Scuba diving equipment, also known as scuba gear, is the equipment used by a scuba diver for the purpose of diving, and includes the breathing apparatus,
diving suit, buoyancy control and weighting systems, fins for mobility, mask for improving underwater vision, and a variety of safety equipment and other accessories.
Breathing apparatus The defining equipment used by a scuba diver is the eponymous
scuba, the self-contained underwater breathing apparatus which allows the diver to breathe while diving, and is transported by the diver. It is also commonly referred to as the scuba set. Breathing gas must be supplied to the diver at ambient pressure, which is the sum of atmospheric pressure on the surface and the hydrostatic pressure due to the weight of the water above the diver. The gas may be delivered via a mouthpiece held by the teeth or a
full-face mask which covers the eyes, nose and mouth, and may allow the diver to breathe through the nose and protect the diver's airway if the diver loses consciousness.
Open-circuit Open-circuit scuba discharges the gas inhaled from the scuba equipment dirctly to the environment, or occasionally into another item of equipment for a special purpose, usually to increase the buoyancy of a lifting device such as a buoyancy compensator, inflatable surface marker buoy or small lifting bag. The breathing gas is generally provided from a high-pressure diving cylinder through a scuba regulator. By always providing the appropriate breathing gas at ambient pressure, demand valve regulators ensure the diver can inhale and exhale naturally and without unnecessary effort, regardless of depth, as and when needed. The most commonly used scuba set configuration uses a "
single-hose" open-circuit 2-stage demand regulator, connected to a single back-mounted high-pressure gas cylinder, with the first stage connected to the cylinder valve and the second stage at the mouthpiece. This arrangement differs from Émile Gagnan's and
Jacques Cousteau's original 1942 "
twin-hose" design, known as the Aqualung, in which the cylinder pressure was reduced to ambient pressure in one or two stages which were all in the housing mounted to the cylinder valve or manifold. The "single-hose" system has significant advantages over the original system for most applications. In the "single-hose" two-stage design, the first stage regulator reduces the cylinder pressure of up to about to an intermediate pressure (IP) of about above ambient pressure. The second stage
demand valve regulator, supplied by a low-pressure hose from the first stage, delivers the breathing gas at ambient pressure to the diver's mouth. The exhaled gases are exhausted directly to the environment as waste through a non-return valve on the second stage housing. The first stage typically has at least one outlet port delivering gas at full tank pressure which is connected to the diver's submersible pressure gauge or dive computer, or a
wireless pressure transmitter, to show how much breathing gas remains in the cylinder.
Rebreather Less common are closed circuit (CCR) and semi-closed (SCR) rebreathers which, unlike open-circuit sets that vent off all exhaled gases, process all or part of each exhaled breath for reuse by removing the carbon dioxide and replacing the oxygen used by the diver. Rebreathers release little or no gas bubbles into the water, and use much less stored gas volume for an equivalent depth and time because exhaled gas is recovered; this has advantages for research, military, photography, and other applications. Rebreathers are more complex and more expensive than open-circuit scuba, and special training and correct maintenance are required for them to be safely used, due to the larger variety of potential failure modes. In a closed-circuit rebreather the oxygen partial pressure in the rebreather is controlled, so it can be maintained at a relatively high safe constant level, which reduces the inert gas (nitrogen and/or helium) partial pressure in the breathing loop. Minimizing the inert gas loading of the diver's tissues for a given dive profile reduces the decompression obligation. This requires continuous monitoring of actual partial pressures with time and for maximum effectiveness requires real-time computer processing by the diver's decompression computer. Tissue gas loads can be much reduced compared to fixed ratio gas mixes used in open circuit scuba systems, and as a result, divers can stay down longer or require less time to decompress. A semi-closed circuit rebreather injects a constant mass flow of a fixed breathing gas mixture into the breathing loop, or replaces a specific percentage of the respired volume, so the partial pressure of oxygen at any time during the dive depends on the diver's oxygen consumption and/or breathing rate. Planning decompression requirements requires a more conservative approach for a SCR than for a CCR, but decompression computers with a real-time oxygen partial pressure input can optimize decompression for these systems. Because rebreathers produce very little volume of exhaust bubbles, they do not disturb marine life or make a diver's presence known at the surface; this is useful for underwater photography, and for covert work.
