CHAPTER 13 — Mixed-Gas Operational Planning 13-1
This chapter discusses the planning associated with mixed-gas diving
operations. Most of the provisions in Chapter 6, Operations Planning, also apply to
mixed-gas operations and should be reviewed for planning. In planning any
mixed-gas operation, the principles and techniques presented in this chapter shall
This chapter outlines a comprehensive planning process that may be used
in whole or in part to effectively plan and execute diving operations in support of
Additional Sources of Information.
This chapter is not the only source of infor-
mation available to the diving team when planning mixed-gas diving operations.
Operation and maintenance manuals for the diving equipment, intelligence
reports, and oceanographic studies all contain valuable planning information. The
nature of the operation will dictate the procedures to be employed and the plan-
ning and preparations required for each. While it is unlikely that even the best
planned operation can ever anticipate all possible contingencies, attention to detail
in planning will minimize complications that could threaten the success of a
Complexity of Mixed-Gas Diving.
Mixed-gas diving operations are complex,
requiring constant support and close coordination among all personnel. Due to
extended decompression obligations, mixed-gas diving can be hazardous if not
properly planned and executed. Seemingly minor problems can quickly escalate
into emergency situations, leaving limited time to research dive protocols or oper-
ational orders to resolve the situation. Each member of the diving team must be
qualified on his watch station and be thoroughly competent in executing appli-
cable operating and emergency procedures. Safety is important in any diving
operation and must become an integral part of all operations planning.
The Diving Officer, Master Diver, and Diving Super-
visor must plan the operation to safeguard the physical and mental well-being of
each diver. All members of the team must thoroughly understand the medical
aspects of mixed-gas, oxygen, and saturation diving. A valuable source of guid-
ance in operations planning is the Diving Medical Officer (DMO), a physician
trained specifically in diving medicine and physiology.
Mixed-gas diving entails additional risks and procedural requirements for the
diver and the support team. At the surface, breathing a medium other than air
causes physiological changes in the body. When a diver breathes an unusual
medium under increased pressure, additional alterations in the functioning of the
mind and body may occur. Each diver must be aware of the changes that can occur
13-2 U.S. Navy Diving Manual—Volume 3
and how they may affect his performance and safety. Mixed-gas diving procedures
that minimize the effects of these changes are described in this and the following
chapters. Every mixed-gas diver must be thoroughly familiar with these
Typical medical problems in mixed-gas and oxygen diving include decompression
sickness, oxygen toxicity, thermal stress, and carbon dioxide retention. Deep satu-
ration diving presents additional concerns, including high pressure nervous
syndrome (HPNS), dyspnea, compression arthralgia, skin infections, and perfor-
mance decrements. These factors directly affect the safety of the diver and the
outcome of the mission and must be addressed during the planning stages of an
operation. Specific information concerning medical problems particular to various
mixed-gas diving modes are contained in Volume 5.
ESTABLISH OPERATIONAL TASKS
Preparing a basic outline and schedule of events for the entire operation ensures
that all phases will be properly coordinated. This chapter gives specific guidelines
that should be considered when analyzing the operational tasks. Mixed-gas diving
requires additional considerations in the areas of gas requirements, decompres-
sion, and medical support.
Mixed-gas diving requires a predetermined supply of breathing gases and carbon
dioxide absorbent material. Operations must be planned thoroughly to determine
usage requirements in order to effectively obtain required supplies in port or at sea
prior to the start of the mission. See paragraph 13-3.10 and Table 13-1 for specific
gas/material requirements. Logistic requirements may include planning for on-site
resupply of mixed gases and other supplies and for relief of diving teams from
Fleet units. Consult unit standing operating procedures for resupply guidance and
personnel procurement (refer to OPNAVINST 3120.32 [series]).
SELECT DIVING METHOD AND EQUIPMENT
Selecting the appropriate diving method is essential to any diving operations plan-
ning. The method will dictate many aspects of an operation including personnel
Table 13-1. Average Breathing Gas Consumption Rates.
MK 21 MOD 0 UBA
MK 21 MOD 1 UBA
165 psi 1.4 acfm (demand)
6.0 acfm (free flow)
2.5 acfm (demand)
6.0 acfm (free flow)
MK 22 MOD 0 UBA 165 psi 1.4 acfm (demand)
6.0 acfm (free flow)
2.5 acfm (demand)
6.0 acfm (free flow)
CHAPTER 13 — Mixed-Gas Operational Planning 13-3
Mixed-Gas Diving Methods.
