Diving cylinder

Diving cylinders to be filled at a diving air compressor station

A diving cylinder, scuba tank or diving tank is a gas cylinder used to store and transport the high pressure breathing gas required by a scuba set. It may also be used for surface-supplied diving or as decompression gas or an emergency gas supply for scuba. Cylinders provide gas to the diver through the demand valve of a diving regulator or the breathing loop of a diving rebreather.

Diving cylinders are usually manufactured from aluminium or steel alloys, and are normally fitted with one of two common types of cylinder valve for filling and connection to the regulator. Other accessories such as manifolds, cylinder bands, protective nets and boots and carrying handles may be provided. Various configurations of harness may be used to carry the cylinder or cylinders while diving, depending on the application. Cylinders used for scuba typically have an internal volume (known as water capacity) of between 3 and 18 litres (0.11 and 0.64 cu ft) and a maximum working pressure rating from 184 to 300 bars (2,670 to 4,350 psi). Cylinders are also available in smaller sizes, such as 0.5, 1.5 and 2 litres, however these are often not used for breathing, instead being used for purposes such as inflation of surface marker buoys, drysuits and buoyancy compensators. Scuba divers may dive with a single cylinder, a pair of similar cylinders, or a main cylinder and a smaller "pony" cylinder, usually carried on the diver's back. For specialised diving, more that two cylinders may be needed, or the cylinders may be mounted at the waist ("side-mount").

When pressurised, a cylinder carries an equivalent volume of free gas greater than its water capacity, because the gas is compressed to several hundred times atmospheric pressure. The selection of an appropriate set of diving cylinders for a diving operation is based on the amount of gas required to safely complete the dive. Diving cylinders are most commonly filled with air, but because the main components of air can cause problems when breathed underwater at higher pressure, divers may choose to breathe from cylinders filled with mixtures of gases other than air. A cylinder containing such mixtures needs to be labelled to indicate its contents for safety reasons. Many jurisdictions have regulations that govern the filling, recording of contents, and labelling for diving cylinders. Periodic inspection and testing of cylinders is often obligatory to ensure the safety of operators of filling stations. Pressurised diving cylinders are considered dangerous goods for commercial transportation, and regional and international rules for colouring and labelling may also apply.

Terminology

The term "diving cylinder" tends to be used by gas equipment engineers, manufacturers, support professionals, and divers speaking British English. "Scuba tank" or "diving tank" is more often used colloquially by non-professionals and native speakers of American English. The term "oxygen tank" is commonly used by non-divers when referring to diving cylinders; however, this is a misnomer. These cylinders typically contain (compressed atmospheric) breathing air, or an oxygen-enriched air mix. They rarely contain pure oxygen, except when used for rebreather diving, shallow decompression stops in technical diving or for in-water oxygen recompression therapy. Breathing pure oxygen at depths greater than 6 metres (20 ft), equivalent to a partial pressure of oxygen of 1.6 bars (1.6 atm), can result in oxygen toxicity, a highly dangerous condition that can trigger seizures and thus lead to drowning.[1]

Diving cylinders have also been referred to as bottles or flasks, usually with one of the epithets scuba, diving, or bailout. Cylinders may also be called aqualungs, a genericized trademark derived from the Aqua-lung equipment made by the Aqua Lung/La Spirotechnique company,[2] although that is more properly applied to an open circuit scuba set or open circuit diving regulator.

Diving cylinders may also be specified by their application, as in bailout cylinders, stage cylinders, deco cylinders, sidemount cylinders, pony cylinders, suit inflation cylinders, etc.

Parts of a cylinder

Two 12 litre steel cylinders connected by an isolation manifold and tank bands

The functional diving cylinder consists of the pressure vessel and a cylinder valve:

The pressure vessel

The pressure vessel is a seamless cylinder normally made of cold-extruded aluminium or forged steel.[1] Filament wound composite cylinders are used in fire fighting breathing apparatus and oxygen first aid equipment because of their low weight, but are rarely used for diving, due to their high positive buoyancy. They are occasionally used when portability for accessing the dive site is critical, such as in cave diving.[3][4] Composite cylinders certified to ISO-11119-2 or ISO-11119-3 may only be used for underwater applications if they are manufactured in accordance with the requirements for underwater use and are marked “UW”.[5]

Aluminium cylinders

An especially common cylinder provided at tropical dive resorts is the "aluminium-S80" which is an aluminium cylinder design with an internal volume of 0.39 cubic feet (11.0 L) rated to hold a nominal volume of 80 cubic feet (2,300 L) of atmospheric pressure gas at its rated working pressure of 3,000 pounds per square inch (207 bar).[6] Aluminium cylinders are also often used where divers carry many cylinders, such as in technical diving in water which is warm enough that the dive suit does not provide much buoyancy, because the greater buoyancy of aluminium cylinders reduces the amount of extra buoyancy the diver would need to achieve neutral buoyancy. They are also sometimes preferred when carried as "sidemount" or "sling" cylinders as the near neutral buoyancy allows them to hang comfortably along the sides of the diver's body, without disturbing trim, and they can be handed off to another diver or stage dropped with a minimal effect on buoyancy. Most aluminium cylinders are flat bottomed, allowing then to stand upright on a level surface, but some were manufactured with domed bottoms.

The aluminium alloys used for diving cylinders are 6061 and 6351. 6351 alloy is subject to sustained load cracking and cylinders manufactured of this alloy should be periodically eddy current tested according to national legislation and manufacturer's recommendations.[7][8] 6351 alloy has been superseded for new manufacture, but many old cylinders are still in service.

Manufacture

Aluminium cylinders are usually manufactured by cold extrusion of aluminium billets in a process which first presses the walls and base, then trims the top edge of the cylinder walls, followed by press forming the shoulder and neck. The final structural process is machining the neck outer surface, boring and cutting the neck threads and O-ring groove. The cylinder is then heat-treated, tested and stamped with the required permanent markings.[9] Aluminium diving cylinders commonly have flat bases, which allows them to stand upright on horizontal surfaces, and which are relatively thick to allow for rough treatment and considerable wear. This makes them heavier than they need to be for strength, but the extra weight at the base also helps keep the centre of gravity low which gives better balance in the water and reduces excess buoyancy.

Steel cylinders

In cold water diving, where a diver wearing a highly buoyant thermally insulating dive suit has a large excess of buoyancy, steel cylinders are often used because they are denser than aluminium cylinders. They also often have a lower mass than aluminium cylinders with the same gas capacity, due to considerably higher material strength, so the use of steel cylinders can result in both a lighter cylinder and less ballast required for the same gas capacity, a two way saving on overall dry weight carried by the diver.[10][11]

Steel cylinders are more susceptible than aluminium to external corrosion, particularly in seawater, and may be galvanized or coated with corrosion barrier paints to resist corrosion damage. It is not difficult to monitor external corrosion, and repair the paint when damaged, and steel cylinders which are well maintained have a long service life, often longer than aluminium cylinders, as they are not susceptible to fatigue damage when filled within their safe working pressure limits.

Steel cylinders are manufactured with domed (convex) and dished (concave) bottoms. The dished profile allows them to stand upright on a horizontal surface, and is the standard shape for industrial cylinders. The cylinders used for emergency gas supply on diving bells are often this shape, and commonly have a water capacity of about 50 litres ("J"). Domed bottoms give a larger volume for the same cylinder mass, and are the standard for scuba cylinders up to 18 litres water capacity, though some concave bottomed cylinders have been marketed for scuba.[12][13]

Manufacture

Steel alloys used for dive cylinder manufacture are authorised by the manufacturing standard. For example, the US standard DOT 3AA requires the use of open-hearth, basic oxygen, or electric steel of uniform quality. Approved alloys include 4130X, NE-8630, 9115, 9125, Carbon-boron and Intermediate manganese, with specified constituents, including manganese and carbon,and molybdenum, chromium, boron, nickel or zirconium.[14]

Steel cylinders may be manufactured from steel plate discs, which are cold drawn to a cylindrical cup form, in two or three stages, and generally have a domed base if intended for the scuba market, so they cannot stand up by themselves. After forming the base and side walls, the top of the cylinder is trimmed to length, heated and hot spun to form the shoulder and close the neck. This process thickens the material of the shoulder. The cylinder is heat-treated by quenching and tempering to provide the best strength and toughness. The cylinders are machined to provide the neck thread and o-ring seat (if applicable), then chemically cleaned or shot-blasted inside and out to remove mill-scale. After inspection and hydrostatic testing they are stamped with the required permanent markings, followed by external coating with a corrosion barrier paint or hot dip galvanising.[15]

Cylinder neck

The neck of the cylinder is internally threaded to fit a cylinder valve. There are several standards for neck threads, these include:

Parallel threads are made to several standards:

The 3/4"NGS and 3/4"BSP are very similar, having the same pitch and a pitch diameter that only differs by about 0.2 mm (0.008 in), but they are not compatible, as the thread forms are different.

