CHAPTER 7 — Scuba Air Diving Operations 7-1
The purpose of this chapter is to familiarize divers with standard and
emergency procedures when diving with scuba equipment.
This chapter covers the use of open-circuit scuba, which is normally
deployed in operations not requiring decompression. Decompression diving using
open-circuit air scuba may be undertaken only if no other option exists and only
with the concurrence of the Commanding Officer or Officer-in-Charge (OIC).
Closed-circuit underwater breathing apparatus is the preferred method of
performing scuba decompression dives. Operation of open-circuit, closed-circuit,
and semiclosed-circuit systems designed for use with mixed-gas or oxygen is
covered in Volume 4.
At a minimum, each diver must be equipped with the following items to safely
conduct an open-circuit scuba dive:
Open-circuit scuba.
Face mask.
Life preserver/buoyancy compensator.*
Weight belt and weights as required.**
Swim fins.
Submersible pressure gauge or Reserve J-valve.
Submersible wrist watch. Only one is required when diving in pairs with a
buddy line.**
Depth gauge. **
* During the problem-solving pool phase of scuba training, CO
cartridges may be
removed and replaced with plugs or expended cartridges that are painted Interna-
tional Orange.
** These items are not required for the pool phase of scuba training.
7-2 U.S. Navy Diving Manual—Volume 2
Equipment Authorized for Navy Use.
Only diving equipment that has been certi-
fied 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://
Open-Circuit Scuba.
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:
Demand regulator assembly
One or more air cylinders
Cylinder valve and manifold assembly
Backpack or harness
Demand Regulator Assembly.
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).
First Stage.
In the regulators 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.
Second Stage.
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.
Single Hose Regulators.
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 divers right shoulder. The second stage has a purge button, which when acti-
vated 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
CHAPTER 7 — Scuba Air Diving Operations 7-3
Figure 7-1.
Schematic of Demand Regulator.
First Stage.
High pressure air flows through the orifice of the first stage into the intermediate chamber. When the pressure in the
intermediate chamber reaches ambient plus diaphragm balance spring set pressure, the first stage assembly closes.
Second Stage.
Upon inhalation the second stage diaphragm moves inward and the horseshoe lever opens the second stage valve
assembly. Intermediate pressure air from the hoses is throttled across the orifice and fills the low pressure chamber to ambient pressure and
flow is provided to the diver. Upon exhalation the diaphragm is pushed outward and the second stage in closed. Expired air is dumped from
the low pressure chamber to the surrounding water through the exhaust valve.
7-4 U.S. Navy Diving Manual—Volume 2
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.
Full Face Mask.
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).
The size and design of scuba mouthpieces differ between manufac-
turers, 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 periodi-
cally. 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).
Sizes of Approved Scuba Cylinders.
Approved scuba cylinders are available in
several sizes and one or two cylinders may be worn to provide the required quan-
tity of air for the dive. The volume of a cylinder, expressed in actual cubic feet or
Figure 7-2.
Full Face Mask.
CHAPTER 7 — Scuba Air Diving Operations 7-5
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.
Figure 7-3.
Typical Gas Cylinder Identification Markings.
Table 7-1. Sample Scuba Cylinder Data.
(Note 1)
Absolute Air
Capacity at Rated
Pressure (Cu.Ft.)
Outside Dimensions (Inches)
(Dia.) (Length)
Steel 72 2,250 0.420 64.7 500 6.80 25.00
Aluminum 50 3,000 0.281 48.5 500 6.89 19.00
Aluminum 63 3,000 0.319 65.5 500 7.25 21.75
Aluminum 80 3,000 0.399 81.85 500 7.25 26.00
Note 1: Fifty cubic feet is the minimum size scuba cylinder authorized. SEAL teams are authorized smaller cylinders for special
7-6 U.S. Navy Diving Manual—Volume 2
Inspection Requirements.
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 corro-
sion 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 spec-
ifications, 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.
Guidelines for Handling Cylinders.
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 Manifold Assemblies.
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
Blowout Plugs and Safety Discs.
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.
Manifold Connectors.
If two or more cylinders are to be used together, a manifold
unit is needed to provide the necessary interconnection. Most manifolds incorpo-
rate 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.
Pressure Gauge Requirements.
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 cylin-
ders. 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
CHAPTER 7 — Scuba Air Diving Operations 7-7
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.
Backpack or Harness.
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
Minimum Equipment.
Face Mask.
The face mask protects the divers 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.
Life Preserver.
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 face-
up 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.
7-8 U.S. Navy Diving Manual—Volume 2
All models used by the Navy must be
authorized by NAVSEA/00C Autho-
rized 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
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 (CO
) 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 accor-
dance 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.
Buoyancy Compensator.
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 charac-
teristics, 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 low-
pressure 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 displace-
ment through inflation of the device, or to decrease displacement by venting.
Figure 7-4.
MK-4 Life Preserver.
CHAPTER 7 — Scuba Air Diving Operations 7-9
Training and practice under controlled conditions are required to master the buoy-
ancy 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 mainte-
nance instructions for the equipment.
Weight Belt.
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 dete-
riorate 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 divers life
preserver, hip, thigh, or calf. The knife must be readily accessible, must not inter-
fere 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.
7-10 U.S. Navy Diving Manual—Volume 2
Swim Fins.
Swim fins increase the efficiency of the diver, permitting faster swim-
ming 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 rela-
tive 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 divers strength and experience.
Wrist Watch.
Analog divers 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 indi-
cate the elapsed time of a dive, are also approved for Navy use.
Depth Gauge.
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 visi-
bility. The gauge mechanism is delicate and should be handled with care. Accurate
depth determination is important to a divers 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 pres-
sure chamber for depth comparison.
The requirements of a specific diving operation determine which items of optional
diving equipment may be necessary. This section lists some of the equipment that
may be used.
Protective Clothing
—Wet Suit
Variable Volume Dry Suit
Boots or hard-soled shoes
Slate and pencil
Tools and light
Signal flare
Tool bag
Acoustic beacons
Lines and floats
Wrist compass
CHAPTER 7 — Scuba Air Diving Operations 7-11
Witness float
Submersible cylinder pressure gauge
Chem light and strobe light
Protective Clothing.
A diver needs some form of protection from cold water,
from heat loss during long exposure in water of moderate temperature, from chem-
ical or bacterial pollution in the water, and from the hazards posed by marine life
and underwater obstacles. Protection can be provided by wet suit, or a dry suit
with or without thermal underwear in Figure 7-5.
Wet Suits.
The wet suit is a form-fitting suit, usually made of closed-cell
neoprene. The suit traps a thin layer of water next to the divers skin, where it is
warmed by the divers body. Wet suits are available in thicknesses of 1/8-, 3/16-,
3/8-, and 1/2-inch, with the thickest providing better insulation. The selection of
the type of wet suit used is left to each diver. Standard size suits are available at
most commercial diving shops. Proper fit is critical in the selection of a wet suit.
The suit must not restrict the divers movements. A custom-fitted suit is recom-
mended. The performance of a suit depends upon suit thickness, water
temperature, and water depth.
Figure 7-5.
Protective Clothing.