Mixed-gas diving methods are defined by the type of
mixed-gas diving equipment that will be used. The three types of mixed-gas
diving equipment are:
Surface-supplied gear (MK 21 MOD 1)
Semiclosed-circuit and closed-circuit UBAs
Saturation deep dive systems
For deep dives (190-300 fsw) of short duration, or for shallower dives where
nitrogen narcosis reduces mental acuity and physical dexterity, helium-oxygen
diving methods should be employed.
Because of the unusual hazards incurred by long exposures to extreme environ-
mental conditions, extended excursions away from topside support, and great
decompression obligations, semiclosed-circuit and closed-circuit diving should
only be undertaken by specially trained divers. Semiclosed-circuit and closed-
circuit diving operations are covered in depth in Volume 4.
Saturation diving is the preferred method for dives deeper than 300 fsw or for
shallow dives where extensive in-water times are required. Disadvantages of satu-
ration diving include the requirement for extensive logistic support and the
inability of the support ship to easily shift position once the mooring is set. For
this reason, it is very important that the ship be moored as closely over the work
site as possible. Using side-scan sonar, remotely operated vehicles (ROVs) or
precision navigation systems will greatly aid in the successful completion of the
operation. Saturation diving is discussed in Chapter 15.
In mixed-gas diving, the principle factors influencing
the choice of a particular method are:
Depth and planned duration of the dive
Quantities of gas mixtures available
Qualifications and number of personnel available
Type of work and degree of mobility required
Environmental considerations such as temperature, visibility, type of bottom,
current, and pollution levels
Need for special operations procedures
Equipment depth limitations are contained in Table 13-2. The limitations
are based on a number of interrelated factors such as decompression obligations,
13-4 U.S. Navy Diving Manual—Volume 3
duration of gas supply and carbon dioxide absorbent material, oxygen tolerance,
and the possibility of nitrogen narcosis when using emergency gas (air). Divers
must be prepared to work at low temperatures and for long periods of time.
Operations deeper than 300 fsw usually require Deep Diving Systems (DDSs).
The decompression obligation upon the diver is of such length that in-water
decompression is impractical. Using a personnel transfer capsule (PTC) to trans-
port divers to a deck decompression chamber (DDC) increases the margin of diver
safety and support-ship flexibility.
Bottom Time Requirements.
The nature of the operation may influence the
bottom time requirements of the diver. An underwater search may be best under-
taken by using multiple divers with short bottom times or by conducting a single
bounce dive simply to identify a submerged object. Other tasks, such as under-
water construction work, may require numerous dives with long bottom times
requiring surface-supplied or saturation diving techniques. Although primarily
intended to support deep diving operations, saturation diving systems may be ideal
to support missions as shallow as 150 fsw where the nature of the work is best
accomplished using several dives with extended bottom times. Under these condi-
tions, time is saved by eliminating in-water decompression obligations for each
diver and by reducing the number of dive team changes, thus compensating for the
increased logistical complexity such operations entail.
Environmental conditions play an important role in planning
mixed-gas diving operations. Environmental factors, such as those addressed in
Chapter 6, should be considered when planning such operations. Mixed-gas diving
operations often involve prolonged dives requiring lengthy decompression and
travels that carry divers great distances from a safe haven. Special attention should
therefore be given to preventing diver hypothermia. Mixed-gas diving apparatus
are designed to minimize thermal stress, but the deepest, longest helium-oxygen
dives place the greatest stress on the diver. Exposure to extreme surface conditions
prior to the dive may leave the diver in a thermally compromised state. A diver
Table 13-2. Equipment Operational Characteristics.
Normal Working Limit
MK 21 MOD 1 UBA 300 (HeO
MK 21 MOD 0 UBA
MK 22 MOD 0 UBA
950 950 Part of system 21
(7 per watch)
1. Depth limits are based on considerations of workin
time, decompression obli
en tolerance and nitro
narcosis. The expected duration of the
as supply, the expected duration of the carbon dioxide absorbent, the adequacy of
thermal protection, or other factors may also limit both the depth and the duration of the dive.
2. An on-station chamber is defined as a certified and ready chamber at the dive site.
CHAPTER 13 — Mixed-Gas Operational Planning 13-5
who has been exposed to adverse environmental conditions should not be consid-
ered for mixed-gas diving until complete rewarming of the diver has taken place,
as shown by sweating, normal pulse, and return of normal core temperature.
Subjective thermal comfort does not accurately indicate adequate rewarming.
Some diving operations may dictate the use of a diving method that is
selected as a result of special mobility requirements in addition to depth, bottom
time and logistical requirements. The MK 21 MOD 1 is the preferred method
when operations require mobility in the water column (see Figure 13-1).