All parallel thread valves are sealed using an O-ring at top of the neck thread which seals in a chamfer or step in the cylinder neck and against the flange of the valve.

The shoulder of the cylinder carries stamp markings providing required information about the cylinder.[20]

The cylinder valve

Regulators with DIN- and yoke-valve.

The purpose of the cylinder valve or pillar valve is to control gas flow to and from the pressure vessel and to provide a connection with the regulator or filling hose.[1] Cylinder valves are usually machined from brass and finished by a protective and decorative layer of chrome-plating.[21] A metal or plastic dip tube or valve snorkel screwed into the bottom of the valve extends into the cylinder to reduce the risk of liquid or particulate contaminants in the cylinder getting into the gas passages when the cylinder is inverted, and blocking or jamming the regulator. Some of these dip tubes have a plain opening, but some have an integral filter.[22][23]

Cylinder valves are classified by four basic aspects: The cylinder thread specification, the connection to the regulator, pressure rating, and other distinguishing features.

Cylinder thread variations

Cylinder threads may be in two basic configurations: Taper thread and parallel thread.[1] These thread specifications are detailed in a previous section. The valve thread specification must exactly match the neck thread specification of the cylinder. Improperly matched neck threads can fail under pressure and can have fatal consequences if someone is hit by the flying valve or cylinder.

Connection to the regulator

Section view of A-clamp-, yoke- or INT-valve, showing the sealing surfaces, according to ISO 12209-3.

A rubber o-ring forms a seal between the metal of the pillar valve and the metal of the diving regulator. Fluoroelastomer (e.g. viton) O-rings may be used with cylinders storing oxygen-rich gas mixtures to reduce the risk of fire.[24] There are two basic types of cylinder valve to regulator connection in general use for Scuba cylinders containing air:

Section view of DIN-valve to regulator connection, showing the sealing surfaces, according to ISO 12209-2.

There are also cylinder valves for scuba cylinders containing gases other than air:

Pressure rating

Yoke valves are rated between 200 and 240 bar, and there does not appear to be any mechanical design detail preventing connection between any yoke fittings, though some older yoke clamps will not fit over the popular 232/240 bar combination DIN/yoke cylinder valve as the yoke is too narrow.

DIN valves are produced in 200 bar and 300 bar pressure ratings. The number of threads and the detail configuration of the connections is designed to prevent incompatible combinations of filler attachment or regulator attachment with the cylinder valve.[29]

Adaptors are available to allow connection of DIN regulators to yoke cylinder valves (A-clamp or yoke adaptor), and to connect yoke regulators to DIN cylinder valves.[29] (plug adaptors and block adaptors) Plug adaptors are rated for 232/240 bar, and can only be used with valves which are designed to accept them. Block adaptors are generally rated for 200 bar, and can be used with almost any 200 bar DIN valve.

Other distinguishing features

Plain valves
A 12-litre, 232 bar cylinder with DIN valve. The shoulder colour-coding is the old UK standard for compressed breathing air prior to 2006
"H"-valve with DIN connections
Reserve valves
A J-valve from c.1960
Draeger 200 bar cylinder valves with manifold and reserve lever
Draeger taper thread cylinder valve with reserve lever
Handed valves

Some cylinder valve models have axial spindles - in line with the cylinder axis, and are not handed. Standard side-spindle valves have the handwheel on the diver's right side when back-mounted. Side-spindle valves used with manifolds must be a handed pair - one with the handwheel to the right and the other with the handwheel to the left, but in all cases the valve is opened by turning the handwheel anticlockwise, and closed by turning it clockwise. This is the convention with almost all valves for all purposes. Left hand side-spindle valves are used by sidemount divers.[12][32]

Bursting disk

Some national standards require that the cylinder valve includes a bursting disk, a pressure relief device that will release the gas before the cylinder fails in the event of overpressurization.[1] If a bursting disk ruptures during a dive the entire contents of the cylinder will be lost in a very short time. The risk of this happening to a correctly rated disc, in good condition, on a correctly filled cylinder is very low.

Accessories

Additional components for convenience, protection or other functions, not directly required for the function as a pressure vessel.

Manifolds

Main article: Manifold (scuba)
Face sealed isolation manifold on twin 12 l steel cylinders. The plastic discs are records of the latest internal inspection
Draeger 200 bar cylinder manifold
Barrel seal isolation manifold
Left side cylinder valve for barrel seal manifold with blanking plug and DIN connection

A cylinder manifold is a tube which connects two cylinders together so that the contents of both can be supplied to one or more regulators.[31][33] There are three commonly used configurations of manifold:

A relatively uncommon manifold system is a connection which screws directly into the neck threads of both cylinders, and has a single valve to release gas to a connector for a regulator. These manifolds can include a reserve valve, either in the main valve or at one cylinder. This system is mainly of historical interest.[13]

Valve cage

Also known as a manifold cage or regulator cage, this is a structure which can be clamped to the neck or shoulder of the cylinder or manifolded cylinders to protect the valves and regulator first stages from impact and abrasion damage while in use[33] and from rolling the valve closed by friction of the handwheel against an overhead. A valve cage is often made of stainless steel,[33] and some designs can snag on obstructions.

Cylinder bands

Cylinder bands are straps, usually of stainless steel, which are used to clamp two cylinders together as a twin set. The cylinders may be manifolded or independent. It is usual to use a cylinder band near the top of the cylinder, just below the shoulders, and one lower down. The conventional distance between centrelines for bolting to a backplate is 11 inches (280 mm).

Cylinder boot

Twinned cylinders showing cylinder boots, nets and lower band

A cylinder boot is a hard rubber or plastic cover which fits over the base of a diving cylinder to protect the paint from abrasion and impact, to protect the surface the cylinder stands on from impact with the cylinder, and in the case of round bottomed cylinders, to allow the cylinder to stand upright on its base.[1] Some boots have flats moulded into the plastic to reduce the tendency of the cylinder to roll on a flat surface.[34] It is possible in some cases for water to be trapped between the boot and the cylinder, and if this is seawater and the paint under the boot is in poor condition, the surface of the cylinder may corrode in those areas.[1][35] This can usually be avoided by rinsing in fresh water after use and storing in a dry place. The added hydrodynamic drag caused by a cylinder boot is trivial in comparison with the overall drag of the diver, but some boot styles may present a slightly increased risk of snagging on the environment.

Cylinder net

A cylinder net is a tubular net which is stretched over a cylinder and tied on at top and bottom. The function is to protect the paintwork from scratching, and on booted cylinders it also helps drain the surface between the boot and cylinder, which reduces corrosion problems under the boot. Mesh size is usually about 6 millimetres (0.24 in). Some divers will not use boots or nets as they can snag more easily than a bare cylinder and constitute an entrapment hazard in some environments such as caves and the interior of wrecks. Occasionally sleeves made from other materials may be used to protect the cylinder.[34]

Cylinder handle

A 15-litre, 232 bar cylinder with "Yoke" connection valve and cylinder handle

A cylinder handle may be fitted, usually clamped to the neck, to conveniently carry the cylinder. This can also increase the risk of snagging in an enclosed environment.

Dust caps and plugs

These are used to cover the cylinder valve orifice when the cylinder is not in use to prevent dust, water or other materials from contaminating the orifice. They can also help prevent the O-ring of a yoke type valve from falling out. The plug may be vented so that the leakage of gas from the cylinder does not pressurise the plug, making it difficult to remove.[36]

Cylinder pressure rating

The thickness of the cylinder walls is directly related to the working pressure, and this affects the buoyancy characteristics of the cylinder. A low-pressure cylinder will be more buoyant than a high-pressure cylinder with similar size and proportions of length to diameter and in the same alloy.

Working pressure

Scuba cylinders are technically all high-pressure gas containers, but within the industry in the US there are three nominal working pressure ratings (WP) in common use;[37]

low pressure (2400 to 2640 psi — 165 to 182 bar),
standard (3000 psi — 207 bar), and
high pressure (3300 to 3500 psi — 227 to 241 bar).

