C H A P T E R1 7MK 16 MOD 0 Closed-Circuit Mixed-gas UBa Diving

17-1 INTRODUCTION

2The MK16 MOD 0 is a 0.75 ata constant partial pressure of oxygen (ppO ) closed- circuit mixed-gas underwater breathing apparatus (UBA) primarily employed by Naval Special Warfare (SPECWAR) forces. The U.S. Navys use of mixed- gas closed circuit UBAs was developed to satisfy the operational requirements of SPECWAR combat swimmers and EOD divers. This equipment combines the mobility of a free-swimming diver with the depth advantages of mixed gas. The term closed circuit refers to the recirculation of 100 percent of the mixed-gas breathing medium and results in bubble-free operation, except during ascent or inadvertent gas release. This capability makes closed circuit UBAs well suited for special warfare operations. The maximum working limits for the MK16 MOD 0

17-10U.S. Navy Diving Manual Volume 4

CHAPTER 17Closed-Circuit Mixed-Gas UBA Diving17-10

22UBA are 150 feet of seawater (fsw) when N O

(air) is used as a diluent or 200 fsw

2when 84/16 HeO

mix is used as a diluent.

17-1.1Purpose. This chapter provides general guidelines for MK 16 MOD 0 UBA diving, operations and procedures (Figure 17-1). For detailed operation and maintenance instructions, see technical manual SS600- AH-MMA-010 (MK 16 MOD 0).17-1.2Scope. This chapter covers MK 16 MOD 0 UBA principles of operations, operational planning, dive procedures, and medical aspects of mixed-gas closed-circuit diving. Refer to Chapter 16 for procedures for mixing divers breathing gas.17-2 PRINCIPLES OF OPERATIONClosed circuit UBAs efficiently use the available gas supply to extend underwater duration by recirculating the breathing gas. To do this efficiently a closed circuit UBA must be able to:n Remove carbon dioxide produced bymetabolic action of the body.

2n Monitor the ppO

and add oxygen in

order to replace the oxygen consumed

by metabolic action of the body.Figure 17-1. MK 16 MOD 0Closed-Circuit Mixed-Gas UBA .

EXHALATIONMOUTHPIECEINHALATION HOSEASSEMBLYHOSEOXYGEN SENSORSTO CENTER SECTIONABSORBENT CANISTERDIAPHRAGM ASSEMBLYTO SECONDARY DISPLAYDILUENT ADDITION VALUETO PRIMARY DISPLAYDIAPHRAGM DUMP VALVEOXYGEN ADDITION VALVECHECK VALVEDILUENT BYPASS VALVEDILUENT INLINE FILTEROXYGEN BYPASS VALVEOXYGEN INLINE FILTEROXYGEN HIGH PRESSURE INDICATORDILUENT HIGH PRESSURE INDICATOROXYGEN BOTTLEDILUENT BOTTLE VALVEOXYGEN BOTTLE VALVEDILUENT REGULATOROXYGEN REGULATORDILUENT BOTTLEPRIMARY BATTERYPRIMARY ELECTRONICSFigure 17-2. MK 16 MOD 0 UBA Functional Block Diagram .

17-2.1Diving Safety. Closed-circuit mixed-gas UBAs are more complex than open- circuit SCUBA and require a high level of diver training and situational awareness. Careful dive planning is essential. Diving safety is achieved only when:n The diver has been thoroughly trained and qualified in the proper use of the UBA.n All equipment has been prepared for the specific diving conditionsexpected.n The dive is conducted within specified depth and duration limits.n The diver strictly adheres to and immediately implements all operational and emergency procedures.

17-2.2Advantages of Closed-Circuit Mixed-Gas UBA. While functionally simpler inprinciple, the closed-circuit mixed-gas UBA tends to be more complex than the

semi-closed UBA because of the oxygen analysis and control circuits required. Offsetting this complexity, however, are several inherent advantages:n Aside from mixed or diluent gas addition during descent, the only gasrequired at depth is oxygen to make up for metabolic consumption.n The partial pressure of oxygen in the system is automatically controlled throughout the dive to a preset value. No adjustment is required during a dive for variations in depth and work rate.n No inert gas leaves the system except by accident or during ascent, making the closed circuit UBArelatively bubble-free and well suited for SPECWAR operations.

17-2.3Recirculation and Carbon Dioxide Removal. The divers breathing medium is recirculated in a closed circuit UBA to remove carbon dioxide and permit reuse of the inert diluent and unused oxygen in the mixture. The basic recirculation system consists of a closed loop that incorporates inhalation and exhalation hoses and associated check valves, a mouthpiece or full face mask (FFM), a carbon dioxide removal unit, and a diaphragm assembly.

17-2 .3 .1 Recirculating Gas. Recirculating gas is normally moved through the circuit by the natural inhalation-exhalation action of the divers lungs. Because the lungs can produce only small pressure differences, the entire circuit must be designed for minimum flow restriction.

17-2 .3 .2 Full Face Mask. The FFM uses an integral oral-nasal mask or T-bit to reduce dead space and the possibility of rebreathing carbon dioxide-rich gas. Similarly, check valves used to ensure one-way flow of gas through the circuit must be close to the divers mouth and nose to minimize dead space. All breathing hoses in the system must be of relatively large diameter to minimize breathing resistance.

17-2 .3 .3 Carbon Dioxide Scrubber. Carbon dioxide is removed from the breathing circuit in a watertight canister filled with an approved carbon dioxide-absorbent material. The bed of carbon dioxide-absorbent material chemically combines with the divers exhaled carbon dioxide, while allowing the unused oxygen and diluent to pass through it. If the canister is improperly filled, channels may form in the absorbent granules permitting gas to bypass the absorbent material and allow the build up of carbon dioxide in the UBA. The canister design must also provide a low flow resistance for the gas while ensuring maximum contact between the gas and the absorbent. Flow resistance is minimized in the MK 16 MOD 0 UBA by employing a radially designed canister to reduce gas flow distance. Since inadvertent wetting of the absorbent material may produce a caustic solution, water absorbent pads are usually placed above and below the canister to collect water produced from both the reaction between carbon dioxide and the carbon dioxide absorbent and by the

2diver himself. The amount of CO

absorbent capacity is one of the major limiting

factors for any closed circuit UBA. Absorbent duration is also directly affected by the environmental operating temperature and depth. Absorbent duration decreases as temperature decreases and as depth increases.

17-2 .3 .4 Diaphragm Assembly. A diaphragm assembly or counter lung is used in all closed circuit UBAs to permit free breathing in the circuit. The need for such devices can be readily demonstrated by attempting to exhale and inhale into an empty bottle. The bottle, similar to the recirculation system without a bag, is unyielding and presents extreme back pressure. In order to compensate, flexible diaphragms or a breathing bag must be placed in the UBA circuit with a maximum displacement equal to the combined volume of both lungs.

Constant buoyancy is inherent in the system because the gas reservoir acts counter to normal lung action. In open-circuit scuba, diver buoyancy decreases during exhalation due to a decrease in lung volume. In closed-circuit scuba, expansion of the breathing bag keeps buoyancy constant. On inhalation, the process is reversed. This cycle is shown in Figure 17-3.

Figure 17-3. UBA Breathing Bag Acts to Maintain the Divers Constant Buoyancy by Responding Counter to Lung Displacement .

The flexible gas reservoir must be located as close to the divers chest as possible to minimize hydrostatic pressure differences between the lungs and the reservoir as the diver changes attitude in the water.

The MK 16 MOD 0 UBA uses a single reservoir built into a streamlined backpack assembly. Using a single reservoir located within the backpack affords minimum encumbrance to the diver and maximum protection for the reservoir.

17-2 .3 .5 Recirculation System. Optimal performance of the recirculation system depends on proper maintenance of equipment, proper filling with fresh absorbent, and accurate metering of oxygen input. To ensure efficient carbon dioxide removal throughout the dive, personnel must carefully limit dive time to the specified canister duration. Any factor that reduces the efficiency of carbon dioxide removal increases the risk of carbon dioxide poisoning.

2WARNINGThe MK 16 MOD 0 UBAprovides no visual warning of excess CO problems.

2The diver should be aware of CO

toxicity symptoms.

17-2.3.6Gas Addition, Exhaust, and Monitoring.

2In addition to the danger of carbon dioxide toxicity, the closed circuit UBA diver encounters the potential hazards of hypoxia and central nervous system (CNS) oxygen toxicity. The UBA must control the partial pressure of oxygen (ppO ) in the breathing medium within narrow limits for safe operation and be monitored frequently by the diver.

Hypoxia can occur when there is insufficient oxygen in the recirculation circuit to meet metabolic requirements. If oxygen is not added to the breathing circuit, the oxygen in the loop will be gradually consumed over a period of 2-5 minutes, at which point the oxygen in the mixture is incapable of sustaining life.

CNS oxygen toxicity can occur whenever the oxygen partial pressure in the divers breathing medium exceeds specified concentration and exposure time limits.

2Consequently, the UBA must function to limit the ppOvalue.

level to the appropriate

The closed-circuit mixed-gas UBA uses a direct control method of maintaining oxygen concentration in the system, rather than the indirect method of a preset mass flow, common to semi-closed apparatus.

17-3 MK16 MOD 0 Closed Circuit UBA

The MK 16 MOD 0 UBA is broken down into four basic systems (housing, recir-culation, pneumatics, and electronics) and their subassemblies as described in the

2following paragraphs. These systems provide a controlled ppOthe diver.

breathing gas to

17-3.1Housing System. Major components of the MK 16 MOD 0 UBA are housed in a reinforced ABS or fiberglass molded case. The equipment case is a contoured backpack assembly designed for minimum interference while swimming, and is equipped with an integral harness assembly. A streamlined, readily detachable outer cover minimizes the danger of underwater entanglement. External to the housing are components such as the mouthpiece, pressure indicators, hoses, and primary and secondary displays.

17-3.2Recirculation System. The recirculation system consists of a closed loop incorporating inhalation and exhalation hoses, a mouthpiece or FFM, a carbon dioxide-absorbent canister, and a flexible breathing diaphragm. The divers breathing gases are recirculated to remove carbon dioxide and permit reuse of the inert component of the diluent and residual oxygen in the breathing mixture. Inhalation and exhalation check valves in the mouthpiece assembly (or manifold of the FFM) ensure the unidirectional flow of gas through the system.

