ISC Product and Projects Experience

ISC Megladon CCR Build Quality & Design Considerations

By Leon Scamahorn

May 2007 updated August 21, 2010

The ISC Megalodon CCR or more fondly called “The Meg” is a CCR system that has been embraced by divers of all skill levels around the world. Meg divers dive from 60fsw to over 742 fsw/225 msw. With its versatility of design, it can be configured to meet any level of diving and keep pace with the “Meg divers” skill levels.

Fundamentally the Meg was designed for the most demanding dives with consideration for the diver and their needs. Addressing not only the basic requirements of performance that a true 3rd party tested CCR must undergo, but also the other considerations that is not considered, such as travel concerns and conducting repairs in remote locations.

The design of the Meg meets fundamental design requirements established by the creator Leon Scamahorn, Founder and CEO of InnerSpace Systems Corp, in the USA. InnerSpace Systems is an ISO 9001:2008 registered company and the only one like it in the USA at this time. ISC is a custom CCR manufacturing company that designs systems to meet customer requirements.

To understand the Meg the reader must understand what a well designed CCR should be able to do and we can start with design considerations:

Robustness:

CCR construction consideration for the Meg was that the unit should feel like a piece of military hardware and that the customer can use it without fear of a failure under serious conditions and with minimal maintenance other than the “Pre-Dive Check List” that Meg users are trained to use. The unit should not feel like a toy that the user must baby and fear damaging something that will keep them out of the water especially on a dive trip.

Redundancy:

The Meg electronics supports 2 truly independent electronic oxygen monitoring systems with 2 independent displays telling the diver what they are breathing at all times. A failure of one system will not affect the other as there is no commonality between the 2 systems; this includes the operation of the automatic oxygen injection system. The system brain operates the oxygen injection system independent of the primary display, but the primary display adjusts set points and indicates PO2 and system status for the system brain. The secondary offers only monitoring and the diver’s heads up display (HUD). Each system has its own voting logic for oxygen cell monitoring. The brains of the oxygen injection, primary display and the secondary monitoring system is protected in a soft potted machined enclosure and further protected inside a ¼ inch thick 6061 T-6 anodized aluminum housing and they are independent from the handsets that only display the data to the diver. The brains of the system being isolated from the two displays protects it from failure as the Meg’s electronics can have both displays flood and the oxygen injection system will not be effected nor will the HUD as it will still operate offering the diver all 3 oxygen cell data. ISC does not believe the CCR systems controllers should be in the handsets as this does not provide adequate electronic system redundancy. The electronics system also can display full time to the diver the electrical output of the oxygen sensors, showing real time data to the diver and the diver can actually dive the system that way instead of the displayed PO2. This method does not require system calibration like the displayed PO2 on the displays. The voting logic is another unique system that each redundant electronic system shares. A sensor or sensors can be voted out if outside parameters. The system can actually maintain the oxygen set point off of one good sensor and this is confirmed by the diver using the displayed millivolt (mV) output on the system monitor page on both handsets. The advanced design of the APECS platform allows for customization of the electronics to meet the customer’s needs such as the APECS electronic cards can be swapped to different sides if the diver wants to have the primary display on the right wrist. With that being the simplest modification, the most extreme is to have two independent solenoids operated by two independent oxygen injection systems and displays. The diver can have the ultimate system. The APECS even allows for ISC approved dive computers to be added to the system for onboard decompression monitoring. Other systems such as the manual oxygen injection and diluent injections systems are either lung demand or physical push button and they may be used by the diver at anytime to over ride the electronics if a too high or too low oxygen condition exists. Other gases may be used or plugged into the breathing loop if the diver runs out of primary gases.