For missions where mobility is an essential operating element and depth and
bottom time requirements are great, closed-circuit diving may be the only avail-
able option. Such diving is frequently required by special warfare and/or explosive
ordnance disposal (EOD) personnel.
Equipment and supplies available for mixed-gas diving
operations by U.S. Navy personnel have been tested under stringent conditions to
ensure that they will perform according to design specifications under the most
difficult conditions that may be encountered. Several types of equipment are avail-
able for mixed-gas operations. Equipment selection is based upon the chosen
diving method, depth of the dive and the operation to be performed. Table 13-3
outlines the differences between equipment configurations.
Searching Through Aircraft Debris on the Ocean Floor.
13-6 U.S. Navy Diving Manual—Volume 3
The UBA MK 21 MOD 0 is an open circuit, demand-regulated diving helmet
designed for saturation, mixed-gas diving at depths in excess of 300 fsw and as
deep as 950 fsw. With the exception of the demand regulator, it is functionally
identical to the UBA MK 21 MOD 1, which is used for air and mixed-gas diving.
The regulator for the MK 21 MOD 0 helmet is the Ultraflow 500, which provides
improved breathing resistance and gas flow over the MK 21 MOD 1.
The UBA MK 22 MOD 0 is an open circuit, demand-regulated, band-mask
version of the UBA MK 21 MOD 0. It is used for the standby diver for saturation,
mixed-gas diving at depths in excess of 300 fsw and as deep as 950 fsw. It is
provided with a hood and head harness instead of the helmet shell to present a
smaller profile for storage.
Equipment operational characteristics are reviewed
in Table 13-2 and specific equipment information can be found in paragraph 13-8.
All diving equipment must be certified or authorized for Navy use. Authorized
equipment is listed in the NAVSEA/00C Authorized for Navy Use (ANU) list. For
proper operation and maintenance of U.S. Navy approved diving equipment, refer
to the appropriate equipment operation and maintenance manual.
Support Equipment and ROVs.
In addition to the UBA, support equipment must
not be overlooked. Items commonly used include tools, underwater lighting,
power sources, and communications systems. The Coordinated Shipboard Allow-
Table 13-3. Mixed-Gas Diving Equipment.
MK 21 MOD 1
(Notes 1 & 3)
Support craft required.
h rate of
Normal 300 fsw.
Maximum: 380 fsw
MK 21 MOD 0
21 (7 per
safety. Bottom time
e support craft
and crew. Limited
h rate of
Varies with DDS
MK 22 MOD 0
Standby diver for
21 (7 per
e in PTC.
e support craft
and crew. Limited
h rate of
Varies with DDS
1. Surface-supplied deep-sea
2. Saturation UBA
3. Minimum personnel consists of topside support and one diver in the water
4. Varies accordin
requirements of deep dive system
CHAPTER 13 — Mixed-Gas Operational Planning 13-7
ance List (COSAL) for the diving platform is a reliable source of support
equipment. Commercial resources may also be available.
Occasionally, a mission is best undertaken with the aid of a remotely operated
vehicle (ROV). ROVs offer greater depth capabilities with less risk to personnel
but at the expense of the mobility, maneuverability, and versatility that only
manned operations can incorporate.
Types of ROV.
There are two types of ROVs, tethered and untethered. Tethered
ROVs receive power, control signals, and data through an umbilical. Untethered
ROVs can travel three to five times faster than tethered ROVs, but because their
energy source must be contained in the vehicle their endurance is limited. ROVs
used in support of diving operations must have ground fault interrupter (GFI)
systems installed to protect the divers.
Currently, much of the Fleet’s requirements for observation
diving are being met by using ROVs. They have been used for search and salvage
since 1966. State-of-the-art ROVs combine short-range search, inspection, and
recovery capabilities in a single system. A typical ROV system includes a control
and display console, a power source, a launch and retrieval system, and the vehicle
itself. Tethered systems are connected to surface support by an umbilical that
supplies power, control signals and data. Untethered search systems that will
greatly increase current search rates with extended endurance rates of 24 hours or
more are currently under development. Figure 13-2 shows a typical NAVSEA
Remotely Operated Vehicle (ROV) Deep Drone.
13-8 U.S. Navy Diving Manual—Volume 3
Diver’s Breathing Gas Requirements.
In air diving, the breathing mixture is
readily available, although pump and compressor capacities and the availability of
back-up systems may impose operational limitations. The primary requirement for
mixed-gas diving is that there be adequate quantities of the appropriate gases on
hand, as well as a substantial reserve, for all phases of the operation. The initial
determinations become critical if the nearest point of resupply is far removed from
the operation site.
