At a minimum, each diver must be equipped with the following items to safely
conduct an open-circuit scuba dive:
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Open-circuit scuba.
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Face mask.
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Life preserver/buoyancy compensator.*
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Weight belt and weights as required.**
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Knife.**
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Swim fins.
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Submersible pressure gauge or Reserve J-valve.
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Submersible wrist watch. Only one is required when diving in pairs with a
buddy line.**
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Depth gauge. **
* During the problem-solving pool phase of scuba training, CO2 cartridges may be
removed and replaced with plugs or expended cartridges that are painted International
Orange.
** These items are not required for the pool phase of scuba training.
The face mask protects the diver’s eyes and nose from the water.
Additionally, it provides maximum visibility by putting a layer of air between the
diver’s eyes and the water.
Face masks are available in a variety of shapes and sizes for diver comfort. To
check for proper fit, hold the mask in place with one hand and inhale gently
through the nose. The suction produced should hold the mask in place. Don the
mask with the head strap properly adjusted, and inhale gently through the nose. If
the mask seals, it should provide a good seal in the water.
Some masks are equipped with a one-way purge valve to aid in clearing the mask
of water. Some masks have indentations at the nose or a neoprene nose pad to
allow the diver to block the nostrils to equalize the pressure in the ears and sinuses.
Several models are available for divers who wear eyeglasses. One type provides a
prescription-ground faceplate, while another type has special holders for separate
lenses. All faceplates must be constructed of tempered or shatterproof safety glass
because faceplates made of ordinary glass can be hazardous. Plastic faceplates are
generally unsuitable as they fog too easily and are easily scratched.
The size or shape of the faceplate is a matter of personal choice, but the diver
should use a mask that provides a wide, clear range of vision.
The principal functions of the life preserver are to assist a diver in
rising to the surface in an emergency and to keep the diver on the surface in faceup
position (Figure 7-4). The low-pressure inflation device on the preserver may
be actuated by the diver, or by a dive partner should the diver be unconscious or
otherwise incapacitated. All models used by the Navy must be
authorized by NAVSEA/00C Authorized
for Navy Use List and have a
manual inflation device in addition to
the low pressure inflation device.
With the exception of the UDT (9C-
4220-00-276-8929), an overinflation
valve or relief valve is required to
ensure against possible rupture of the
life preserver on ascent. Some ANU
models are available commercially
while others may be procured through
the Navy supply system. In selecting
a life preserver for a specific task, the
individual technical manuals should
be consulted. The use of certain
closed and semi-closed UBAs will
require the wearing of a life
preserver
The life preserver must be sturdy enough to resist normal wear and tear, and of
sufficient volume to raise an unconscious diver safely from maximum dive depth
to the surface.
Most life preservers currently in use employ carbon dioxide (CO2) cartridges to
provide inflation in an emergency. The cartridges must be the proper size for the
life preserver. Cartridges must be weighed upon receipt and prior to use, in accordance
with the planned maintenance system (PMS) for the life preserver, to ensure
the actual weight is in compliance with the weight tolerance for the cartridge
cylinder. Carbon dioxide cartridges used with commercially available life
preservers with low-pressure inflators do not have the weight stamped on the
cartridge cylinder. The actual weight of these cartridges must be inscribed on the
cartridge, and be within the tolerance for weight.
Figure 7.4. MK-4 Life Preserver.
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When a life preserver is not required by a specific
UBA, a buoyancy compensator may be used at the Diving Supervisor’s discretion.
When selecting a buoyancy compensator, a number of factors must be considered.
These factors include: type of wet suit, diving depth, breathing equipment characteristics,
nature of diving activity, accessory equipment, and weight belt. A list of
approved buoyancy compensators is contained in the NAVSEA/00C Authorized
for Navy Use List.
As a buoyancy compensating device, the compensator can be inflated by a lowpressure
inflator connected to the first-stage regulator, or an oral inflation tube.
Any buoyancy compensator selected for Navy use must have an over-pressure
relief valve. The compensator is used in conjunction with the diver weights to
control buoyancy in the water column by allowing the diver to increase displacement
through inflation of the device, or to decrease displacement by venting.
Training and practice under controlled conditions are required to master the buoyancy
compensation technique. Rapid, excessive inflation can cause excessive
buoyancy and uncontrolled ascent. The diver must systematically vent air from the
compensator during ascent to maintain proper control. Weights installed in a vest
type bouyancy compesator must be jettisonable.
Refer to the appropriate technical manual for complete operations and maintenance
instructions for the equipment.
Scuba is designed to have nearly neutral buoyancy. With full tanks, a
unit tends to have negative buoyancy, becoming slightly positive as the air supply
is consumed. Most divers are positively buoyant and need to add extra weight to
achieve a neutral or slightly negative status. This extra weight is furnished by a
weighted belt worn outside of all other equipment and strapped so that it can easily
released in the event of an emergency.
Each diver may select the style and size of belt and weights that best suit the diver.
A number of different models are available. A weight belt shall meet certain basic
standards: the buckle must have a quick-release feature, easily operated by either
hand; the weights (normally made of lead) should have smooth edges so as not to
chafe the diver’s skin or damage any protective clothing, and the belt should be
made of rot- and mildew-resistant fabric, such as nylon webbing.