17-3.2.1Closed-Circuit Subassembly. The closed-circuit subassembly has a removable cover, a center section attached to the fiberglass equipment case, a flexible rubber

2breathing diaphragm, and a CO

scrubber assembly. Moisture-absorbent pads

inside the scrubber assembly absorb any condensation formed on the cover walls. The space between the scrubber canister and the cover serves as a gas plenum, insulating the canister from the ambient cold water.17-3.2.2Scrubber Functions. The scrubber has two functions:n Carbon Dioxide Removal. Beforethediversexhaledbreathreachesthebreathing diaphragm, it passes through the scrubber canister. The scrubber canister is filled with an approved, high efficiency, granular carbon dioxide-absorbent material. Two filter discs in the scrubber canister serve as gas distributors to minimize effects of any channeling in the absorbent. After passing through the filters, the exhaled gas passes through the carbon dioxide-absorbent bed, chemically combining with the carbon dioxide created by metabolic use of the divers breathing oxygen but allowing the diluent and unused oxygen to pass through it.

n Water Removal. Moisture produced by diver exhalation and the reaction between carbon dioxide and carbon dioxide-absorbent is absorbed by mois- ture-absorbent pads located outside the canister.

17-3.3Pneumatics System. The pneumatics system comprises:n High-pressure bottles for storing oxygen and diluent gases.

n Indicators to permit monitoring of the remaining gas supply.

n Regulators, fittings, tubing, filters and valves to regulate and deliver oxygenand diluent gases to the recirculation system.

17-3.4Electronics System. The electronics system maintains a constant partial pressure of oxygen in the closed-circuit UBA by processing and conditioning signal outputs from the oxygen sensors located in the breathing loop, stimulating the oxygen- addition valve, and controlling the output of the primary display.17-3 .4 .1 Oxygen Sensing. The partial pressure of oxygen within the recirculation system is monitored by three sensors. Each sensors output is evaluated by the primary electronics package through a voting logic circuit negating the output from a faulty sensor. Sensor averages are shown by the primary display. Backup reading of each individual sensor can be read on the secondary display which requires no outside power source.17-3 .4 .2 Oxygen Control. Oxygen concentration in the recirculation system is measured by sensors. The sensors send signals to the primary electronics assembly and the secondary display. The primary electronics assembly compares these sensor signals with the setpoint value, providing output to the primary display and controlling the

2oxygen-addition valve. An actual ppO

value less than the setpoint automatically

actuates the oxygen-addition valve to admit oxygen to the breathing loop. Oxygen control involves several factors:n System Redundancy. The primary electronics assembly in the MK 16 MOD 0 UBA treats each of the sensor signals as a vote. The sensor vote is either above or below the predetermined setpoint. If a simple majority of the sensors is below the predetermined setpoint, a drive signal is sent to the oxygen-addition valve; when a majority of the sensors is above the predetermined setpoint, the signal is terminated. In effect, the electronics circuit ignores the highest and lowest sensor signals and controls the oxygen-addition valve with the middle sensor. Similarly, the electronics circuit displays a high-oxygen alarm (flashing green) if a majority of the sensors signals indicates a high oxygen level and displays a low-oxygen alarm (flashing red) if a majority of the sensors signals indicates a low oxygen level. If only one sensor indicates a high oxygen level and/or only one sensor indicates a low oxygen level, the electronics circuit output alternates between the two alarm states (alternating red/green).

2n Setpoint Calibration. The normal operational ppO

setpoint for the MK 16

Mod 0 UBA is 0.75 ata. Appropriate calibration procedures are used to preset

2the specific ppO

setting.

n Oxygen Addition. In response to the sensor outputs, the oxygen-addition valveadmits oxygen to the breathing loop in the recirculation system. The control

2circuits continuously monitor the average ppO

level. If the oxygen partial

pressure in the recirculation system is lower than the setpoint level, the oxygen-

2addition valve is energized to admit oxygen. When the ppO

reaches the required

level, the automatic control system maintains the oxygen-addition valve in the SHUT position. Should the oxygen-addition valve fail in an OPEN position, the resulting free flow of oxygen in the MK 16 MOD 0 is restricted by the tubing diameter and the orifice size of the piezoelectric oxygen-addition valve.

217-3.4.3Displays. The MK 16 MOD 0 UBA has two displays that provide continuous information to the diver about ppO , battery condition, and oxygen sensormalfunction.17-3 .4 .3 .1 Primary Display. The primary display consists of two light-emitting diodes (LEDs) that are contained within the primary display housing. This display is normally mounted on the face mask, within the peripheral vision of the diver. The two LEDs (one red and one green) powered by the primary electronics assembly battery indicate the general overall condition of various electronic components and the

2ppO

in the breathing loop as follows:

2n Steady green: Normal oxygen range, 0.60 to 0.90 ata ppO of 0.75 ata).

(using a set point

n Steady red or simultaneously illuminated steady red and green: Primaryelectronics failure.

Figure 17-4. Underwater Breathing Apparatus MK 16 MOD 0 .

2n Flashing green: High oxygen content, greater than 0.90 ata ppO .

2n Flashing red: Low oxygen content, less than 0.60 ata ppO .

2n Alternating red/green: Normal transition period (ppO

is transitioning from

normal to low, from low to normal, from normal to high, or from high to normal), one sensor out of limits, low primary battery power (displayed on secondary display) or primary electronics failure.n No display (display blanked): Electronics assembly or primary battery failure.

17-3 .4 .3 .2 Secondary Display. The MK 16 MOD 0 secondary display is designed to provide quantitative information to the diver on the condition of the breathing medium, the primary battery voltage and the condition of the secondary batteries. It also serves as a backup for the primary display in the event of a failure or malfunction to the primary electronics assembly, the primary display, or the primary battery. The secondary display functions concurrently with, but independently of, the primary

2display and displays the O

sensor readings and primary battery information in digital

form. The secondary display is powered by four 1.5-volt batteries for illumination of the LED display only. It does not rely on the primary electronics subassembly, but receives signals directly from the oxygen sensors and the primary battery. It will continue to function in the event of a primary electronics assembly failure.17-4 OPERATIONAL PLANNINGChapter 6 provides general guidelines for operational planning. The information provided in this section is supplemental to Chapter 6 and the MK 16 MOD 0 UBA

O&M manual. Units should allow frequent opportunity for training, ensuring diver familiarity with equipment and procedures. Workup dives are strongly recommended prior to diving at depths greater than 130 fsw. MK 16 MOD 0 diver qualifications may be obtained by completion of the Naval Special Warfare Center MK 16 MOD 0 qualifications course. Qualifications remain in effect as long as diver qualifications are maintained in accordance with Military Personnel Manual Article 1220. However, a diver who has not made a MK 16 MOD 0 dive in the previous six months must refamiliarize himself with the MK 16 MOD 0 EPs and OPs and must complete a training dive prior to making an operational dive. Prior to conducting a decompression dive, a diver who has not conducted a MK 16 MOD 0 decompression dive within the previous six months must complete open water decompression training dives. The minimum personnel requirements for MK 16 MOD 0 diving operations are the same as open circuit SCUBA, see Figure 6-16.

17-4.1Operating Limitations. The dive depth and time limits are based on considerations of working time, decompression obligation, oxygen tolerance, and nitrogen narcosis. The expected duration of the gas 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. Diving Supervisors must consider these limiting factors when planning closed-circuit UBA operations.

17-4 .1 .1 Oxygen Flask Endurance. In calculating the endurance of the MK 16 MOD 0, only the oxygen flask is considered. The endurance of the oxygen flask is dependent upon the following:n Flask floodable volumen Initial predive pressuren Required reserve pressuren Oxygen consumption by the divern Effect of cold water immersion on flask pressure

17-4 .1 .1 .1 Flask Floodable Volume. The oxygen flask floodable volume (fv) is 0.1 cubic foot (2.9 liters).

17-4 .1 .1 .2 Initial Predive Pressure. The initial pressure is the pressure of the oxygen flask at ambient temperature when it has cooled following charging. A reserve pressure of 500 psig is required to drive the reducer. Calculation of initial pressure must also account for gas loss resulting from UBA predive calibration. Oxygen consumption by the diver is computed as 0.049 scfm (1.4 lpm). This is a conservative value for a diver swimming at 0.85 knots. Refer to Table 17-1 for information on the

2average breathing gas consumption rates and CO

absorbent usage.

17-4 .1 .1 .3 Effect of Cold Water Immersion on Flask Pressure. Immersion in cold water will reduce the flask pressure and actual cubic feet (acf) of gas available for the diver, in accordance with Charles/Gay-Lussacs gas law. Based upon direct measurement, available data, or experience, the coldest temperature expected during the dive is used.

2Table 17-1. Average Breathing Gas Consumption Rates and CO

Absorbent Usage .

DivingGas ConsumptionGas Consumption Equipment(Normal)(Heavy Work)CO2 AbsorbentCapacityDuration 40FDuration 70F (lbs .)(Note 1)(Note 1)

MK 16 MOD12-1515-170 UBApsi/minpsi/min7.75-8.05h6h 40m

Note:1 . CO2 absorbent duration is based upon a comfortable work rate (0 .8-knot swimming speed) .

17-4.1.1.4Calculating Gas Endurance. Combining these factors produces the formula for MK 16 MOD 0 gas endurance:

MK 16 MOD 0 gas endurance =

T P 2P

1F

T1

R 492

VVO

14.7 psiT

22

Where:

FV=Floodable volume of flask in cubic feet

PI=Initial Pressure in psia

PR=Reserve Pressure in psia

2VO=Oxygen consumption in medical scfm (32F)

T1=Ambient air temperature in R

T2=Coldest water temperature expected in R

Rankine conversion factor:R=F + 460

All pressure and temperature units must be absolute.

