CHAPTER 8 — Surface-Supplied Air Diving Operations 8-1
Surface-supplied air diving includes those forms of diving where air is
supplied from the surface to the diver by a flexible hose. The Navy Surface-
Supplied Diving Systems (SSDS) are used primarily for operations to 190 feet of
seawater (fsw).
This chapter identifies the required equipment and procedures for using
the UBA MK 21 MOD 1 and the UBA MK 20 MOD 0 surface-supplied diving
MK 21 MOD 1
The MK 21 MOD 1 is an open-cir-
cuit, demand, diving helmet (Figure
8-1). The maximum working depth
for air diving operations using the
MK 21 MOD 1 system is 190 fsw.
The MK 21 MOD 1 system may be
used up to 60 fsw without an Emer-
gency Gas Supply (EGS). An EGS is
mandatory at depths deeper than 60
fsw and when diving inside a wreck
or enclosed space. The Diving Super-
visor may elect to use an EGS that
can be man-carried or located outside
the wreck or enclosed space and con-
nected to the diver with a 50 to 150
foot whip. Planned air dives below
190 fsw require CNO approval.
Operation and Maintenance.
The technical manual for the MK 21 MOD 1 is
NAVSEA S6560-AG-OMP-010, Technical Manual, Operation and Maintenance
Instructions, Underwater Breathing Apparatus MK 21 MOD 1 Surface-Supported
Diving System. To ensure safe and reliable service, the MK 21 MOD 1 system
must be maintained and repaired in accordance with PMS procedures and the MK
21 MOD 1 operation and maintenance manual.
Air Supply.
Air for the MK 21 MOD 1 system is supplied from the surface by
either an air compressor or a bank of high-pressure air flasks as described in para-
graph 8-6.2.3.
Figure 8-1.
8-2 U.S. Navy Diving Manual—Volume 2
Emergency Gas Supply Requirements.
The emergency breathing supply valve
provides an air supply path parallel to the nonreturn valve and permits attachment
of the EGS whip. The EGS system consists of a steel 72 (64.7 cubic-foot
[minimum]) scuba bottle with either a K- or J- valve and a first-stage regulator set
at 135 ± 5 psi over bottom pressure. A relief valve set at 180
5 psi over bottom
pressure must be installed on the first-stage regulator to prevent rupture of the
low-pressure hose should the first-stage regulator fail. The flexible low-pressure
hose from the first-stage regulator attaches to the emergency supply valve on the
helmet sideblock. A submersible pressure gauge is also required on the first-stage
When using an EGS whip 50 to 100 feet in length, set at manufacturers recom-
mended pressure, but not lower than 135 psi. If the diving scenario dictates
leaving the EGS topside, adjust the first-stage regulator to 150 psig.
Flow Requirements.
When the MK 21 MOD 1 system is used, the air supply
system must be able to provide an average sustained flow of 1.4 acfm to the diver.
The air consumption of divers using the MK 21 MOD 1 varies between 0.75 and
1.5 acfm when used in a demand mode, with occasional faceplate and mask
clearing. When used in a free-flow mode, greater than eight acfm is consumed.
NOTE When plannin
a dive, calculations are based on 1.4 acfm.
To satisfactorily support the MK 21 MOD 1 system, the air supply must:
Replenish the air consumed from the system (average rate of flow)
Replenish the air at a rate sufficient to maintain the required pressure
Provide the maximum rate of flow required by the diver
Pressure Requirements.
Because the MK 21 MOD 1 helmet is a demand-type
system, the regulator has an optimum overbottom pressure that ensures the lowest
possible breathing resistance and reduces the possibility of overbreathing the regu-
lator (demanding more air than is available). The optimum overbottom pressure
for all dives shallower than 130 fsw is 135 psi. For those systems which cannot
maintain 135 psig when diving shallower than 60 fsw, 90 psi is permissible. The
manifold supply pressure requirement for dives 130-190 fsw is 165 psi. For those
systems not capable of sustaining 165 psi overbottom due to design limitations,
135 psi overbottom is acceptable.
This ensures that the air supply will deliver air at a pressure sufficient to overcome
bottom seawater pressure and the pressure drop that occurs as the air flows
through the hoses and valves of the mask.
Sample Problem 1.
Determine the air supply manifold pressure required to dive
the MK 21 MOD 1 system to 175 fsw.
CHAPTER 8 — Surface-Supplied Air Diving Operations 8-3
Determine the bottom pressure at 175 fsw:
Bottom pressure at 175 fsw = 175
.445 psi
= 77.87 psig (round to 78)
Determine the overbottom pressure for the MK 21 MOD 1 system (see
paragraph 8-2.2.3). Because the operating depth is 175 fsw, the overbottom
pressure is 165 psig.
Calculate the minimum manifold pressure (MMP) by adding the bottom
pressure to the overbottom pressure:
The minimum manifold pressure for a 175-fsw dive must be 243 psig.
Sample Problem 2.
Determine if air from a bank of high-pressure flasks is
capable of supporting two MK 21 MOD 1 divers and one standby diver at a depth
of 130 fsw for 30 minutes. There are 5 flasks in the bank; only 4 are on line. Each
flask has a floodable volume of 8 cubic feet and is charged to 3,000 psig.
NOTE These calculations are based on an assumption of an avera
e of 1.4
acfm diver air consumption over the total time of the dive. Hi
her con-
sumption over short periods can be expected based on diver work rate.
Calculate minimum manifold pressure (MMP).
Round up to 223 psig
Calculate standard cubic feet (scf) of air available. The formula for calculating
the scf of air available is:
= Flask pressure = 3,000 psig
= Minimum flask pressure = 220 psig
MMP = 223 psig
V = Capacity of flasks = 8 cffv
N = Number of flasks = 4
MMP 78 psig 165 psig+=
243 psig=
MMP psig
165 psig+=
0.455 130
165 psig+=
222.85 psig=
scf available
8-4 U.S. Navy Diving Manual—Volume 2
Calculate scf of air required to make the dive. You will need to calculate the
air required for the bottom time, the air required for each decompression stop,
and the air required for the ascent. The formula for calculating the air required
D = Depth (feet)
V = acfm needed per diver
N = Number of divers
T = Time at depth (minutes)
Bottom time: 30 minutes
Decompression stops: A dive to 130 fsw for 30 minutes requires the following
decompression stops:
3 minutes at 20 fsw
18 minutes at 10 fsw
Ascent time: 5 minutes (rounded up from 4 minutes 20 seconds) from 130 fsw
to the surface at 30 feet per minute.
scf available
3000 220 223+
5566.26 scf (round down to 5566)=
scf required
cf required
130 33+
1.4 3
622.36 scf=
scf required
20 33+
1.4 3
scf required
10 33+
1.4 3
98.51 scf=
average depth
65 feet==
scf required
65 33+
1.4 3
62.36 scf=
CHAPTER 8 — Surface-Supplied Air Diving Operations 8-5
Calculate the air remaining at the completion of the dive to see if there is
sufficient air in the air supply flasks to make the dive.
scf remaining = scf available – scf required
= 5609 scf – 804 scf
= 4805 scf
More than sufficient air is available in the air supply flasks to make this dive.
NOTE Planned air usa
e estimates will vary from actual air usa
e. The air
requirements for a standby diver must also be taken into account for all
operations. The Divin
Supervisor must note initial volume/pres-
sure and continually monitor consumption throu
hout dive. If actual
consumption exceeds planned consumption, the Divin
Supervisor may
be required to curtail the dive in order to ensure there is adequate air
in the primary air supply to complete decompression.
MK 20 MOD 0
The MK 20 MOD 0 is a surface-sup-
plied UBA consisting of a full face
mask, diver communications compo-
nents, equipment harness, and an um-
bilical assembly (Figure 8-2). One of its
primary uses is in enclosed spaces, such
as submarine ballast tanks. The MK 20
MOD 0 is authorized for use to a depth
of 60 fsw with surface-supplied air and
must have an Emergency Gas Supply
when used for enclosed space diving.
