jagged edges of wreckage. Vulnerable areas were reinforced by extra layers of fabric. Different types of standard diving dress are defined by the clamping of the collar seal to the rim of the corselet or to the joint between bonnet and corselet, and the number of bolts used for this purpose. In some suits the legs could be laced at the back to limit inflated volume, which would limit the volume of excess gas that could be trapped in the legs and reduce the risk of it dragging an inverted diver to the surface.
The waterproof rubberised fabric, the seal to the helmet and the cuff seals kept the diver dry, allowing sufficient clothing to be worn under the suit to keep warm depending on the water temperature and expected level of exertion. The suit was usually a very baggy fit on the diver, and if over-inflated, would be too bulky to allow the diver to reach the control valves for air supply and exhaust. This contributed to the risk of suit blowup, which could cause an uncontrollable buoyant ascent, with high risk of decompression illness. To add to this problem, a runaway ascent could cause sufficient internal pressure to burst the seal at the corselet, which could result in a catastrophic loss of buoyancy, and the injured diver sinking back to the bottom in a flooded suit. Consequently, divers would ensure that they were weighted enough to remain sufficiently negative when underwater to minimise this risk, and to allow reasonably stable walking on the bottom. The bulkiness of fit, weighted boots, lack of fins, and lack of fine buoyancy control made swimming impracticable. At the surface the diver could struggle a short distance using the arms, but underwater would normally walk on the bottom and climb up and down over obstacles, taking care to avoid passing under anything that could foul the air hose. The diver needed to remain upright when ascending to allow venting of excess air through the helmet exhaust valve, and would either be lowered and pulled up by the tenders, or would slide down the shotline and climb back up it.
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 folding up the sealing area of the jacket, and overlapping the sealing area of the trousers, then and folding the overlap down over itself more than once before securing it in place over a profiled heavy rubber waistband using an elastic belt which pulls the multiply folded 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.
In 1945, the Spearfisherman Company, of Huntington Beach, California was approached by the US Navy to produce a rubber suit. These were advertised in the first issue of the Skin Diver magazine in December 1951. They were tunnel entry suits, and were available as full length or shortie suits with integral hood. Later versions had a neck level entry chute and a nape valve to purge trapped air. The shortie version was also rebranded as Kellys 7-seas suit.
In 1946 Jacques Cousteau developed a constant volume drysuit which was inflated by blowing air under the mask skirt into the hood of the suit. Valves in the hood, wrists, and ankles, allowed venting in most positions.
Seamless dipped latex one and two-piece suits were available In the US from the early 1950s. Two piece suits were connected and sealed by a rolled overlap at the waist or with a "ring and rail" waist seal, and were available in long or short leg versions and long or short sleeved versions, all with integral neck, and cuff or arm and thigh seals, and in a range of sizes and colours. The one piece suits were available with long or short legs and sleeves, and with front or back tunnel, pocket, or neck entry. Separate hoods and boots or reinforced feet for the long leg versions were available as options. Suits were manufactured in dipped latex, 2 and 3 ply gum rubber and textile backed rubber. Some were assembled from cut components, while others were dipped one-piece seamless latex construction. Kits were also available for home completion. Manufacturers included Waterwear of Newport Beach, California, Healthways, Voit, Bel-Aqua Water Sports Company of Los Angeles, (later Aquala Sports Manufacturing Company), Totes Isotoner of Loveland, Ohio, and the Dolphin Manufacturing Company of California.
The UK-based Dunlop Rubber Company produced drysuits for military and commercial divers and the Dunlop Aquafort range for recreational use.
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. For a few years after C.E. Heinke & Co. Ltd. was taken over by Siebe Gorman in 1961, dry suits were marketed under the Siebe-Heinke label. The Siebe-Heinke Dip Suit for recreational diving, swimming, yachting and fishing, was a seamless black dipped-latex jacket with neck and cuff seals, and trousers with separate yellow latex cummerbund for the waist-seal. A yellow hood and black protective over-bootees were optional extras. The Siebe-Heinke Frogman dry suit for professional and recreational use, introduced in 1963, was available in stockinette proofed with black rubber, or proofed fawn twill. The suit consisted 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, connected by a rolled waist seal and cummerbund.
Injection moulded plastic zippers have been developed that are cheaper and require less force to open and close than the metal toothed version, but may leak more if not completely closed, and may not last as long under heavy loads.
Training in the use of a dry suit for diving 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.
Watertight zippers are supplied to dry suit manufacturers by German company TiZip (plastic teeth) and BDM, Dynat and OEB from the YKK group (bronze teeth), and SZIP. (Chinese)
Past and present dry suit manufacturers include:
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