17-4 .1 .1 .5 Example. The endurance of a MK 16 MOD 0 UBA charged to 2,500 psig for a dive in 50 F water when the ambient air temperature is 65 F would be computed as follows:

MK 16 MOD 0 gas endurance = 0.1[(2, 514.7 510 / 525) 514.7] 492

= 258 minutes

0.049 14.7

510

This duration assumes no gas loss from the UBA during the dive and only considers metabolic consumption of oxygen by the diver. Divers must be trained to minimize gas loss by avoiding leaks and unnecessary depth changes. Clearing a flooded face mask is a common cause of gas loss from the UBA. When a full face mask (FFM) is used, gas can pass from the UBA breathing loop into the FFM and escape into the surrounding seawater due to a poor face seal. Leaks that continue unchecked can

deplete UBA gas supply rapidly. Additionally, during diver ascent, the dump valve opens to discharge breathing gas into the surrounding water, thereby preventing overinflation of the breathing diaphragm. Depth changes should be avoided as much as possible to minimize this gas loss.

17-4 .1 .2 Diluent Flask Endurance. Under normal conditions the anticipated duration of the MK 16 MOD 0 diluent flask will exceed that of the oxygen flask. The MK 16 MOD 0 diluent bottle holds approximately 21 standard cubic feet (595 liters) of gas at a stored pressure of 3,000 psig. Diluent gas is used to maintain the required gas volume in the breathing loop and is not depleted by metabolic consumption. As the diver descends, diluent is added to maintain the total pressure within the recirculation system at ambient water pressure. Loss of UBA gas due to off gassing at depth requires the addition of diluent gas to the breathing loop either automatically through the diluent add valve or manually through the diluent bypass valve to make up lost volume. Excessive gas loss caused by face mask leaks, frequent depth changes, or improper UBA assembly will deplete the diluent gas supply rapidly.

17-4 .1 .3 Canister Duration. Canister duration is estimated by using a working diver scenario. This allows an adequate safety margin for the diver in any situation. Table 17-2 shows the canister duration limits for the MK 16 MOD 0 UBA.

Table 17-2. MK 16 MOD 0 Canister Duration Limits .

Canister Duration with HeO2Water Temperature (F)Depth (fsw)Time (minutes)

40 and above0-30030029-390-10030035-39101-30024029-34101-300120

Canister Duration with N202Water Temperature (F)Depth (fsw)Time (minutes)

29 and above0-5030040 and above51-15020029-3951-150100

NAVSEA-approved Sodalime CO2 absorbents for the MK 16 MOD 0 are listed in the ANU list .

17-4 .1 .4 Thermal Protection. Divers must be equipped with adequate thermal protection to perform effectively and safely. A cold diver will either begin to shiver or increase his exercise rate, both of which will increase oxygen consumption and decrease oxygen supply duration and canister duration. Refer to Chapter 11 for guidance on thermal protection.

17-62U.S. Navy Diving Manual Volume 4

CHAPTER 17Closed-Circuit Mixed-Gas UBA Diving17-6217-4.2Equipment Requirements. Equipment requirements for MK16 MOD 0 trainingdives are provided in Table 17-3. Two equipment items merit special comment:

Table 17-3. MK 16 MOD 0 UBA Diving Equipment Requirements .

GeneralDiving SupervisorDiversStandby Diver

1 . Motorized safety boat (Note 1)2 . Radio (communications with parent unit, chamber, communication between safety boats when feasible)3 . High-intensity, wide- beam light (night operations)4. Dive flags and/or special operations lights as required5. Sufficient (2 quarts) fresh water in case of chemical injury1 . Dive watch 2 . Dive Bill list3 . Air Decompression Tables4 . Closed-Circuit Mixed-Gas UBADecompression Tables using 0 .7 ATA Constant Partial Pressure Ox- ygen in Nitrogen and in Helium .5 . Recall device1 . Dive watch (Note 2) 2 . Face mask3 . Fins4 . Dive knife5 . Approved life preserver or buoyancy compensator (BC)6 . Appropriate thermal protection7 . Depth gauge (Note 2) 8 . Buddy line (asappropriate forSPECWAR operations) (Note 1)9 . Tending line1 . Dive watch 2 . Face mask 3 . Fins4 . Dive knife5 . Approved life preserver or buoyancy compensator (BC)6 . Appropriate thermal protection7 . UBA with same depth capability8 . Depth gauge9 . Weight belt (if needed) 10 . Tending line

Notes:1 . See paragraph 17-4 .22 . See paragraph 17-4 .2 .6

n Safety Boat. A minimum of one motorized safety boat must be present for all open-water dives. A safety boat is also recommended for tended pier dives or diving from shore. Safe diving practice in many situations, however, will require the presence of more than one safety boat. The Diving Supervisor must determine the number of boats required based on the diving area, medical evacuation plan, night operations, and the number of personnel participating in the dive operation.

n Buddy Lines. Buddy lines are considered important safety equipment for closed-circuit UBA dives. In special diving situations, such as certain combat swimmer operations or tended diving, the use of buddy lines may not be feasi- ble. The Diving Supervisor shall conduct dives without buddy lines only in situations where their use is not feasible or where their use will pose a greater hazard to the divers than by diving without them.

17-4 .2 .1 Distance Line. Any buddy line over 10 feet (3 meters) in length is referred to as a distance line. The length of the distance line shall not exceed 81 feet (25 meters). Distance lines shall be securely attached to both divers.

17-4 .2 .2 Standby Diver. When appropriate during training and non-influence diving operations, open circuit SCUBA may be used to a maximum depth of 130 fsw.

17-4 .2 .3 Lines. Diver marker lines shall be manufactured from any light line that is buoyant and easily marked as directed in paragraph 17-4.2.4 (one-quarter inch polypropylene is quite suitable).

17-4 .2 .4 Marking of Lines. Lines used for controlling the depth of the diver(s) for decompression diving shall be marked. This includes tending lines, marker lines, and lazy-shot lines. Lines shall be marked with red and yellow or black bands starting at the diver(s) or clump end. Red bands will indicate 50 feet and yellow or black bands will mark every 10 feet.

17-4 .2 .5 Diver Marker Buoy. Diver marker buoys will be constructed to provide adequate visual reference to monitor the divers location. Additionally, the amount of line will be of sufficient length for the planned dive profile.

17-4.2.6Depth Gauge/Wrist Watch. A single depth gauge and wrist watch may be usedwhen diving with a partner and using a distance line.

17-4.3Recompression Chamber Considerations. A recompression chamber and a Diving Medical Officer are not required on the dive station (on the dive station is defined as at the dive location) as prerequisites for closed-circuit UBA diving operations, unless the dive(s) will exceed the maximum working limit. However, the following items should be determined prior to beginning diving operations:n Location of the nearest functional recompression chamber. Positive confirma- tion of the chambers availability in case of emergency should be obtained.n Location of the nearest available Diving Medical Officer if not at the nearestrecompression chamber.n Location of the nearest medical facility for treatment of injuries and medicalproblems not requiring recompression therapy.n The optimal method of transportation to the treatment chamber or medical facility. If coordination with other units for aircraft/boat/vehicle support is necessary, the Diving Supervisor shall know the telephone numbers and points of contact necessary to make these facilities available as quickly as possible in case of emergency. A medical evacuation plan should be included in the Diving Supervisor brief. Preparing an emergency assistance checklist similar to that in Chapter 6 is recommended.

17-4.4Ship Safety. When operations are to be conducted in the vicinity of ships, the guidelines provided in the Ship Repair Safety Checklist (see Chapter 6) must be followed.

17-4.5Operational Area Clearance. Notification of intent to conduct diving operationsshould be coordinated in accordance with local directives.

17-5 PREDIVE PROCEDURES

17-5.1Diving Supervisor Brief. A thorough, well-prepared dive briefing reinforces the confidence level of the divers and increases safety, and is an important factor in successful mission accomplishment. It should normally be given by the Diving Supervisor, who will be in charge of all diving operations on the scene. The briefing shall be given separately from the overall mission briefing and shall focus on the diving portion of the operation, with special attention to the items shown in Table 17-4. For MK 16 MOD 0 UBA diving, use the appropriate checklist provided in the MK16 MOD 0 UBA O&M Manual.

17-5.2Diving Supervisor Check. As the divers set up their UBAs prior to the dive, the Diving Supervisor must ensure that each diver checks his own equipment, that setup is completed properly by checking the UBA, and that each diver completes a UBA predive checklist from the appropriate UBA operation and maintenance manual. The second phase of the Diving Supervisor check is a predive inspection conducted after the divers are dressed. The Diving Supervisor ensures that the UBA and related gear (life preserver, weight belt, etc.) are properly donned, that mission-related equipment (compass, depth gauge, dive watch, buddy lines, tactical equipment, etc.) are available, and that the UBA functions properly before allowing the divers to enter the water. Appropriate check lists to confirm proper functioning of the UBA are provided in the MK 16 MOD 0 O&M manual.

17-6 WATER ENTRy AND DESCENT

2The maximum descent rate is 60 feet per minute. During descent, the UBA will automatically compensate for increased water pressure and provide an adequate volume of gas for breathing. During descent the oxygen partial pressure may increase as oxygen is added to the breathing mixture as a portion of the diluent. Depending on rate and depth of descent, the primary display on the MK 16 MOD 0 UBA may illuminate flashing green. It may take from 2 to 15 minutes to consume the additional oxygen added by the diluent during descent. While breathing down the ppO , the diver should continuously monitor the primary and secondary display

2until the ppO

returns to setpoint level.

Table 17-4. MK 16 MOD 0 UBA Dive Briefing.