Reliability:

CCR systems can be subjected to very demanding conditions in the field and by the diver. This takes the best of materials to withstand punishment dished out by the conditions. The materials that the Meg uses is a 6060 T-6 anodized aluminum the same material that aluminum SCUBA cylinders are made from and the plastic the Meg uses is machined copolymer acetyl. All materials are not just provided by just any provider but called out on the specs for the building of the Meg and only the best materials are used. The diver does not wish to have their CCR system “fall apart” underwater or during a vacation thus costing them their trip and fun. The CCR you dive should be tough enough to be used in a reasonable fashion with moments of high demand, and availability of high levels of care for the unit is not an option at this time. You also want the unit to perform consistently the same as if it was new out of the box years later other than the regular wear and tear of solid use.

Recoverability:

The CCR diver has many issues to address during a dive and one of the worse is a system flood that would contribute to a “Caustic Cocktail” to the diver. This event must be avoided with systems in place to protect the diver from this major event. The Meg has many water trapping and water and gas expelling design features. The first one is water expulsion from the exhaust side counter lung. If the diver loses their Dive/Surface Valve (DSV) from their mouth then water will move to the exhaust counter lung and the Meg diver can expel the water from the exhalation counter lung thus preventing water from moving to the scrubber canister area. The Meg also has a water trap inside the gas plenum canister that houses the CO2 scrubber canister and traps water from moving to the diver. The breathing hose assembly also has two water traps that move the water from any point in the loop to the counter lungs thus insuring the diver does not breathe in a caustic mix. The Oxygen sensors are also between the diver and scrubber canister, this allows the O2 sensors to act like a water sensor if a caustic solution is moving to the inhale side of the breathing loop giving the diver a early detection to transition off of the breathing loop and on to a alternate breathing system (ABS). The Meg may also be fitted with a water tolerant CO2 canister that will prevent any water touching the CO2 absorbent material at all. This is a bit of overkill as the breathing loop design will itself protect the diver and give an obvious indication of potential flood giving the diver time to bail out to another system. CCR systems that do not have an over the shoulder counter lung design or do not have adequate water trapping or water expulsion system are prone to give the diver a caustic cocktail with little or no warning.

Regulation:

A rebreather sold in Europe must fall into the EN 14143 standard. As of yet, the Meg is not rated, but ISC is expected to have the Meg rated by the end of the 2010. CCR systems must be held up to a standard and EN 14143:2003 or the new 14143:2010, is a place to start and promotes quality of the CCR system, the other standard or “guidelines is the U.S. Navy 01-94 Unmanned test methods in which the Meg has successfully passed and beat the U.S. Navy MK-16 in performance. The Meg even passed tests that are not yet written. The Megs performance was so good that 01-94 will be rewritten. The Megalodon and the APECS 2.5/2.7 has been 3rd party tested by the U.S. Navy, the HSE lab, ANSTI, and Dive lab. No other rebreather manufacturer can say that.

Repair:

The Meg is designed to be easily repaired by not only the factory but by the customer that has been trained by ISC to do all major repairs. ISC provides the opportunity for all customers to participate in the training an actually build their own Meg and demystify the CCR itself. Major film crews use the Meg as they can repair the unit on the spot if it was damaged during an action shoot. The Meg component design lets you replace components without having to ship it back to the factory or be charged for a major overhaul or replacement of the electronics head assembly as other designs allow, for something simple such as a failed solenoid that may be potted and unreachable for replacement. In the event of a major repair of the Meg, ISC has repair techs in Europe and Asia that can repair and test the system as if it was sent back to ISC.

Remote travel:

The Meg packs easily into the overhead so the diver may carry the Meg with them and observe the inspection agent scrutinizing the Meg if necessary, this is better than having an agent look at it and damage the unit before it goes under the airplane. The Meg may also use any size cylinders and you may use any size that you want at your dive destination or you may plumb into your out board cylinders instead of using two back mounted cylinders.

Product Improvement:

ISC applies the same design considerations into all of its products to give the diver the best buy for the money with extremely high quality. ISC wants all of our customers to enjoy all our CCR systems. All ISC systems are upgradable to the latest electronics and other new subsystems as ISC product improvement develops.

Survivability:

Taking the above design into account an example of complete systematic failures induced by number unrealistic fictional factors, the reader can understand what the Meg/APECS system can do in such a extreme situation. The Meg can have the following failures and the diver can complete the dive mission without harm.