Operation and Maintenance.
considerations and working procedures
are covered in Chapter 6. NAVSEA
SS600-AK-MMO-010 Technical Man-
ual, Operations and Maintenance In-
struction Manual is the technical man-
ual for the MK 20 MOD 0. To ensure
safe and reliable service, the MK 20
MOD 0 system must be maintained and
repaired in accordance with PMS pro-
cedures and the MK 20 MOD 0 opera-
tion and maintenance manual.
Total air required 622.36 20.24 98.51 62.36+++=
803.48 scf (round to 804 scf)=
Figure 8-2.
MK 20 MOD 0 UBA.
8-6 U.S. Navy Diving Manual—Volume 2
Air Supply.
Air for the MK 20 MOD 0 system is supplied from the surface by
either an air compressor or a bank of high-pressure flasks as described in para-
graph 8-6.2.3.
EGS Requirements for MK 20 MOD 0 Enclosed-Space Diving.
In order to ensure
a positive emergency air supply to the diver when working in a ballast tank, mud
tank, or confined space, an Emergency Gas Supply (EGS) assembly must be used.
As a minimum, the EGS assembly consists of:
Single scuba cylinder steel 72 (minimum 64.7 cubic feet) with either a K- or J-
valve, charged to a minimum of 1,800 psi.
An approved scuba regulator set at manufacturers recommended pressure, but
not lower than 135 psi, with an extended EGS whip 50 to 150 feet in length. If
the diving scenario dictates leaving the EGS topside, adjust the first-stage reg-
ulator to 150 psig.
An approved submersible pressure gauge.
The scuba cylinder may be left on the surface and the EGS whip may be married
to the divers umbilical, or it may be secured at the opening of the enclosed space
being entered. The diver may then enter the work space with the extended EGS
whip trailing. The second-stage regulator of the EGS is securely attached to the
diver’s harness before entering the work space so that the diver has immediate
access to the EGS regulator in an emergency.
Flow Requirements.
The MK 20 MOD 0 requires a breathing gas flow of 1.4
acfm and an overbottom pressure of 90 psig. Flow and pressure requirement calcu-
lations are identical to those for the MK 21 MOD 1 (see paragraph 8-2.2.3).
MK 3 MOD 0 Lightweight Dive System (LWDS).
The MK 3 MOD 0 LWDS is a
portable, self-contained, surface-supplied diver life-support system (DLSS). The
MK 3 MOD 0 LWDS can be arranged in three different configurations and may be
deployed pierside or from a variety of support platforms. Each LWDS includes a
control console assembly, volume tank assembly, medium-pressure air
compressor (optional), and stackable compressed-air rack assemblies, each
consisting of three high-pressure composite flasks (0.97 cu ft floodable volume
each). Each flask holds 198 scf of compressed air at 3,000 psi. The MK 3 MOD 0
LWDS provides sufficient air for two working divers and one standby diver oper-
ating at a moderately heavy work rate to a maximum depth of 60 fsw in
configuration 1, 130 fsw in configuration 2, and 190 fsw in configuration 3. The
MK 3 MOD 0 will support diving operations with both UBA MK 20 MOD 0 and
UBA MK 21 Mod 1. Set-up and operating procedures for the LWDS are found in
the Operating and Maintenance Instructions for Lightweight Dive System
(LWDS) MK 3 MOD 0, SS500-HK-MMO-010.
CHAPTER 8 — Surface-Supplied Air Diving Operations 8-7
MK 3 MOD 0 Configuration 1.
Air is supplied by a medium-pressure diesel-driven
compressor unit supplying primary air to the divers at 18 standard cubic feet per
minute (scfm) with secondary air being supplied by one air-rack assembly. Total
available secondary air is 594 scf. See Figure 8-3.
MK 3 MOD 0 Configuration 2.
Primary air is supplied to the divers using three
flask rack assemblies. Secondary air is supplied by one flask rack assembly. Total
available primary air is 1782 scf at 3,000 psi. Total available secondary air is 594
scf. See Figure 8-4.
MK 3 MOD 0 Configuration 3.
Primary air is supplied to the divers using three
flask rack assemblies. Secondary air is supplied by two flask rack assemblies.
Total available primary air is 1,782 scf. Total available secondary air is 1,188 scf.
See Figure 8-5.
MK 3 MOD 1 Lightweight Dive System.
This system is identical to the MK 3
MOD 0 LWDS except that the control console and volume tank have been modi-
fied to support 5,000 psi operations for use with the Flyaway Dive System (FADS)
III. With appropriate adapters the system can still be used to support normal
LWDS operations. See Figure 8-6.
Figure 8-3.
MK 3 MOD 0 Configuration 1.
8-8 U.S. Navy Diving Manual—Volume 2
Figure 8-4.
MK 3 MOD 0 Configuration 2.
Figure 8-5.
MK 3 MOD 0 Configuration 3.
CHAPTER 8 — Surface-Supplied Air Diving Operations 8-9
ROPER Diving Cart.
The ROPER diving cart is a trailer-mounted diving system,
designed to suport one working and one standby diver in underwater operational
tasks performed by Ship Repair Activities to 60 fsw (Figure 8-7). The system is
self-contained, transportable, and certifiable in accordance with U.S. Navy Diving
and Hyperbaric System Safety Certification Manual, NAVSEA SS521-AA-MAN-
010. The major components/subsystems mounted within the cart body are:
Diving control station
. A single operator controls and monitors the air supply
and operates the communication system.
Power distribution system
. External power for communications and control
station lighting.
Intercommunication system (AC/DC)
. Provides communications between
divers and the diving control station.
Air supply system
. Primary air source of two 6 cu ft, 3,000 psi air flasks; sec-
ondary air source of a single 1.52 cu ft, 3,000 psi air flask; and a scuba
charging station.
Detailed information and operating instructions are covered in Operations and
Maintenance Instructions for Ready Operational Pierside Emergency Repair
(ROPER) Diving Cart, SS500-AS-MMA-010.
Flyaway Dive System (FADS) I.
The FADS I is an air transportable, 0–190 fsw
system that can be delivered to a suitable diving platform quickly. The system
Figure 8-6.
MK 3 MOD 1 Lightweight Dive System.
8-10 U.S. Navy Diving Manual—Volume 2
consists of a filter control console (FCC) intended for use with the medium-pres-
sure flyaway air compressors and/or conventional air supplies. In its present
configuration, the system can service up to four divers depending on the diving
equipment in use. MK 21 MOD 1 and MK 20 equipment may be employed with
the FADS I. See Figure 8-8.
Operational instructions for FADS I and II are covered in Fly Away Diving System
Filter/Console Operation and Maintenance Instructions, S9592-AD-MMM.FLTR
CONT CSL; Fly Away Diving System Compressor Model 5120 Operation and
Maintenance Instructions, S9592-AE-MMM-010/MOD 5120; and Fly Away
Diving System Diesel Driven Compressor Unit Ex 32 Mod 0, PN 5020559, Opera-
tion and Maintenance Instructions, S9592-AC-MMM-010/Detroit DSL 3-53.
Flyaway Dive System (FADS) II.
The FADS II is a self-supported, air transport-
able, 0–190 fsw air diving system, designed and packaged for rapid deployment
worldwide to a vessel of opportunity (see Figure 8-9). Primarily intended for use
in salvage or inspection and emergency ship repairs, the system’s main compo-
nents are:
Diving outfit
. Four demand helmet (MK 21 MOD 1) assemblies with umbili-
cals, communication system, tool kit, and repair parts kit.
Two medium-pressure air compressors (MPAC)
. Diesel-driven QUINCY 250
psi, 87 standard cubic feet per minute (scfm), skid mounted.
Figure 8-7.
CHAPTER 8 — Surface-Supplied Air Diving Operations 8-11
High pressure air compressor (HPAC)
. Diesel-driven INGERSOLL RAND
10T2, 3,000 psi, 15 scfm, skid-mounted.
Filter control console
. Regulates and filters air from MPAC, HPAC, or HP
banks to support four divers, skid-mounted.
Suitcase filter control console
. Filters MPAC air to support three divers.
Double-lock aluminum recompression chamber
. Standard USN chamber,
skid-mounted and designed to interface with filter control console.