A. Dive PlanF.1 .Operating depth2 .Dive times3 .CSMD tables or decompression tables 4 .Distance, bearing, and transit times5 .All known obstacles or hazardsCommunications1 .Frequencies, primary/secondary 2 .Call signsG. Emergency Procedures1 .2 .B. Environment1 .2 .3 .4 .5 .6 .7 .Weather conditionsWater/air temperatures Water visibility Tides/currentsDepth of water Bottom type Geographic location3 .C. Personnel Assignments1 .2 .3.4 .5 .6 .Dive pairsDiving Supervisor Diving Officer Standby diverDiving medical personnelBase of operations support personnel4 .5 .6 .D. Special Equipment for:1 .2 .3 .4 .Divers (include thermal garments)Diving Supervisor Standby diver Medical personnelSymptoms of CO2 buildupReview of management of CO2 toxicity, hypoxia, chemical injury, unconscious diverUBA malfunction (refer to maintenance manual for detailed discussion)n Oxygen sensor failuren Low partial pressure of oxygen n High partial pressure of oxygen n Electronics failuren Low batteryn Diluent free flown Diluent addition valve failuren System floodingLost swim pair procedures Omitted decompression plan Medical evacuation plann Nearest available chambern Nearest Diving Medical Officern Transportation plann Recovery of other swim pairsH.I.Times for OperationsTime CheckE.Review of Dive Signals1 .Hand signals

17-7 UNDERWATER PROCEDURES

17-7.1General Guidelines. The divers shall adhere to the following guidelines as the dive is conducted.WARNINGFailure to adhere to these guidelines could result in serious injury or death.n Monitor primary and secondary display frequently (every 2-3 minutes).n Wear adequate thermal protection.n Know and use the proper amount of weights for the thermal protection wornand the equipment carried.n Check each others equipment carefully for leaks at the start of the dive.n Do not exceed the UBA canister duration and depth limitations for the dive(paragraph 17-4.1.3).

n Minimize gas loss from the UBA(avoid mask leaks and frequent depth changes,if possible).n Maintain frequent visual or touch checks with buddy.n Be alert for symptoms suggestive of a medical disorder (paragraph 17-11).n Use tides and currents to maximum advantage.

17-7.2At Depth. If the UBA is performing normally at depth, no adjustments will be

2required. The ppO

control system will add oxygen from time to time. Monitor

UBA primary and secondary displays and high pressure gauges in strict accordance with the MK 16 MOD 0 O&M manual. Items to monitor include:n Primary Display. Primary Display. Check the primary display frequently to ensure that the oxygen level remains at the setpoint during normal activity at a constant depth.n Secondary Display. Secondary Display. Check the secondary display frequently (every 2-3 minutes) to ensure that all sensors are consistent with the primary display and that plus and minus battery voltages are properly indicating.n High-Pressure Indicators. Check the oxygen and diluent pressure indicatorsfrequently to ensure that the gas supply is adequate to complete the dive.

17-8 ASCENT PROCEDURES

The maximum ascent rate for the MK 16 MOd 0 is 30 feet per minute. During ascent, when water pressure decreases, the diaphragm dump valve compensates for increased gas volume by discharging the excess gas into the water. As a result,

2oxygen in the breathing gas mixture may be vented faster than O

is replaced by

the addition valve. In this case, the primary display may alternate red/green before

2the low ppO

signal (blinking red) appears. This is a normal transition period and

shall not cause concern. Monitor the secondary display frequently on ascent and add oxygen by depressing the bypass valve during this instance.

17-9 POSTDIVE PROCEDURES

Postdive procedures shall be completed in accordance with the appropriate post- dive checklists in the MK 16 MOD 0 UBA O&M manual.

17-10 DECOMPRESSION PROCEDURES

2When diving with an open-circuit UBA, ppO

increases with depth. With a closed

2circuit UBA, ppO

remains constant at a preset level regardless of depth. Therefore,

standard U.S. Navy decompression tables cannot be used. The three methods to determine a MK16 MOD 0 divers decompression obligation are listed below.n Navy Dive Computer. The Navy Dive Computer (NDC) is a diver worn decompression computer that calculates the divers decompression obligation in real time. It is authorized for use with the MK16 MOD 0 UBA when air

is used as a diluent. The NDC assumes the diver is breathing air at depths shallower than 78 fsw and is using a MK16 MOD 0 at deeper depths.n Combat Swimmer Multilevel Dive Tables. Combat Swimmer Multilevel Dive (CSMD) procedures provide SPECWAR divers with the option of conducting multiple-depth diving with the MK 16 MOD 0 UBA to a depth of 70 fsw. However, the CSMD procedures may be used for dives between 70 and 110 fsw by adding 10 fsw to the depth when entering the table.

2n Constant 0.7 ata ppO

Decompression Tables. The constant 0.7 ata ppO

2decompression tables Oxygen in Nitrogen (Table 17-9) and Oxygen in Helium (Table 17-10) are discussed in paragraph 17-10.1 below. These tables were computed assuming an oxygen setpoint of 0.70 ata.

NOTESurface decompression is not authorized for MK 16 MOD 0 operations.Appropriate surface decompression tables have not been developed for

2constant 0.7 ata ppO

closed-circuit diving.

217-10.1Rules for Using 0.7 ata Constant ppO

in Nitrogen and in Helium Decompression

Tables.

2NOTEThe rules using the 0.7 ata ppO

tables are the same for nitrogen and

helium; however, the tables are not interchangeable.n These tables are designed to be used with the MK 16 MOD 0 UBA (or any

2other constant ppO

closed-circuit UBA) with an oxygen setpoint of 0.70 ata or

greater.n When using helium as the inert gas, the amount of nitrogen must be minimized in the breathing loop. Flush the UBA well with helium-oxygen using the purge procedure given in the MK 16 MOD 0 UBA O&M manual.n Tables are grouped by depth. Within each decompression table, exceptional exposure dives are separated by a dashed line. These tables are designed to be dived to the exceptional exposure line. Exceptional exposure schedules are provided in case of unforseen circumstances when a diver might experience an inadvertent downward excursion or for an unforeseen reason overstay the planned bottom time. Planned exceptional exposure dives require prior CNO approval.n Tables/schedules are selected according to the maximum depth obtained dur- ing the dive and the bottom time (time from leaving the surface to leaving the bottom).

2n Monitoring ppO . During decompression, it is very important to frequently

2monitor the secondary display and ensure a 0.75 ata ppO

is maintained as

2closely as possible. Always use the appropriate decompression table when surfacing, even if UBA malfunction has significantly altered the ppO .n General rules for using these tables are the same as for the air decompression tables and include the use of the RNT exception rule when calculating the equivalent single dive time for repetitive dives.

1. Enter the table at the listed depth that is exactly equal to or is next greater than the maximum depth attained during the dive.

2. Select the bottom time from those listed for the selected depth that is exactly equal to or is next greater than the bottom time of the dive.

3. Never attempt to interpolate between decompression schedules.

4. Use the decompression stops listed for the selected bottom time.

5. Ensure that the divers chest is maintained as close as possible to eachdecompression depth for the number of minutes listed.

6. Maximum ascent rate is 30 feet per minute. The rules for compensating for variations in the rate of ascent are identical to those for air diving (see Chapter 9, paragraph 9-11).

7. Begin timing the first stop when the diver arrives at the stop. For all subsequent stops, begin timing the stop when the diver leaves the previous stop. Ascent time between stops is included in the subsequent stop time.

8. The last stop may be taken at 20 fsw if desired. After completing the prescribed 20 fsw stop, remain at any depth between 10 fsw and 20 fsw inclusive for the 10 fsw stop time as noted in the appropriate decompression table.

9. Use the appropriate decompression table for the selected decompression method unless an emergency or equipment malfunction has occurred. Interpolating between different methods of decompression in order to shorten the decompression obligation is not authorized.

10. When selecting the proper decompression table, all dives within the past 18 hours must be considered. Repetitive dives are allowed. Repetitive diving decompression procedures vary depending on the breathing medium(s) selected for past dives and for the current dive. If a dive resulted in breathing from the an alternate air supply then no repetitive dives shall be made within the next 18 hours. Refer to the following tables and figures for repetitive diving.n Table 17-5 for Repetitive Dive Procedures for Various Gas Mediums.

n Figure 17-5 for the Dive Worksheet for Repetitive 0.7 ata Constant Partial Pressure Oxygen in Nitrogen Dives.

n Table 17-6 for the No-Decompression Limits and Repetitive Group Designation Table for No-Decompression 0.7 ata Constant Partial Pressure Oxygen in Nitrogen Dives.

n Table 17-7 for the Residual Nitrogen Timetable for Repetitive 0.7 ata Constant Partial Pressure Oxygen in Nitrogen Dives.

Table 17-5. Repetitive Dive Procedures for Various Gas Mediums .

WARNINGNo repetitive dives are authorized after an emergency procedure requiring a shift to the EBS.

Selection of Repetitive Procedures for Various Gas Mediums

Previous Breathing MediumRepetitive Dive(Refer to Notes 1, 2, and 3)Breathing MediumNote

N2O2N2O2AAirN2O2BN2O2AirCHeO2HeO2DHeO2AirEAirHeO2FHeO2N2O2GN2O2HeO2H

Notes:1 .If a breathing medium containing helium was breathed at any time during the 18-hour period immediately preceding a dive, use HeO2 as the previous breathing medium .

2 .If 100 percent oxygen rebreathers are used on a dive in conjunction with other breathing gases, treat that portion of the dive as if 0 .7 ATA O2 in N2 was breathed .

3 .If both air and 0 .7 ATA O2 in N2 are breathed during a dive, treat the entire dive as an air dive . If the 0 .7 ata O2 in N2 is breathed at depths 80 fsw or deeper, add the following correction factors to the maximum depth when selecting the appropriate air table .

Maximum Depth on N2O2Correction Factor

Not exceeding 80 FSW081-99Plus 5100-119Plus 10120-139Plus 15140-150Plus 20

Notes:A .(1) If the surface interval is less than 10 minutes, determine the table and schedule for the repetitive dive by adding the bottom times and taking the deepest depth of all the dives in the series, including the planned repetitive dive .