The situation is a diver is at 330 fsw/100 msw at a water temperature of 28°F/-2.22°C on a saturation dive using a 8lb/3.62kg radial scrubber and he has used 3 of the 5 hours with two remaining. His work effort is equivalent to a 1.35 lpm Co2 Combat swim pace.

• Primary and automatic injection system failure. Diver can inject oxygen manually.
• Flooded Secondary handset, secondary battery below 4.8 volts. HUD is operational displaying single operating sensor and alarming on the two bad sensors.
• Two oxygen sensor failures, but one sensor is still operational. Set point can still be maintained.
• Leaking KOH from sensors into exhaust side of breathing loop not inhales side.
• 1/3rd of exhale counter lung was removed leading to a partial breathing loop flood, but loop is still functional as is scrubber. No fear of caustic cocktail due to water traps.
• Loss of onboard gases. Diver plugs into external sources.
• Loss of ADV and isolator.

Looking at the Meg and its design, the Meg diver may use a variety of subsystems that will meet their needs for a desired dive. The Meg may be used with a variety of CO2 scrubber systems, cylinders, back plates, BC’s, and harnesses. The diver may also elect to buy the Meg from ISC under a variety of configurations and save themselves’ money if they already own various components. The Meg is a diver’s diver rebreather and it truly sets the standard for quality and functionality in the diver’s kit.

Advanced Personnel Environmental Controller System (APECS™)

The APECS™ family of electronics is used to support ISC closed circuit rebreathing systems. The APECS™ has been in the field for 10 years and is FCC approved and tested the stringent EN 61000 standard. The APECS™ system is designed to be used in a variety of roles to fit the operational needs of the customer. The APECS™ system is used in some of the most challenging places on Earth, with cave exploration at the top of the list. Cave divers using the APECS™ system to explore over 2 miles/3.2km through the earth and as deep as 700ffw/212mfw for hours at a time depend on the proven system with their lives, as the option of a safe and fast exit is not possible if a critical failure of the electronics is experienced. Other diving operations that the APECS™ are designed to operate in are: saturation operations, scientific, military, recreational, and other roles relating to deeper exploration diving. The APECS electronics has been tested to extreme temperatures down to 28° F/-2.22° C and the set point maintained perfectly at tested depths deeper than 330fsw/100 msw. APECS™ electronics provide the operational user the flexibility of conducting a greater operational role from one package, thus decreasing operational costs and inventory. Please see attachments for feature list and operational description.

APECS™ System Design Description

The Meg electronics supports 2 truly independent electronic oxygen monitoring systems with 2 independent displays telling the diver what they are breathing at all times. A failure of one system will not affect the other as there is no commonality between the 2 systems; this includes the operation of the automatic oxygen injection system. The system brain operates the oxygen injection system independent of the primary display, but the primary display adjusts set points and indicates PO2 and system status for the system brain. The secondary offers only monitoring and the diver’s heads up display (HUD). Each system has its own voting logic for oxygen cell monitoring. The brains of the oxygen injection, primary display and the secondary monitoring system is protected in a soft potted machined enclosure and further protected inside a ¼ inch thick 6061 T-6 anodized aluminum housing and they are independent from the handsets that only display the data to the diver. The brains of the system being isolated from the two displays protects it from failure as the Meg’s electronics can have both displays flood and the oxygen injection system will not be effected nor will the HUD as it will still operate offering the diver all 3 oxygen cell data. ISC does not believe the CCR systems controllers should be in the handsets as this does not provide adequate electronic system redundancy. The electronics system also can display full time to the diver the electrical output of the oxygen sensors, showing real time data to the diver and the diver can actually dive the system that way instead of the displayed PO2. This method does not require system calibration like the displayed PO2 on the displays. The voting logic is another unique system that each redundant electronic system shares. A sensor or sensors can be voted out if outside parameters. The system can actually maintain the oxygen set point off of one good sensor and this is confirmed by the diver using the displayed millivolt (mV) output on the system monitor page on both handsets. The advanced design of the APECS platform allows for customization of the electronics to meet the customer’s needs such as the APECS electronic cards can be swapped to different sides if the diver wants to have the primary display on the right wrist. With that being the simplest modification, the most extreme is to have two independent solenoids operated by two independent oxygen injection systems and displays. The diver can have the ultimate system. The APECS even allows for ISC approved dive computers to be added to the system for onboard decompression monitoring. Other systems such as the manual oxygen injection and diluent injections systems are either lung demand or physical push button and they may be used by the diver at anytime to over ride the electronics if a too high or too low oxygen condition exists.