Gas mixtures cylinder marked up for use showing maximum safe operating depth (MOD) For some diving, gas mixtures other than normal atmospheric air (21% oxygen, 78%
nitrogen, 1% trace gases) can be used, so long as the diver is competent in their use. The most commonly used mixture is
nitrox, also called Enriched Air Nitrox (EAN or EANx), which is air with extra oxygen, often with 32% or 36% oxygen, and thus less nitrogen, reducing the risk of
decompression sickness or allowing longer exposure to the same pressure for equal risk. The reduced nitrogen may also allow for no stops or shorter decompression stop times or a shorter surface interval between dives. The increased partial pressure of oxygen due to the higher oxygen content of nitrox increases the risk of oxygen toxicity, which becomes unacceptable below the
maximum operating depth of the mixture. To displace nitrogen without the increased oxygen concentration, other diluent gases can be used, usually
helium, when the resultant three gas mixture is called
trimix, and when the nitrogen is fully substituted by helium,
heliox. For dives requiring long decompression stops, divers may carry cylinders containing different gas mixtures for the various phases of the dive, typically designated as travel, bottom, and decompression gases. These different gas mixtures may be used to extend bottom time, reduce inert gas narcotic effects, and reduce
decompression times.
Back gas refers to any gas carried on the diver's back, usually bottom gas.
Diver mobility tank To take advantage of the freedom of movement afforded by scuba equipment, the diver needs to be mobile underwater. Personal mobility is enhanced by swimfins and optionally diver propulsion vehicles. Fins have a large blade area and use the more powerful leg muscles, so are much more efficient for propulsion and maneuvering thrust than arm and hand movements, but require skill to provide fine control. Several types of fin are available, some of which may be more suited for maneuvering, alternative kick styles, speed, endurance, reduced effort or ruggedness. Neutral buoyancy will allow propulsive effort to be directed in the direction of intended motion and will reduce induced drag. Streamlining dive gear will also reduce drag and improve mobility. Balanced trim which allows the diver to align in any desired direction also improves streamlining by presenting the smallest section area to the direction of movement and allowing propulsion thrust to be used more efficiently. Occasionally a diver may be towed using a "
sled", an unpowered device towed behind a surface vessel that conserves the diver's energy and allows more distance to be covered for a given air consumption and bottom time. The depth is usually controlled by the diver by using diving planes or by tilting the whole sled. Some sleds are faired to reduce drag on the diver.
Buoyancy control equipment Buoyancy control is a critical skill for safety, and as the typical scuba diver with their basic equipment is not inherently neutrally buoyant, other equipment is used to allow control of buoyancy. Most excess buoyancy is due to the diving suit volume, and this varies with suit thermal insulation and depth. The ability to ascend at a controlled rate and remain at a constant depth is important for correct decompression. Recreational divers who do not incur decompression obligations can get away with imperfect buoyancy control, but when long decompression stops at specific depths are required, the risk of decompression sickness is increased by depth variations while at a stop. Decompression stops are typically done when the breathing gas in the cylinders has been largely used up, and the reduction in weight of the cylinders increases the buoyancy of the diver. Enough ballast weight must be carried to allow the diver to decompress at the end of the dive with nearly empty cylinders, and enough buoyancy compensation must be possible to remain at the surface before the dive with full cylinders.
Diver weighting Scuba diving equipment can make the diver buoyant, requiring the addition of ballast to make it possible to submerge and remain submerged until the diver wants to surface. The amount and distribution of dive weights affects the convenience, efficiency, environmental impact, and safety of the diver. Buoyancy changes with depth variation are proportional to the compressible part of the volume of the diver and equipment, and to the proportional change in pressure, which is greater per unit of depth near the surface. Minimizing the volume of gas required in the buoyancy compensator will minimize the buoyancy fluctuations with changes in depth. This can be achieved by accurate selection of ballast weight, which should be the minimum to allow neutral buoyancy with depleted gas supplies at the surface at the end of the dive unless there is an operational requirement for greater negative buoyancy during the dive.