Table 17-5. Repetitive Dive Procedures for Various Gas Mediums . (Continued)

Notes continued:A . (2) If the surface interval is longer than 10 minutes, use the repetitive dive worksheet (Figure 17-5) to determine the table and schedule:a) Determine the repetitive group letter for the depth and time of dive conducted from Table 17-6 for no- decompression dives or from Table 17-9 for decompression dives . If the exact time or depth is not found, go to the longer time or the next deeper depth .b) Locate the repetitive group letter in Table 17-7 . Move across the table to the correct surface interval time . Move down to the bottom of the column for the new group designation .c) Move down the column of the new group designation to the depth of the planned dive . This is the residual Nitrogen time (RNT). Add this to the planned bottom time of the next dive to find the decompression schedule and the new group designation .(3) The RNT exception rule applies to repetitive MK 16 MOD 0 diving . Determine the table and schedule for the repetitive dive by adding the bottom times and taking the deepest depth of all the MOD 0 dives in the series, including the planned repetitive dive . If the resultant table and schedule requires less decompression than the table and schedule obtained using the repetitive dive worksheet, it may be used instead of the worksheet table and schedule .B .Use the repetitive group designation from the air decompression table or the no-decompression limits and repetitive group designation table for no-decompression air dives to enter Table 17-7 . Compute the RNT as in Note A . Donot use the residual nitrogen timetable for repetitive air dives to find the RNT. The RNT exception rule applies to repetitive air/MK 16 MOD 0 diving . In order to apply the RNT exception rule, convert the depth of any air dive in the series to its equivalent MK 16 MOD 0 depth before taking the deepest depth in the series . Equivalent MOD 0 Depth= (0 .79 x Depth on Air) + 18 fsw .C . (1) Determine the repetitive group designation for depth and time of dive conducted from Table 17-6 or Table 17-9 .If the exact time or depth is not found, go to the next longer time or the next deeper depth .(2) Using the repetitive group designator, enter Table 9-8 on the diagonal . Move across the table to the correct surface interval time . Move down to the bottom of the column for the new repetitive group designation .(3) Continue to read down the column of Table 9-8 to the depth that is exactly equal to or greater than the depth ofthe repetitive dive to find the RNT.D . Add the bottom time of the planned repetitive dive to the sum of the bottom times for all dives within the past 18 hours to get the adjusted bottom time . Use the maximum depth attained within the past 18 hours and the adjusted bottom time to select the appropriate schedule from Table 17-10 .E .Add the bottom times of all dives within the past 18 hours to get an adjusted bottom time . Using the air decompression table, find the maximum depth attained during the past 18 hours and the adjusted bottom time. The repetitive group from this air table may then be used as the surfacing repetitive group from the last dive . The residual nitrogen timetable for repetitive air dives is used to find the repetitive group at the end of the current surface interval and the appropriate residual nitrogen time for the repetitive air dive .F . Compute the RNT from the residual nitrogen timetable for repetitive air dives using the depth of the planned dive . Add the RNT to the planned bottom time to get the adjusted bottom time . Use Table 17-10 for the adjusted bottom time at the planned depth .G . Add the bottom times of all dives within the past 18 hours to get an adjusted bottom time . Using Table 17-9, find the maximum depth attained during the past 18 hours and the adjusted bottom time . The repetitive group from the table may then be used as the surfacing repetitive group from the last dive . Table 17-7 is used to find the repetitive group at the end of the current surface interval and the appropriate RNT for the current dive .H . Compute the RNT from Table 17-7 using the depth of the planned dive . Add the RNT to the planned bottom time to get the adjusted bottom time . Use Table 17-10 for the adjusted bottom time at the planned depth .

REPETITIVE DIVE WORKSHEETFOR0.7 ATA N2O2 DIVES

Part 1 . Previous Dive:minutes feetrepetitive group designator from Table 17-6 or 17-9

Part 2 . Surface Interval:hoursminutes on the surface final repetitive group from Table 17-7

Part 3 . Equivalent Single Dive Time:

Enter Table 17-10 at the depth row for the new dive and the column of the final repetitive group to find the corresponding Residual Nitrogen Time (RNT) .minutes RNT+minutes planned bottom time=minutes equivalent single dive time

Part 4 . Decompression Schedule for the Repetitive Dive:minutes equivalent single dive time from Part 3 feet, depth of the repetitive dive .

Ensure RNT exception rule does not apply .

Figure 17-5. Dive Worksheet for Repetitive 0 .7 ata Constant Partial Pressure Oxygen in Nitrogen Dives .

Table 17-6. No-Decompression Limits and Repetitive Group Designation Table for 0 .7 ata Constant ppO2 in Nitrogen Dives .

DepthRepetitive Group Designator (fsw)No-Stop LimitABCDEFGHIJKLMNOZ

10Unlimited

15Unlimited

20Unlimited154425*

30Unlimited31507398128165211274375643*

4036917273850637691107125144167192223259305369

501431219263341505968788899111123137143

607491419253137435056637174

7051711152025293439445051

8040691316202428323640

9032581114172024273132

10027479121518212427

11023368111316182123

1202035791214161820

1301646810121416

140144679111314

1501135781011

Exceptional Exposure ------------------------------------------------------------------------------------------------------------------------------------------

160103468910

1709345789

Diver does not acquire a repetitive group designator during dives to these depths .* Highest repetitive group that can be achieved at this depth regardless of bottom time .

0:102:20 *Table 17-7. Residual Nitrogen Timetable for Repetitive 0 .7 ata Constant ppO2 in Nitrogen Dives .

BC0:10 1:171:16 3:36 *0:100:56 2:120:552:11 4:31 *ALocate the divers repetitive group designation from his previous dive along the diagonal line above the table . Read horizontally to the interval in which the divers surface interval lies .Next, read vertically downward to the new repetitive group designation .Continue downward in this same column to the row that represents

the depth of the repetitive dive . The time given at the intersection is residual nitrogen time, in minutes, to be applied to the repetitive dive .

Dives following surface intervals longer than this are not repetitive dives . Use actual bottom times in the Table 17-9 tocompute decompression for such dives .

D0:100:531:48 3:040:521:473:03 5:23 *E0:100:531:452:40 3:560:521:442:393:55 6:15 *F0:100:531:452:383:32 4:490:521:442:373:314:48 7:08 *G0:100:531:452:383:304:24 5:410:521:442:373:294:235:40 8:00 *H0:100:531:452:383:304:225:17 6:330:521:442:373:294:215:166:32 8:52 *

I0:100:531:452:383:304:225:146:09 7:250:521:442:373:294:215:136:087:24 9:44 *J0:100:531:452:383:304:225:146:077:01 8:170:521:442:373:294:215:136:067:008:16 10:36 *K0:100:531:452:383:304:225:146:076:597:53 9:100:521:442:373:294:215:136:066:587:529:09 11:29 *L0:100:531:452:383:304:225:146:076:597:518:45 10:020:521:442:373:294:215:136:066:587:508:44 10:01 12:21 *M0:100:531:452:383:304:225:146:076:597:518:439:38 10:540:521:442:373:294:215:136:066:587:508:429:37 10:53 13:13 *N0:100:531:452:383:304:225:146:076:597:518:439:35 10:30 11:460:521:442:373:294:215:136:066:587:508:429:34 10:29 11:45 14:05 *O0:100:531:452:383:304:225:146:076:597:518:439:35 10:28 11:22 12:380:521:442:373:294:215:136:066:587:508:429:34 10:27 11:21 12:37 14:58 *

Z0:100:531:452:383:304:225:146:076:597:518:439:35 10:28 11:20 12:14 13:310:521:442:373:294:215:136:066:587:508:429:34 10:27 11:19 12:13 13:30 15:50 *

ZONMLKJIHGFERepetitive Group at the End of the Surface IntervalDCBADive Depth10

15

20****************************420153

30************62637227321116512999735131

4036530325822219216714412510791776351392818

501671511371231119988786859504234271912

601131049587797164575044383226201510

708679736761565045403530252116128

806964605550464137332925211814107

90585450464339353228252218151296

100504744403734312825221916131185

11044413836333027252219171412975

12039373432292725222018151311964

13036333129272422201816141210864

1403330282624222018171513119754

1503028262422211917151412108753

160282624232119181614131198653

170262423211918161513121097643

Residual Nitrogen Times (Minutes) Repetitive dives to these depths are equivalent to remaining on the surface . Add the bottom time of the dive to the preceding surface interval . Use the Surface Interval Credit Table (SICT) to determine the repetitive group at the end of the dive .** Residual Nitrogen Time cannot be determined using this table (see paragraph 9-9 .1 for instructions) .

11. The partial pressure of nitrogen in the MK 16 MOD 0 UBA at depths up to 15 fsw is lower than the partial pressure of nitrogen in air at the surface. A diver diving to these depths, therefore, loses rather than gains body nitrogen during the dive. Accordingly, the diver does not acquire a repetitive group designator when making these shallow dives. If the dive is a repetitive dive up to 15 fsw, the diver will lose more nitrogen during the repetitive dive than if he remained on the surface. The dive can be considered the equivalent of remaining on the surface for the duration of the dive. The repetitive group designator at the end of the repetitive dive can be determined by adding the bottom time of the repetitive dive to the preceding surface interval, then using the surface interval credit table to determine the ending repetitive group.

217-10.2PPO

Variances. The ppO

in the MK 16 UBAs is expected to vary slightly from 0.6

2- 0.9 ata for irregular brief intervals. This does not constitute a rig malfunction.

2When addition of oxygen to the UBA is manually controlled, ppO

should be

maintained in accordance with techniques and emergency procedures listed in theMK 16 MOD 0 O&M manual.

The Diving Supervisor and medical personnel should recognize that a diver who

2has been breathing a mixture with ppO

lower than 0.6 ata for any length of time

may have a greater risk of developing decompression sickness. Once the diver reaches surface he will be given a neurological exam and observed for an hour. The diver will not require recompression treatment unless symptoms of decompression sickness occur.

17-10.3 Emergency Breathing System (EBS). When planning a MK16 MOD 0 decompression dive, the Diving Supervisor must ensure an alternate air source is available to the diver in the event of a MK 16 failure. The air source must be sufficient to allow the diver to complete his decompression obligation as determined below. See Chapter 7 for procedures to calculate the volume of air required.

17-10 .3 .1 Emergency Decompression on Air. In emergency situations (e.g., UBA flood- out or failure), the diver should immediately ascend to the first decompression stop according to the original decompression schedule and shift to the alternate air supply. An alternate air supply can be any ANU approved SCUBA bottle(s) and regulator. The subsequent decompression is modified according to the diluent gas originally breathed.