Each system has its own remote power supply with its own power switch that cannot be turned off during the dive operation. The primary and secondary being independent are also designed with a disparity in power requirements from each other. The primary system has duration of over 70 hours if the solenoid was continuously injecting. The primary system will indicate a low power to the diver and keep driving the oxygen injector. If the diver ignores the alarm and power indicator for another 10 hours then the handset may blink on and off during the injection cycle and the diver can still see his displayed information and the O2 injector will still inject. The unit if still ignored, again for 10 hours will have the display fade out forcing the diver to observe the HUD or the secondary system. Oxygen will at some point not be injected when the battery has reached its threshold.

The secondary can last for over 200 hours as it does not drive any injection system but only displays the oxygen data and drives the HUD. This convention follows the methodology of the MK-16 eCCR system used by modern militaries.

The above system can use 3 different power supplies; 5 alkaline AA wired in series. A nine volt battery with an adapter plug for the connector, or two lithium C cells wired in series. Each battery has its own low battery characteristics and must be monitored appropriately.

ISC Failure mode list for ISC Megalodon CCR systems

FMCA list

6 April 2009

Updated 14 October 09

Note: Preventive action is something you are trying to prevent from happening, Corrective action is an action taken after the event has taken place. Corrective action may also be used as an action taken to keep something from happening again such as a design change or training change. Taken from ISC ISO CAPA processes.

Time of exposure, swimming position, and where the failure occurs will determine the specific severity, and detection, but not occurrence. This will also determine if it is recoverable, or non-recoverable.

This FMECA list assumes that the reader understands the fundamentals of CCR diving and mixed gas diving to include open circuit scuba systems. This is also to include fundamentals of scuba diving. The reader will see that all failures are obvious to users other than the early detection of the 3 H’s, hypoxia, hyperoxia, and hypercapnia or unknown manifestations effecting judgment. The diver should do everything possible to avoid all categories of failures by acting with due diligence, high attention to detail and a prevention mindset.

Abnormal manifestations of physical and/or emotional changes other than considered normal:

During the dive, while on the breathing loop the diver experiences a physical or emotional manifestation other than what was considered normal on the surface before the dive. Panic is also included as an extreme case, or anything that will affect the diver’s judgment. Mechanical failure is excluded.

Severity: High to low
Detection: High to low

• Mandatory preventive action: See mandatory preventive action for Hypercapnia, Hyperoxia, and Hypoxia. Condition may also be from physical or emotional issues, in this case the diver is responsible for insuring that they are fit for diving by regular annual physicals by a Dive doctor, and stress tests for cardiovascular health. Mental health should also be evaluated and the diver should not dive if under any unreasonable undue stress in any form. All medications should be cleared for diving use before exposure to activity.
• Mandatory corrective action: Diver switches to high performance Alternate Breathing Source (ABS) with appropriate breathing gas and volume. Alternate breathing source transition should be less than 3 seconds from start of removing breathing loop to inhaling first breath on ABS. If first breath is longer than 3 seconds and less than 5 seconds then Open loop diluent flush(Crush and Flush) is preferred method and then open loop while searching for ABS.