Underclothing affords
insulating air space
Water warmed to
body temperature
Foam Neoprene
Sheet Rubber
7-12 U.S. Navy Diving Manual—Volume 2
Dry Suits.
The Variable Volume Dry Suit (VVDS) has proven to be effective in
keeping divers warm in near-freezing water. It is typically constructed of 1/4-inch
closed-cell neoprene with nylon backing on both sides. Boots are provided as an
integral part of the suit, but the hood and three finger gloves are usually separate.
The suit is entered by means of a water- and pressure-proof zipper. Inflation is
controlled using inlet and outlet valves which are fitted into the suit. Air is
supplied from a pressure reducer on an auxiliary cylinder or from the emergency
gas supply or the scuba bottle. About 0.2 actual cubic foot of air is required for
normal inflation. Because of this inflation, slightly more weight than would be
used with a wet suit must be carried. Normally, thermal underwear can be worn
under the suit for insulation.
Gloves are an essential item of protective clothing. They can be made of
leather, cloth, or rubber, depending upon the degree and type of protection
required. Gloves shields the hands from cuts and chafing, and provide protection
from cold water. Some styles are designed to have insulating properties but may
limit the diver’s dexterity.
Wet or dry suits can be worn with hoods, gloves, boots, or hard-soled shoes
depending upon conditions. If the diver will be working under conditions where
the suit may be easily torn or punctured, the diver should be provided with addi-
tional protection such as coveralls or heavy canvas chafing gear.
Writing Slate.
A rough-surfaced sheet of acrylic makes an excellent writing slate
for recording data, carrying or passing instructions, and communicating between
divers. A grease pencil or graphite pencil should be attached to the slate with a
Signal Flare.
A signal flare is used to attract attention if the diver has surfaced
away from the support crew. Any waterproof flare that can be carried and safely
ignited by a diver can be used, but the preferred type is the MK 124 MOD 0 (NSN
1370-01-030-8330). These are day-or-night signals that give off a heavy reddish
or orange smoke for daytime and a brilliant red light at night. Each signal lasts for
approximately 20 seconds. The “night” end of the flare is identified by a ring of
raised beads. Flares should be handled with care. For safety, each diver should
carry a maximum of two flares.
Acoustic Beacons.
Acoustic beacons or pingers are battery-operated devices that
emit high-frequency signals when activated. The devices may be worn by divers to
aid in keeping track of their position or attached to objects to serve as fixed points
of reference. The signals can be picked up by hand-held sonar receivers, which are
used in the passive or listening mode, at ranges of up to 1,000 yards. The hand-
held sonar enables the search diver to determine the direction of the signal source
and swim toward the pinger using the heading noted on a compass.
Lines and Floats.
A lifeline should be used when it is necessary to exchange
signals, keep track of the divers location, or operate in limited visibility. There are
three basic types of lifelines: the tending line, the float line, and the buddy line.
CHAPTER 7 — Scuba Air Diving Operations 7-13
A single diver will be tended with either a tending line or a float line. When direct
access to the surface is not available a tending line is mandatory. A float line may
not be used.
The float line reaches from the diver to a suitable float on the surface. This float
can be a brightly painted piece of wood, an empty sealed plastic bottle, a life ring,
or any similar buoyant, visible object. An inner tube with a diving flag attached
makes an excellent float and provides a hand-hold for a surfaced diver. If a pair of
divers are involved in a search, the use of a common float gives them a rendezvous
point. Additional lines for tools or other equipment can be tied to the float. A
buddy line, 6 to 10 feet long, is used to connect the diver partners at night or when
visibility is poor.
Any line used in scuba operations should be strong and have neutral or slightly
positive buoyancy. Nylon, Dacron, and manila are all suitable materials. Always
attach a lifeline to the diver, never to a piece of equipment that may be ripped
away or may be removed in an emergency.
A snorkel is a simple breathing tube that allows a diver to swim on the
surface for long or short distances face-down in the water. This permits the diver
to search shallow depths from the surface, conserving the scuba air supply. When
snorkels are used for skin diving, they are often attached to the face mask with a
lanyard or rubber connector to the opposite side of the regulator.
Small magnetic compasses are commonly used in underwater naviga-
tion. Such compasses are not highly accurate, but can be valuable when visibility
is poor. Submersible wrist compasses, watches, and depth gauges covered by
NAVSUPINST 5101.6 series are items controlled by the Nuclear Regulatory
Commission and require leak testing and reporting every 6 months.
Submersible Cylinder Pressure Gauge.
The submersible cylinder pressure gauge
provides the diver with a continual read-out of the air remaining in the cylinder(s).
Various submersible pressure gauges suitable for Navy use are commercially
available. Most are equipped with a 2- to 3-foot length of high-pressure rubber
hose with standard fittings, and are secured directly into the first stage of the regu-
lator. When turning on the cylinder air, the diver should should turn the face of the
gauge away in the event of a blowout. When worn, the gauge and hose should be
tucked under a shoulder strap or otherwise secured to avoid its entanglement with
bottom debris or other equipment. The gauge must be calibrated in accordance
with the equipment planned maintenance system.
An important early step in any scuba dive is computing the air supply requirement.
The air supply requirement is a function of the expected duration of the dive at a
specific working depth. The duration of the air supply in the scuba cylinders
depends on the depth at which the air is delivered. Air consumption rate increases
with depth.
7-14 U.S. Navy Diving Manual—Volume 2
Duration of Air Supply.
The duration of the air supply of any given cylinder or
combination of cylinders depends upon:
The diver’s consumption rate, which varies with the diver’s work rate,
The depth of the dive, and
The capacity and recommended minimum pressure of the cylinder(s).
Temperature is usually not significant in computing the duration of the air supply,
unless the temperature conditions are extreme. When diving in extreme tempera-
ture conditions, Charles’/Gay-Lusac’s law must be applied.
There are three steps in calculating how long a divers air supply will last:
Calculate the divers consumption rate by using this formula:
C = Divers consumption rate, standard cubic feet per minute (scfm)
D = Depth, fsw
RMV = Divers Respiratory Minute Volume, actual cubic feet per minute
(acfm) (from Figure 7-6)
Calculate the available air capacity provided by the cylinders. The air capacity
must be expressed as the capacity that will actually be available to the diver,
rather than as a total capacity of the cylinder. The formula for calculating the
available air capacity is:
= Measured cylinder pressure, psig
= Recommended minimum pressure of cylinder, psig
FV = Internal volume (scf)
N = Number of cylinders
= Capacity available (scf)
Calculate the duration of the available capacity (in minutes) by using this
Duration =
CHAPTER 7 — Scuba Air Diving Operations 7-15
Figure 7-6.
Oxygen Consumption and RMV at Different Work Rates.