2n Helium-Oxygen Diluent. Follow the original HeO without modification while breathing air.

decompression schedule

n Nitrogen-Oxygen(Air) Diluent. Doubleallremainingdecompressionstopswhile breathing air. If the switch to emergency air is made while at a decompression stop, then double the remaining time at that stop and all shallower stops. If the dive falls within the no-decompression limit and a switch to an alternate air supply has occurred, a mandatory 10-minute stop at 20 fsw is required.

If either of these procedures is used, the diver will be given a neurological exam and observed on the surface for one hour. The diver will not require recompression treatment unless symptoms of decompression sickness occur.

17-10.4 Asymptomatic Omitted Decompression. Certain emergencies may interrupt or prevent specified decompression. UBA failure, exhausted diluent or oxygen gas supply, and bodily injury are examples that constitute such emergencies. The omitted decompression procedures for an asymptomatic MK 16 MOD 0 diver are contained in Table 17-8. If the diver switches from the MK 16 MOD 0 to an alternate air source then the decompression obligations must also be modified in accordance with paragraph 17-10.3.1.

Table 17-8. Management of Asymptomatic Omitted Decompression MK 16 MOD 0 Diver .

Deepest Decompression Stop OmittedDecompression StatusSurface IntervalAction

Chamber AvailableNo Chamber Available

NoneNo decompression stops requiredNAObserve on surface for 1 hourObserve on surface for 1 hour

20 fsw or shallower

Decompression stops required1 minReturn to depth of stop . Multiply 20-fsw and/or 10-fsw stop times by 1 .5 . Resume decompression . Or: Treatment Table 5 for surface interval 5 min

Return to depth of stop . Multiply 20-fsw and/or 10-fsw stop times by 1 .5 . Resume decompression .

Deeper than 20 fsw

Decompression stops required (30 min missed)AnyTreatment Table 6Descend to the deepest stop omitted . Multiply all stops 40 fsw and shallower by 1 .5 . Resume decompression .

17-10.5 Symptomatic Omitted Decompression. If the diver shows evidence of decompression sickness or arterial gas embolism before recompression for omitted decompression can be carried out, immediate treatment using the appropriate oxygen or air treatment table is essential. Guidance for table selection and use is given in Chapter 20.

17-11 MEDICAL ASPECTS OF CLOSED-CIRCUIT MIxED-GAS UBA

When using a closed-circuit mixed-gas UBA, the diver is susceptible to the usual diving-related illnesses (i.e., decompression sickness, arterial gas embolism, barotraumas, etc.). Only the diving disorders that merit special attention for closed-

circuit mixed gas divers are addressed in this chapter. Refer to Chapter 3 for a detailed discussion of diving related physiology and related disorders.

17-11.1 Central Nervous System (CNS) Oxygen Toxicity. High pressure oxygen poisoning is known as CNS oxygen toxicity. High partial pressures of oxygen are associated with many biochemical changes in the brain, but which specific changes are responsible for the signs and symptoms of CNS oxygen toxicity is presently unknown. CNS oxygen toxicity is not likely to occur at oxygen partial pressures below 1.3 ata, though relatively brief exposure to partial pressures above this, when it occurs at depth or in a pressurized chamber, can result in CNS oxygen toxicity causing CNS-related symptoms.

17-11 .1 .1Causes of CNS Oxygen Toxicity. Factors that increase the likelihood of CNSoxygen toxicity are:n Increased partial pressure of oxygen.n Increased time of exposure.n Prolonged immersion.n Stress from strenuous physical exercise.n Carbon dioxide buildup. The increased risk for CNS oxygen toxicity may occur even before the diver is aware of any symptoms of carbon dioxide buildup.n Cold stress resulting from shivering or an increased exercise rate as thediver attempts to keep warm.n Systemic diseases that increase oxygen consumption. Conditions asso- ciated with increased metabolic rates (such as certain thyroid or adrenal disorders) tend to cause an increase in oxygen sensitivity. Divers with these diseases should be excluded from mixed gas diving.

17-11 .1 .2 Symptoms of CNS Oxygen Toxicity. The symptoms of CNS oxygen toxicity may not always appear and most are not exclusively symptoms of oxygen toxicity. The most serious symptom of CNS oxygen toxicity is convulsion, which may occur suddenly without any previous symptoms, and may result in drowning or arterial gas embolism. Twitching is perhaps the clearest warning of oxygen toxicity, but it may occur late if at all. The mnemonic device VENTID-C is a helpful reminder of the most common symptoms of CNS oxygen toxicity. The appearance of any one of these symptoms usually represents a bodily signal of distress of some kind and should be heeded.

V:Visual symptoms. Tunnel vision, a decrease in the divers peripheral vision,and other symptoms, such as blurred vision, may occur.E: Ear symptoms. Tinnitus is any sound perceived by the ears but not resulting from an external stimulus. The sound may resemble bells ringing, roaring, or a machinery-like pulsing sound.N:Nausea or spasmodic vomiting. These symptoms may be intermittent.

T: Twitching and tingling symptoms. Any of the small facial muscles, lips, or muscles of the extremities may be affected. These are the most frequent and clearest symptoms.I: Irritability. Any change in the divers mental status; including confusion,agitation, and anxiety.D:Dizziness. Symptoms include clumsiness, incoordination, and unusual fatigue.C: Convulsions.

The following additional factors should be noted regarding an oxygen convulsion:

n The diver is unable to carry on any effective breathing during the convulsion.

n After the diver is brought to the surface, there will be a period of unconscious- ness or neurologic impairment following the convulsion; these symptoms are indistinguishable from those of arterial gas embolism.

n No attempt should be made to insert any object between the clenched teeth of a convulsing diver. Although a convulsive diver may suffer a lacerated tongue, this trauma is preferable to the trauma that may be caused during the insertion of a foreign object. In addition, the person providing first aid may incur signif- icant hand injury if bitten by the convulsing diver.

n There may be no warning of an impending convulsion to provide the diver the opportunity to return to the surface. Therefore, buddy lines are essential to safe closed-circuit mixed gas diving.

17-11 .1 .3 Treatment of Non-Convulsive Symptoms. If non-convulsive symptoms of CNS oxygen toxicity occur, action must be taken immediately to lower the oxygen partial pressure. Such actions include:

n Ascend. Daltons law will lower the oxygen partial pressure.

n Add diluent to the breathing loop.

n Secure the oxygen cylinder if oxygen addition is uncontrolled.

Though an ascent from depth will lower the partial pressure of oxygen, the diver may still suffer other or worsening symptoms. The divers should notify the Diving Supervisor and terminate the dive.

17-11 .1 .4 Treatment of Underwater Convulsion. The following steps should be taken when treating a convulsing diver:

1. Assume a position behind the convulsing diver. Release the victims weight belt only if progress to the surface is significantly impeded.

2. Do not ascend in the water until the convulsion subsides.

3. Open the victims airway and leave the mouthpiece in his mouth. If it is not in his mouth, do not attempt to replace it; however, ensure that the mouthpiece is switched to the SURFACE POSITION to prevent unnecessary negative buoyancy from a flooded UBA.

4. Grasp the victim around his chest above the UBA or between the UBA and his body. If difficulty is encountered in gaining control of the victim in this manner, the rescuer should use the best method possible to obtain control.

5. 2Ventilate the UBA with diluent to lower the ppO

and maintain depth until the

convulsion subsides.

6. Make a controlled ascent to the first decompression stop, maintaining a slight pressure on the divers chest to assist exhalation.n If the diver regains control, continue with appropriate decompression.n If the diver remains incapacitated, surface at a moderate rate, establish an air- way, and treat for symptomatic omitted decompression as outlined in paragraph 17-10.5.

n Frequent monitoring of the primary and secondary displays as well as the oxy- gen- and diluent-bottle pressure gauges will keep the diver well informed of his breathing gas and rig status.

7. If additional buoyancy is required, activate the victims life jacket. The rescuer should not release his own weight belt or inflate his life jacket.

8. Upon reaching the surface, inflate the victims life jacket if not previouslydone.

9. Remove the victims mouthpiece and switch the valve to SURFACE to prevent the possibility of the rig flooding and weighing down the victim.

10. Signal for emergency pickup.

11. Ensure the victim is breathing. Mouth-to-mouth breathing may be initiated ifnecessary.

12. If an upward excursion occurred during the actual convulsion, transport to the nearest chamber and have the victim evaluated by an individual trained to recog- nize and treat diving-related illness.

17-11 .1 .5Prevention of CNS Oxygen Toxicity. All predive checks must be performed to ensure proper functioning of the oxygen sensors and the oxygen-addition valve.

Frequent monitoring of both the primary and secondary displays will help ensure

2that the proper ppO

is maintained.

17-11 .1 .6 Off-Effect. The off-effect, a hazard associated with CNS oxygen toxicity, may occur several minutes after the diver comes off gas or experiences a reduction of oxygen partial pressure. The off-effect is manifested by the onset or worsening of CNS oxygen toxicity symptoms. Whether this paradoxical effect is truly caused by the reduction in partial pressure or whether the association is coincidental is unknown.

17-11.2 Pulmonary Oxygen Toxicity. Pulmonary oxygen toxicity can result from prolonged exposure to elevated partial pressures of oxygen. This form of oxygen toxicity produces lung irritation with symptoms of chest pain, cough, and pain on inspiration that develop slowly and become increasingly worse as long as the elevated level of oxygen is breathed. Although hyperbaric oxygen may cause serious lung damage, if the oxygen exposure is discontinued before the symptoms become too severe, the symptoms will slowly abate. This form of oxygen toxicity is generally seen during oxygen recompression treatment and saturation diving, and on long, shallow, in-water oxygen exposures.

17-11.3 Oxygen Deficiency (Hypoxia). Hypoxia is an abnormal deficiency of oxygen in the arterial blood in which the partial pressure of oxygen is too low to meet the metabolic needs of the body. Chapter 3 contains an in-depth description of this disorder. Although all cells in the body need oxygen, the initial symptoms of hypoxia are a manifestation of central nervous system dysfunction.