Preferred order of bailout

Preferred order of bailout options from the compromised breathing loop is determined by time from start of removing breathing loop to inhalation of first breath off of ABS. It is assumed that the ABS has adequate gas volume and breathing mix appropriate for the depth. Secondary ABS must be in place for other gas changes at shallower depths if dive plan and conditions warrant. It is also assumed that the diver uses ABS that has been 3rds party lab tested in a breathing simulator and shown to work as designed, and meets the minimal work of breathing as per the U.S. Navy performance guidelines or the EN 250 standard.

The Bail Out Valve (BOV) and all second stages used as an ABS must be purged before inhalation. This is to insure breathing gas flow before the divers inhales on the ABS. The BOV must be purged of water inside the 2nd stage chamber before the diver inhales. This is especially true of an unconscious diver rescue. The rescuer will flood the unconscious diver’s oral cavity drowning the diver.

Options:

• Bailout valve: Less than 1 second for diver/dive companion to activate. Diver must ensure that BOV is connected to adequate breathing gas volume connector that passes 200 liters/min breathing gas, another second stage on a 7ft/2 meter hose with bolt snap and is properly stowed as to not entangle or hose lock making removal for the just in time use impossible. This second stage is for another diver in an out of breathing gas emergency.
• Second stage just below chin on retaining collar: 1 to 3 seconds. The diver’s second stage is connected to adequate breathing gas and volume and has another second stage on a 7ft/2 meter hose with a bolt snap and is properly stowed as to not entangle or hose lock making removal for just in time use impossible. Dive companion cannot activate on unconscious diver.
• Open loop diluent flush(Crush and Flush): 3 to 5 seconds.(Nose breathing off of loop while evacuating loop gas from nose through mask and vent valve using breathable diluent at depth to flood breathing loop with a breathable gas source quickly). NOTE: Technique is taught as a universal means of self-rescue. The technique shares commonality with other emergency counter measures such as dewatering from a flood, open loop breathing, gas switching, purging the loop, or diluent flush. The method also requires non-removal of the DSV and may be used to save another unconscious diver who still has the DSV retained in the mouth.
• Second stage on bailout cylinder: Properly secured and easy for quick removal. Location of second stage must be known at all times by the diver and dive companions. Second stage must me on a 7ft/2 meter hose with a bolt snap and is properly stowed as to not entangle or hose lock making removal for just in time use impossible. Dive companion cannot activate on unconscious diver.

Hypercapnia:

Severity: high
Detection: low to moderate

Diver induced anomalies or unauthorized modifications, CO2 scrubber canister duration exceeded, poorly packed CO2 canister, settling of sorb due to travel or handling, unapproved CO2 absorbent use, CO2 canister duration not tested and design exceeded clogged screens in CO2 scrubber canister, or pores of CO2 canister hydrophobic membrane clogged, no CO2 absorbent in breathing loop, wet CO2 absorbent, CO2 absorbent poorly manufactured, poor storage of absorbent or CO2 canister, work load exceeds canister design, cold adding to premature failure, canister used and then dumped for storage and repacked for use again, Co2 bypass from the following: Check valve failure, O-rings not present or adequate for use, loose or missing sensors in sensor carriage, broken sensor into sensor carriage. Failure to install/correct scrubber support. Installations of the wrong sized scrubber canister, incorrect installation of sensor carriage, incorrect installation of DSV check valves. Check valve folded over, check valve missing. Cartridge physically damaged or under packed promoting bypass. Breathing restriction on breathing loop from the following: DSV lever not all the way open, Breathing loop physically to small for diver, breathing loop volume inadequate by design, hydrostatic lung loading exceeded, gross change of counter lung position, pinched or twisted breathing hoses, breathing loop reversed water in breathing loop impeding breathing gas flow, breathing loop restricted, to fast of decent reducing and restricting breathing volume, Bail out second stage low performance by failure of design, detuned second stage, first stage I.P. inadequate, Mouth piece oral cavity too small, mouth piece teeth surfaces too thin impeding breathing gas flow, Full face mask or helmet does not use a mouth piece. Rebreathing exhaled breathing gas from to large pocket mask or oral tube. Full face mask or helmet acts as pliable gas volume counter lung, inadequate gas exchange in diver’s body do to physiological failures.