Rest 0.24 0.35 10
, standin
quietly 0.40 0.42 12 Li
in tank, minimum rate 0.58 0.53 15 Li
ht activity in chamber 0.70 0.64 18 Li
, muddy bottom, minimum rate 0.80 0.71 20 Moderate
in tank, maximum rate 1.10 0.99 28 Moderate
, muddy bottom, maximum rate 1.20 1.14 32 Moderate
Swim, 0.8 knot (avera
e speed)
(use for planning purposes, round up to 1.4)
1.40 1.34 38 Moderate
Swim, 1 knot 1.70 1.59 45 Heavy
Swim, 1.2 knot 2.50 2.12 60 Severe
7-16 U.S. Navy Diving Manual—Volume 2
= Capacity available, scf
C = Consumption rate, scfm
Sample Problem.
Determine the duration of the air supply of a diver doing
moderate work at 70 fsw using twin 72-cubic-foot steel cylinders charged to 2,250
Calculate the diver’s consumption rate in scfm. According to Figure 7-6, the
diver’s consumption rate at depth is 1.4 acfm.
Calculate the available air capacity provided by the cylinders. Table 7-1
contains the cylinder data used in this calculation:
Floodable Volume = 0.420 scf
Rated working pressure = 2250 psig
Reserve pressure for twin 72-cubic-foot cylinders = 250 psig
Calculate the duration of the available capacity.
The total time for the dive, from initial descent to surfacing at the end of the
dive, is limited to 26 minutes.
Compressed Air from Commercial Sources.
Compressed air meeting the estab-
lished standards can usually be obtained from Navy sources. In the absence of
appropriate Navy sources, air may be procured from commercial sources. Usually,
any civilian agency or firm which handles compressed oxygen can provide pure
70 33+
4.37 scfm=
2250 250
0.420 2
114 scf=
114 scf
4.37 scfm
26 minutes=
CHAPTER 7 — Scuba Air Diving Operations 7-17
compressed air. Air procured from commercial sources must meet the require-
ments of Grade A Source I or Source II air as specified by FED SPEC BB-A-
1034B. Refer to Table 4-2 in Chapter 4 for the air purity requirements.
Methods for Charging Scuba Cylinders.
raph 7-4.5 addresses safety precautions for char
and handlin
Scuba cylinders shall be charged only with air that meets diving air purity stan-
dards. A diving unit can charge its own cylinders by one of two accepted methods:
(1) by cascading or transferring air from banks of large cylinders into the scuba
tanks; or (2) by using a high-pressure air compressor. Cascading is the fastest and
most efficient method for charging scuba tanks. The NAVSEA/00C ANU list lists
approved high-pressure compressors and equipment authorized for scuba air
The normal cascade system consists of supply flasks connected together by a
manifold and feeding into a scuba high-pressure whip. This whip consists of a
scuba yoke fitting, a pressure gauge, and a bleed valve for relieving the pressure in
the lines after charging a cylinder. A cascade system, with attached whip, is shown
in Figure 7-7.
Figure 7-7.
Cascading System for Charging Scuba Cylinders.
7-18 U.S. Navy Diving Manual—Volume 2
Scuba charging lines shall be fabricated using SAE 100R7 hose for 3,000 psi
service and SAE 100R8 hose for 5,000 psi service. The service pressure of the
scuba charging lines shall be no greater than the working pressure of the hose
The working pressure of a hose is determined as one-fourth of its burst pressure.
While this criteria for working pressure was developed based on the characteris-
tics of rubber hose, it has also been determined to be appropriate for use with the
plastic hoses cited above.
Fleet units using charging lines shall not exceed the rated working pressure of the
hose. If the charging line working pressure rating does not meet service require-
ments, restrict the service pressure of the hose to its working pressure and initiate
replacement action immediately.
The use of strain reliefs made from cable, chain, 21-thread, or 3/8-inch nylon,
married at a minimum of every 18 inches and at the end of the hose, is a required
safety procedure to prevent whipping in the event of hose failure under pressure.
Marrying cord shall be 1/8-inch nylon or material of equivalent strength. Tie
wraps, tape, and marlin are not authorized for this purpose.
Operating Procedures for Charging Scuba Tanks.
Normally, scuba tanks are
charged using the following operating procedures (OPs), which may be tailored to
each unit:
Determine that the cylinder is within the hydrostatic test date.
Check the existing pressure in the scuba cylinder with an accurate pressure
Attach the cylinder to the yoke fitting on the charging whip, and attach the
safety strain relief.
For safety and to dissipate heat generated in the charging process, when
facilities are available, immerse the scuba cylinder in a tank of water while it
is being filled. A 55-gallon drum is a suitable container for this purpose.
Tighten all fittings in the system.
Close the bleed valve.
Place reserve mechanism lever in the open (lever down) position.
Open the cylinder (on/off) valve. This valve is fully opened with about two
turns on the handle, counter-clockwise. However, the valve must not be used
in a fully open position as it may stick or be stripped if force is used to open a
valve that is incorrectly believed to be closed. The proper procedure is to open
the valve fully and then close or back off one-quarter to one-half turn. This
will not impede the flow of air.
CHAPTER 7 — Scuba Air Diving Operations 7-19
Open the supply flask valve.
Slowly open the charging valve. The sound of the air flowing into the scuba
cylinder is noticeable. The operator will control the flow so that the pressure in
the cylinder increases at a rate not to exceed 400 psig per minute. If unable to
submerge scuba cylinders during charging, the charging rate must not exceed
200 psig per minute. The rate of filling must be controlled to prevent
overheating; the cylinder must not be allowed to become too hot to touch.
Monitor the pressure gauge carefully. When the reading reaches the rated
pressure for the scuba cylinder, close the valve on the first cylinder and take a
Close the charging valve.
Close the on/off valve on the scuba cylinder.
Ensure that all valves in the system are firmly closed.
Let the scuba cylinder cool to room temperature. Once the cylinder is cool, the
pressure will have dropped and you may need to top off the scuba cylinder.
Topping off the Scuba Cylinder.
Follow this procedure to top off a scuba
Open the on/off valve on the scuba cylinder.
Select a supply flask with higher pressure than the scuba rated limit.
Open the supply valve on the flask.
Throttle the charging valve to bring the scuba cylinder up to the rated limit.
Close all valves.
Open the bleed valve and depressurize the lines.
When air has stopped flowing through the bleed valve, disconnect the scuba
cylinder from the yoke fitting.
Reset the reserve mechanism (lever in up position).
In the absence of high-pressure air systems, large-volume air compressors can be
used to charge scuba cylinders directly. However, few compressors can deliver air
in sufficient quantity at the needed pressure for efficient operation. Small
compressors should be used only if no other suitable source is available.
If a suitable compressor is available, the basic charging procedure will be the same
as that outlined for cascading except that the compressor will replace the bank of
cylinders. Special considerations that apply when using air compressors are:
7-20 U.S. Navy Diving Manual—Volume 2
The compressor must be listed in the NAVSEA/00C ANU list if it is not part
of a certified system.
The compressor must deliver air that meets the established purity standards.
The compressor shall be equipped with ANU particulate filters. Chemically
active filters are not authorized.
An engine-driven compressor must always be mounted so there is no danger
of taking in exhaust fumes from the engine, stack gas, or other contaminated
air from local sources.
Only approved diving compressor lubricants are to be used in accordance with
PMS procedures or manufacturers recommendations.
Additional information on using air compressors is found in paragraph 8-6.2.2.
Safety Precautions for Charging and Handling Cylinders.