Two HP air banks
. Two sets of HP banks providing secondary diver and
chamber air.
HP oxygen tank
. One bank of HP oxygen providing chamber support.
Figure 8-8.
Flyaway Air Diving System (FADS) I.
8-12 U.S. Navy Diving Manual—Volume 2
5 kW diesel generator
. Provides power for communications, chamber light-
ing, miscellaneous.
5 kW diesel light tower
. Provides power to tripod lights, mast lights, underwa-
ter lights.
Hydraulic tool package and underwater lights
. As required.
Equipment shelter
. Fiberglass container houses filter control console and div-
ing station.
Two conex boxes
. Steel containers for equipments storage.
Flyaway Dive System (FADS) III.
The FADS III is a portable, self-
contained, surface-supplied diver
life-support system designed to
support dive missions to 190 fsw
(Figure 8-9). Compressed air at
5,000 psi is contained in nine 3.15
cu ft floodable volume composite
flasks vertically mounted in an Air
Supply Rack Assembly (ASRA).
The ASRA will hold 9600 scf of
compressed air at 5,000 psi.
Compressed air is provided by a
5,000 psi air compressor assembly
which includes an air purification
system. The FADS III also
includes a control console
assembly and a volume tank
assembly. Three banks of two,
three, and four flasks allow the
ASRA to provide primary and secondary air to the divers as well as air to support
chamber operations. Set-up and operating procedures for the FADS III are found
in the Operating and Maintenance Technical Manual for Fly Away Dive System
(FADS) III Air System, S9592-B1-MMO-010.
Accessory equipment that is often useful in surface-supplied diving operations
includes the following items:
Lead Line
. The lead line is used to measure depth.
Descent Line
. The descent line guides the diver to the bottom and is used to
pass tools and equipment. A 3-inch double-braid line is recommended, to pre-
vent twisting and to facilitate easy identification by the diver on the bottom. In
Figure 8-9.
Control Console Assembly of
CHAPTER 8 — Surface-Supplied Air Diving Operations 8-13
use, the end of the line may be fastened to a fixed underwater object, or it may
be anchored with a weight heavy enough to withstand the current.
Circling Line
. The circling line is attached to the bottom end of the descent
line. It is used by the diver as a guide in searching and for relocating the
descent line.
. Constructed to carry one or more divers, the stage is used to put divers
into the water and to bring them to the surface, especially when decompres-
sion stops must be made. The stage platform is made in an open grillwork
pattern to reduce resistance from the water and may include seats. Guides for
the descent line, several eyebolts for attaching tools, and steadying lines or
weights are provided. The frames of the stages may be collapsible for easy
storage. A safety shackle or screw-pin shackle seized with wire or with a cot-
ter pin must be used to connect the stage to the lifting line when raising or
lowering. Stages must be weight tested in accordance with PMS.
Stage Line
. Used to raise and lower the stage, the stage line is to be 3-inch
double braid, or 3/8-inch wire rope minimum, taken to a capstan or run off a
winch and davit.
Diving Ladder
. The diving ladder is used to enter the water from a vessel.
. Cast iron or lead weights are used to weight the descent line.
Tool Bag
. The tool bag is used to carry tools.
. Stopwatches are used to time the total dive time, decompression
stop time, travel time, etc.
The divers air supply may originate from an air compressor, a bank of high-pres-
sure air flasks, or a combination of both.
Requirements for Air Supply.
Regardless of the source, the air must meet certain
established standards of purity, must be supplied in an adequate volume for
breathing, and must have a rate of flow that properly ventilates the helmet or
mask. The air must also be provided at sufficient pressure to overcome the bottom
water pressure and the pressure losses due to flow through the diving hose,
fittings, and valves. The air supply requirements depend upon specific factors of
each dive such as depth, duration, level of work, number of divers being
supported, and type of diving system being used.
Air Purity Standards.
Air taken directly from the atmosphere and pumped to the
diver may not meet established purity standards. It may be contaminated by engine
exhaust or chemical smog. Initially pure air may become contaminated while
passing through a faulty air compressor system. For this reason, all divers’ air
8-14 U.S. Navy Diving Manual—Volume 2
must be periodically sampled and analyzed to ensure the air meets purity stan-
dards. Refer to Table 4-1 for compressed air purity requirements.
To meet these standards, specially designed compressors must be used with the air
supplied passed through a highly efficient filtration system. The compressed air
found in a shipboard service system usually contains excessive amounts of oil and
is not suitable for diving unless filtered. Air taken from any machinery space, or
downwind from the exhaust of an engine or boiler, must be considered to be
contaminated. For this reason, care must be exercised in the placement and opera-
tion of diving air compressors to avoid such conditions. Intake piping or ducting
must be provided to bring uncontaminated air to the compressor. The outboard end
of this piping must be positioned to eliminate sources of contamination. To ensure
that the source of divers breathing air satisfactorily meets the standards estab-
lished above, it must be checked at intervals not to exceed 8 months, in accordance
with the PMS.
Air Supply Flow Requirements.
The required flow from an air supply depends
upon the type of diving apparatus being used. The open-circuit air supply system
must have a flow capacity (in acfm) that provides sufficient ventilation at depth to
maintain acceptable carbon dioxide levels in the mask or helmet. Carbon dioxide
levels must be kept within safe limits during normal work, heavy work, and
If demand breathing equipment is used, such as the MK 21 MOD 1 or the MK 20
MOD 0, the supply system must meet the divers flow requirements. The flow
requirements for respiration in a demand system are based upon the average rate
of air flow demanded by the divers under normal working conditions. The
maximum instantaneous (peak) rate of flow under severe work conditions is not a
continuous requirement, but rather the highest rate of airflow attained during the
inhalation part of the breathing cycle. The divers requirement varies with the
respiratory demands of the diver’s work level.
Supply Pressure Requirements.
In order to supply the diver with an adequate
flow of air, the air source must deliver air at sufficient pressure to overcome the
bottom seawater pressure and the pressure drop that is introduced as the air flows
through the hoses and valves of the system. Table 8-1 shows the values for air
consumption and minimum over-bottom pressures required for each of the
surface-supplied air diving systems.
Water Vapor Control.
A properly operated air supply system should never permit
the air supplied to the diver to reach its dewpoint. Controlling the amount of water
vapor (humidity) in the supplied air is normally accomplished by one or both of
the following methods:
. As high-pressure air expands across a pressure
reducing valve, the partial pressure of the water vapor in the air is decreased.
Since the expansion takes place at essentially a constant temperature (isother-
mal), the partial pressure of water vapor required to saturate the air remains
unchanged. Therefore, the relative humidity of the air is reduced.
CHAPTER 8 — Surface-Supplied Air Diving Operations 8-15
. Cooling the air prior to expanding it raises its relative humidity, per-
mitting some of the water to condense. The condensed liquid may then be
drained from the system.
Standby Diver Air Requirements.
Air supply requirements cannot be based solely
on the calculated continuing needs of the divers who are initially engaged in the
operation. There must be an adequate reserve to support a standby diver should
one be needed.
Primary and Secondary Air Supply.
All surface-supplied diving systems must
include a primary and a secondary air supply in accordance with the U.S. Navy
Diving and Manned Hyperbaric Systems Safety Certification Manual, SS521-AA-
MAN-010. The primary supply must be able to support the air flow and pressure
requirements for the diving equipment designated (Table 8-1). The capacity of the
primary supply must meet the consumption rate of the designated number of
divers for the full duration of the dive (bottom time plus decompression time). The
maximum depth of the dive, the number of divers, and the equipment to be used
must be taken into account when sizing the supply. The secondary supply must be
sized to be able to support recovery of all divers using the equipment and dive
profile of the primary supply if the primary supply sustains a casualty at the worst-
case time (for example, immediately prior to completion of planned bottom time
of maximum dive depth, when decompression obligation is greatest). Primary and
secondary supplies may be either high-pressure (HP) bank-supplied or
Requirements for Operating Procedures and Emergency Procedures.
ing procedures (OPs) and emergency procedures (EPs) must be available to
support operation of the system and recovery from emergency situations. OPs and
EPs are required to be NAVSEA or NAVFAC approved in accordance with para-
graph 4-2.6.3. Should the surface-supplied diving system be integrated with a
recompression chamber, an air supply allowance for chamber requirements (Vol-
ume 5) must be made.