US made aluminum cylinders usually have a standard working pressure of 3,000 pounds per square inch (210 bar), and the compact aluminum range have a working pressure of 3,300 pounds per square inch (230 bar). Some steel cylinders manufactured to US standards are permitted to exceed the nominal working pressure by 10% and this is indicated by a '+' symbol. This extra pressure allowance is dependent on the cylinder passing the appropriate higher standard periodical hydrostatic test.[22]

Those parts of the world using the metric system usually refer to the cylinder pressure directly in bar but would generally use "high pressure" to refer to a 300 bars (4,400 psi) working pressure cylinder, which can not be used with a yoke connector on the regulator. 232 bar is a very popular working pressure for scuba cylinders in both steel and aluminium.

Test pressure

Hydrostatic test pressure (TP) is specified by the manufacturing standard. This is usually 1.5 × working pressure, or in the USA, 1.67 × working pressure.

Developed pressure

Cylinder working pressure is specified at a reference temperature, usually 15 °C or 20 °C.[38] and cylinders also have a specified maximum safe working temperature, often 65 °C.[38] The actual pressure in the cylinder will vary with temperature, as described by the gas laws, but this is acceptable in terms of the standards provided that the developed pressure when corrected to the reference temperature does not exceed the specified working pressure stamped on the cylinder. This allows cylinders to be safely and legally filled to a pressure that is higher than the specified working pressure when the filling temperature is greater than the reference temperature, but not more than 65 °C, provided that the filling pressure does not exceed the developed pressure for that temperature, and cylinders filled according to this provision will be at the correct working pressure when cooled to the reference temperature.[38]

Cylinder capacity

12 litre and 3 litre steel diving cylinders: Typical Primary and Pony sizes

There are two commonly used conventions for describing the capacity of a diving cylinder. One is based on the internal volume of the cylinder. The other is based on nominal volume of gas stored.

Internal volume

The internal volume is commonly quoted in most countries using the metric system. This information is required by ISO 13769 to be stamped on the cylinder shoulder. It can be measured easily by filling the cylinder with fresh water. This has resulted in the term 'water capacity', abbreviated as WC which is often marked on the cylinder shoulder. It's almost always expressed as a volume in litres, but sometimes as mass of the water in kg. Fresh water has a density close to one kilogram per litre so the numerical values will be similar.[20]

Standard sizes by internal volume

These are representative examples, for a larger range, the on-line catalogues of the manufacturers such as Faber, Pressed Steel, Luxfer, and Catalina may be consulted. The applications are typical, but not exclusive.

Nominal volume of gas stored

The nominal volume of gas stored is commonly quoted as the cylinder capacity in the USA. It is a measure of the volume of gas that can be released from the full cylinder at atmospheric pressure.[44] Terms used for the capacity include 'free gas volume' or 'free gas equivalent'. It depends on the internal volume and the working pressure of a cylinder. If the working pressure is higher, the cylinder will store more gas for the same volume.

The nominal working pressure is not necessarily the same as the actual working pressure used. Some steel cylinders manufactured to US standards are permitted to exceed the nominal working pressure by 10% and this is indicated by a '+' symbol. This extra pressure allowance is dependent on the cylinder passing the appropriate periodical hydrostatic test and is not necessarily valid for US cylinders exported to countries with differing standards. The nominal gas content of these cylinders is based on the 10% higher pressure.[22]

For example, common Aluminum 80 (Al80) cylinder is an aluminum cylinder which has a nominal 'free gas' capacity of 80 cubic feet (2,300 L) when pressurized to 3,000 pounds per square inch (210 bar). It has an internal volume of 10.94 litres (0.386 cu ft).

Standard sizes by volume of gas stored

Applications and configurations of diving cylinders

Technical diver with decompression gases in side mounted stage cylinders.

Divers may carry one cylinder or multiples, depending on the requirements of the dive. Where diving takes place in low risk areas, where the diver may safely make a free ascent, or where a buddy is available to provide an alternative air supply in an emergency, recreational divers usually carry only one cylinder. Where diving risks are higher, for example where the visibility is low or when recreational divers do deeper or decompression diving, and particularly when diving under an overhead, divers routinely carry more than one gas source.

Diving cylinders may serve different purposes. One or two cylinders may be used as a primary breathing source which is intended to be breathed from for most of the dive. A smaller cylinder carried in addition to a larger cylinder is called a "pony bottle". A cylinder to be used purely as an independent safety reserve is called a "bailout bottle" or Emergency Gas Supply (EGS).[31] A pony bottle is commonly used as a bailout bottle, but this would depend on the time required to surface.

Divers doing technical diving often carry different gases, each in a separate cylinder, for each phase of the dive:[47]

For safety, divers sometimes carry an additional independent scuba cylinder with its own regulator to mitigate out-of-air emergencies should the primary breathing gas supply fail. For much common recreational diving where a controlled emergency swimming ascent is acceptably safe, this extra equipment is not needed or used. This extra cylinder is known as a bail-out cylinder, and may be carried in several ways, and can be any size that can hold enough gas to get the diver safely back to the surface.[1]

Open-circuit scuba

For open-circuit scuba divers, there are several options for the combined cylinder and regulator system:

15 litre, 232 bar, A-clamp single cylinder open circuit scuba set
7 litre, 232 bar, DIN pillar valve independent twin set. The left cylinder shows manufacturer markings. The right cylinder shows test stamps
Isolation manifolded twin 12 litre, 232 bar scuba set with two A-clamp pillar valves and two regulators
Long 9.2 litre aluminium cylinder rigged for sling mounting
Sidemount cylinder set with regulators fitted.

Rebreathers

Main article: Rebreather diving
Two 3 litre, 232 bar, DIN valved cylinders inside an Inspiration electronically controlled closed circuit diving rebreather.

Diving cylinders are used in rebreather diving in two roles:

  • oxygen rebreathers have an oxygen cylinder
  • semi-closed circuit rebreathers have a cylinder which usually contains nitrox or a helium based gas.[53]
  • closed circuit rebreathers have an oxygen cylinder and a "diluent" cylinder, which contains air, nitrox or a helium based gas.[53]

Surface supplied diver emergency gas supply

Commercial surface supplied diver wearing a single bailout cylinder plumbed into the helmet bailout block

Surface supplied divers are usually required to carry an emergency gas supply sufficient to allow them to return to a place of safety if the main gas supply fails. The usual configuration is a back mounted single cylinder supported by the diver's safety harness, with first stage regulator connected by a low pressure hose to a bailout block, which may be mounted on the side of the helmet or band-mask or on the harness to supply a lightweight full-face mask.[31][55][56] Where the capacity of a single cylinder in insufficient, plain manifolded twins or a rebreather may be used. For closed bell bounce and saturation dives the bailout set must be compact enough to allow the diver to pass through the bottom hatch of the bell. This sets a limit on the size of cylinders that can be used.[50][51]

Emergency gas supply on diving bells

Exterior view of closed bell used for saturation diving showing emergency gas supply cylinders

Diving bells are required to carry an on-board supply of breathing gas for use in emergencies.[57][58] The cylinders are mounted externally as there is insufficient space inside. They are fully immersed in the water during bell operations, and may be considered diving cylinders.

Gas calculations

Further information: Scuba gas planning

It is necessary to know the approximate length of time that a diver can breathe from a given cylinder so that a safe dive profile can be planned.[59]

There are two parts to this problem: The cylinder and the diver.

The cylinder's capacity to store gas

Two features of the cylinder determine its gas carrying capacity:

To calculate the quantity of gas:

Volume of gas at atmospheric pressure = (cylinder volume) x (cylinder pressure) / (atmospheric pressure)

In those parts of the world using the metric system the calculation is relatively simple as atmospheric pressure may be approximated as 1 bar, So a 12-litre cylinder at 232 bar would hold almost 12 × 232 / 1 = 2,784 litres (98.3 cu ft) of air at atmospheric pressure (also known as free air).

In the US the capacity of a diving cylinder is specified directly in cubic feet of free air at the nominal working pressure, as the calculation from internal volume and working pressure is relatively tedious in imperial units. For examle, in the US and in many diving resorts in other countries, one might find aluminum cylinders of US manufacture with an internal capacity of 0.39 cubic feet (11 L) filled to a working pressure of 3,000 psi (210 bar); Taking atmospheric pressure as 14.7 psi, this gives 0.39 × 3000 / 14.7 = 80 ft³ These cylinders are described as "80 cubic foot cylinders", (the common "aluminum 80").

Up to about 200 bar the ideal gas law remains valid and the relationship between the pressure, size of the cylinder and gas contained in the cylinder is linear; at higher pressures there is proportionally less gas in the cylinder. A 3-litre cylinder filled to 300 bar will only carry contain 810 litres (29 cu ft) of atmospheric pressure gas and not the 900 litres expected from the ideal gas law.