The following safety
rules apply to charging and handling scuba cylinders:
Carry cylinders by holding the valve and body of the cylinder. Avoid carrying
a cylinder by the backpack or harness straps as the quick-release buckle can be
accidentally tripped or the straps may fail.
Do not attempt to fill any cylinder if the hydrostatic test date has expired or if
the cylinder appears to be substandard. Dents, severe rusting, bent valves,
frozen reserve mechanisms, or evidence of internal contamination (e.g., water
scales or rust) are all signs of unsuitability. See CGA Pamphlet C-6, Standards
for Visual Inspection of Compressed Gas Cylinders.
Always use gauges to measure cylinder pressure. Never point the dial of a
gauge to which pressure is being applied toward the operators face.
Never work on a cylinder valve while the cylinder is charged.
Make sure that the air reserve mechanism is open (lever down) before
Use only compressed air for filling conventional scuba cylinders. Never fill
scuba cylinders with oxygen. Air is color-coded black, while oxygen is color-
coded green.
Tighten all fittings before pressurizing lines.
When fully charged, close the air reserve (lever up). Mark the filled tank to
indicate the pressure to which it was charged.
Handle charged cylinders with care. If a charged cylinder is damaged or if the
valve is accidentally knocked loose, the cylinder tank can become an
CHAPTER 7 — Scuba Air Diving Operations 7-21
explosive projectile. A cylinder charged to 2,000 psi has enough potential
energy to propel itself for some distance, tearing through any obstructions in
its way.
Store filled cylinders in a cool, shaded area. Never leave filled cylinders in
direct sunlight.
Cylinders should always be properly secured aboard ship or in a diving boat.
Predive procedures for scuba operations include equipment preparation, diver
preparation, and conducting a predive inspection before the divers enter the water.
Equipment Preparation.
Prior to any dive, all divers must carefully inspect their
own equipment for signs of deterioration, damage, or corrosion. The equipment
must be tested for proper operation. Predive preparation procedures must be stan-
dardized, not altered for convenience, and must be the personal concern of each
Air Cylinders.
Inspect air cylinder exteriors and valves for rust, cracks, dents, and any
evidence of weakness.
Inspect O-ring.
Verify that the reserve mechanism is closed (lever in up position) signifying a
filled cylinder ready for use.
Gauge the cylinders according to the following procedure:
Attach pressure gauge to O-ring seal face of the on/off valve.
Close gauge bleed valve and open air reserve mechanism (lever in down
position). Slowly open the cylinder on/off valve, keeping a cloth over the
face of the gauge.
Read pressure gauge. The cylinder must not be used if the pressure is not
sufficient to complete the planned dive.
Close the cylinder on/off valve and open the gauge bleed valve.
When the gauge reads zero, remove the gauge from the cylinder.
Close the air reserve mechanism (lever in up position).
If the pressure in cylinders is 50 psi or greater over rating, open the
cylinder on/off valve to bleed off excess and regauge the cylinder.
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Harness Straps and Backpack.
Check for signs of rot and excessive wear.
Adjust straps for individual use and test quick-release mechanisms.
Check backpack for cracks and other unsafe conditions.
Breathing Hoses.
Check the hoses for cracks and punctures.
Test the connections of each hose at the regulator and mouthpiece assembly by
tugging on the hose.
Check the clamps for corrosion and damage; replace as necessary and in
accordance with PMS procedures.
Attach regulator to the cylinder manifold, ensuring that the O-ring is properly
Crack the cylinder valve open and wait until the hoses and gauges have
Next open the cylinder valve completely and then close (back off) one-quarter
Check for any leaks in the regulator by listening for the sound of escaping air.
If a leak is suspected, determine the exact location by submerging the valve
assembly and the regulator in a tank of water and watch for escaping bubbles.
Frequently the problem can be traced to an improperly seated regulator and is
corrected by closing the valve, bleeding the regulator, detaching and reseating.
If the leak is at the O-ring and reseating does not solve the problem, replace
the O-ring and check again for leaks.
Life Preserver/Buoyancy Compensator (BC)
Orally inflate preserver to check for leaks and then squeeze out all air. The
remaining gas should be removed after entry into the water by rolling onto the
back and depressing the oral inflation tube just above the surface. Never suck
the air out, as it may contain excessive carbon dioxide.
Inspect the carbon dioxide cartridges to ensure they have not been used (seals
intact) and are the proper size for the vest being used and for the depth of dive.
The cartridges shall be weighed in accordance with the Planned Maintenance
CHAPTER 7 — Scuba Air Diving Operations 7-23
The firing pin should not show wear and should move freely.
The firing lanyards and life preserver straps must be free of any signs of
When the life preserver inspection is completed, place it where it will not be
damaged. Life preservers should never be used as a buffer, cradle, or cushion
for other gear.
Face Mask.
Check the seal of the mask and the condition of the head strap.
Check for cracks in the skirt and faceplate.
Swim Fins.
Check straps for signs of cracking.
Inspect blades for signs of cracking.
Dive Knife.
Test the edge of the knife for sharpness.
Ensure the knife is fastened securely in the scabbard.
Verify that the knife can be removed from the scabbard without difficulty, but
will not fall out.
Inspect the snorkel for obstructions.
Check the condition of the mouthpiece.
Weight Belt.
Check the condition of the weight belt.
Make sure that the proper number of weights are secure and in place.
Verify that the quick-release buckle is functioning properly.
Submersible Wrist Watch.
Ensure wrist watch is wound and set to the correct time.
Inspect the pins and strap of the watch for wear.
Depth Gauge and Compass.
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Inspect pins and straps.
If possible, check compass with another compass.
Make comparative checks on depth gauges to ensure depth gauges read zero
fsw on the surface.
Miscellaneous Equipment.
Inspect any other equipment that will be used on the dive as well as any spare
equipment that may be needed during the dive including spare regulators,
cylinders, and gauges.
Check all protective clothing, lines, tools, flares, and other optional gear.
Diver Preparation and Brief.
When the divers have completed inspecting and
testing their equipment, they shall report to the Diving Supervisor. The divers shall
be given a predive briefing of the dive plan. This briefing is critical to the success
and safety of any diving operation and shall be concerned with only the dive about
to begin. All personnel directly involved in the dive should be included in the
briefing. Minimum items to be covered are:
Dive objectives
Time and depth limits for the dive
Task assignments
Buddy assignments
Work techniques and tools
Phases of the dive
Route to the work site
Special signals
Anticipated conditions
Anticipated hazards
Emergency procedures (e.g., unconscious diver, trapped diver, loss of air,
aborted dive, injured diver, lost diver, etc.)
When the Diving Supervisor determines all requirements for the dive have been
met, the divers may dress for the dive.
Donning Gear.
Although scuba divers should be able to put on all gear them-
selves, the assistance of a tender is encouraged. Dressing sequence is important as
CHAPTER 7 — Scuba Air Diving Operations 7-25
the weight belt must be outside of all backpack harness straps and other equipment
in order to facilitate its quick release in the event of an emergency. The following
is the recommended dressing sequence to be observed:
Protective clothing. Ensure adequate protection is provided with a wet suit.