Buoyancy compensator To dive safely, divers must control their rate of descent and ascent in the water and be able to maintain a constant depth in midwater. Ignoring other forces such as water currents and swimming, the diver's overall
buoyancy determines whether they ascend or descend. Equipment such as
diving weighting systems, diving suits, and
buoyancy compensators(BC) can be used to adjust the overall buoyancy. When divers want to remain at constant depth, they try to achieve neutral buoyancy. This minimizes the effort of swimming to maintain depth and therefore reduces gas consumption. A buoyancy compensator (BC), also called a buoyancy control device (BCD), is the equipment used by divers to establish
neutral buoyancy underwater and positive
buoyancy at the surface, when needed. The buoyancy is usually controlled by adjusting the volume of gas in an inflatable bladder, which is filled with ambient pressure gas from the diver's primary breathing gas cylinder via a low-pressure hose from the regulator first stage, directly from a small cylinder dedicated to this purpose, or from the diver's mouth through the oral inflation valve. Ambient pressure bladder buoyancy compensators can be broadly classified as having the buoyancy primarily in front, surrounding the torso, or behind the diver. This affects the
ergonomics, and to a lesser degree, the safety of the unit. The buoyancy force on the diver is the weight of the volume of the liquid that they and their equipment
displace minus the weight of the diver and their equipment; if the result is
positive, that force is upwards. The buoyancy of any object immersed in water is also affected by the density of the water. The density of fresh water is about 3% less than that of ocean water. Therefore, divers who are neutrally buoyant at one dive destination will predictably be positively or negatively buoyant when using the same equipment at destinations with different water densities. The removal ("ditching" or "shedding") of diver weighting systems can be used to reduce the diver's weight and cause a buoyant ascent in an emergency. Diving suits made of compressible materials decrease in volume as the diver descends, and expand again as the diver ascends, causing buoyancy changes. Diving in different environments also necessitates adjustments in the amount of weight carried to achieve neutral buoyancy. The diver can inject air into a dry suit to counteract the compression effect and
squeeze, but dry suits are not suitable for general buoyancy compensation. Buoyancy compensators allow easy and fine adjustments in the diver's overall volume and therefore buoyancy. Neutral buoyancy in a diver is an unstable state. It is changed by small differences in ambient pressure caused by a change in depth, and the change has a positive feedback effect. A small descent will increase the pressure, which will compress the gas-filled spaces and reduce the total volume of diver and equipment. This will further reduce the buoyancy, and unless counteracted, will result in sinking more rapidly. The equivalent effect applies to a small ascent, which will trigger an increased buoyancy and will result in an accelerated ascent unless counteracted. The diver must continuously adjust buoyancy or depth to remain neutral. Fine control of buoyancy can be achieved by controlling the average lung volume in open-circuit scuba, but this feature is not available to the closed circuit rebreather diver, as exhaled gas remains in the breathing loop. This is a skill that improves with practise until it becomes second nature.
Diver trim The trim of a diver is the orientation of the body in the water, determined by posture and the distribution of weight and volume along the body and equipment, as well as by any other forces acting on the diver. Both static trim and its stability affect the convenience and safety of the diver while under water and at the surface.
Midwater trim is usually considered at approximately neutral buoyancy for a swimming scuba diver, but surface trim may be at significant positive buoyancy to keep the head above water. Trim can significantly affect drag of a diver. The effect of swimming with a head up angle of about 15°, as is quite common in poorly trimmed divers, can be an increase in drag in the order of 50%.
Underwater vision Water has a higher
refractive index than air – similar to that of the
cornea of the eye. Light entering the cornea from water is hardly refracted at all, leaving only the eye's
crystalline lens to focus light. This leads to very severe
hypermetropia. People with severe
myopia, therefore, can see better underwater without a mask than normal-sighted people.
Diving masks and
helmets solve this problem by providing an air space in front of the diver's eyes. The
refraction error created by the water is mostly corrected as the light travels from water to air through a flat lens, except that objects appear approximately
34% bigger and 25% closer in water than they actually are. The faceplate of the mask is supported by a frame and skirt, which are opaque or translucent, therefore the total field-of-view is significantly reduced and eye-hand coordination must be adjusted. Divers who need corrective lenses to see clearly outside the water would normally need the same prescription while wearing a mask. Generic corrective lenses are available off the shelf for some two-window masks, and custom lenses can be bonded onto masks that have a single front window or two windows. As a diver descends, they must periodically exhale through their nose to equalize the internal pressure of the mask with that of the surrounding water. Swimming goggles are not suitable for diving because they only cover the eyes and thus do not allow for equalization. Failure to equalize the pressure inside the mask may lead to a form of barotrauma known as mask squeeze. Masks tend to fog when warm humid exhaled air condenses on the cold inside of the faceplate. To
prevent fogging many divers spit into the dry mask before use, spread the saliva over the inside of the glass and rinse it out with a little water. The saliva residue allows condensation to wet the glass and form a continuous wet film, rather than tiny droplets. There are several commercial products that can be used as an alternative to saliva, some of which are more effective and last longer, but there is a risk of getting the anti-fog agent in the eyes.
Dive lights Water attenuates light by selective absorption. Pure water preferentially absorbs red light, and to a lesser extent, yellow and green, so the colour that is least absorbed is blue light. Dissolved materials may also selectively absorb colour in addition to the absorption by the water itself. In other words, as a diver goes deeper on a dive, more colour is absorbed by the water, and in clean water the colour becomes blue with depth. Colour vision is also affected by the turbidity of the water which tends to reduce contrast. Artificial light is useful to provide light in the darkness, to restore contrast at close range, and to restore natural colour lost to absorption. Dive lights can also attract fish and a variety of other sea creatures.