Diver gas consumption

There are three main factors to consider:

To calculate the quantity of gas consumed:

gas consumed = surface air consumption × time × ambient pressure

Metric examples:

A diver with a RMV of 20 L/min at 30 msw (4 bar), will consume 20 x 4 x 1 = 80 L/min surface equivalent.
A diver with a RMV of 40 L/min at 50 msw (6 bar) for 10 minutes will consume 40 x 6 x 10 = 2400 litres of free air – the full capacity of a 12 litre 200 bar cylinder.

Imperial examples:

A diver with a SAC of 0.5 cfm (cubic feet per minute) at 100 fsw (4 ata) will consume 0.5 x 4 x 1 = 2 cfm surface equivalent.
A diver with a SAC of 1 cfm at 231 fsw (8 ata) for 10 minutes will consume 1 x 8 x 10 = 80 ft3 of free air – the full capacity of an 80 ft3 cylinder

Keeping this in mind, it is not hard to see why technical divers who do long deep dives require multiple cylinders or rebreathers, and commercial divers normally use surface-supplied diving equipment, and only carry scuba as an emergency gas supply.

Breathing gas endurance

The amount of time that a diver can breathe from a cylinder is also known as air or gas endurance.

Absolute maximum breathing duration (BT) for a given depth can be calculated as

BT = available air / rate of consumption[1]

which, using the ideal gas law, is

BT = (available cylinder pressure × cylinder volume) / (rate of air consumption at surface) × (ambient pressure)[1]

This may be written as

(1) BT = (PC-PA)*VC/(SAC*PA)

with

BT = Breathing Time
PC = Cylinder Pressure
VC = Cylinder internal volume
PA = Ambient Pressure
SAC = Surface air consumption

in any consistent system of units.

Ambient pressure (PA) is the surrounding water pressure at a given depth and is made up of the sum of the hydrostatic pressure and the air pressure at the surface. It is calculated as

(2) PA = D*g*ρ + atmospheric pressure[1]

with

D = depth
g = Standard gravity
ρ = water density

in a consistent system of units

For metric units, this formula can be approximated by

(3) PA = D/10 + 1

with depth in m and pressure in bar

Ambient pressure is deducted from cylinder pressure, as the quantity of air represented by PA can in practice not be used for breathing by the diver as it required to balance the ambient pressure of the water.

This formula neglects the cracking pressure required to open both first and second stages of the regulator, and pressure drop due to flow restrictions in the regulator,both of which are variable depending on the design and adjustment of the regulator, and flow rate, which depends on the breathing pattern of the diver and the gas in use. These factors are not easily estimated, so the calculated value for breathing duration will be more than the real value.

However, in normal diving usage, a reserve is always factored in. The reserve is a proportion of the cylinder pressure which a diver will not plan to use other than in case of emergency. The reserve may be a quarter or a third of the cylinder pressure or it may be a fixed pressure, common examples are 50 bar and 500 psi. The formula above is then modified to give the usable breathing duration as

(4) BT = (PC-PR)*VC/(SAC*PA)

where PR is the reserve pres

For example, (using the first formula (1) for absolute maximum breathing time), a diver at a depth of 15 meters in water with an average density of 1020 kg/m³ (typical seawater), who breathes at a rate of 20 litres per minute, using a dive cylinder of 18 litres pressurized at 200 bars, can breathe for a period of 72 minutes before the cylinder pressure falls so low as to prevent inhalation. In some open circuit scuba systems this can happen quite suddenly, from a normal breath to the next abnormal breath, a breath which may not be fully drawn. (There is never any difficulty exhaling). The suddenness of this effect depends on the design of the regulator and the internal volume of the cylinder. In such circumstances there remains air under pressure in the cylinder, but the diver is unable to breathe it. Some of it can be breathed if the diver ascends, as the ambient pressure is reduced, and even without ascent, in some systems a bit of air from the cylinder is available to inflate buoyancy compensator devices (BCDs) even after it no longer has pressure enough to open the demand valve.

Using the same conditions and a reserve of 50 bar, the formula (4) for usable breathing time is follows:

Ambient pressure = water pressure + atmospheric pressure = 15 msw/10 bar per msw + 1 = 2.5 bar
Usable pressure = fill pressure - reserve pressure = 200 bar - 50 bar = 150 bar
Usable air = usable pressure * cylinder capacity = 150 bar * 18 litres per bar = 2700 litres
Rate of consumption = surface air consumption * ambient pressure = 20 litres per minute per bar * 2.5 bar = 50 litres/min
Usable breathing time = 2700 litres / 50 litres per min = 54 minutes

This would give a dive time of 54 min at 15 m before reaching the reserve of 50 bar.

Reserves

It is strongly recommended by diver training organisations and codes of practice that a portion of the usable gas of the cylinder be held aside as a safety reserve. The reserve is designed to provide gas for longer than planned decompression stops or to provide time to resolve underwater emergencies.[1]

The size of the reserve depends upon the risks involved during the dive. A deep or decompression dive warrants a greater reserve than a shallow or a no stop dive. In recreational diving for example, it is recommended that the diver plans to surface with a reserve remaining in the cylinder of 500 psi, 50 bar or 25% of the initial capacity, depending of the teaching of the diver training organisation. This is because recreational divers practicing within "no-decompression" limits can normally make a direct ascent in an emergency. On technical dives where a direct ascent is either impossible (due to overhead obstructions) or dangerous (due to the requirement to make decompression stops), divers plan larger margins of safety. The simplest method uses the rule of thirds: one third of the gas supply is planned for the outward journey, one third is for the return journey and one third is a safety reserve.[61]

Some training agencies teach the concept of minimum gas, rock bottom gas management or critical pressures which allows a diver to calculate an acceptable reserve to get two divers to the surface in an emergency from any point in the planned dive profile.[47]

Professional divers may be required by legislation or industry codes of practice to carry sufficient reserve gas to enable them to reach a place of safety, such as the surface, or a diving bell, based on the planned dive profile.[55][56] This reserve gas is usually required to be carried as an independent emergency gas supply (EGS), also known as a bailout cylinder, set or bottle.[62] This usually also applies to professional divers using surface-supplied diving equipment.[55]

Weight of gas consumed

The density of air at sea level and 15 °C is approximately 1.225 kg/m3.[63] Most full-sized diving cylinders used for open circuit scuba hold more than 2 kilograms (4.4 lb) of air when full, and as the air is used, the buoyancy of the cylinder increases by the weight removed. The decrease in external volume of the cylinder due to reduction of internal pressure is relatively small, and can be ignored for practical purposes.

As an example, a 12-litre cylinder may be filled to 230 bar before a dive, and be breathed down to 30 bar before surfacing, using 2,400 litres or 2.4 m3 of free air. The mass of gas used during the dive will depend on the mixture - if air is assumed, it will be approximately 2.9 kilograms (6.4 lb).

The loss of the weight of the gas taken from the cylinder makes the cylinder and diver more buoyant. This can be a problem if the diver is unable to remain neutrally buoyant towards the end of the dive because most of the gas has been breathed from the cylinder. The buoyancy change due to gas usage from back mounted cylinders is easily compensated by carrying sufficient diving weights to provide neutral buoyancy with empty cylinders at the end of a dive, and using the buoyancy compensator to neutralise the excess weight until the gas has been used.

The change in buoyancy of diving cylinder during the dive can be more problematic with side-mounted cylinders, and the actual buoyancy at any point during the dive is a consideration with any cylinder that may be separated from the diver for any reason. Cylinders which will be stage-dropped or handed off to another diver should not change the diver's buoyancy beyond what can be compensated using their buoyancy compensator. Cylinders with approximately neutral buoyancy when full generally require the least compensation when detached.

Table showing the buoyancy of diving cylinders in water when empty and full of air
Cylinder specification Air capacity Weight in air Buoyancy in water
Material Volume
(litre)		 Pressure
(bar)		 Volume
(litre)		 Weight
(kg)		 Empty
(kg)		 Full
(kg)		 Empty
(kg)		 Full
(kg)
Steel 12 200 2400 3.0 16.0 19.0 -1.2 -4.2
15 200 3000 3.8 20.0 23.8 -1.4 -5.2
16 (XS 130) 230 3680 4.4 19.5 23.9 -0.9 -5.3
2x7 200 2800 3.4 19.5 23.0 -2.2 -5.6
8 300 2400 2.9 13.0 16.0 -3.6 -6.5
10 300 3000 3.6 17.0 20.8 -4.2 -7.8
2x4 300 2400 2.9 15.0 18.0 -4.1 -7.0
2x6 300 3600 4.4 21.0 25.6 -5.2 -9.6
Aluminium 9 (AL 63) 207 1863 2.3 12.2 13.5 +1.8 -0.5
11 (AL 80) 207 2277 2.8 14.4 17.2 +1.7 -1.1
13 (AL100) 207 2584 3.2 17.1 20.3 +1.4 -1.8
Assumes 1 litre of air at atmospheric pressure and 15 °C weighs 1.225 g.[64]
Cylinder, valve and manifold weights will vary depending on model, so actual values will value accordingly.