Booties and hood.
Dive knife.
Life preserver, with inflation tubes in front and the actuating lanyards exposed
and accessible.
Scuba. Most easily donned with the tender holding the cylinders in position
while the diver fastens and adjusts the harness. The scuba should be worn
centered on the divers back as high up as possible but not high enough to
interfere with head movement. All quick-release buckles must be positioned
so that they can be reached by either hand. All straps must be pulled snug so
the cylinders are held firmly against the body. The ends of the straps must
hang free so the quick-release feature of the buckles will function. If the straps
are too long, they should be cut and the ends whipped with small line or a
plastic sealer. At this time, the cylinder on/off valve should be opened fully
and then backed off one-quarter to one-half turn. Ensure buoyancy
compensator whip is connected to the buoyancy compensator.
Accessory equipment (diving wrist watch, depth gauge, snorkel).
Weight belt.
Swim fins.
Face mask or full face mask.
Predive Inspection.
The divers must report to the Diving Supervisor for a final
inspection. During this final predive inspection the Diving Supervisor must:
Ensure that the divers are physically and mentally ready to enter the water.
Verify that all divers have all minimum required equipment (scuba, face mask,
life preserver or buoyancy compensator, weight belt, dive knife, scabbard,
swim fins, watch and depth gauge). When diving scuba and a buddy line is
used, only one depth gauge and one watch per dive team is required.
Verify that the cylinders have been gauged and that the available volume of air
is sufficient for the planned duration of the dive.
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Ensure that all quick-release buckles and fastenings can be reached by either
hand and are properly rigged for quick release.
Verify that the weight belt is outside of all other belts, straps, and equipment
and will not become pinched under the bottom edge of the cylinders.
Verify that the life preserver or buoyancy compensator is not constrained and
is free to expand, and that all air has been evacuated.
Check position of the knife to ensure that it will remain with the diver no
matter what equipment is left behind.
Ensure that the cylinder valve is open fully and backed off one-quarter to one-
half turn.
Ensure that the hose supplying air passes over the divers right shoulder and
the exhaust hose on the double-hose unit passes over the left shoulder. Double-
hose regulators are attached so that the exhaust ports face up when the tank is
standing upright.
With mouthpiece or full face mask in place, breathe in and out for several
breaths, ensuring that the demand regulator and check valves are working
With a single-hose regulator, depress and release the purge button at the
mouthpiece and listen for any sound of leaking air. Breathe in and out several
times ensuring valves are working correctly.
Give the breathing hoses and mouthpiece a final check; ensure that none of the
connections have been pulled open during the process of dressing.
Check that the air reserve mechanism lever is up (closed position).
Conduct a brief final review of the dive plan.
Verify that dive signals are displayed and personnel and equipment are ready
to signal other vessels in the event of an emergency.
The divers are now ready to enter the water, where their scuba shall be given
another brief inspection by their dive partners or tenders prior to descent.
Water Entry.
There are several ways to enter the water, with the choice usually
determined by the nature of the diving platform (Figure 7-8a and Figure 7-8b).
Whenever possible, entry should be made by ladder, especially in unfamiliar
waters. Several basic rules apply to all methods of entry:
Look before jumping or pushing off from the platform or ladder.
CHAPTER 7 — Scuba Air Diving Operations 7-27
Figure 7-8a.
Scuba Entry Techniques.
Front jump or step-in
. On edge of platform, one
hand holding face mask and regulator, the other
holding the cylinders, the diver takes a long step
forward, keeping his legs astride.
Front roll
. Diver sits on edge of platform with a slight
forward lean to offset the weight of the cylinders.
Holding his mask and cylinders, the diver leans
Side roll
. Tender assists diver in taking a seated
position. Tender stands clear as diver holds his mask
and cylinders and rolls into the water.
Rear roll
. The diver, facing inboard, sits on the
gunwale. With chin tucked in, holding his mask,
mouthpiece, and cylinders, the diver rolls backwards,
basically completing a full backward somersault.
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Tuck chin into chest and hold the
cylinders with one hand to
prevent the manifold from hitting
the back of the head.
Hold the mask in place with the
fingers and the mouthpiece in
place with the heel of the hand.
Step-In Method.
The step-in method
is the most frequently used, and is
best used from a stable platform or
vessel. The divers should simply take
a large step out from the platform,
keeping legs in an open stride. They
should try to enter the water with a
slightly forward tilt of the upper body
so that the force of entry will not
cause the cylinder to hit the back of
the head.
Rear Roll Method.
The rear roll is the
preferred method for entering the
water from a small boat. A fully
outfitted diver standing on the edge of
a boat would upset the stability of the craft and would be in danger of falling either
into the boat or into the water. To execute a rear roll, the diver sits on the gunwale
of the boat, facing inboard. With chin tucked in and one hand holding the mask
and mouthpiece in place, the diver rolls backward, basically moving through a full
backward somersault.
Entering the Water from the Beach.
Divers working from the beach choose their
method of entry according to the condition of the surf and the slope of the bottom.
If the water is calm and the slope gradual, the divers can walk out, carrying their
swim fins until they reach water deep enough for swimming. In a moderate to high
surf, the divers, wearing swim fins, should walk backwards into the waves until
they have enough depth for swimming. They should gradually settle into the
waves as the waves break around them.
Predescent Surface Check.
Once in the water, and before descending to oper-
ating depth, the divers make a final check of their equipment. They must:
Make a breathing check of the scuba. Breathing should be easy, with no
resistance and no evidence of water leaks.
Visually check dive partners equipment for leaks, especially at all connection
points (i.e., cylinder valve, hoses at regulator and mouthpiece).
Check partner for loose or entangled straps.
Rear step-in
. The diver steps backward
pushing himself away with his feet.
Figure 7-8b.
Scuba Entry Techniques
CHAPTER 7 — Scuba Air Diving Operations 7-29
Check face mask seal. A small amount of water may enter the mask upon the
diver’s entry into the water. The mask may be cleared through normal methods
(see paragraph 7-7.2).
Check buoyancy. Scuba divers should strive for neutral buoyancy. When car-
rying extra equipment or heavy tools, the divers might easily be negatively
buoyant unless the weights are adjusted accordingly.
If wearing a dry suit, check for leaks. Adjust suit inflation for proper buoy-
Orient position with the compass or other fixed reference points.
When satisfied that all equipment checks out properly, the divers report their
readiness to the Diving Supervisor. The Diving Supervisor directs the divers to
zero their watches and bottom time begins. The Diving Supervisor gives a signal
to descend and the divers descend below the surface.
Surface Swimming.
The diving boat should be moored as near to the dive site as
possible. While swimming, dive partners must keep visual contact with each other
and other divers in the group. They should be oriented to their surroundings to
avoid swimming off course. The most important factor in surface swimming with
scuba is to maintain a relaxed pace to conserve energy. The divers should keep
their masks on and breathe through the snorkel. When surface swimming with a
scuba regulator, hold the mouthpiece so that air does not free-flow from the
Divers should use only their legs for propulsion and employ an easy kick from the
hips without lifting the swim fins from the water. Divers can rest on their backs
and still make headway by kicking. Swimming assistance can be gained by
partially inflating the life preserver or buoyancy compensator. However, the
preserver must be deflated again before the dive begins.