All valves and electrical switches that directly influence the air supply shall be
Table 8-1. Primary Air System Requirements.
Air Consumption
System Minimum Manifold Pressure (MMP) Average Over Period of Dive
MK 21 MOD 1 (Depth in fsw
0.445) + 90 to 165 psi,
depending on the depth of the dive
1.4 (Note 1)
MK 20 MOD 0 (Depth in fsw
0.445) + 90 psi 1.4
Note 1: The manifold supply pressure requirement is 90 psig over-bottom pressure for depths to 60 fsw,
and 135 psig over-bottom pressure for depths from 60-129 fsw. For dives from 130-190 fsw,
165 psi over-bottom pressure shall be used.
8-16 U.S. Navy Diving Manual—Volume 2
Banks of flasks and groups of valves require only one central label at the main
stop valve.
A volume tank must be part of the air supply system and be located between the
supply source and the diver’s manifold hose connection. This tank maintains the
air supply should the primary supply source fail, providing time to actuate the
secondary air supply, and to attenuate the peak air flow demand.
Air Compressors.
Many air supply systems used in Navy diving operations
include at least one air compressor as a source of air. To properly select such a
compressor, it is essential that the diver have a basic understanding of the princi-
ples of gas compression. The NAVSEA/00C ANU list contains guidance for
Navy-approved compressors for divers’ air systems. See Figure 8-10.
Reciprocating Air Compressors.
Reciprocating air compressors are the only
compressors authorized for use in Navy air diving operations. Low-pressure (LP)
models can provide rates of flow sufficient to support surface-supplied air diving
or recompression chamber operations. High-pressure models can charge high-
pressure air banks and scuba cylinders.
Compressor Capacity Requirements.
Air compressors must meet the flow and
pressure requirements outlined in paragraph 8-6.1.2 and 8-6.1.3. Normally, recip-
rocating compressors have their rating (capacity in cubic feet per minute and
delivery pressure in psig) stamped on the manufacturers identification plate. This
rating is usually based on inlet conditions of 70°F (21.1°C), 14.7 psia barometric
pressure, and 36 percent relative humidity (an air density of 0.075 pound per cubic
foot). If inlet conditions vary, the actual capacity either increases or decreases
from rated values. If not provided directly, capacity will be provided by
conducting a compressor output test. Since the capacity is the volume of air at
defined atmospheric conditions, compressed per unit of time, it is affected only by
the first stage, as all other stages only increase the pressure and reduce tempera-
ture. All industrial compressors are stamped with a code, consisting of at least two,
but usually four to five, numbers that specify the bore and stroke.
The actual capacity of the compressor will always be less than the displacement
because of the clearance volume of the cylinders. This is the volume above the
piston that does not get displaced by the piston during compression. Compressors
having a first-stage piston diameter of four inches or larger normally have an
actual capacity of about 85 percent of their displacement. The smaller the first-
stage piston, the lower the percentage capacity, because the clearance volume
represents a greater percentage of the cylinder volume.
Reciprocating piston compressors are either oil lubricated or water
lubricated. The majority of the Navy’s diving compressors are lubricated by petro-
leum or synthetic oil. In these compressors, the lubricant:
Prevents wear between friction surfaces
CHAPTER 8 — Surface-Supplied Air Diving Operations 8-17
Seals close clearances
Protects against corrosion
Transfers heat away from heat-producing surfaces
Transfers minute particles generated from normal system wear to the oil sump
or oil filter if so equipped
Lubricant Specifications.
Unfortunately, the lubricant vaporizes into the air
supply and, if not condensed or filtered out, will reach the diver. Lubricants used
in air diving compressors must conform to military specifications MIL-L-17331
(2190 TEP) for normal operations, or MIL-H-17672 (2135 TH) for cold weather
operations. Where the compressor manufacturer specifically recommends using a
synthetic base oil, the recommended oil may be used in lieu of MIL-L-17331 or
MIL-H-17672 oil.
Maintaining an Oil-Lubricated Compressor.
Using an oil-lubricated compressor
for diving is contingent upon proper maintenance to limit the amount of oil intro-
duced into the divers air (see Topside Tech Notes, March 1997). When using any
lubricated compressor for diving, the air must be checked for oil contamination.
Diving operations shall be aborted at the first indication that oil is in the air being
delivered to the diver. An immediate air analysis must be conducted to determine
whether the amount of oil present exceeds the maximum permissible level in
accordance with table Table 4-1.
It should be noted that air in the higher stages of a compressor has a greater
amount of lubricant injected into it than in the lower stages. It is recommended
that the compressor selected for a diving operation provide as close to the required
pressure for that operation as possible. A system that provides excessive pressure
contributes to the buildup of lubricant in the air supply..
Intercoolers are heat exchangers that are placed between the stages
of a compressor to control the air temperature. Water, flowing through the heat
exchanger counter to the air flow, serves both to remove heat from the air and to
cool the cylinder walls. Intercoolers are frequently air cooled. During the cooling
process, water vapor is condensed out of the air into condensate collectors. The
condensate must be drained periodically during operation of the compressor,
either manually or automatically.
As the air is discharged from the compressor, it passes through a moisture
separator and an approved filter to remove lubricant, aerosols, and particulate
contamination before it enters the system. Approved filters are listed in the
NAVSEA/00C ANU list.
Pressure Regulators.
A back-pressure regulator will be installed downstream of
the compressor discharge. A compressor only compresses air to meet the supply
pressure demand. If no demand exists, air is simply pumped through the
compressor at atmospheric pressure. Systems within the compressor, such as the
8-18 U.S. Navy Diving Manual—Volume 2
Figure 8-10.
HP Compressor Assembly (top); MP Compressor Assembly (bottom).
MP Compressor Assembly
HP Compressor Assembly
CHAPTER 8 — Surface-Supplied Air Diving Operations 8-19
intercoolers, are designed to perform with maximum efficiency at the rated pres-
sure of the compressor. Operating at any pressure below this rating reduces the
efficiency of the unit. Additionally, compression reduces water vapor from the air.
Reducing the amount of compression increases the amount of water vapor in the
air supplied to the diver.
The air supplied from the compressor expands across the pressure regulator and
enters the air banks or volume tank. As the pressure builds up in the air banks or
volume tank, it eventually reaches the relief pressure of the compressor, at which
time the excess air is simply discharged to the atmosphere. Some electrically-
driven compressors are controlled by pressure switches installed in the volume
tank or HP flask. When the pressure reaches the upper limit, the electric motor is
shut off. When sufficient air has been drawn from the volume tank or HP flask to
lower its pressure to some lower limit, the electric motor is restarted.
All piping in the system must be designed to minimize pressure drops. Intake
ducting, especially, must be of sufficient diameter so that the rated capacity of the
compressor can be fully utilized. All joints and fittings must be checked for leaks
using soapy water. Leaks must be repaired. All filters, strainers, and separators
must be kept clean. Lubricant, fuel, and coolant levels must be periodically
Any diving air compressor, if not permanently installed, must be firmly secured in
place. Most portable compressors are provided with lashing rings for this purpose.
High-Pressure Air Cylinders and Flasks.
HP air cylinders and flasks are vessels
designed to hold air at pressures over 600 psi. Convenient and satisfactory diving
air supply systems can be provided by using a number of these HP air cylinders or
flasks. Any HP vessel to be used as a diving air supply unit must bear appropriate
Department of Transportation (DOT) or military symbols certifying that the cylin-
ders or flasks meet high-pressure requirements.
A complete air supply system includes the necessary piping and manifolds, HP
filter, pressure reducing valve, and a volume tank. An HP gauge must be located
ahead of the reducing valve and an LP gauge must be connected to the volume
In using this type of system, one section must be kept in reserve. The divers take
air from the volume tank in which the pressure is regulated to conform to the air
supply requirements of the dive. The duration of the dive is limited to the length of
time the banks can provide air before being depleted to 200 psi over minimum
manifold pressure. This minimum pressure of 200 psi must remain in each flask or
As in scuba operations, the quantity of air that can be supplied by a system using
cylinders or flasks is determined by the initial capacity of the cylinders or flasks
and the depth of the dive. The duration of the air supply must be calculated in
advance and must include a provision for decompression.