Filling cylinders

Dive shop scuba filling station
Small stationary HP compressor installation

Legal constraints to filling scuba cylinders will vary by jurisdiction.

Diving cylinders should only be filled with suitably filtered air from diving air compressors or with other breathing gases using gas blending or decanting techniques.[65] In some jurisdictions, suppliers of breathing gases are required by legislation to periodically test the quality of compressed air produced by their equipment and to display the test results for public information.[38] The standards for industrial gas purity and filling equipment and procedures may allow some contaminants at levels unsafe for breathing,[1] and their use in breathing gas mixtures at high pressure could be harmful or fatal.

Special precautions need to be taken with gases other than air:

Contaminated air at depth can be fatal. Common contaminants are: carbon monoxide - a by-product of combustion, carbon dioxide - a product of metabolism, and oil and lubricants from the compressor.[65]

Keeping the cylinder slightly pressurized at all times reduces the possibility of inadvertently contaminating the inside of the cylinder with corrosive agents, such as sea water, or toxic material, such as oils, poisonous gases, fungi or bacteria.[35]

Contamination by water during filling may be due two two causes. Inadequate filtration and drying of the compressed air can introduce small quantities of fresh water condensate, or an emulsion of water and compressor lubricant, and failing to clear the cylinder valve orifice of water which may have dripped from wet dive gear, which can allow contamination by fresh or seawater. Both cause corrosion, but seawater contamination can cause a cylinder to corrode rapidly to the extent that it may be unsafe or condemned after even a fairly short period. This problem is exacerbated in hot climates, where chemical reactions are faster, and is more prevalent where filling staff are badly trained or overworked.[66]

The blast caused by a sudden release of the gas pressure inside a diving cylinder makes them very dangerous if mismanaged. The greatest risk of explosion exists while filling,[1] but cylinders have also been known to burst when overheated. The cause of failure can range from reduced wall thickness or deep pitting due to internal corrosion, neck thread failure due to incompatible valve threads, or cracking due to fatigue, sustained high stresses, or overheating effects in aluminum.[35][67]

Inspection and testing

Condemned diving cylinders set aside for metal recycling

Most countries require diving cylinders to be checked on a regular basis. This usually consists of an internal visual inspection and a hydrostatic test. The inspection and testing requirements for scuba cylinders may be very different from the requirements for other compressed gas containers due to the more corrosive environment.[38]

Water jacket hydrostatic test test diagram

A hydrostatic test involves pressurising the cylinder to its test pressure (usually 5/3 or 3/2 of the working pressure) and measuring its volume before and after the test. A permanent increase in volume above the tolerated level means the cylinder fails the test and must be permanently removed from service.[1]

An inspection includes external and internal inspection for damage, corrosion, and correct colour and markings. The failure criteria vary according to the published standards of the relevant authority, but may include inspection for bulges, overheating, dents, gouges, electrical arc scars, pitting, line corrosion, general corrosion, cracks, thread damage, defacing of permanent markings, and colour coding.[1][38]

When a cylinder is manufactured, its specification, including manufacturer, working pressure, test pressure, date of manufacture, capacity and weight are stamped on the cylinder.[72]

After a cylinder passes the test, the test date, (or the test expiry date in some countries such as Germany), is punched into the shoulder of the cylinder for easy verification at fill time. [note 1] There is an international standard for the stamp format.[72]

Compressor operators may be required to check these details before filling the cylinder and may refuse to fill non-standard or out-of-test cylinders. [note 2]

Safety

Before any cylinder is filled, verification of testing dates and a visual examination for external damage and corrosion are required by law in some jurisdictions,[38] and are prudent even if not legally required at other places. Test dates can be checked by looking at the visual inspection sticker and the hydro-test date is stamped on top of the cylinder.[38]

Before use the user should verify the contents of the cylinder and check the function of the cylinder valve. This is usually done with a regulator connected to control the flow. Pressure and gas mixture are critical information for the diver, and the valve should open freely without sticking or leaks from the spindle seals. Breathing gas bled from a cylinder may be checked for smell. If the gas does not smell right it should not be used. Breathing gas should be almost free of smell, though a very slight aroma of the compressor lubricant is fairly common. No smell of combustion products or volatile hydrocarbons should be discernible.[1] Failure to recognize that the gas was not on or that cylinder was empty by divers conducting a pre-dive evaluation has been noted.[73]

A neatly assembled setup, with regulators, gauges, and delicate computers stowed inside the BCD, or clipped where they will not be walked on, and stowed under the boat bench or secured to a rack, is the practice of a competent diver.

As the scuba set is a life support system, no unauthorised person should touch a diver's gear, even to move it, without their knowledge and approval.

Full cylinders should not be exposed to temperatures above 65 °C[38] and cylinders should not be filled to pressures greater than the developed pressure appropriate to the certified working pressure of the cylinder.[38]

Cylinders should be clearly labelled with their current contents. A generic "Nitrox" or "Trimix" label will alert the user that the contents may not be air, and must be analysed before use. In some parts of the world a label is required specifically indicating that the contents are air, and in other places a colour code without additional labels indicates by default that the contents are air.[38]

In a fire, the pressure in a gas cylinder rises in direct proportion to its absolute temperature. If the internal pressure exceeds the mechanical limitations of the cylinder and there are no means to safely vent the pressurized gas to the atmosphere, the vessel will fail mechanically. If the vessel contents are ignitable or a contaminant is present this event may result in an explosion.[74]

Accidents

The major diving accident and fatality research studies that have been conducted globally including work by the Divers Alert Network, the Diving Incident Monitoring Study, and Project Stickybeak have each identified cases where the mortality was associated with the diving cylinder.[75][76]

Some recorded accidents associated with diving cylinders:[67]

Cases of lateral epicondylitis have been reported caused by the handling of diving cylinders.[77]

Handling

Cylinders should not be left standing unattended unless secured[38] so that they can not fall in reasonably foreseeable circumstances as an impact could damage the cylinder valve mechanism, and conceivably fracture the valve at the neck threads. This is more likely with taper thread valves, and when it happens most of the energy of the compressed gas is released within a second, and can accelerate the cylinder to speeds which can cause severe injury or damage to the surroundings.[1][31]

Long term storage

Breathing quality gases do not normally deteriorate during storage in steel or aluminium cylinders. Provided there is insufficient water content to promote internal corrosion, the stored gas will remain unchanged for years if stored at temperatures within the allowed working range for the cylinder, usually below 65 °C. If there is any doubt, a check of oxygen fraction will indicate whether the gas has changed (the other components are inert). Any unusual smells would be an indication that the cylinder or gas was contaminated at the time of filling. However some authorities recommend releasing most of the contents and storing cylinders with a small positive pressure.[31]

Transportation

See also: Dangerous goods

Diving cylinders are classified by the UN as dangerous goods for transportation purposes (US: Hazardous materials). Selecting the Proper Shipping Name (well known by the abbreviation PSN) is a way to help ensure that the dangerous goods offered for transport accurately represent the hazards.[78]

IATA Dangerous Goods Regulations (DGR) 55th Edition defines the Proper Shipping Name as "the name to be used to describe a particular article or substance in all shipping documents and notifications and, where appropriate, on packagings".[78]

The International Maritime Dangerous Goods Code (IMDG Code) defines the Proper Shipping Name as "that portion of the entry most accurately describing the goods in the Dangerous Goods List which is shown in upper-case characters (plus any letters which form an integral part of the name)."[78]

Hazardous materials
descriptions and
proper shipping names
(PSN)[79][80][81]		 Hazard class
or division		 Identification
numbers		 Label codes Quantity
limitations
Air, compressed 2.2 UN1002 2.2 Passenger aircraft/rail: 75 kg
Cargo aircraft only: 150 kg
Argon, compressed 2.2 UN1006 2.2
Helium, compressed 2.2 UN1046 2.2
Nitrogen, compressed 2.2 UN1066 2.2
Oxygen, compressed 2.2 UN1072 2.2, 5.1
Compressed gas N.O.S. (not otherwise specified)
e.g. normoxic and hypoxic Heliox and Trimix		 2.2 UN1956 2.2
Compressed gas, oxidising, N.O.S
e.g. Nitrox 		2.2 UN3156 2.2, 5.1