The divers may swim down or they may use a descending line to pull
themselves down. The rate of descent will generally be governed by the ease with
which the divers will be able to equalize the pressure in their ears and sinuses, but
it should never exceed 75 feet per minute. If either diver experiences difficulty in
clearing, both divers must stop and ascend until the situation is resolved. If the
problem persists after several attempts to equalize, the dive shall be aborted and
both divers shall return to the surface. When visibility is poor, the divers should
extend an arm to ward off any obstructions.
Upon reaching the operating depth, the divers must orient themselves to their
surroundings, verify the site, and check the underwater conditions. If conditions
appear to be radically different from those anticipated and seem to pose a hazard,
the dive should be aborted and the conditions reported to the Diving Supervisor.
The dive should be aborted if the observed conditions call for any major change in
the dive plan. The divers should surface, discuss the situation with the Diving
Supervisor, and modify the dive plan.
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In a scuba dive, bottom time is at a premium because of a limited supply of air.
Divers must pace their work, conserve their energy, and take up each task or
problem individually. At the same time they must be flexible. They must be ready
to abort the dive at any time they feel that they can no longer progress toward the
completion of their mission or when conditions are judged unsafe. The divers must
be alert for trouble at all times and must monitor the condition of the dive partner
Breathing Technique.
When using scuba for the first time, a novice diver is likely
to experience anxiety and breathe more rapidly and deeply than normal. The diver
must learn to breathe in an easy, slow rhythm at a steady pace. The rate of work
should be paced to the breathing cycle, rather than changing the breathing to
support the work rate. If a diver is breathing too hard, he should pause in the work
until breathing returns to normal. If normal breathing is not restored soon, the
diver must signal the dive partner and break off the operation, and together they
should ascend to the surface.
Some divers, knowing that they have a limited air supply, will attempt to conserve
air by holding their breath. One common technique is to skip-breathe: to insert an
unnatural, long pause between each breath.
WARNING Skip-breathin
may lead to hypercapnia and shall not be practiced.
Increased breathing resistance results from the design of the equipment and
increased air density. For normal diving, a marked increase of breathing resistance
should not occur until the primary air supply has been almost depleted. This
increase in breathing resistance is a signal to the diver to activate the reserve air
supply and to begin an ascent with the partner immediately. When equipped with a
submersible bottle gauge, the diver shall monitor his air supply pressure and must
terminate the dive whenever bottle pressure is reduced to 500 psi for a single
bottle or 250 psi for a set of double bottles.
Mask Clearing.
Some water seepage into the face mask is a normal condition and
is often useful in defogging the lens. From time to time the quantity may build to a
point that it must be removed. On occasion, a mask may become dislodged and
flooded. To clear a flooded mask not equipped with a purge valve, the diver should
roll to the side or look upward, so that the water will collect at the side or bottom
of the mask. Using either hand, the diver applies a firm direct pressure on the
opposite side or top of the mask and exhales firmly and steadily through the nose.
The water will be forced out under the skirt of the mask. When the mask has a
purge valve, the diver tilts his head so that the accumulated water covers the valve,
presses the mask against the face and then exhales firmly and steadily through the
nose. The increased pressure in the mask will force the water through the valve.
Occasionally, more than one exhalation will be required.
Hose and Mouthpiece Clearing.
The mouthpiece and the breathing hoses can
become flooded if the mouthpiece is accidentally pulled from the mouth. With a
CHAPTER 7 — Scuba Air Diving Operations 7-31
single-hose scuba this is not a serious problem since the hose (carrying air at
medium pressure) will not flood and the mouthpiece can be cleared quickly by
depressing the purge button as the mouthpiece is being replaced.
To clear a double-hose scuba regulator that has flooded, the diver, swimming in a
horizontal position, should grasp the mouthpiece. The diver should then blow into
the mouthpiece, forcing any water trapped in it out through the regulator’s exhaust
ports. The diver should carefully take a shallow breath. If water is still trapped in
the mouthpiece, the diver should blow through it once more and resume normal
breathing. If the diver is out of breath, he should roll over onto his back and the
regulator will free flow.
Swimming Technique.
In underwater swimming, all propulsion comes from the
action of the legs. The hands are used for maneuvering. The leg kick should be
through a large, easy arc with main thrust coming from the hips. The knees and
ankles should be relaxed. The rhythm of the kick should be maintained at a level
that will not tire the legs unduly or bring on muscle cramps.
Diver Communications.
Some common methods of diver communications are:
through-water communication systems, hand signals, slate boards, and line-pull
signals. Communication between the surface and a diver can be best accomplished
with through-water voice communications. However, when through-water
communications are not available, hand signals or line-pull signals can be used.
Figure 7-9.
Clearing a Face Mask. To clear a flooded face mask, push gently on the
upper or side portion of the mask and exhale through the nose into the mask. As water is
forced out, tilt the head backward or sideway until the mask is clear.
Head-Up Method
Side-Tilt Method
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Through-Water Communication Systems.
Presently, several types of through-
water communication systems are available for scuba diving operations. Acoustic
systems provide one-way, topside-to-diver communications. The multidirectional
audio signal is emitted through the water by a submerged transducer. Divers can
hear the audio signal without signal receiving equipment. Amplitude Modulated
(AM) and Single Sideband (SSB) systems provide round-robin, diver-to-diver,
diver-to-topside, and topside-to-diver communications. Both the AM and SSB
systems require transmitting and receiving equipment worn by the divers. AM
systems provide a stronger signal and better intelligibility, but are restricted to
line-of-sight use. SSB systems provide superior performance in and around obsta-
cles. Before any through-water communication system is used, consult the
NAVSEA/00C Authorized for Navy Use (ANU) list.
Hand and Line-Pull Signals.
Navy divers shall only use hand signals that have
been approved for Navy diving use. Figure 7-10a and Figure 7-10b present the
U.S. Navy approved hand signals. Under certain conditions, special signals appli-
cable to a specific mission may be devised and approved by the Diving Supervisor.
If visibility is poor, the dive partners may be forced to communicate with line-pull
signals on a buddy line. Line-pull signals are discussed in Table 8-2. Hand signals
and line-pull signals should be delivered in a forceful, exaggerated manner so that
there is no ambiguity and no doubt that a signal is being given. Every signal must
be acknowledged.
Buddy Diver Responsibilities.
The greatest single safety practice in Navy scuba
operations is the use of the buddy system. Dive partners operating in pairs are
responsible for both the assigned task and each other’s safety. The basic rules for
buddy diving are:
Always maintain contact with the dive partner. In good visibility, keep the
partner in sight. In poor visibility, use a buddy line.
Know the meaning of all hand and line-pull signals.
If a signal is given, it must be acknowledged immediately. Failure of a dive
partner to respond to a signal must be considered an emergency.
Monitor the actions and apparent condition of the dive partner. Know the
symptoms of diving ailments. If at any time the dive partner appears to be in
distress or is acting in an abnormal manner, determine the cause immediately
and take appropriate action.