8-20 U.S. Navy Diving Manual—Volume 2
Sample calculations for dive duration, based on bank air supply, are presented in
Sample Problem 1 in paragraph 8-2.2.3 for the MK 21 MOD 1. The sample prob-
lems in this chapter do not take the secondary air system requirements into
account. The secondary air system must be able to provide air in the event of
failure of the primary system per U.S. Navy Diving and Manned Hyperbaric
Systems Safety Certification Manual, SS521-AA-MAN-010. In the MK 21 sample
problem (Sample Problem 2), this would mean decompressing three divers with a
30-minute bottom time using 1.4 acfm per diver. An additional requirement must
be considered if the same air system is to support a recompression chamber. Refer
to Chapter 22 for information on the additional capacity required to support a
recompression chamber.
Shipboard Air Systems.
Many Navy ships have permanently installed shipboard
air supply systems that provide either LP or HP air. These systems are used in
support of diving operations provided they meet the fundamental requirements of
purity, capacity, and pressure.
In operation, a volume source (such as a diesel or electrically driven compressor)
pumps air into a volume tank. The compressor automatically keeps the tank full as
long as the amount of air being used by the diver does not exceed the capacity of
the compressor. The ability of a given unit to support a diving operation may be
determined from the capacity of the system.
The surface-supplied diver has two means of communicating with the surface,
depending on the type of equipment used. If the diver is using the MK 21 MOD 1,
or the MK 20 MOD 0, both voice communications and line-pull signals are avail-
able. Voice communications are used as the primary means of communication.
Line-pull signals are used only as a backup. Diver-to-diver communications are
available through topside intercom, diver-to-diver hand signals or slate boards.
Diver Intercommunication Systems.
The major components of the intercommu-
nication system include the diver’s earphones and microphone, the
communication cable to each diver, the surface control unit, and the tender’s
speaker and microphone. The system is equipped with an external power cord and
can accept 115 VAC or 12 VDC. The internal battery is used for backup power
requirements. It should not be used as the primary power source unless an external
power source is not available.
The intercom system is operated by a designated phone talker at the diving station.
The phone talker monitors voice communications and keeps an accurate log of
significant messages. All persons using the intercom system should lower the
pitch of their voices and speak slowly and distinctly. The conversation should be
kept brief and simple, using standard diving terminology. Divers must repeat
verbatim all directions and orders received from topside.
CHAPTER 8 — Surface-Supplied Air Diving Operations 8-21
The approved Navy diver communication system is compatible with the MK 21
MOD 1 and the MK 20 MOD 0. This is a surface/underwater system that allows
conference communications between the tender and up to three divers. It incorpo-
rates voice correction circuitry that compensates for the distortion caused by
divers speaking in a helium-oxygen atmosphere.
The divers’ voices are continuously monitored on the surface. All communications
controls are located at the surface. The topside supervisor speaks with any or all of
the divers by exercising the controls on the front panel. It is necessary for a phone
talker to monitor and control the underwater communications system at all times.
Line-Pull Signals.
A line-pull signal consists of one pull or a series of sharp, dis-
tinct pulls on the umbilical that are strong enough to be felt by the diver (Figure
8-11). All slack must be taken out of the umbilical before the signal is given.
The line-pull signal code (Table 8-2) has been established through many years of
experience. Standard signals are applicable to all diving operations; special signals
may be arranged between the divers and Diving Supervisor to meet particular mis-
sion requirements. Most signals are acknowledged as soon as they are received.
This acknowledgment consists of replying with the same signal. If a signal is not
properly returned by the diver, the surface signal is sent again. A continued ab-
sence of confirmation is assumed to mean one of three things: the line has become
fouled, there is too much slack in the line, or the diver is in trouble.
If communications are lost, the Div-
ing Supervisor must be notified
immediately and steps taken to
identify the problem. The situation
is treated as an emergency (see
paragraph 6-
There are three line-pull signals that
are not answered immediately. Two
of these, from diver to tender, are
“Haul me up” and “Haul me up im-
mediately.” Acknowledgment con-
sists of initiation of the action. The
other signal, from the tender to
diver, is “Come up.” This signal is
not acknowledged until the diver is
ready to leave the bottom. If for
some reason the diver cannot re-
spond to the order, the diver must
communicate the reason via the
voice intercom system or through
the line-pull signal meaning “I un-
derstand,” followed (if necessary)
by an appropriate emergency signal.
Figure 8-11.
8-22 U.S. Navy Diving Manual—Volume 2
A special group of searching signals is used by the tender to direct a diver in
moving along the bottom. These signals are duplicates of standard line-pull
signals, but their use is indicated by an initial seven-pull signal to the diver that
instructs the diver to interpret succeeding signals as searching signals. When the
tender wants to revert to standard signals, another seven-pull signal is sent to the
diver which means searching signals are no longer in use. Only the tender uses
searching signals; all signals initiated by the diver are standard signals. To be
properly oriented for using searching signals, the diver must face the line (either
the lifeline or the descent line, if a circling line is being employed).
Table 8-2.
Line-Pull Signals.
From Tender to Diver Searching Signals (Without Circling Line)
1 Pull “Are you all ri
ht?” When diver is descendin
one pull means “Stop.”
7 Pulls “Go on (or off) searchin
2 Pulls “Goin
Down.” Durin
ascent, two pulls mean
“You have come up too far;
o back down until
we stop you.”
1 Pull “Stop and search where you are.”
3 Pulls “Stand by to come up.” 2 Pulls “Move directly away from the tender if
slack; move toward the tender if strain is taken
on the life line.”
4 Pulls “Come up.” 3 Pulls “Face your umbilical, take a strain, move ri
2-1 Pulls “I understand” or “Talk to me.” 4 Pulls “Face your umbilical, take a strain, move left.”
3-2 Pulls “Ventilate.”
4-3 Pulls “Circulate.”
From Diver to Tender Searching Signals (With Circling Line)
1 Pull “I am all ri
ht.” When descendin
, one pull
means “Stop” or “I am on the bottom.”
7 Pulls Same
2 Pulls “Lower” or “Give me slack.” 1 Pull Same
3 Pulls “Take up my slack.” 2 Pulls “Move away from the wei
4 Pulls “Haul me up.” 3 Pulls “Face the wei
ht and
o ri
2-1 Pulls “I understand” or “Talk to me.” 4 Pulls “Face the wei
ht and
o left.”
3-2 Pulls “More air.”
4-3 Pulls “Less air.”
Special Signals From the Diver Emergency Signals From the Diver
1-2-3 Pulls “Send me a square mark.” 2-2-2 Pulls “I am fouled and need the assistance of another
5 Pulls “Send me a line.” 3-3-3 Pulls “I am fouled but can clear myself.”
2-1-2 Pulls “Send me a slate.” 4-4-4 Pulls “Haul me up immediately.”
CHAPTER 8 — Surface-Supplied Air Diving Operations 8-23
The predive activities for a surface-supplied diving operation involve many people
and include inspecting and assembling the equipment, activating the air supply
systems, and dressing the divers.
Predive Checklist.
A comprehensive predive checklist is developed to suit the
requirements of the diving unit and of the particular operation. This is in addition
to the general Diver Safety and Planning Checklist (Figure 6-19a) and suggested
Predive Checklist (Figure 6-21a).
Diving Station Preparation.
The diving station is neatly organized with all diving
and support equipment placed in an assigned location. Deck space must not be
cluttered with gear; items that could be damaged are placed out of the way (prefer-
ably off the deck). A standard layout pattern should be established and followed.
Air Supply Preparation.
The primary and secondary air supply systems are
checked to ensure that adequate air is available. Air compressors of the divers’ air
system are started and checked for proper operation. The pressure in the accumu-
lator tanks is checked. If HP air cylinders are being used, the manifold pressure is
checked. If a compressor is being used as a secondary air supply, it is started and
kept running throughout the dive. The air supply must meet purity standards (see
paragraph 8-6.1.1).