International air

International Civil Aviation Organisation (ICAO) Technical Instructions for the Safe Transport of Dangerous Goods by Air states that provided that pressure in diving cylinders is less than 200 kilopascals (2 bar; 29 psi), these can be carried as checked in or carry-on baggage. It maybe necessary to empty the cylinder to verify this. Once emptied, the cylinder valve should be closed to prevent moisture entering the cylinder. Security restrictions implemented by individual countries may further limit or forbid the carriage of some items permitted by ICAO, and airlines and security screening agencies have the right to refuse the carriage of certain items.[82]

Europe

Since 1996 the carriage of dangerous goods legislation of the UK has been harmonized with that of Europe.[83]

Road transport

The 2009 (amended 2011) UK Carriage of Dangerous Goods and Use of Transportable Pressure Equipment Regulations (CDG Regulations) implement the European Agreement Concerning the International Carriage of Dangerous Goods by Road (ADR). Dangerous goods to be carried internationally in road vehicles must comply with standards for the packaging and labelling of the dangerous goods, and appropriate construction and operating standards for the vehicles and crew.[80][83]

The regulations cover transportation of gas cylinders in a vehicle in a commercial environment. Transportation of pressurised diving gas cylinders with a combined water capacity of less than 1000 litres on a vehicle for personal use is exempt from ADR.[80][83][84]

Transport of gas cylinders in a vehicle, for commercial purposes, must follow basic legal safety requirements and, unless specifically exempted, must comply with ADR. The driver of the vehicle is legally responsible for the safety of the vehicle and any load being carried, and insurance for the vehicle should include cover for the carriage of dangerous goods.[80][83]

Diving gases, including compressed air, oxygen, nitrox, heliox, trimix, helium and argon, are non-toxic, non flammable, and may be oxidizer or asphyxiant, and are rated in Transport category 3.[83] The threshold quantity for these gases is 1000 litres combined water capacity of the cylinders. Pressure must be within the rated working pressure of the cylinder. Empty air cylinders at atmospheric pressure are rated in Transport category 4, and there is no threshold quantity.[80][83]

Commercial loads below the 1000 litres threshold level are exempt from some of the requirements of ADR, but must comply with basic legal and safety requirements, including:[83]

All loads above the threshold must comply with the full requirements of ADR.[80][83]

USA

Transportation of hazardous materials for commercial purposes[85] in the USA is regulated by Code of Federal Regulations Title 49 - Transportation, (abbreviated 49 CFR).[86] A cylinder containing 200 kPa (29.0 psig/43.8 psia) or greater at 20 °C (68 °F) of non-flammable, nonpoisonous compressed gas, and being transported for commercial purposes is classified as HAZMAT (hazardous materials) in terms of 49 CFR 173.115(b) (1).[87] Cylinders manufactured to DOT standards or special permits (exemptions)issued by the Pipeline and Hazardous Materials Safety Administration and filled to the authorized working pressure are legal for commercial transport in the USA under the provisions and conditions of the regulations.[86][88] Cylinders manufactured outside the USA may be transported under a special permit, and these have been issued for solid metal and composite cylinders with working pressures of up to 300 bar (4400 psi) by several manufacturers.

Surface transport

Commercial transportation of breathing gas cylinders with a combined weight of more than 1000 pounds may only be done by a commercial HAZMAT transportation company. Transport of cylinders with a combined weight of less than 1000 pounds requires a manifest, the cylinders must have been tested and inspected to federal standards, and the contents marked on each cylinder. Transportation must be done in a safe manner, with the cylinders restrained from movement. No special licence is required. DOT regulations require content labels for all cylinders under the regulations, but according to PSI, labelling of breathing air will not be enforced. Oxygen or non-air oxidizing (23.5+% O2) mixtures must be labelled. Private (non-commercial) transport of scuba cylinders is not covered by this regulation.[89]

Air transport

Empty scuba tanks or scuba tanks pressurized at less than 200 kPa are not restricted as hazardous materials.[90] Scuba cylinders are only allowed in checked baggage or as a carry-on if the cylinder valve is completely disconnected from the cylinder and the cylinder has an open end to allow for a visual inspection inside.[91]

Gas cylinder colour-coding and labeling

A contents label for oxygen usage (UK), which incorporates the hazardous materials diamonds for compressed gas (green) and oxidizer (yellow)
A steel 15 litre cylinder with net and boot and a bare 12 litre aluminium cylinder. Both are labeled for Nitrox use. The aluninium cylinder also displays a triangular label specifying the date of the most recent internal inspection and an oval label recording the most recent neck thread eddy current test.

Worldwide

The colours permitted for diving cylinders vary considerably by region, and to some extent by the gas mixture contained.

In some parts of the world there is no legislation controlling the colour of diving cylinders. In other regions the colour of cylinders used for commercial diving, or for all underwater diving may be specified by national standards.[38]

In many recreational diving settings where air and nitrox are the widely used gases, nitrox cylinders are identified with a green stripe on yellow background. Aluminium diving cylinders may be painted or anodized and when anodized may be coloured or left in their natural silver. Steel diving cylinders are usually painted, to reduce corrosion, often yellow or white to increase visibility. In some industrial cylinder identification colour tables, yellow shoulders means chlorine and more generally within Europe it refers to cylinders with toxic and/or corrosive contents; but this is of no significance in scuba since gas fittings would not be compatible.

Cylinders that are used for partial pressure gas blending with pure oxygen may also be required to display an "oxygen service certificate" label indicating they have been prepared for use with high partial pressures and gas fractions of oxygen.

European Union

Nitrox contents and hazard label used in the UK. The diver has added a temporary maximum operating depth (MOD) indication for easy reference.

In the European Union gas cylinders may be colour-coded according to EN 1098-3. In the UK this standard is optional. The "shoulder" is the domed top of the cylinder between the parallel section and the pillar valve. For mixed gases, the colours can be either bands or "quarters".[92]

These breathing gas cylinders must also be labeled with their contents. The label should state the type of breathing gas contained by the cylinder.[92]

Offshore

Breathing gas containers for offshore use may be coded and marked according to IMCA D043.[92][93]

IMCA colour coding for individual cylinders allows the body of the cylinder to be any colour that is not likely to cause misinterpretation of the hazard identified by the colour code of the shoulder.

Commonly accepted gas container colour coding in the diving industry.[93]
Gas Symbol Typical shoulder colours Cylinder shoulder Quad upper frame/
frame valve end
Calibration gases as appropriate
Pink Pink
Carbon dioxide CO2
Grey Grey
Helium He
Brown Brown
Medical oxygen O2
White White
Nitrogen N2
Black Black
Oxygen and helium mixtures
(Heliox)		 O2/He Brown and white
quarters or bands		 Brown and white
short (8 inches (20 cm))
alternating bands
Oxygen, helium and nitrogen
mixtures (Trimix)		 O2/He/N2 Black, white and brown
quarters or bands 		Black, white and brown
short (8 inches (20 cm))
alternating bands
Oxygen and nitrogen mixtures
(Nitrox) including air 		N2/O2 Black and white
quarters or bands 		Black and white
short (8 inches (20 cm))
alternating bands

South Africa

Scuba cylinders are required to comply with the colours and markings specified in SANS 10019:2006.[38]

Notes

  1. ↑ This is a European requirement.
  2. ↑ This is a European requirement, a requirement of the US DOT, and a South African requirement.