Never leave a partner unless the partner has become trapped or entangled and
cannot be freed without additional assistance. If surface assistance must be
sought, mark the location of the distressed diver with a line and float or other
locating device. Do not leave a partner if voice communications or line-pull
signals are being used; contact the surface and await assistance or instructions.
Establish a lost-diver plan for any dive. If partner contact is broken, follow the
CHAPTER 7 — Scuba Air Diving Operations 7-33
Meaning/Signal Comment
Clenched fist.
Hand flat, fin
ers to
ether, palm out, thumb
down then hand rockin
back and forth on
axis of forearm.
This is the opposite of Okay. The
nal does not indicate an emer-
Thumb and forefin
er makin
a circle with
three remainin
ers extended (if
Divers wearin
mittens may not be
able to extend three remainin
ers distinctly. Short ran
e use.
ht hand raised overhead
nal with fin
Given when diver is close to
pickup boat.
Both hands touchin
overhead with both
arms bent at 45° an
Given when diver is at a distance
from the pickup boat.
Hand wavin
overhead (diver may also
thrash hand in water).
Indicates immediate aid is
Diver points to either watch or depth
When indicatin
time, this si
nal is
commonly used for bottom time
Two fin
ers up, two fin
ers and thumb
ainst palm.
Four fin
ers pointin
up, thumb a
Hand slashin
or choppin
at throat.
Indicates si
naler is out of air.
ers pointin
to mouth or re
nalers re
ulator may be in or
out of mouth.
Figure 7-10a.
Scuba Hand Si
7-34 U.S. Navy Diving Manual—Volume 2
Hand to chest, repeated.
er to chest, repeated.
ers to
ether and arm movin
in and
over, under, or around movement.
Diver si
nals intention to move
over, under, or around an object.
ers and thumb spread out and hand
back and forth in a level position.
Fist clenched with thumb pointin
down, ri
ht, or left.
Indicates which direction to swim.
ers clenched, thumb and hand rotatin
ht and left.
Diver pointin
to either ear.
Divers should ascend a few feet. If
problem continues, both divers
must surface.
Both arms crossed over chest.
Hand extended, palm down, in short up-
and-down motion.
Index fin
ers extended, one hand forward
of the other.
Meaning/Signal Comment
Figure 7-10a.
Scuba Hand Si
CHAPTER 7 — Scuba Air Diving Operations 7-35
If one member of a dive team aborts a dive, for whatever reason, the other
member also aborts and both must surface.
Know the proper method of buddy breathing.
Buddy Breathing Procedure.
If a diver runs out of air or the scuba malfunctions,
air may be shared with the dive partner. The most efficient method of buddy
breathing is for the two divers to face each other, each alternately breathing from
the same mouthpiece while ascending. Buddy breathing may be used in an emer-
gency and must be practiced so that each diver will be thoroughly familiar with the
The distressed diver should remain calm and signal the partner by pointing to
scuba mouthpiece.
The partner and the distressed diver should hold on to each other by grasping a
strap or the free arm. The divers must be careful not to drift away from each
The partner must make the first move by taking a breath and passing the
mouthpiece to the distressed diver. The distressed diver must not grab for the
Figure 7-10b.
Scuba Hand Signals (continued).
(Buddy at Distance)
When buddy is near, use re
ular hand
nals in front of li
is wron
I require assistance.
e, rapid up-and-down
motions with arm extended).
I am Okay.
Are you Okay?
e, slow circles with
7-36 U.S. Navy Diving Manual—Volume 2
dive partners mouthpiece. The dive partner guides it to the distressed divers
mouth. Both divers maintain direct hand contact on the mouthpiece.
The mouthpiece may have flooded during the transfer. In this case, clear the
mouthpiece by using the purge button (if single-hose) or by exhaling into the
mouthpiece before a breath can be taken. If using a double-hose regulator, the
mouthpiece should be kept slightly higher than the regulator so that free-
flowing air will help keep the mouthpiece clear.
The distressed diver should take two full breaths (exercising caution in the
event that all of the water has not been purged) and guide the mouthpiece back
to the partner. The partner should then purge the mouthpiece as necessary and
take two breaths.
The divers should repeat the breathing cycle and establish a smooth rhythm.
No attempt should be made to surface until the cycle is stabilized and the
proper signals have been exchanged.
ascent, the diver without the mouthpiece must exhale to offset
the effect of decreasin
pressure on the lun
s which could cause an air
Buddy breathing may also be accomplished by use of an “octopus” (secondary
second-stage regulator). Approved secondary second stage regulators are
contained in the diving equipment Authorized for Navy Use (ANU) list.
Tending with a Surface or Buddy Line.
When a diver is being tended by a line
from the surface or a buddy line, several basic considerations apply.
Lines should be kept free of slack.
Line signals must be given in accordance with the procedures given in Table
Any signals via the line must be acknowledged immediately by returning the
same signal.
The tender should signal the diver with a single pull every 2 or 3 minutes to
determine that the diver is all right. A return signal of one pull indicates that
the diver is all right.
If the diver fails to respond to line-pull signals after several attempts, the
standby diver must investigate immediately.
The diver must be particularly aware of the possibilities for the line becoming
snagged or entangled.
CHAPTER 7 — Scuba Air Diving Operations 7-37
Tending with No Surface Line.
If a surface line is not being used, the tender must
keep track of the general location of the divers by observing the bubble tracks or
the float or locating device (such as a pinger or strobe light). When tending a
single diver, the tender shall continually monitor the diver float for diver location
and line pull signals.
Working with Tools.
The near-neutral buoyancy of a scuba diver poses certain
problems when working with tools. A diver is at a disadvantage when applying
leverage with tools. When applying force to a wrench, for example, the diver is
pushed away and can apply very little torque. If both sides of the work are acces-
sible, two wrenches—one on the nut and one on the bolt—should be used. By
pulling on one wrench and pushing on the other, the counter-force permits most of
the effort to be transmitted to the work. When using any tool that requires leverage
or force (including pneumatic power tools), the diver should be braced with feet, a
free hand, or a shoulder.
NOTE When usin
externally powered tools with scuba, the diver must have
voice communications with the Divin
Any tools to be used should be organized in advance. The diver should carry as
few items as possible. If many tools are required, a canvas tool bag should be used
to lower them to the diver as needed. Further guidelines for working underwater
are provided in the U.S. Navy Underwater Ship Husbandry Manual (NAVSEA
S0600-AA-PRO-010). Authorized power tools are listed in the NAVSEA/00C
ANU list.
Adapting to Underwater Conditions.
Through careful and thorough planning, the
divers can be properly prepared for the underwater conditions at the diving site
and be provided with appropriate auxiliary equipment, protective clothing, and
tools. However, the diver may have to employ the following techniques to offset
the effects of certain underwater conditions:
Stay 2 or 3 feet above a muddy bottom; use a restricted kick and avoid stirring
up the mud. A diver should be positioned so that the current will carry away
any clouds of mud.
Avoid coral or rocky bottoms, which may cause cuts and abrasions.
Avoid abrupt changes of depth.
Do not make excursions away from the dive site unless the excursions have
been included in the dive plan.