Line Preparation.
Depth soundings are taken and descent line, stage, stage lines,
and connections are checked, with decompression stops properly marked.
Recompression Chamber Inspection and Preparation.
If available, the recom-
pression chamber is inspected and all necessary equipment and a copy of
appropriate recompression treatment tables are placed on hand at the chamber.
Two stop watches and the decompression tables are also required. Adequate air
supply for immediate pressurization of the chamber is verified and the oxygen
supply system is charged and made ready for operation in accordance with
Chapter 22.
Predive Inspection.
When the Diving Supervisor is satisfied that all equipment is
on station and in good operating condition, the next step is to dress the divers.
Donning Gear.
Dressing the divers is the responsibility of the tender.
Diving Supervisor Predive Checklist.
The Diving Supervisor must always use a
predive checklist prior to putting divers in the water. This checklist must be
tailored by the unit to the specific equipment and systems being used. Chapter 6
contains typical predive checklists for surface-supplied equipment. Refer to the
appropriate operations and maintenance manual for detailed checklists for specific
8-24 U.S. Navy Diving Manual—Volume 2
Once the predive procedures have been completed, the divers are ready to enter
the water. There are several ways to enter the water, with the choice usually deter-
mined by the nature of the diving platform. Regardless of the method of entry, the
divers should look before entering the water. Three methods for entering the water
are the:
Ladder method
Stage method
Step-in method
Predescent Surface Check.
In the water and prior to descending to operating
depth, the diver makes a final equipment check.
The diver immediately checks for leaks in the suit or air connections.
If two divers are being employed, both divers perform as many checks as pos-
sible on their own rigs and then check their dive partner’s rig. The tender or
another diver can be of assistance by looking for any telltale bubbles.
A communications check is made and malfunctions or deficiencies not previ-
ously noted are reported at this time.
When satisfied that the divers are ready in all respects to begin the dive, they
notify the Diving Supervisor and the tenders move the divers to the descent line.
When in position for descent, the diver adjusts for negative buoyancy and signals
readiness to the Diving Supervisor.
Descent may be accomplished with the aid of a descent line or stage.
Topside personnel must ensure that air is being supplied to the diver in sufficient
quantity and at a pressure sufficient to offset the effect of the steadily increasing
water pressure. The air pressure must also include an overbottom pressure allow-
ance to protect the diver against a serious squeeze if he or she falls.
While descending, the diver adjusts the air supply so that breathing is easy and
comfortable. The diver continues to equalize the pressure in the ears as necessary
during descent and must be on guard for any pain in the ears or sinuses, or any
other warning signals of possible danger. If any such indications are noted, the
descent is halted. The difficulty may be resolved by ascending a few feet to regain
a pressure balance; if this is not effective, the diver is returned to the surface.
Some specific guidelines for descent are as follows:
With a descent line, the diver locks the legs around the line and holds on to the
line with one hand.
In a current or tideway, the diver descends with back to the flow in order to be
held against the line and not be pulled away. If the current measures more than
CHAPTER 8 — Surface-Supplied Air Diving Operations 8-25
1.5 knots, the diver wears additional weights or descends on a weighted stage,
so that descent is as nearly vertical as possible.
When the stage is used for descent, it is lowered with the aid of a winch and
guided to the site by a shackle around the descent line. The diver stands in the
center of the stage, maintaining balance by holding on to the side bails. Upon
reaching the bottom, the diver exits the stage as directed by the Diving
The maximum allowable rate of descent, by any method, shall not exceed 75
feet per minute (fpm), although such factors as the diver’s ability to clear the
ears, currents and visibility and the need to approach an unknown bottom with
caution may render the actual rate of descent considerably less.
The diver signals arrival on the bottom and quickly checks bottom conditions.
Conditions that are radically different than expected are reported to the Diving
Supervisor. If there is any doubt about the safety of the diver or the diver’s
readiness to operate under the changed conditions, the dive is aborted.
A diver should thoroughly ventilate when reaching the bottom, at subsequent
intervals as the diver feels necessary and as directed from the surface. On
dives deeper than 100 fsw, the diver may not notice the CO
warning symp-
toms because of nitrogen narcosis. It is imperative that the Diving Supervisor
monitors his or her divers’ ventilation.
Adapting to Underwater Conditions.
Through careful and thorough planning, the
divers can be properly prepared for the underwater conditions at the diving site.
The diver will employ the following techniques to adapt to underwater conditions:
Upon reaching the bottom and before leaving the area of the stage or descent
line, the diver adjusts buoyancy and makes certain that the air supply is
The diver becomes oriented to the bottom and the work site using such clues
as the lead of the umbilical, natural features on the bottom, the direction of
current. However, bottom current may differ from the surface current. The
direction of current flow may change significantly during the period of the
dive. If the diver has any trouble in orientation, the tender can guide the diver
by using the line-pull searching signals.
The diver is now ready to move to the work site and begin the assignment.
Movement on the Bottom.
Divers should follow these guidelines for movement
on the bottom areas:
8-26 U.S. Navy Diving Manual—Volume 2
Before leaving the descent line or stage, ensure that the umbilical is not fouled.
Loop one turn of the lifeline and air hose over an arm; this acts as a buffer
against a sudden surge or pull on the lines.
Proceed slowly and cautiously to increase safety and to conserve energy.
If obstructions are encountered, adjust buoyancy to pass over the obstruction
(not under or around). If you pass around an obstruction, you must return by
the same side to avoid fouling lines.
When using buoyancy adjustments to aid in movement, avoid bouncing along
the bottom; all diver movements are controlled.
If the current is strong, stoop or crawl to reduce body area exposed to the cur-
rent. Adjust the inflation of the dress to compensate for any change in depth,
even if the change is only a few feet.
When moving on a rocky or coral bottom, make sure lines do not become
fouled on outcroppings, guarding against tripping and getting feet caught in
crevices. Watch for sharp projections that can cut hoses, diving dress or unpro-
tected hands. The tender is particularly careful to take up any slack in the
diver’s umbilical to avoid fouling.
Guard against slipping and falling on gravel bottoms, especially on slopes.
Avoid unnecessary movements that stir up the bottom and impair visibility.
CAUTION Avoid overinflation and be aware of the possibility of blowup when
loose from mud. It is better to call for aid from the standby
diver than to risk blowup.
Mud and silt may not be solid enough to support your weight. Many hours
may be spent working under mud without unreasonable risk. The primary haz-
ard with mud bottoms comes from the concealment of obstacles and
dangerous debris.
Searching on the Bottom.
If appropriate electronic searching equipment is not
available, it may be necessary to use unaided divers to conduct the search. Proce-
dures for searching on the bottom with unaided divers are:
A diver search of the bottom can be accomplished with a circling line, using
the descent line as the base point of the search. The first sweep is made with
the circling line held taut at a point determined by the range of visibility. If
possible, the descent line should be in sight or, if visibility is limited, within
reach. The starting point is established by a marker, a line orientation with the
current or the light, signals from topside, or a wrist compass. After a full 360-
degree sweep has been made, the diver moves out along the circling line
CHAPTER 8 — Surface-Supplied Air Diving Operations 8-27
another increment (roughly double the first) and makes a second sweep in the
opposite direction to avoid twisting or fouling the lifeline and air hose.
If the object is not found when the end of the circling line has been reached,
the base point (the descent line) is shifted. Each base point in succession
should be marked by a buoy to avoid unnecessary duplication in the search. If
the search becomes widespread, many of the marker buoys can be removed,
leaving only those marking the outer limits of the area.
If the diver is unable to make a full circle around the descent line because of
excessive current or obstructions, the search patterns are adjusted accordingly.
A linear search pattern (Jack-Stay) can be established by laying two large
buoys and setting a line between them. A diving launch, with a diver on the
bottom, can follow along the line from buoy to buoy, coordinating progress
with the diver who is searching to each side of the established base line. These
buoys may be readjusted to enlarge search areas.