Gas Consumption Rates.
The gas consumption rates and carbon dioxide absor-
bent durations for various types of underwater breathing apparatus are shown in
Table 13-1. Refer to Chapter 4 for required purity standards.
Surface-Supplied Diving Requirements.
For surface-supplied diving, the diver
gas supply system is designed so that helium-oxygen, oxygen, or air can be
supplied to the divers as required. All surface-supplied mixed-gas diving systems
require a primary and secondary source of breathing medium consisting of
helium-oxygen and oxygen in cylinder banks and an emergency supply of air from
compressors or high-pressure flasks. Each system must be able to support the gas
flow and pressure requirements of the specified equipment. The gas capacity of
the primary system must meet the consumption rate of the designated number of
divers for the duration of the dive. The secondary system must be able to support
recovery operations of all divers and equipment if the primary system fails. This
may occur immediately prior to completing the planned bottom time at maximum
depth when decompression obligations are the greatest. Emergency air supply is
provided in the event all mixed-gas supplies are lost.
Deep Diving System Requirements.
A deep diving system must be able to store
and supply enough gas to support saturation diving to the maximum certified
depth. Deep diving systems can handle and store pure gases, and mix the required
percentages of helium-oxygen as needed. When DDS-type equipment is
employed, additional quantities of gas must be included for DDC and PTC
charging and for replacing losses due to leakage, transfer trunk and service lock
usage and scrubber cycling. A DDS must also have an air system capable of
supporting surface-supplied air diving operations and initial pressurization of the
DDS for saturation operations.
SELECTING AND ASSEMBLING THE DIVE TEAM
Selecting a properly trained team for a particular diving mission is critical. Refer
to Chapter 6 for an expanded discussion on dive team selection, as well as the
criteria for selecting qualified personnel for various tasks. It is critical to ensure
that only formally qualified personnel are assigned. The Diving Officer, Master
Diver, and Diving Supervisor must verify the qualification level of each team
member. The size and complexity of deep dive systems reinforces the need for a
detailed and comprehensive watch station qualification program.
Training must be given the highest command priority. The
command that dives infrequently, or with insufficient training and few work-up
dives between operations, will be ill-prepared in the event of an emergency. The
CHAPTER 13 — Mixed-Gas Operational Planning 13-9
dive team must be exercised on a regular diving schedule using both routine and
nonroutine drills to remain proficient not only in the water but on topside support
tasks as well. Cross-training ensures that divers are qualified to substitute for one
another when circumstances warrant.
To ensure a sufficient number of properly trained and
qualified individuals are assigned to the most critical positions on a surface-
supplied mixed-gas dive station, the following minimum stations shall be manned
by formally trained (NDSTC) mixed-gas divers:
Diving Medical Officer (required on-site for all dives exceeding the normal
Diving Medical Technician
All other assignments to a surface-supplied mixed-gas dive station shall be filled
in accordance with Table 13-4.
Fatigue will predispose a diver to decompression sickness. A tired
diver is not mentally alert. Mixed-gas dives shall not be conducted using a
fatigued diver. The command must ensure that all divers making a mixed-gas dive
are well rested prior to the dive. All divers making mixed-gas dives must have at
least 8 hours of sleep within the last 24 hours before diving.
BRIEFING THE DIVE TEAM
Large personnel requirements and the increased complexities of mixed-gas diving
operations make comprehensive briefings of all personnel extremely important.
For mixed-gas surface-supplied operations, briefings of each day’s schedule are
appropriate. In addition, during saturation diving operations, a dive protocol is
required to be read and signed in accordance with the unit’s instructions. The
briefing should cover all aspects of the operation including communications,
equipment, gas supply, and emergencies such as fouling and entrapment. Each
diving member should understand his own role as well as that of his diving
companions and the support crew (Figure 13-3).
While the operation is in progress, divers returning to the surface or to the PTC
should be promptly debriefed. This ensures that topside personnel are kept advised
of the progress of the dive and have the information necessary to modify the dive
plan or protocol as appropriate.