Be aware of the peculiar properties of light underwater. Depth perception is
altered so that an object appearing to be 3 feet away is actually 4 feet away,
and objects appear larger than they actually are.
7-38 U.S. Navy Diving Manual—Volume 2
Be aware of unusually strong currents, particularly rip currents near a
shoreline. If caught in a rip current, relax and ride along with it until it
diminishes enough to swim clear.
If practical, swim against a current to approach a job site. The return swim
with the current will be easier and will offset some of the fatigue caused by the
Stay clear of lines or wires that are under stress.
When it is time to return to the surface, either diver may signal the end of the dive.
When the signal has been acknowledged, the divers shall ascend to the surface
together at a rate not to exceed 30 feet per minute. For a normal ascent, the divers
will breathe steadily and naturally. Divers must never hold their breath during
ascent, because of the danger of an air embolism. While ascending, divers must
keep an arm extended overhead to watch for obstructions and should spiral slowly
while rising to obtain a full 360 degree scan of the water column.
Emergency Free-Ascent Procedures.
If a diver is suddenly without air or if the
scuba is entangled and the dive partner cannot be reached quickly, a free ascent
must be made. Guidelines for a free ascent are:
Drop any tools or objects being carried by hand.
Abandon the weight belt.
If the scuba has become entangled and must be abandoned, actuate the quick-
release buckles on the waist, chest, shoulder, and crotch straps. Slip an arm out
of one shoulder strap and roll the scuba off the other arm. An alternate method
is to flip the scuba over the head and pull out from underneath. Ensure that the
hoses do not wrap around or otherwise constrict the neck. The neck straps
packed with some single-hose units can complicate the overhead procedure
and should be disconnected from the unit and not used.
If the reason for the emergency ascent is a loss of air, drop all tools and the
weight belt and actuate the life preserver to surface immediately. Do not drop
the scuba unless it is absolutely necessary.
If a diver is incapacitated or unconscious and the dive partner anticipates
difficulty in trying to swim the injured diver to the surface, the partner should
activate the life preserver or inflate the buoyancy compensator. The weight
belt may have to be released also. However, the partner should not lose direct
contact with the diver.
Exhale continuously during ascent to let the expanding air in the lungs escape
CHAPTER 7 — Scuba Air Diving Operations 7-39
Ascent From Under a Vessel.
When underwater ship husbandry tasks are
required, surface-supplied lightweight equipment is preferred. Scuba diving is
permitted under floating hulls; however, a tending line to the scuba diver must be
provided. In the event of casualty and the lack of immediate assistance by the dive
partner, the scuba diver will be able to return to the surface using the tending line.
Ships are often moored against closed-face piers or heavy camels and care must be
exercised to ensure that the tending line permits a clear path for emergency
surfacing of the diver.
Due to the unique nature of EOD operations involving limpet search and neutral-
ization, the use of tending lines is not practical and is not required. During EOD
limpet mine training, the use of tending lines is required.
Scuba dive plans on deep-draft ships should restrict diving operations to one quad-
rant of the hull at a time. This theoretical quartering of the ships hull will
minimize potential diver disorientation caused by multiple keel crossings or fore
and aft confusion.
When notified of a lost diver, a search shall be conducted by a tended diver in the
area where the lost diver was last seen.
Predive briefs must include careful instruction on life preserver use when working
under a hull to prevent panic blowup against the hull. Life preservers should not be
fully inflated until after the diver passes the turn of the bilge.
Open-circuit scuba dives are normally planned as no-decom-
pression dives. Open-circuit scuba dives requiring decompression may be made
only when considered absolutely necessary and authorized by the Commanding
Officer or Officer in Charge (OIC). Under this unique situation, the following
provides guidance for scuba decompression diving.
The Diving Supervisor shall determine the required bottom time for each dive.
Based upon the time and depth of the dive, the required decompression profile
from the tables presented in Chapter 9 shall be computed. The breathing supply
required to support the total time in the water must then be calculated. If the air
supply is not sufficient, a backup scuba will have to be made available to the
divers. The backup unit can be strapped to a stage or tied off on a descent line
which also has been marked to indicate the various decompression stops to be
When the divers have completed the assigned task, or have reached the maximum
allowable bottom time prescribed in the dive plan, they must ascend to the stage or
the marked line and signal the surface to begin decompression. With the stage
being handled from the surface, the divers will be taken through the appropriate
stops while the timekeeper controls the progress. Before each move of the stage,
the tender will signal the divers to prepare for the lift and the divers will signal
back when prepared. When using a marked line, the tender will signal when each
stop has been completed, at which point the divers will swim up, signaling their
7-40 U.S. Navy Diving Manual—Volume 2
arrival at the next stop. Stop times will always be regulated by the Dive
In determining the levels for the decompression stops, the sea state on the surface
must be taken into consideration. If large swells are running, the stage or marker
line will be constantly rising and falling with the movements of the surface-
support craft. The depth of each decompression stop should be calculated so that
the divers’ chests will never be brought above the depths prescribed for the stops
in the decompression tables.
In the event of an accidental surfacing or an emergency, the Diving Supervisor
will have to determine if decompression should be resumed in the water or if the
services of a recompression chamber are required. The possibility of having to
make such a choice should be anticipated during the planning stages of the opera-
tion (Chapters 1 and 5).
Surfacing and Leaving the Water.
When approaching the surface, divers must not
come up under the support craft or any other obstruction. They should listen for
the sound of propellers and delay surfacing until satisfied that there is no obstruc-
tion. On the surface, the diver should scan immediately in all directions and check
the location of the support craft, other divers, and any approaching surface traffic.
If they are not seen by the support craft, they should attempt to signal the support
craft with hand signals, whistle, or flare.
On the surface, the divers can rest while waiting to be picked up. For buoyancy,
life vests or buoyancy compensators can be inflated orally or the diver can use a
snorkel for breathing.
As the divers break the surface, the tender and other personnel in the support craft
must keep them in sight constantly and be alert for any signs of trouble. While one
diver is being taken aboard the support craft, attention must not be diverted from
the divers remaining in the water. The dive is completed when all divers are safely
Usually, getting into the boat will be easier if the divers remove the weight belts
and scuba and then hand them to the tenders. If the boat has a ladder, swim fins
should also be removed. Without a ladder, the swim fins will help to give the diver
an extra push to get aboard. A small boat may be boarded over the side or over the
stern depending on the type of craft and the surface conditions. As each diver
comes aboard a small boat or a raft, other personnel in the boat should remain
The Diving Supervisor should debrief each returning diver while the experience of
the dive is still fresh. The Diving Supervisor should determine if the assigned tasks
were completed, if any problems were encountered, if any changes to the overall
dive plan are indicated and if the divers have any suggestions for the next team.
CHAPTER 7 — Scuba Air Diving Operations 7-41
When satisfied with their physical condition, the divers’ first responsibility after
the dive is to check their equipment for damage and get it properly cleaned and
stowed. Each diver is responsible for the immediate postdive maintenance and
proper disposition of the equipment used during the dive. The Planned Mainte-
nance System provides direction for postdive maintenance.
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