Once the object of a search is located, it is marked. The diver can secure the
circling line to the object as an interim measure, while waiting for a float line
to be sent down.
Enclosed Space Diving.
Divers are often required to work in enclosed or
confined spaces. Enclosed space diving shall be supported by a surface-supplied
air system (MK 20 MOD 0 and MK 21 MOD 1).
Enclosed Space Hazards.
The interior of sunken ships, barges, submarine ballast
tanks, mud tanks, sonar domes, and cofferdams is hazardous due to limited access,
poor visibility, and slippery surfaces. Enclosed spaces may be dry or flooded, and
dry spaces may contain a contaminated atmosphere.
NOTE When a diver is workin
in an enclosed or confined space, the Divin
Supervisor shall have the diver tended by another diver at the access
. Ultimately, the number of tendin
divers deployed depends on
the situation and the
ood jud
ement of the Divin
Officer, Master Diver,
or Divin
Supervisor on the site.
Enclosed Space Safety Precautions.
Because of the hazards involved in en-
closed space operations, divers must rigorously adhere to the following warnings.
enclosed space divin
, all divers shall be outfitted with MK 21
MOD 1 with EGS or MK 20 MOD 0 that includes a diver-to-diver and diver-
to-topside communications system and an EGS for the diver inside the
WARNING The divers shall not remove their divin
equipment until the atmosphere
has been flushed twice with air from a compressed air source meetin
the requirements of Chapter 4, or the submarine L.P. blower, and tests
confirm that the atmosphere is safe for breathin
. Tests of the air in the
8-28 U.S. Navy Diving Manual—Volume 2
enclosed space shall be conducted hourly. Testin
shall be done in
accordance with NSTM 074, Volume 3, Gas Free En
STM-030/CH-074) for forces afloat, and NAVSEA S-6470-AA-SAF-010 for
shore-based facilities. If the divers smell any unusual odors they shall
immediately don their masks.
WARNING If the divin
equipment should fail, the diver shall immediately switch to
the EGS and abort the dive.
Working Around Corners.
When working around corners where the umbilical is
likely to become fouled or line-pull signals may be dissipated, a second diver
(tending diver) may be sent down to tend the lines of the first diver at the obstruc-
tion and to pass along any line-pull signals. Line-pull signals are used when audio
communications are lost, and are passed on the first diver’s lines; the tending diver
uses his own lines only for signals directly pertaining to his own situation.
Working Inside a Wreck.
When working inside a wreck, the same procedure of
deploying tending divers is followed. This technique applies to the tending divers
as well: every diver who penetrates a deck level has another tending diver at that
level, or levels, above. Ultimately, the number of tending divers deployed depends
on the situation and the good judgment of the Diving Officer, Master Diver, or
Diving Supervisor on the site. Obviously, an operation requiring penetration
through multiple deck levels requires detailed advanced planning in order to
provide for the proper support of the number of divers required. MK 21 MOD 1
and MK 20 MOD 0 are the only equipment approved for working inside a wreck.
The diver enters a wreck feet first and never uses force to gain entry through an
Working With or Near Lines or Moorings.
When working with or near lines or
moorings, observe the following rules:
Stay away from lines under strain.
Avoid passing under lines or moorings if at all possible; avoid brushing
against lines or moorings that have become encrusted with barnacles.
If a line or mooring is to be shifted, the diver is brought to the surface and, if
not removed from the water, moved to a position well clear of any hazard.
If a diver must work with several lines (messengers, float lines, lifting lines,
etc.) each should be distinct in character (size or material) or marking (color
codes, tags, wrapping).
Never cut a line unless the line is positively identified.
When preparing to lift heavy weights from the bottom, the lines selected must
be strong enough and the surface platform must be positioned directly over the
object to be raised. Prior to the lift, make sure the diver is clear of the lift area
or leaves the water.
CHAPTER 8 — Surface-Supplied Air Diving Operations 8-29
Bottom Checks.
Bottom checks are conducted after returning to the stage or
descent line and prior to ascent. The checks are basically the same for each rig.
Ensure all tools are ready for ascent.
Check that all umbilicals and lines are clear for ascent.
Assess and report your condition (level of fatigue, remaining strength,
physical aches or pains, etc.) and mental acuity.
Job Site Procedures.
The range of diving jobs is wide and varied. Many jobs
follow detailed work procedures and require specific predive training to ensure
familiarity with the work. The U.S. Navy Underwater Work Techniques Manual,
Volumes 1 and 2, NAVSEA 0994-LP-007-8010 and NAVSEA 0994-LP-007-
8020, presents guidance for most commonly encountered jobs, such as clearing
fouled propellers, patching collision damage, replacing underwater valves or
fittings, preparing for salvage of sunken vessels, and recovering heavy objects
from the bottom.
Underwater Ship Husbandry Procedures.
With the advent of more highly tech-
nical underwater work procedures, the Underwater Ship Husbandry Manual,
S0600-AA-PRO-010, was published. Like the Naval Ships Technical Manual
(NSTM), the manual is published in separately bound chapters, each dealing with
a separate area of underwater work. Chapter 1 of the manual (S0600-AA-PRO-
010) is the Index and User Guide, which provides information on the subsequent
chapters of the manual.
Working with Tools.
Underwater work requires appropriate tools and materials,
such as cement, foam plastic, and patching compounds. Many of these are stan-
dard hand tools (preferably corrosion-resistant) and materials; others are specially
designed for underwater work. A qualified diver will become familiar with the
particular considerations involved in working with these various tools and mate-
rials in an underwater environment. Hands-on training experience is the only way
to get the necessary skills. Consult the appropriate operations and maintenance
manuals for the use techniques of specific underwater tools. In working with tools
the following basic rules always apply:
Never use a tool that is not in good repair. If a cutting tool becomes dulled,
return it to the surface for sharpening.
Do not overburden the worksite with unnecessary tools, but have all tools that
may be needed readily available.
Tools are secured to the diving stage by lanyard, carried in a tool bag looped
over the diver’s arm, or lowered on the descent line using a riding shackle and
a light line for lowering. Prior to ascent or descent, secure power to all tools.
Attach lanyards to all tools, connectors, shackles and shackle pins.
8-30 U.S. Navy Diving Manual—Volume 2
Using the diving stage as a worksite permits organization of tools while pro-
viding for security against loss. The stage also gives the diver leverage and
stability when applying force (as to a wrench), or when working with a power
tool that transmits a force back through the diver.
Tying a hogging line to the work also gives the diver leverage while keeping
him close to his task without continually having to fight a current.
Safety Procedures.
The best safety factors are a positive, confident attitude about
diving and careful advance planning for emergencies. A diver in trouble under-
water should relax, avoid panic, communicate the problem to the surface and
carefully think through the possible solutions to the situation. Topside support
personnel should implement emergency job-site procedures as indicated in
Chapter 6. In all situations, the Diving Supervisor should ensure that common
sense and good seamanship prevail to safely resolve each emergency.
Emergency procedures are covered specifically for each equipment in its appro-
priate operations and maintenance manual and in general in Chapter 6. However,
there are a number of situations a diver is likely to encounter in the normal range
of activity which, if not promptly solved, can lead to full-scale emergencies. These
situations and the appropriate action to be taken follow.
Fouled Umbilical Lines.
As soon as a diver discovers that the umbilical has
become fouled, the diver must stop and examine the situation. Pulling or tugging
without a plan may only serve to complicate the problem and could lead to a
severed hose. The Diving Supervisor is notified if possible (the fouling may
prevent transmission of line-pull signals). If the lines are fouled on an obstruction,
retracing steps should free them. If the lines cannot be cleared quickly and easily,
the standby diver is sent down to assist. The standby diver is sent down as normal
procedure, should communications be interrupted and the tender be unable to haul
the diver up. The standby diver, using the first divers umbilical (as a descent line),
should be able to trace and release the lines. If it is impossible to free the first
diver, the standby diver should signal for a replacement umbilical.
Fouled Descent Lines.