Several types of knives are available. For EOD and other special missions,
a nonmagnetic knife designed for use when diving near magnetic-influence mines
is used.
Diving knives should have corrosion-resistant blades and a handle of plastic, hard
rubber, or wood. Handles made of wood should be waterproofed with paint, wax,
or linseed oil. Handles of cork or bone should be avoided, as these materials deteriorate
rapidly when subjected to constant saltwater immersion. Cork may also
float the knife away from the diver.
Knives may have single- or double-edged blades with chisel or pointed tips. The
most useful knife has one sharp edge and one saw-toothed edge. All knives must
be kept sharp.
The knife must be carried in a suitable scabbard and worn on the diver’s life
preserver, hip, thigh, or calf. The knife must be readily accessible, must not interfere
with body movement, and must be positioned so that it will not become fouled
while swimming or working. The scabbard should hold the knife with a positive
but easily released lock.
The knife and scabbard must not be secured to the weight belt.If the weights
are released in an emergency, the knife may be also dropped unintentionally.
Swim fins increase the efficiency of the diver, permitting faster swimming
over longer ranges with less expenditure of energy. Swim fins are made of a
variety of materials and styles.
Each feature—flexibility, blade size, and configuration—contributes to the relative
power of the fin. A large blade will transmit more power from the legs to the
water, provided the legs are strong enough to use a larger blade. Small or soft
blades should be avoided. Ultimately, selection of blade type is a matter of
personal preference based on the diver’s strength and experience.
Analog diver’s watches must be waterproof, pressure proof, and
equipped with a rotating bezel outside the dial that can be set to indicate the
elapsed time of a dive. A luminous dial with large numerals is also necessary.
Additional features such as automatic winding, nonmagnetic components, and
stop watch action are available. Digital watches, with a stop watch feature to indicate
the elapsed time of a dive, are also approved for Navy use.
The depth gauge measures the pressure created by the water
column above the diver and is calibrated to provide a direct reading of depth in
feet of sea water. It must be designed to be read under conditions of limited visibility.
The gauge mechanism is delicate and should be handled with care. Accurate
depth determination is important to a diver’s safety. The accuracy of a gauge must
be checked in accordance with the planned maintenance system or whenever a
malfunction is suspected. This can be done by taking the gauge to a known depth
and checking the reading, or by placing it in a recompression chamber or test pressure
chamber for depth comparison.
Only diving equipment that has been certified
or authorized for use by the NAVSEA/00C ANU list shall be used in a Navy
dive. However, many items, such as hand tools, which are not specifically listed in
the ANU list or do not fit under the scope of certification and are deemed valuable
to the success of the dive, can be used. A current copy must be maintained by all
diving activities. The ANU list can be found on the Internet at http://
www.navsea.navy.mil/sea00c/doc/anu_disc.html.
Figure 7-1. Schematic of Demand Regulator.
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All open-circuit scuba authorized for Navy use employ a
demand system that supplies air each time the diver inhales. The basic open-circuit
scuba components are:
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Demand regulator assembly
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One or more air cylinders
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Cylinder valve and manifold assembly
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Backpack or harness
The demand regulator assembly is the central
component of the open-circuit system. The regulator delivers air to the diver after
reducing the high-pressure air in the cylinder to a pressure that can be used by the
diver. There are two stages in a typical system (Figure 7-1).
In the regulator’s first stage, high-pressure air from the cylinder
passes through a regulator that reduces the pressure of the air to a predetermined
level over ambient pressure. Refer to the regulator technical manual for the
specific setting.
In the second stage of a regulator, a movable diaphragm is linked
by a lever to the low-pressure valve, which leads to a low-pressure chamber. When
the air pressure in the low-pressure chamber equals the ambient water pressure,
the diaphragm is in the center position and the low-pressure valve is closed. When
the diver inhales, the pressure in the low-pressure chamber is reduced, causing the
diaphragm to be pushed inward by the higher ambient water pressure. The
diaphragm actuates the low-pressure valve which opens, permitting air to flow to
the diver. The greater the demand, the wider the low-pressure valve is opened, thus
allowing more air flow to the diver. When the diver stops inhaling, the pressure on
either side of the diaphragm is again balanced and the low-pressure valve closes.
As the diver exhales, the exhausted air passes through at least one check valve and
vents to the water.
In the single-hose, two-stage demand regulator the first
stage is mounted on the cylinder valve assembly. The second-stage assembly
includes the mouthpiece and a valve to exhaust exhaled air directly into the water.
The two stages are connected by a length of low-pressure hose, which passes over
the diver’s right shoulder. The second stage has a purge button, which when activated
allows low-pressure air to flow through the regulator and the mouthpiece,
forcing out any water which may have entered the system. Buddy breathing (a
diver providing air from the scuba to a partner) is more easily accomplished with
the single-hose regulator. Use of an additional second stage regulator with an octopus hose is an alternative and preferred method to accomplish buddy
breathing. The principal disadvantages of the single-hose unit are an increased
tendency to freeze up in very cold water and the exhaust of air in front of the
diver’s mask. While the Navy PMS system provides guidance for repairing and
maintaining scuba regulators, the manufacturer’s service manual should be
followed for specific procedures.