References

  1. 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 NOAA Diving Manual, 4th Edition CD-ROM prepared and distributed by the National Technical Information Service(NTIS) in partnership with NOAA and Best Publishing Company
  2. ↑ "Aqua Lung UK". Aqua Lung International. 2014. Retrieved 9 October 2015.
  3. 1 2 Stone, WC (1986). "Design of fully redundant autonomous life support systems.". In: Mitchell, CT (eds.) Diving for Science 86. Proceedings of the American Academy of Underwater Sciences Sixth Annual Scientific Diving Symposium. (American Academy of Underwater Sciences). Retrieved 2016-01-07.
  4. ↑ "History of Stone Aerospace". Retrieved 2016-01-07.
  5. ↑ US Department of Transport. "CFR Title 49: Transportation". §173.301b Additional general requirements for shipment of UN pressure receptacles. (g) Composite cylinders in underwater use. Retrieved 21 January 2016.
  6. ↑ Staff. "Catalina aluminium cylinders" (PDF). Catalogue. Xscuba.com. Retrieved 25 December 2015.
  7. ↑ "Sustained-load cracking (SLC) in ruptured scuba cylinder made from 6351 aluminum alloy". The Luxfer Group. 22 October 2007. Retrieved 9 October 2015.
  8. ↑ High, Bill (23 February 2005). "Cracking and Ruptures of SCBA and SCUBA Aluminum Cylinders Made from 6351 Alloy" (PDF). University of Hawai‘i. Retrieved 9 October 2015.
  9. ↑ Staff (2015). "Manufacturing processes: All-aluminum cylinders". 5 Anchorage Quay, Salford: Luxfer Gas Cylinders , Luxfer Holdings PLC. Retrieved 25 December 2015.
  10. ↑ Staff (19 October 2006). "A Consumer's Guide to Scuba Tanks". scubadiving.com. Scuba Diving. A Bonnier Corporation Company. Retrieved 6 January 2016.
  11. ↑ webStaff, Leisurepro diver emporium,. "About Faber High Pressure Steel Tank". Retrieved 6 January 2016.
  12. 1 2 Staff. "12L Concave Euro Cylinder with Left or Right Hand Valve". DirDirect Worldwide product catalog. Underwater Explorers Ltd. Retrieved 16 January 2016.
  13. 1 2 3 4 5 Fred M. Roberts (1963); Basic Scuba: Self contained underwater breathing apparatus: Its operation, maintenance and use, Second edition, Van Nostrand Reinholdt, New York
  14. ↑ Legal Information Institute. "49 CFR 178.37 - Specification 3AA and 3AAX seamless steel cylinders. (DOT 3AA)".
  15. ↑ Worthington steel. "Making a Worthington X-Series Steel Scuba Cylinder".
  16. ↑ International standard ISO 11116-1, First edition 1999-04-01 Gas cylinders - 17E taper thread for connection of valves to gas cylinders
  17. 1 2 3 International standard ISO 13341, 1st ed. 1997-10-15 Transportable gas cylinders - Fitting of valves to gas cylinders, First edition 1997.
  18. ↑ British Standard 2779
  19. 1 2 Catalina cylinders, Technical support document, Valving of Scuba (air) cylinders, Nov 2005,
  20. 1 2 International Standard ISO 13769, Gas cylinders - Stamp markings. First edition 2002
  21. ↑ Staff (2016). "Advanced Open Water Diver Course - Standard Scuba Tank Features". PADI. Retrieved 16 January 2016.
  22. 1 2 3 Vance Harlow (1999) Scuba regulator maintenance and repair, Airspeed press, Warner NH, ISBN 0 9678873 0 5
  23. 1 2 Steven Barsky and Tom Neuman, (2003); Investigating Recreational and Commercial Diving Accidents, Hammerhead Press, Santa Barbara, CA. ISBN 0-9674305-3-4
  24. 1 2 3 4 Vance Harlow (2001); Oxygen Hacker's Companion, 4th edition, Airspeed Press, Warner, NH
  25. ↑ Compressed Gas Association (1990). Handbook of Compessed Gases (3rd ed.). New York: Chapman and Hall. p. 229. ISBN 978-1-4612-8020-0. Retrieved 2016-01-17.
  26. ↑ "Valves and Neck Threads - Regulator Fittings and SCUBA Valves". Dive Gear Express, LLC. Retrieved 16 January 2016.
  27. 1 2 Staff. "Valves & Neck Threads". Dive Gear Express, LLC. Retrieved 6 January 2016.
  28. ↑ Dräger Ray Mixed Gas-Rebreather Instructions for Use
  29. 1 2 3 4 Staff. "San-o-Sub DIN/K Cylinder Valve - 232 bar". 1/49 Peninsula Ave, Rye, Melbourne, Victoria, 3941, Australia: The Scuba Doctor. Retrieved 6 January 2016.
  30. ↑ Dowding, Scott (2003). The Recreational Diver's Dictionary & Historical Timeline. iUniverse. ISBN 9780595294688.
  31. 1 2 3 4 5 6 7 US Navy Diving Manual Revision 6, chapter 6-10.1 http://navydiving.tpub.com/NavyDiving/css/Dive_Man_ChangeA_166.htm
  32. ↑ Staff. "Apeks Left and Right hand Cylinder Valve". Apeks Marine Equipment, Neptune Way, Blackburn, United Kingdom BB1 2BT. Retrieved 16 January 2016.
  33. 1 2 3 4 5 6 Gilliam, Bret C; Von Maier, Robert; Crea, John (1992). Deep diving: an advanced guide to physiology, procedures and systems. Watersport Publishing, Inc. ISBN 0-922769-30-3. Retrieved 2016-01-10.
  34. 1 2 Jackson, Jack (2005). Complete Diving Manual. London: New Holland. ISBN 1-84330-870-3.
  35. 1 2 3 Hendrick W, Zaferes A, Nelson C (2000). Public Safety Diving. PennWell Books. ISBN 0912212942. Retrieved 2016-01-11.
  36. ↑ Staff. "DIN Valve Cover Plug - Machined Delrin". Retrieved 21 January 2016.
  37. 1 2 Staff, Dive Gear Express: How to select a SCUBA tank. http://www.divegearexpress.com/library/tanks.shtml accessed 17 August 2013.
  38. 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 South African National Standard SANS 10019:2008
  39. 1 2 3 4 5 Staff. "Faber cylinders for Scuba Diving". Calalog page for 15 to 22 litre steel cylinders. Faber Industrie S. p. A. Retrieved 31 January 2016.
  40. 1 2 Staff. "Faber cylinders for Scuba Diving". Calalog page for 12 to 14.5 litre steel cylinders. Faber Industrie S. p. A. Retrieved 31 January 2016.
  41. ↑ Staff. "Faber cylinders for Scuba Diving". Calalog page for 9.5 to 11,9 litre steel cylinders. Faber Industrie S. p. A. Retrieved 31 January 2016.
  42. 1 2 Staff. "Faber cylinders for Scuba Diving". Calalog page for 6 litre to 9.5 litre steel cylinders. Faber Industrie S. p. A. Retrieved 31 January 2016.
  43. 1 2 3 4 5 6 Staff. "Faber cylinders for Scuba Diving". Calalog page for 1 litre to 5.5 litre steel cylinders. Faber Industrie S. p. A. Retrieved 31 January 2016.
  44. ↑ US Navy (2006). US Navy Diving Manual, 6th revision. United States: US Naval Sea Systems Command. Retrieved 2008-06-15.
  45. 1 2 3 4 5 Staff. "Scuba specifications" (PDF). Garden Grove, CA.: Catalina Cylinders Inc. Retrieved 31 January 2016.
  46. ↑ Staff, XS Scuba, Worthington steel cylinder specifications, http://www.xsscuba.com/tank_steel_specs_metric.html#2 accessed 17 August 2013.
  47. 1 2 3 4 Beresford, M.: CMAS-ISA Normoxic Trimix Manual
  48. 1 2 Lang, M.A. and M.D.J. Sayer (eds.) (2007). Proceedings of the International Polar Diving Workshop. Svalbard: Smithsonian Institution.
  49. ↑ "Spare Air". Submersible Systems. 2009-07-07. Retrieved 2009-09-19.
  50. 1 2 Austin, Doug. "Extended endurance saturation diving emergency bailout system" (PDF). Divex. pp. 6–9. Retrieved 6 January 2016.
  51. 1 2 Staff. "Products:A.P.VALVES MK4 JUMP JACKET". Pommec diving equipment. Retrieved 6 January 2016.
  52. ↑ Bogaert, Steve (5 May 2011). "Multi Stage Dive by Steve Bogaerts with the new Razor Side Mount System". Retrieved 6 January 2016.
  53. 1 2 Staff (19 October 2006). "Are you ready for rebreathers?". Scuba Diving online magazine. Scuba Diving. A Bonnier Corporation Company. Retrieved 6 January 2016.
  54. 1 2 3 Verdier C, Lee DA (2008). "Motor skills learning and current bailout procedures in recreational rebreather diving.". In: Verdier (ed). Nitrox Rebreather Diving. DIRrebreather publishing. Retrieved 2016-01-07.
  55. 1 2 3 Diving Regulations 2009 of the South African Occupational Health and Safety Act, 1993. Government notice R41, Government Gazette #32907 of 29 January 2010, Government Printer, Pretoria