13-10 U.S. Navy Diving Manual—Volume 3
Table 13-4. Surface-Supplied Mixed-Gas Dive Team
Deep-Sea (MK 21)
Designation One Diver Two Divers
Medical Officer 1
(Notes 1 and 4)
(Notes 1 and 4)
Supervisor/Master Diver 1
(Notes 1 and 5)
(Notes 1 and 5)
Medical Technician 1
(Notes 1 and 6)
(Notes 1 and 6)
Standby Diver 1
Rack Operator 1
Winch Operator 1
Console Operator 1
Total Personnel Required 12 15
1. To ensure sufficient properly trained and qualified individuals are assi
ned to the most critical positions on a surface-
as dive station, the followin
minimum stations shall be manned by formally trained (NDSTC) mixed-
Time Keeper - Recorder
2. The followin
stations shall be manned by formally trained (NDSTC) surface-supplied divers:
3. The followin
stations should be a qualified diver. When circumstances require the use of a non-diver, the Divin
er, Master Diver, and Divin
Supervisor must ensure that the required personnel has been thorou
hly instructed in the
required duties. These stations include:
4. A Divin
Medical Officer is required on site for all dives exceedin
the normal workin
5. Master Diver may serve as the Divin
Officer if so desi
nated in writin
by the Commandin
Medical Technician required when no Divin
Medical Officer is available.
CHAPTER 13 — Mixed-Gas Operational Planning 13-11
FINAL PREPARATIONS AND SAFETY PRECAUTIONS
Prior to the start of a mixed-gas diving operation, it is important to check that all
necessary preparations have been made and that all safety precautions have been
checked. This ensures that the diving team is properly supported in its mission and
that all possible contingencies have been evaluated in case an unexpected circum-
stance should arise.
Chapter 5 describes the objectives and importance of maintaining accurate
records. The Diving Officer, Master Diver, and Diving Supervisor should identify
the records required for their respective systems and tailor them to suit their needs.
The purpose of any record is to provide an accurate and detailed account of every
facet of the diving operation and a tabulation of supplies expended to support the
operation (e.g., gases, carbon dioxide absorbent, etc.). Any unusual circumstances
regarding dive conduct (i.e., treatments, operational/emergency procedures, or
deviation from procedures) established in the U.S. Navy Diving Manual shall be
brought to the attention of the Commanding Officer and logged in the Command
Smooth Diving Log.
MIXED-GAS DIVING EQUIPMENT
There are several modes of diving that are characterized by the diving equipment
used. The following descriptions outline capabilities and logistical requirements
for various mixed-gas diving systems.
Dive Team Brief for Divers.
13-12 U.S. Navy Diving Manual—Volume 3
Minimum Required Equipment.
Minimum required equipment for the pool phase
of dive training conducted at Navy diving schools may be modified as necessary.
Any modifications to the minimum required equipment listed herein must be
noted in approved lesson training guides.
MK 21 MOD 1 helmet with tethered umbilical
Thermal protection garment
Swim fins or shoes/booties
EGS bottle with submersible tank pressure gauge
Integrated diver’s vest/harness
MK 21 MOD 1 Lightweight Surface-Supplied Helium-Oxygen Description.
Principle of Operation:
Surface-supplied open-circuit mixed-
Adequate mixed-gas supply
Master Diver required on station
for mixed-gas operations
Diving Medical Officer required
on-site for dives deeper than 300
Recompression chamber required
Planned exceptional exposure
dives or dives exceeding normal
working limits require CNO ap-
Breathing gas heater
Hot water suit
MK 21 MOD 1 UBA.
CHAPTER 13 — Mixed-Gas Operational Planning 13-13
Flyaway Dive System III Mixed Gas System (FMGS).
The FADS III Mixed Gas
System (FMGS) is a portable, self-contained, surface-supplied diver life-support
system designed to support mixed gas dive missions to 300 fsw (Figure 13-5 and
Figure 13-6). The FMGS consists of five gas rack assemblies, one air supply rack
assembly (ASRA), one oxygen supply rack assembly (OSRA), and three helium-
oxygen supply rack assemblies (HOSRA). Each rack consists of nine 3.15 cu ft
floodable volume composite flasks vertically mounted in rack assembly. The
ASRA will hold 9600 scf of compressed air at 5000 psi. Compressed air is
provided by a 5000 psi air compressor assembly, which includes an air purifica-
tion system. Oxygen is stored at 3000 psi. The FMGS also includes a mixed-gas
control console assembly (MGCCA) and two gas booster assemblies for use in
charging the OSRA and HOSRA. Three banks of two, three, and four flasks allow
the ASRA to provide air to the divers as well as air to support chamber operations.
Set-up and operating procedures for the FMGS are found in the Operating and
Maintenance Technical Manual for Fly Away Dive System (FADS) III Mixed Gas
FADS III Mixed Gas System (FMGS).
13-14 U.S. Navy Diving Manual—Volume 3
FMGS Control Console Assembly.