The AGA/Divator full face mask may be used with an approved
single-hose first-stage regulator with an octopus, to the maximum approved depth
of the regulator, as indicated in the NAVSEA/00C ANU list (Figure 7-2).
Figure 7-2. Full Face Mask.
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The size and design of scuba mouthpieces differ between manufacturers,
but each mouthpiece provides relatively watertight passageways for
delivering breathing air into the diver’s mouth. The mouthpiece should fit
comfortably with slight pressure from the lips.
Scuba cylinders (tanks or bottles) are designed to hold high pressure
compressed air. Because of the extreme stresses imposed on a cylinder at these
pressures, all cylinders used in scuba diving must be inspected and tested periodically.
Seamless steel or aluminum cylinders which meet Department of
Transportation (DOT) specifications (DOT 3AA, DOT 3AL, DOT SP6498, and
DOT E6498) are approved for Navy use. Each cylinder used in Navy operations
must have identification symbols stamped into the shoulder (Figure 7-3).
Figure 7-3. STypical Gas Cylinder Identification Markings.
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Approved scuba cylinders are available in
several sizes and one or two cylinders may be worn to provide the required quantity
of air for the dive. The volume of a cylinder, expressed in actual cubic feet or cubic inches, is a measurement of the internal volume of the cylinder. The capacity
of a cylinder, expressed in standard cubic feet or liters, is the amount of gas
(measured at surface conditions) that the cylinder holds when charged to its rated
pressure. Table 7-1 lists the sizes of some standard scuba cylinders. Refer to the
NAVSEA/00C ANU list for a list of approved scuba cylinders.
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Table 7-1. Sample Scuba Cylinder Data.
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Open-circuit scuba cylinders must be visually
inspected at least once every 12 months and every time water or particulate matter
is suspected in the cylinder. Cylinders containing visible accumulations of corrosion
must be cleaned before being placed into service. Commercially available
steel and aluminum scuba cylinders, as specified in the NAVSEA/00C ANU list,
which meet DOT specifications, as well as scuba cylinders designed to Navy specifications,
must be visually inspected at least annually and must be hydrostatically
tested at least every five years in accordance with DOT regulations and
Compressed Gas Association (CGA) pamphlets C-1 and C-6.
General safety regulations governing the
handling and use of compressed gas cylinders aboard Navy ships are contained in
NAVSEA 0901-LP-230-0002, NSTM Chapter 550, “Compressed Gas Handling.”
Persons responsible for handling, storing, and charging scuba cylinders must be
familiar with these regulations. Safety rules applying to scuba cylinders are
contained in paragraph 7-4.5. Because scuba cylinders are subject to continuous
handling and because of the hazards posed by a damaged unit, close adherence to
the rules is mandatory.
Cylinder valves and manifolds make
up the system that passes the high-pressure air from the cylinders to the first-stage
regulator. The cylinder valve serves as an on/off valve and is sealed to the tank by
a straight-threaded male connection containing a neoprene O-ring on the valve’s
body
The cylinder valve contains a high-pressure
blowout plug or safety disc plug in the event of excessive pressure buildup. When
a dual manifold is used, two blowout plugs or safety disc plugs are installed as
specified by the manufacturers’ technical manual.
For standard diving equipment, a safety disc plug similar to new issue equipment
is recommended. The safety disc plug and safety disc are not always identified by
a National Stock Number (NSN), but are available commercially.
If two or more cylinders are to be used together, a manifold
unit is needed to provide the necessary interconnection. Most manifolds incorporate
an O-ring as a seal, but some earlier models may have a tapered (pipe) thread
design. One type will not connect with the other type.
A cylinder valve with an air reserve (J valve) is
preferred. When a cylinder valve without an air reserve (K valve) is used, the
scuba regulator must be equipped with a submersible pressure gauge to indicate
pressure contents of the cylinder. The dive must be terminated when the cylinder
pressure reaches 500 psi for a single cylinder or 250 psi for twin manifold cylinders.
The air reserve mechanism alerts the diver that the available air supply is
almost exhausted and provides the diver with sufficient reserve air to reach the
surface. The air reserve mechanism contains a spring-loaded check valve. When it
becomes increasingly difficult to obtain a full breath, the diver must reach over the left shoulder and push down the reserve lever, opening the reserve valve to make
the remaining air available.
Dive planning should not extend bottom time by including the use of reserve air.
The diver should never assume that the reserve air supply will be provided. When
the resistance to breathing becomes obvious, the diver should notify the dive
partner that the air supply is low and both should start for the surface immediately.
The dive must be terminated when either diver shifts to reserve air.
A variety of backpacks or harnesses, used for holding the
scuba on the diver’s back, have been approved for Navy use. The backpack may
include a lightweight frame with the cylinder(s) held in place with clamps or
straps. The usual system for securing the cylinder to the diver uses shoulder and
waist straps. All straps must have a quick-release feature, easily operated by either
hand, so that the diver can remove the cylinder and leave it behind in an
emergency.