Preventive action for the following hypercapnia issues:CO2 canister and scrubber.

CO2 scrubber canister duration exceeded, poorly packed CO2 canister, settling of sorb due to travel or handling, unapproved CO2 absorbent use, CO2 canister duration not tested and design exceeded clogged screens in CO2 scrubber canister, or pores of CO2 canister hydrophobic membrane clogged, no CO2 absorbent in breathing loop, wet CO2 absorbent, CO2 absorbent poorly manufactured, poor storage of absorbent or CO2 canister, work load exceeds canister design, cold adding to premature failure, canister used and then dumped for storage and repacked for use again.

• Mandatory preventive action: Do everything possible to avoid the above. Follow Pre-dive check sheet, pre-breath sequence before entering water, diving manual, and training from authorized and current instructor and training agency. Contact manufacturer if in doubt of proper operation.
• Mandatory corrective action: Self-rescue may not be possible due to the immediate exposure to elevated levels to CO2. Bailout sequence and plan initiated on U.S. Navy/EN-250 approved high performance O/C system with adequate breathing gas and volume.

Preventive action for the following hypercapnia issues:

C02 bypass from the following: Check valve failure, O-rings not present or adequate for use, loose or missing sensors in sensor carriage, broken sensor into sensor carriage. Failure to install/correct scrubber support. Installation of the wrong sized scrubber canister, incorrect installation of sensor carriage, incorrect installation of DSV check valves. Check valve folded over, check valve missing. Cartridge physically damaged promoting bypass.

• Mandatory preventive action: Do everything possible to avoid the above. Follow Pre-dive check sheet, pre-breath sequence before entering water, diving manual, and training from authorized and current instructor and training agency. Contact manufacturer if in doubt of proper operation.
• Mandatory corrective action: Self-rescue may not be possible due to the immediate exposure to elevated levels to CO2. Bailout sequence and plan initiated on U.S. Navy performance guidelines or meet EN-250 high performance O/C system with adequate breathing gas and volume.

Preventive action for the following issues:

Breathing restriction on breathing loop from the following: DSV lever not all the way open, Breathing loop physically to small for diver, breathing loop volume inadequate, hydrostatic lung loading exceeded, gross change of counter lung position, pinched or twisted breathing hoses, breathing loop reversed water in breathing loop impeding breathing gas flow, breathing loop restricted, to fast of decent reducing and restricting breathing volume, Bail out second stage low performance by failure of design, detuned second stage, first stage I.P. inadequate, Mouth piece oral cavity too small, mouth piece teeth surfaces too thin impeding breathing gas flow, Full face mask or helmet does not use a mouth piece. The rebreathing of exhaled breathing gas from to large pocket mask or oral tube, full face mask or helmet acts as pliable volume (counter lung), inadequate gas exchange in diver’s body do to physiological failures.

• Mandatory preventive action: Do everything possible to avoid the above. Follow Pre-dive check sheet, pre-breath sequence before entering water, CCR operational manual, and training from authorized, current and approved ISC instructor and training agency. Diver must buy product based off of a proven performance standard and design not price. Diver has dive physical once a year along with stress test. Diver pays attention to changes in static lung loading, by watching for activation of ADV and vent valve activations on breathing cycle. Diver should also pay attention to negative mechanical resistance on inhalation indicating reduced breathing loop capacity or high resistive lung effort. Contact manufacture if in doubt of proper operation.
• Mandatory corrective action: Self-rescue may not be possible due to the immediate exposure to elevated levels to CO2. Bailout sequence and plan initiated on U.S. Navy class A/EN-250 approved high performance O/C system with adequate breathing gas and volume.