17-11 .3 .1Causes of Hypoxia. The primary cause of hypoxia for a MK16 diver is failure ofthe oxygen addition valve or primary electronics. However, during a rapid ascent

2Daltons law may cause the ppO

to fall faster than can be compensated for by

the oxygen-addition system. If, during ascent, low levels of oxygen are displayed, slow the ascent and add oxygen if necessary. Depletion of the oxygen supply or malfunctioning oxygen sensors can also lead to a hypoxic gas mixture.

17-11 .3 .2 Symptoms of Hypoxia. Hypoxia may have no warning symptoms prior to loss of consciousness. Other symptoms that may appear include confusion, loss of coordination, dizziness, and convulsion. It is important to note that if symptoms of unconsciousness or convulsion occur at the beginning of a closed-circuit dive, hypoxia, not oxygen toxicity, is the most likely cause.

17-11 .3 .3 Treating Hypoxia. If symptoms of hypoxia develop, the diver must take immediate action to raise the oxygen partial pressure. If unconsciousness occurs, the buddy diver should add oxygen to the rig while monitoring the secondary display. If the diver does not require decompression, the buddy diver should bring the afflicted diver to the surface at a moderate rate, remove the mouthpiece or mask, and have him breathe air. If the event was clearly related to hypoxia and the diver recovers fully with normal neurological function shortly after breathing surface air, the diver does not require treatment for arterial gas embolism.

17-11 .3 .4 Treatment of Hypoxic Divers Requiring Decompression. If the divers require decompression, the buddy diver should bring the afflicted diver to the first decompression stop.

n If consciousness is regained, continue with normal decompression.

n If consciousness is not regained, ascend to the surface at a moderate rate (not to exceed 30 fpm), establish an airway, administer 100-percent oxygen, and treat for symptomatic omitted decompression as outlined in paragraph 17-10.5. If possible, immediate assistance from the standby diver should be obtained and the unaffected diver should continue normal decompression.

17-11.4Carbon Dioxide Toxicity (Hypercapnia). Carbon dioxide toxicity, or hypercapnia,is an abnormally high level of carbon dioxide in the blood and body tissues.

17-11 .4 .1 Causes of Hypercapnia. Hypercapnia is generally a result of the failure of the carbon dioxide-absorbent material. The failure may be a result of channeling, flooding or saturation of the absorbent material. Skip breathing or controlled

2ventilation by the diver, which results in an insufficient removal of CO divers body, may also cause hypercapnia.17-11 .4 .2Symptoms of Hypercapnia. Symptoms of hypercapnia are:n Increased breathing rate

from the

n Shortness of breath, sensation of difficult breathing or suffocation (dyspnea)

n Confusion or feeling of euphoria

n Inability to concentrate

n Increased sweating

n Drowsiness

n Headache

n Unconsciousness.

WARNINGHypoxia and hypercapnia may give the diver little or no warning prior to onset of unconsciousness.Symptoms are dependent on the partial pressure of carbon dioxide, which is a function of both the fraction of carbon dioxide and the absolute pressure. Thus, symptoms would be expected to increase as depth increases. The presence of a high partial pressure of oxygen may also reduce the early symptoms of hypercapnia. Elevated levels of carbon dioxide may result in an episode of CNS oxygen toxicity on a normally safe dive profile.

17-11 .4 .3Treating Hypercapnia. If symptoms of hypercapnia develop, the diver should:n Immediately stop work and take several deep breaths.

n Increase ventilation if skip-breathing is a possible cause.

n Ascend. This will reduce the partial pressure of carbon dioxide both in the rigand the lungs.

n If symptoms do not rapidly abate, the diver should abort the dive.

n During ascent, while maintaining a vertical position, the diver should activate his bypass valve, adding fresh gas to his UBA. If the symptoms are a result of canister floodout, an upright position decreases the likelihood that the diver will sustain chemical injury.

n If unconsciousness occurs at depth, the same principles of management forunderwater convulsion as described in paragraph 17-11.1.4 apply.

17-11 .4 .4Prevention of Hypercapnia. To minimize the risk of hypercapnia:n Use only an approved carbon dioxide absorbent in the UBA canister.

n Follow the prescribed canister-filling procedure to ensure that the canister iscorrectly packed with carbon dioxide absorbent.

n Dip test the UBA carefully before the dive. Watch for leaks that may result in canister floodout.

n Do not exceed canister duration limits for the water temperature.

n Ensure that the one-way valves in the supply and exhaust hoses are installedand working properly.

n Swim at a relaxed, comfortable pace.

n Avoid skip-breathing. There is no advantage to this type of breathing in a closed-circuit rig and it may cause elevated blood carbon dioxide levels even with a properly functioning canister.

17-11.5 Chemical Injury. The term chemical injury refers to the introduction of a caustic solution from the carbon dioxide scrubber of the UBA into the upper airway of a diver.17-11 .5 .1 Causes of Chemical Injury. A caustic alkaline solution results when water leaking into the canister comes in contact with the carbon dioxide absorbent. When the diver is in a horizontal or head down position, this solution may travel through the inhalation hose and irritate or injure the upper airway.

17-11 .5 .2 Symptoms of Chemical Injury. Before actually inhaling the caustic solution, the diver may experience labored breathing or headache, which are symptoms of carbon dioxide buildup in the breathing gas. This occurs because an accumulation of the caustic solution in the canister may be impairing carbon dioxide absorption. If the problem is not corrected promptly, the alkaline solution may travel into the breathing hoses and consequently be inhaled or swallowed. Choking, gagging, foul taste, and burning of the mouth and throat may begin immediately. This condition is sometimes referred to as a caustic cocktail. The extent of the injury depends on the amount and distribution of the solution.17-11 .5 .3Management of a Chemical Incident. If the caustic solution enters the mouth,nose, or face mask, the diver must take the following steps:n Immediately assume an upright position in the water.

n Depress the manual diluent bypass valve continuously.

n If the dive is a no-decompression dive, make a controlled ascent to the surface,exhaling through the nose to prevent overpressurization.

n If the dive requires decompression, shift to the EBS or another alternative breathing supply. If it is not possible to complete the planned decompression, surface the diver and treat for omitted decompression as outlined in paragraph 17-10.4.

Using fresh water, rinse the mouth several times. Several mouthfuls should then be swallowed. If only sea water is available, rinse the mouth but do not swallow. Other fluids may be substituted if available, but the use of weak acid solutions (vinegar or lemon juice) is not recommended. Do not attempt to induce vomiting.

A chemical injury may cause the diver to have difficulty breathing properly on ascent. He should be observed for signs of an arterial gas embolism and should be treated if necessary. A victim of a chemical injury should be evaluated by a physi- cian or corpsman as soon as possible. Respiratory distress which may result from the chemical trauma to the air passages requires immediate hospitalization.

17-11 .5 .4 Prevention of Chemical Injury. Chemical injuries are best prevented by the performance of a careful dip test during predive set-up to detect any system leaks. Special attention should also be paid to the position of the mouthpiece rotary valve upon water entry and exit to prevent the entry of water into the breathing loop. Additionally, dive buddies should perform a careful leak check on each other before leaving the surface at the start of a dive.

17-11.6 Decompression Sickness in the Water. Decompression sickness may develop in the water during MK 16 MOD 0 diving. The symptoms of decompression sickness may be joint pain or may be more serious manifestations such as numbness, loss of muscular function, or vertigo.

Managing decompression sickness in the water will be difficult in the best of circumstances. Only general guidance can be presented here. Management deci- sions must be made on site, taking into account all known factors. The advice of a Diving Medical Officer should be sought whenever possible.

17-11 .6 .1Diver Remaining in Water. If the diver signals that he has decompression sicknessbut feels that he can remain in the water:

1. Dispatch the standby diver to assist.2. Have the diver descend to the depth of relief of symptoms in 10-fsw increments, but no deeper than two increments (i.e., 20 fsw).3. Compute a new decompression profile by multiplying all stops by 1.5. If recompression went deeper than the depth of the first stop on the original decompression schedule, use a stop time equal to 1.5 times the first stop in the original decompression schedule for the one or two stops deeper than the original first stop.4. Ascend on the new profile.

5. Lengthen stops as needed to control symptoms.

6. Upon surfacing, transport the diver to the nearest chamber. If he is asymptomatic, treat on Treatment Table 5. If he is symptomatic, treat in accordance with the guidance given in Chapter 20.

17-11 .6 .2Diver Leaving the Water. If the diver signals that he has decompression sicknessbut feels that he cannot remain in the water:

1. Surface the diver at a moderate rate (not to exceed 30 fpm).

2. If a recompression chamber is on site (i.e., within 30 minutes), recompress the diver immediately. Guidance for treatment table selection and use is given in Chapter 20.

3. If a recompression chamber is not on site, follow the management guidancegiven in Volume 5.

17-11.7.Altitude Diving Procedures and Flying After Diving

Ascent to altitude following a MK 16 MOD 0 dive at sea level will increase the risk of decompression sickness if the interval on the surface before ascent is not long enough to permit excess nitrogen or helium to be eliminated from the body. To determine the safe surface interval before ascent, take the following steps:n Nitrogen-Oxygen dives1. Determine the highest repetitive group designator obtained in the previous24-hour period using either Table 17-6 or Table 17-9.

2. Using the highest repetitive group designator, enter Table 9-6 in Chapter 9. Read across the row to the altitude that is exactly equal to or next higher than the planned change in altitude. The required surface interval is given at the intersection of the row and the column.n helium-Oxygen dives1. For no-decompression dives with bottom times less than 2 hours, wait 12hours on the surface before ascending to altitude.

2. For no-decompression dives with bottom times greater than 2 hours or for decompression dives, wait 24 hours on the surface before ascending to altitude.

The MK 16 MOD 0 decompression procedures may be used for diving at altitudes up to 1000 feet without modification. Contact NAVSEA 00C for guidance for any planned dives at altitudes greater than 1000 feet.

17-12MK 16 MOD 0 DIVING EQUIPMENT REFERENCE DATA

Figure 17-6 outlines the capabilities and logistical requirements of the MK 16 MOD 0 UBA mixed-gas diving system. Minimum required equipment for the pool phase of diving conducted at Navy diving schools and MK 16 MOD 0 RDT&E commands may be modified as necessary. Any modification to the minimum required equipment listed herein must be noted in approved lesson training guides or SOPs.