If the diver becomes fouled with the descent line and
cannot be easily cleared, it is necessary to haul the diver and the line to the surface,
or to cut the weight free of the line and attempt to pull it free from topside. If the
descent line is secured to an object or if the weight is too heavy, the diver may
have to cut the line before being hauled up. For this reason, a diver should not
descend on a line that cannot be cut.
WARNING If job conditions call for usin
a steel cable or a chain as a descent line,
the Divin
Officer must approve such use.
When working at mid-depth in the water column, the diver should keep a
hand on the stage or rigging to avoid falling. The diver avoids putting an arm over-
head in a dry suit; air leakage around the edges of the cuffs may change the suit
buoyancy and increase the possibility of a fall in the water column.
CHAPTER 8 — Surface-Supplied Air Diving Operations 8-31
Damage to Helmet and Diving Dress.
If a leak occurs in the helmet, the divers
head is lowered and the air pressure slightly increased to prevent water leakage. A
leak in the diving suit only requires remaining in an upright position; water in the
suit does not directly endanger breathing.
Tending the Diver.
Procedures for tending the diver follow.
Before the dive, the tender carefully checks the diving dress with particular
attention to the nonreturn valve, air control valve, helmet locking device,
intercom system, helmet seal and harness.
When the diver is ready, the tenders dress and assist the diver to the stage or
ladder or waters edge, always keeping a hand on the umbilical.
The primary tender and a backup tender as required are always on station to
assist the diver. As the diver enters the water, the tenders handle the umbilical,
using care to avoid sharp edges. The umbilical must never be allowed to run
free or be belayed around a cleat or set of bitts. Pay out of the umbilical is at a
steady rate to permit the diver to descend smoothly. If a stage is being used,
the descent rate is coordinated with the winch operator or line handlers.
Throughout the dive the tender keeps slack out of the line while not holding it
too tautly. Two or three feet of slack permits the diver freedom of movement
and prevents the diver from being pulled off the bottom by surging of the
support craft or the force of current acting on the line. The tender occasionally
checks the umbilical to ensure that movement by the diver has not resulted in
excessive slack. Excessive slack makes signaling difficult, hinders the tender
from catching the diver if falling and increases the possibility of fouling the
The tender monitors the umbilical by feel and the descent line by sight for any
line-pull signals from the diver. If an intercom is not being used, or if the diver
is silent, the tender periodically verifies the diver’s condition by line-pull
signal. If the diver does not answer, the signal is repeated; if still not answered,
the Diving Supervisor is notified. If communications are lost, the situation is
treated as an emergency (see paragraph 6- for loss-of-communication
Monitoring the Diver’s Movements.
The Diving Supervisor and designated mem-
bers of the dive team constantly monitor the divers progress and keep track of his
relative position.
Supervisor Actions
Follow the bubble trail, while considering current(s). If the diver is
searching the bottom, bubbles move in a regular pattern. If the diver is
working in place, bubbles do not shift position. If the diver has fallen, the
bubbles may move rapidly off in a straight line.
8-32 U.S. Navy Diving Manual—Volume 2
Monitor the pneumofathometer pressure gauge to keep track of operating
depth. If the diver remains at a constant depth or rises, the gauge provides
a direct reading, without the need to add air. If the diver descends, the hose
must be cleared and a new reading made.
Tender Actions
. Feel the pull of the umbilical.
Additional Personnel Actions
. Monitor the gauges on the supply systems for
any powered equipment. For example, the ammeter on an electric welding unit
indicates a power drain when the arc is in use; the gas pressure gauges for a
gas torch registers the flow of fuel. Additionally, the pop made by a gas torch
being lighted will probably be audible over the intercom and bubbles from the
torch will break on the surface, giving off small quantities of smoke.
Follow these ascent procedures when it is time for the divers to return to the
To prepare for a normal ascent, the diver clears the job site of tools and
equipment. These can be returned to the surface by special messenger lines
sent down the descent line. If the diver cannot find the descent line and needs a
special line, this can be bent onto his umbilical and pulled down by the diver.
The diver must be careful not to foul the line as it is laid down. The tender then
pulls up the slack. This technique is useful in shallow water, but not practical
in deep dives.
If possible, the diving stage is positioned on the bottom. If some malfunction
such as fouling of the descent line prevents lowering the stage to the bottom,
the stage should be positioned below the first decompression stop if possible.
Readings from the pneumofathometer are the primary depth measurements.
If ascent is being made using the descent line or the stage has been positioned
below the first decompression stop, the tender signals the diver “Standby to
come up” when all tools and extra lines have been cleared away. The diver
acknowledges the signal. The diver, however, does not pull up. The tender lifts
the diver off the bottom when the diver signals “Ready to come up,” and the
tender signals “Coming up. Report when you leave the bottom.” The diver so
If, during the ascent, while using a descent line, the diver becomes too buoyant
and rises too quickly, the diver checks the ascent by clamping his legs on the
descent line.
The rate of ascent is a critical factor in decompressing the diver. Ascent must
be carefully controlled at 30 feet per minute by the tender. The ascent is
monitored with the pneumofathometer. As the diver reaches the stage and
climbs aboard, topside is notified of arrival. The stage is then brought up to the
CHAPTER 8 — Surface-Supplied Air Diving Operations 8-33
first decompression stop. Refer to Chapter 9 for decompression procedures,
including an explanation of the tables.
While ascending and during the decompression stops, the diver must be
satisfied that no symptoms of physical problems have developed. If the diver
feels any pain, dizziness, or numbness, the diver immediately notifies topside.
During this often lengthy period of ascent, the diver also checks to ensure that
his umbilical is not becoming fouled on the stage line, the descent line, or by
any steadying weights hanging from the stage platform.
Upon arrival at the surface, topside personnel, timing the movement as
dictated by any surface wave action, coordinate bringing the stage and
umbilical up and over the side.
If the diver exits the water via the ladder, the tenders provide assistance. The
diver will be tired, and a fall back into the water could result in serious injury.
Under no conditions is any of the divers gear to be removed before the diver
is firmly on deck.
Disadvantages of In-Water Decompression.
Decompression in the water column
is time consuming, uncomfortable, and inhibits the ability of the support vessel to
get underway. Delay could also present other problems for the support vessel:
weather, threatened enemy action or operating schedule constraints. In-water
decompression delays medical treatment, when needed, and increases the possi-
bility of severe chilling and accident. For these reasons, decompression is often
accomplished in a recompression chamber on the support ship (Figure 8-12).
Refer to Chapter 9 for surface decompression procedures.
Transferring a Diver to the Chamber.
When transferring a diver from the water to
the chamber, the tenders are allowed no more than 3
minutes to undress the
diver. A tender or diving medical personnel, as required by the nature of the dive
or the condition of the diver, must be in the chamber with any necessary supplies
prior to arrival of the diver. The time factor is critical and delays cannot be toler-
ated. Undressing a diver for surface decompression should be practiced until a
smooth, coordinated procedure is developed.
Postdive procedures are planned in advance to ensure personnel are carefully
examined for any possible injury or adverse effects and equipment is inspected,
maintained and stowed in good order.
Personnel and Reporting.
Immediate postdive activities include any required
medical treatment for the diver and the recording of mandatory reports.
Medical treatment is administered for cuts or abrasions. The general condition
of the diver is monitored until problems are unlikely to develop. The Diving
8-34 U.S. Navy Diving Manual—Volume 2
Supervisor resets the stopwatch after the diver reaches the surface and remains
alert for irregularities in the diver’s actions or mental state. The diver must
remain within 30 minutes’ travel time of the diving unit for at least 2 hours
after surfacing.
Mandatory records and reports are covered in Chapter 5. Certain information
is logged as soon as the diving operations are completed, while other record
keeping is scheduled when convenient. The Diving Supervisor is responsible
for the diving log, which is kept as a running account of the dive. The diver is
responsible for making appropriate entries in the personal diving record. Other
personnel, as assigned, are responsible for maintaining equipment usage logs.
A postdive checklist, tailored to the equipment used, is followed to
ensure equipment receives proper maintenance prior to storage. Postdive mainte-
nance procedures are contained in the equipment operation and maintenance
manual and the planned maintenance system package.
Figure 8-12.
Surface Decompression.