Hyperoxia:

Severity: high
Detection: low to high

Diver induced anomalies or unauthorized modifications, non aware of displays 1-4 min rule, exceeded CNS limits to high for too long. Too fast of a decent spiking O2 for too long, Sensor millivolt limited, sensor failure, moisture on sensors, procedural failure of calibration. Calibrate with wrong O2% making electronics believe 100%, wrong O2 % setting, wrong altitude setting, free flow of oxygen in breathing loop by solenoid, or manual bypasses. The IP is too high for leaky O2 valve thus spiking O2 in loop. O2 leaking into breathing loop via loose Swagelok fittings. Breathing too high of PO2 through manual oxygen bypass usage by injecting too much at one time or incrementally to close together, Oxygen cylinder installed on diluent side feeding into ADV, to rich of O2 in diluent cylinder. Mixed gas bypass used for oxygen bypass, O2 rich open circuit bailout gas for too deep of depth, Diver lets O2 build up in loop by not breathing and solenoid keeps injecting. Breathing on O2 rich open circuit bailout is too deep and for too long, loss of diluent to dilute oxygen relative to depth.

• Mandatory preventive action: Do everything possible to avoid the above. Follow Pre-dive check sheet, pre-breath sequence before entering water, diving manual, and training from authorized and current instructor and training agency. Contact manufacture if in doubt of proper operation.
• Mandatory corrective action: Self-rescue may not be possible, due to the exposure to elevated levels to O2 which leads diver to unconsciousness. Diver drops elevated PO2 level by flooding loop with diluent until PO2 levels have dropped to acceptable at or below set point and/or Bailout sequence and plan initiated via U.S. Navy class A/EN-250 approved high performance O/C system with adequate breathing gas volumes.

Hypoxia:

Severity: high
Detection: low

Diver induced anomalies or unauthorized modifications, non aware of displays 1-4 min rule, exceeded metabolic requirements too low for to long, failure to add oxygen via bypass valve, O2 valve off, O2 feed not engaged, solenoid failed in closed positioned, sensor failure, moisture on sensors, procedural failure of calibration, calibrate with wrong O2 % making electronics believe 100%, Wrong altitude setting, wrong O2% setting for calibration, Free flow of hypoxic dil into loop at too shallow of depth. Manual addition of hypoxic mix on surface or too shallow of depth through ADV or mixed gas bypass, manual addition of hypoxic mix using O2 bypass for mixed gas bypass to shallow of depth. Wrong cylinder (diluent) feeding into solenoid or O2 bypass during ascents, Wrong gas in diluent cylinder, no O2 in cylinder, no O2 cylinder, Manual bypass valve not functioning. Breathing off of bail out valve (BOV) on hypoxic mix at surface to shallow of depth, blocked filter on first stage, I.P. too low for solenoid injection or leaky valve. Too fast ascent for injection system especially if the breathing loop PO2 is too low at depth. Breathing on open circuit bailout using hypoxic mixes or wrong mix too shallow for too long.

• Mandatory preventive action: Do everything possible to avoid the above. Follow Pre-dive check sheet, pre-breath sequence before entering water, diving manual, and training from authorized and current instructor and training agency. Contact manufacturer if in doubt of proper operation.
• Mandatory corrective action: Self-rescue may not be possible due to the immediate exposure to reduced levels of oxygen. Bailout sequence and plan initiated on U.S. Navy/EN-250 approved O/C system with adequate breathing gas and volume.

Breathing loop negative lung volume:

Severity: low to high
Detection: high

Diver not correcting breathing volume during descents, diver descending to fast, diver not halting decent, ADV not adding gas when appropriate or fast enough, O2 bypass not adding gas or enough gas when appropriate, mixed gas bypass not adding gas when appropriate or fast enough, solenoid not adding gas when appropriate, positional axis of breathing loop in water column inducing negative lung loading. Breathing loop too small, breathing loop volume restricted, loss of breathing volume from flood, vent valve left on during descents, too much gas volume vented through vent valve, hose or mouth at any point of dive. Diver running out of diluent gas.