Exposure protection where the water is cold Protection from heat loss in cold water is usually provided by wetsuits or dry suits. These also provide protection from sunburn, abrasion and stings from some marine organisms. Where thermal insulation is not important, lycra suits or
diving skins may be sufficient. A wetsuit is a garment, usually made of foamed neoprene, which provides thermal insulation, abrasion resistance and buoyancy. The insulation properties depend on bubbles of gas enclosed within the material, which reduce its ability to conduct heat. The bubbles also give the wetsuit a low density, providing buoyancy in water. Suits range from a thin (2 mm or less) "shortie", covering just the torso, to a full 8 mm semi-dry, usually complemented by neoprene boots, gloves and hood. A good close fit and few zips help the suit to remain waterproof and reduce flushing – the replacement of water trapped between suit and body by cold water from the outside. Improved seals at the neck, wrists and ankles and baffles under zips produce a suit known as "semi-dry". A
dry suit also provides
thermal insulation to the wearer while immersed in water, and generally protects the entire body except the head, hands, and sometimes the feet. In some configurations, these are also covered. Dry suits are usually used where the water temperature is below 15 °C (60 °F) or for extended immersion in water above 15 °C (60 °F), where a wetsuit user would get cold, and with an integral helmet, boots, and gloves for personal protection when diving in contaminated water. Dry suits are designed to prevent water from entering. This generally allows better insulation making them more suitable for use in cold water. They can be uncomfortably hot in warm or hot air, and are typically more expensive and more complex to don. They add some task loading for the diver as the suit must be inflated and deflated with changes in depth in order to avoid "squeeze" on descent or uncontrolled rapid ascent due to over-buoyancy. Divers may also use the gas
argon to inflate their dry suits because it has a low thermal conductivity.
Monitoring and navigation Unless the maximum depth of the water is known, and is quite shallow, a diver must monitor the depth and duration of a dive to avoid decompression sickness. Traditionally this was done by using a
depth gauge and a diving watch, but electronic
dive computers are now in general use, as they are programmed to do real-time modelling of decompression requirements for the dive, and automatically allow for surface interval. Many can be set for the gas mixture to be used on the dive, and some can accept changes in the gas mix during the dive. Most dive computers provide a fairly conservative decompression model, and the level of
conservatism may be selected by the user within limits. Most decompression computers can also be set for altitude compensation to some degree, and some will automatically take altitude into account by measuring actual atmospheric pressure and using it in the calculations. If the dive site and dive plan require the diver to navigate, a
compass may be carried, and where retracing a route is critical, as in cave or wreck penetrations, a
guide line is laid from a dive reel. In less critical conditions, many divers simply navigate by landmarks and memory, a procedure also known as
pilotage or natural navigation. A scuba diver should always be aware of the remaining breathing gas supply, and the duration of diving time that this will safely support, taking into account the time required to surface safely and an allowance for foreseeable contingencies. This is usually monitored by using a
submersible pressure gauge on each cylinder. Some dive computers have a facility known as
gas integration for remote monitoring of the pressure in one or more cylinders via signals from a
wireless pressure transmitter mounted to the regulator first stage.
Safety equipment Any scuba diver who will be diving below a depth from which they are competent to do a safe emergency swimming ascent in all reasonably foreseeable circumstances should ensure that they have an alternative breathing gas supply available at all times in case of a failure of the equipment they are breathing from at the time. Several systems are in common use depending on the planned dive profile. Most common, but least reliable, is relying on the
dive buddy for gas sharing using a secondary second stage, commonly called an
octopus regulator connected to the primary first stage. This system relies entirely on the dive buddy being immediately available and competent to provide emergency gas. More reliable systems require the diver to carry an alternative gas supply sufficient to allow the diver to safely reach a place where more breathing gas is available. For open water recreational divers this is the surface, for technical divers on a penetration dive, it may be a stage cylinder positioned at a point on the exit path, and for divers with a decompression obligation, it may be a depth at which decompression gas is acceptably safe to breathe. An emergency gas supply must be sufficiently safe to breathe at any point on the planned dive profile at which it may be needed. This equipment may be a
bailout cylinder, a
bailout rebreather, a
travel gas cylinder, or a
decompression gas cylinder. A
bailout cylinder provides emergency breathing gas sufficient for a safe emergency ascent. When using a travel gas or decompression gas, the
back gas (main gas supply) may be the designated emergency gas supply.
Cutting tools such as knives, line cutters or shears are often carried by divers to cut loose from entanglement in nets or lines. A
surface marker buoy (SMB) on a line held by the diver indicates the position of the diver to the surface personnel. This may be an inflatable marker deployed by the diver at the end of the dive, or a sealed buoyant float, towed for the whole dive. A surface marker also allows easy and accurate control of ascent rate and stop depth for safer decompression. Various
surface detection aids may be carried to help surface personnel spot the diver after ascent. In addition to the surface marker buoy, divers may carry mirrors, lights, strobes, whistles,
flares or
emergency locator beacons.
Accessories and tools Divers may carry underwater photographic or
video equipment, or tools for a specific application in addition to diving equipment. Professional divers will routinely carry and use tools to facilitate their
underwater work, while most recreational divers will not engage in underwater work. ==Breathing from scuba==