MK 16 MOD 0 UBA GeneralCharacteristicsDisadvantages:1 .Principle of Operation:2 .3 .Self-contained closed-circuit constant ppO2 systemExtended decompression requirement forlong bottom times or deep dives . Limited physical and thermal protection No voice communications (unless FFM used)4 .Extensive predive/postdive proceduresMinimum Equipment:1 .2 .3.4 .5 .6 .7 .An approved Life Preserver or BuoyancyCompensator (BC) . When using an approved BC, a Full Face Mask is required .Dive knifeSwim finsFace mask or full face mask (FFM) Weight belt (as required)Dive watch or Dive Timer/Depth Gauge (DT/DG) (as required)Depth gauge or DT/DG (as required)Restrictions:Working limit 150 feet, air diluent; 200 fsw, HeO2 diluentOperational Considerations:1 .2 .3 .Principal Applications:Dive teamSafety boat(s) requiredMK 16 MOD 0 decompression schedule must be used (unless using NDC, CSMD procedure 110 fsw and shallower, or air decompression procedures 70 fsw and shallower)1 .Special warfare2 .Search and inspection3 .Light repair and recoveryAdvantages:1 .Minimal surface bubbles2.Optimum efficiency of gas supply3 .Portability4 .Excellent mobility5 .Communications (when used with an approved FFM)6 .Modularized assembly7 .Low acoustic signatureFigure 17-6. MK 16 MOD 0 General Characteristics .

Table 17-9. Closed-Circuit Mixed-Gas UBA Decompression Table Using 0 .7 ata Constant Partial Pressure Oxygen in Nitrogen .

DECOMPRESSION STOPS (FSW)Stop times (min) include travel time,except first stop8070605040302010(DESCENT RATE 60 FPMASCENT RATE 30 FPM)

Bottom Time (min)40 FSW

Time to First Stop (M:S)

Total Ascent Time (M:S)

Repet Group

3691:2001:20Z3701:0012:20Z

3801:0023:20Z3901:0034:20Z

50 FSW

1431:4001:40O

1501:2034:40O

1601:2089:40O

1701:201213:40O

1801:201516:40Z

1901:201920:40Z

2001:202223:40Z

2101:202526:40Z

2201:202930:40Z

2301:203334:40Z

2401:203738:40Z

2501:204243:40Z

2601:204546:40Z

2701:204950:40Z

2801:205253:40Z

2901:205657:40Z

3001:205960:40Z

3101:206162:40Z

3201:206465:40Z

3301:206768:40Z

Exceptional Exposure -----------------------------------------------------------------------------------------------------------------

3401:206970:40

3501:207374:40

3601:207778:40

3701:208081:40

3801:208384:40

3901:208788:40

Table 17-9. Closed-Circuit Mixed-Gas UBA Decompression Table Using 0 .7 ata Constant Partial Pressure Oxygen in Nitrogen (Continued) .

DECOMPRESSION STOPS (FSW)Stop times (min) include travel time,except first stop8070605040302010(DESCENT RATE 60 FPMASCENT RATE 30 FPM)

Bottom Time (min)60 FSW

Time to First Stop (M:S)

Total Ascent Time (M:S)

Repet Group

742:0002:00L751:4013:00L

801:4035:00L901:40810:00M

1001:401214:00N1101:401618:00O

1201:402426:00O1301:403234:00O

1401:403840:00Z1501:404446:00Z

1601:405052:00Z1701:405557:00Z

1801:2036064:40Z1901:2086271:40Z

2001:20126578:40Z2101:20156985:40Z

2201:20197191:40Z2301:20227497:40Z

2401:202576102:40Z

2601:203082113:402701:203285118:402801:203588124:402901:204090131:403001:204393137:403101:204794142:403201:205196148:403301:205498153:403401:2057100158:403501:2060102163:403601:2063105169:403701:2065109175:403801:2068112181:403901:2070115186:402501:202780108:40Z

Exceptional Exposure -----------------------------------------------------------------------------------------------------------------

Table 17-9. Closed-Circuit Mixed-Gas UBA Decompression Table Using 0 .7 ata Constant Partial Pressure Oxygen in Nitrogen (Continued) .

DECOMPRESSION STOPS (FSW)Stop times (min) include travel time,except first stop8070605040302010(DESCENT RATE 60 FPMASCENT RATE 30 FPM)

Bottom Time (min)70 FSW

Time to First Stop (M:S)

Total Ascent Time (M:S)

Repet Group

512:2002:20K552:0046:20K

602:00911:20K702:001719:20L

802:002426:20M901:4022933:00N

1001:4073443:00O1101:40123953:00O

1201:40154663:00O1301:40185272:00Z

1401:40215780:00Z1501:40295889:00Z

1601:403662100:00Z1701:404266110:00Z

1801:404870120:00ZExceptional Exposure -----------------------------------------------------------------------------------------------------------------1901:2015373128:40

2001:2025777137:402101:2065781145:40

2201:20105784152:402301:20145987161:40

2401:20186289170:402501:20216691179:40

2601:20246994188:402701:20267297196:40

2801:20297599204:402901:203178102212:40

3001:203381105220:403101:203583110229:40

3201:203786113237:403301:204186118246:40

3401:204586124256:403501:204988127265:40

Table 17-9. Closed-Circuit Mixed-Gas UBA Decompression Table Using 0 .7 ata Constant Partial Pressure Oxygen in Nitrogen (Continued) .

DECOMPRESSION STOPS (FSW)Stop times (min) include travel time,except first stop8070605040302010(DESCENT RATE 60 FPMASCENT RATE 30 FPM)

Bottom Time (min)80 FSW

Time to First Stop (M:S)

Total Ascent Time (M:S)

Repet Group

402:4002:40J452:20810:40K

502:201517:40K552:202123:40L

602:202729:40L702:0092839:20M

802:00172948:20N902:00243662:20O

1001:402294376:00O1101:407295088:00Z

1201:40122957100:00ZExceptional Exposure -----------------------------------------------------------------------------------------------------------------1301:40153758112:00

1401:40184362125:001501:40214967139:00

1601:40235670151:001701:40295775163:00

1801:40365780175:001901:40425785186:00

2001:201486086196:402101:202526490209:40

2201:202576893221:402301:206577396233:40

2401:20105777100245:402501:20145781104257:40

2601:20185685110270:402701:20215986116283:40

2801:20246385124297:402901:20266786129309:40

3001:20297088134322:403101:20317392137334:40

3201:20337695141346:40

Table 17-9. Closed-Circuit Mixed-Gas UBA Decompression Table Using 0 .7 ata Constant Partial Pressure Oxygen in Nitrogen (Continued) .

DECOMPRESSION STOPS (FSW)Stop times (min) include travel time,except first stop8070605040302010(DESCENT RATE 60 FPMASCENT RATE 30 FPM)

Bottom Time (min)90 FSW

Time to First Stop (M:S)

Total Ascent Time (M:S)

Repet Group

323:0003:00J352:4058:00J

402:401417:00K452:402326:00K

502:2032833:40L552:20102840:40L

602:20172847:40M702:20282959:40N

802:0010293475:20O902:0018294493:20Z

Exceptional Exposure -----------------------------------------------------------------------------------------------------------------1002:00252952108:201101:403293356123:00

1201:408294162142:001301:4012294967159:00

1401:4016295673176:001501:4019365776190:00

1601:4021435781204:001701:4023505789221:00

1801:4025566291236:001901:4031576795252:00

100 FSW

273:2003:20I

303:0069:20J

353:001821:20J

403:002831:20K

452:40102841:00L

502:40192850:00M

552:40272959:00M

602:207282865:40N

652:2014282872:40O

Exceptional Exposure -----------------------------------------------------------------------------------------------------------------

702:2020283282:40

752:2026283793:40

802:003282942104:20

902:0012292853124:20

1002:0020293461146:20

1102:0027284466167:20

Table 17-9. Closed-Circuit Mixed-Gas UBA Decompression Table Using 0 .7 ata Constant Partial Pressure Oxygen in Nitrogen (Continued) .

DECOMPRESSION STOPS (FSW)Stop times (min) include travel time,except first stop8070605040302010(DESCENT RATE 60 FPMASCENT RATE 30 FPM)

Bottom Time (min)110 FSW

Time to First Stop (M:S)

Total Ascent Time (M:S)

Repet Group

233:4003:40I253:2047:40J

303:201821:40J353:0032834:20K

403:00142946:20L453:00252957:20L

502:407292867:00M552:4016292876:00N

Exceptional Exposure -----------------------------------------------------------------------------------------------------------------602:4025282985:00652:20429283396:40

702:2011292840110:40802:2024282952135:40

902:00629283465164:20

120 FSW

204:0004:00I253:401418:00J

303:2032733:40J353:20152947:40K

403:004252860:20L453:0012292872:20M

Exceptional Exposure -----------------------------------------------------------------------------------------------------------------502:40123282883:00552:40529282994:00

602:4015282835109:00702:20328292850140:40

802:201728293168175:40

Table 17-9. Closed-Circuit Mixed-Gas UBA Decompression Table Using 0 .7 ata Constant Partial Pressure Oxygen in Nitrogen (Continued) .

DECOMPRESSION STOPS (FSW)Stop times (min) include travel time,except first stop8070605040302010(DESCENT RATE 60 FPMASCENT RATE 30 FPM)

Bottom Time (min)130 FSW

Time to First Stop (M:S)

Total Ascent Time (M:S)

Repet Group

164:2004:20H204:0059:20I

253:4042028:00J303:202112844:40K

353:207212960:40LExceptional Exposure -----------------------------------------------------------------------------------------------------------------403:00114282874:20

453:00721282988:20503:0012282829100:20

552:40320282934117:00602:40726282943136:00

702:402328282967178:00

140 FSW

144:4004:40H154:2015:40H

204:0031118:20J253:40372438:00K

303:2017172856:40LExceptional Exposure -----------------------------------------------------------------------------------------------------------------353:20413242973:40

403:201118282888:40453:00414252928103:20

503:001018282935123:20602:4051