  56. 1 2 3 Staff (2002). Paul Williams, ed. The Diving Supervisor’s Manual (IMCA D 022 May 2000, incorporating the May 2002 erratum ed.). Carlyle House, 235 Vauxhall Bridge Road, London SW1V 1EJ, UK: International Marine Contractors' Association. ISBN 1-903513-00-6.
  57. ↑ Staff (February 2014). "4.7.5 Emergency breathing gas cylinders for diving basket/wet bell". IMCA D014 International Code of Practice for Offshore Diving (PDF) (Revision 2 ed.). International Marine Contractors Association. p. 19. Retrieved 2016-01-30.
  58. ↑ Staff (July 2014). "Section 5 - Diving Bell: 5.23 - Onboard gas, and 5.24 - Onboard oxygen". IMCA D024 Rev 2 - Part 2 DESIGN for Saturation (Bell) Diving Systems (PDF) (Revision 2 ed.). International Marine Contractors Association. pp. 4 of 10. Retrieved 2016-01-30.
  59. ↑ Buzzacott P, Rosenberg M, Heyworth J, Pikora T (2011). "Risk factors for running low on gas in recreational divers in Western Australia". Diving and Hyperbaric Medicine 41 (2): 85–9. PMID 21848111. Retrieved 2016-01-07.
  60. ↑ British Sub-Aqua Club members (1982). British Sub-Aqua Club Diving Manual (10th ed.). British Sob-Aqua Club. p. 567. ISBN 0950678619.
  61. ↑ Bozanic, JE (1997). "AAUS Standards for Scientific Diving Operations in Cave and Cavern Environments: A Proposal.". In: SF Norton (ed). Diving for Science...1997. Proceedings of the American Academy of Underwater Sciences (17th Annual Scientific Diving Symposium). Retrieved 2016-01-07.
  62. ↑ Sheldrake, S; Pedersen, R; Schulze, C; Donohue, S; Humphrey, A (2011). "Use of Tethered Scuba for Scientific Diving". In: Pollock NW, ed. Diving for Science 2011. Proceedings of the American Academy of Underwater Sciences 30th Symposium. Retrieved 2016-01-09.
  63. ↑ International Organization for Standardization, Standard Atmosphere, ISO 2533:1975, 1975.
  64. ↑ "Cylinders". Gas Diving UK. 26 January 2003. Retrieved 9 October 2015.
  65. 1 2 Millar IL; Mouldey PG (2008). "Compressed breathing air – the potential for evil from within". Diving and Hyperbaric Medicine. (South Pacific Underwater Medicine Society) 38 (2): 145–51. PMID 22692708. Retrieved 2009-02-28.
  66. ↑ Trigger, John (April 1999). "High Pressure Rusting: a Problem with High Pressure Steel Tanks?". Undercurrent. Sausalito, CA: Undercurrent (www.undercurrent.org). Retrieved 16 January 2016.
  67. 1 2 Staff. "Scuba Cylinder Servicing and High Pressure Valve Support Pages". ScubaEngineer.com. Retrieved 16 January 2016.
  68. ↑ Henderson, NC; Berry, WE; Eiber, RJ; Frink, DW (1970). "Investigation of scuba cylinder corrosion, Phase 1". National Underwater Accident Data Center Technical Report Number 1 (University of Rhode Island). Retrieved 2011-09-24.
  69. ↑ BS EN 1802:2002 Transportable gas cylinders. Periodic inspection and testing of seamless aluminium alloy gas cylinders
  70. ↑ BS EN 1968:2002 Transportable gas cylinders. Periodic inspection and testing of seamless steel gas cylinders
  71. ↑ AS 2030.1—1999 Australian Standard: The verification, filling, inspection, testing and maintenance of cylinders for storage and transport of compressed gases. Part 1: Cylinders for compressed gases other than acetylene, Third edition 1999. Reissued incorporating Amendment No. 1 (March 2002). Standards Australia International Ltd, GPO Box 5420, Sydney, NSW 2001, Australia ISBN 0-7337-2574-0
  72. 1 2 International standard ISO 13769, 1st Ed.2002-07-01 Gas cylinders - Stamp marking
  73. ↑ Acott, CJ (1995). "A pre-dive check; An evaluation of a safety procedure in recreational diving: Part 1.". Journal of the South Pacific Underwater Medicine Society 25 (2). Retrieved 2016-01-07.
  74. ↑ "Incident Insights - Trust But Verify". Divers Alert Network.
  75. ↑ Denoble PJ, Caruso JL, Dear Gde L, Pieper CF, Vann RD (2008). "Common causes of open-circuit recreational diving fatalities". Undersea & Hyperbaric Medicine : Journal of the Undersea and Hyperbaric Medical Society, Inc 35 (6): 393–406. PMID 19175195. Retrieved 2016-01-07.
  76. ↑ Acott, CJ (2003). "Recreational scuba diving equipment problems, morbidity and mortality: an overview of the Diving Incident Monitoring Study and Project Stickybeak.". Journal of the South Pacific Underwater Medicine Society 33 (1). Retrieved 2016-01-07.
  77. ↑ Barr, Lori L; Martin, Larry R (1991). "Tank carrier's lateral epicondylitis: Case reports and a new cause for an old entity". Journal of the South Pacific Underwater Medicine Society 21 (1). Retrieved 2011-11-21.
  78. 1 2 3 DGM_Support (16 April 2014). "How to select the correct Proper Shipping Name?". Retrieved 31 January 2016.
  79. ↑ Staff (2010-01-08). "§ 172.101 HAZARDOUS MATERIALS TABLE". 49 CFR Ch. I Subpart B -Table of Hazardous Materials and Special Provisions (PDF). Pipeline and Hazardous Materials Safety Admin., DOT. pp. 134, 207, 249. Retrieved 2016-01-31.
  80. 1 2 3 4 5 6 Economic Commission for Europe Committee on Inland Transport (2014). European Agreement Concerning the International Carriage of Dangerous Goods by Road (ADR) (PDF). New York and Geneva: United Nations. ISBN 978-92-1-056691-9. Retrieved 2016-01-31.
  81. ↑ Staff (2015). "Packing Instruction 200, Table 1: Compressed gases". Recommendations on the TRANSPORT OF DANGEROUS GOODS Model Regulations (PDF) II (Nineteenth revised ed.). New York and Geneva: United Nations. p. 44. Retrieved 2016-02-02.
  82. ↑ Staff. "Items that are allowed in baggage: Information for Passengers on Dangerous Goods". Civil Aviation Authority. Retrieved 2 February 2016.
  83. 1 2 3 4 5 6 7 8 Guidance note 27: Guidance for the carriage of gas cylinders on vehicles (Revision 1 ed.). Derby, UK: British Compressed Gases Association. 2015. ISSN 0260-4809.
  84. ↑ Staff (2015). "The carriage of small quantities of gas cylinders on vehicles". Leaflet 1: Revision 5. British Compressed Gases Association. Retrieved 31 January 2016.
  85. ↑ DOT (January 2016). "§171.1 Applicability of Hazardous Materials Regulations (HMR) to persons and functions.". Electronic Code of Federal Regulations, Title 49 - Transportation. US Department of Transport. Retrieved 2016-02-02.
  86. 1 2 US Department of Transport (2016-01-20). "PART 173—SHIPPERS—GENERAL REQUIREMENTS FOR SHIPMENTS AND PACKAGINGS". Code of Federal Regulations Title 49 - Transportation. US Government publishing office. Retrieved 23 January 2016.
  87. ↑ US Department of Transport. "Code of Federal Regulations 49 - Transportation". 49 CFR 173.115 - Class 2, Divisions 2.1, 2.2, and 2.3. Cornell University Law School Legal Information Institute. Retrieved 21 January 2016.
  88. ↑ PHMSA staff. "Special Permits list". Retrieved 23 January 2016.
  89. ↑ Monahan, Corey (2011-07-01). "Cylinders are HAZMAT?". Retrieved 21 January 2016.
  90. ↑ Staff (2013-03-19). "Pack Safe: Scuba tanks, pressurized". Federal Aviation Administration. Retrieved 21 January 2016.
  91. ↑ Staff. "My TSA". Search results for Scuba cylinder. Transportation Security. Retrieved 21 January 2016.
  92. 1 2 3 British Compressed Gases Association, 4a Mallard Way, Pride Park, Derby, UK, DE24 8GX. www.bcga.co.uk Technical Information Sheet 6, Revision 2: 2012 Cylinder Identification. Colour Coding and Labelling Requirements.
  93. 1 2 Staff (2007). Marking and Colour Coding of Gas Cylinders, Quads and Banks for Diving Applications IMCA D043 (PDF). International Marine Contractors Association. Retrieved 2016-02-01.

External links

Media related to Diving cylinders at Wikimedia Commons

This article is issued from Wikipedia - version of the Sunday, February 07, 2016. The text is available under the Creative Commons Attribution/Share Alike but additional terms may apply for the media files.