• Mandatory preventive action: Do everything possible to avoid the above. Follow Pre-dive check sheet, 5 min. pre-breath sequence before entering water, diving manual, and training from authorized and current instructor and training agency. Diver must buy product based off of a proven performance standard and design not price. Diver has dive physical once a year along with stress test. Diver pays attention to changes in static lung loading, by watching for activation of ADV and vent valve activations on breathing cycle. Diver should also pay attention to negative mechanical resistance on inhalation indicating reduced breathing loop capacity or high resistive lung effort. Contact manufacture if in doubt of proper operation.
• Mandatory corrective action: Add diluent immediately if deeper than minimum operating depth. If in doubt; bailout sequence and plan initiated U.S. Navy/EN-250 approved O/C system with adequate breathing gas volumes.

Note: The time period of the loss of the breathing loop integrity and where the loss of integrity was, determines the severity, and detection.

Flooding or partial flooding of exhaust side of the breathing loop (Recoverable).

Severity: low
Detection: high

Loose lips on DSV, loose mouth piece on DSV due to compromised cable tie, hole in mouth piece, loss of DSV out of mouth, DSV lever not closed or fully closed and leaking water into loop, loosened counter lung couplings on exhaust counter lung, leaking vent valve, large leak in exhaust counter lung, damaged mixed gas bypass valve nut that does not lock down bypass valves, damaged of forward exhaust side breathing hose, threaded coupling on ADV not tightened down, missing or damaged O-rings on ADV.

• Preventive action: Exercise use of pre-dive sheet and scheduled maintenance to ID mechanical issues and proper diving habits to avoid water in breathing loop.
• Corrective action: Gurgling accompanied by high resistive work of breathing in exhale side of breathing loop, the diver must be aware of flooding of the entire breathing loop. Diver will taste compromised CO2 absorbent and O2 sensors will indicate flooding of the inhalation side of breathing loop. Diver is to abort off of breathing loop onto ABS and surface.

Inhalation side breathing hose failure non-recoverable

Right side breathing hose failure, torn inhalation counter lung, O2 manual bypass nut failure, loosened counter lung couplings, separated breathing hose connectors from threaded fittings, threaded fitting on tee coupling not tightened down

• Preventive action: Exercise use of pre-dive sheet and scheduled maintenance to ID mechanical issues and proper diving habits to avoid water in breathing loop.
• Corrective action: Gurgling accompanied by high resistive work of breathing in exhale side of breathing loop, the diver must be aware of flooding of the entire breathing loop. Diver will taste compromised CO2 absorbent and O2 sensors will indicate flooding of the inhalation side of breathing loop. Diver is to abort off of breathing loop onto ABS and surface.

Total loop failure by flooding, Non recoverable:

Severity: high
Detection: high

Loss of breathing hose from mouth and no recovery action, breathing hose failure, threaded couplings not being tightened down, loose hose clamps, torn counter lungs, pulled out couplings from counter lung, Missing or damaged O-rings in breathing loop. Failure of primary diaphragm on diaphragm style ADV.

• Preventive action: Exercise use of pre-dive sheet and scheduled maintenance to ID mechanical issues and proper diving habits to avoid water in breathing loop.
• Corrective action: Gurgling accompanied by high resistive work of breathing in exhale side of breathing loop, the diver must be aware of flooding of the entire breathing loop. Diver will taste compromised CO2 absorbent and O2 sensors will indicate flooding of the inhalation side of breathing loop. Diver is to abort off of breathing loop onto ABS and surface.

Caustic cocktail:

Severity: high
Detection: high

Flooding of gas plenum canister and scrubber system due to loss of breathing loop integrity. Flooding of inhalation side of breathing loop except from aft breathing hose going to diver.

• Preventive action: Exercise use of pre-dive sheet and scheduled maintenance to ID mechanical issues and proper diving habits to avoid water in breathing loop.
• Corrective action: Gurgling accompanied by high resistive work of breathing in exhale side of breathing loop, the diver must be aware of flooding of the entire breathing loop. Diver will taste compromised CO2 absorbent and O2 sensors will indicate flooding of the inhalation side of breathing loop. Diver is to abort off of breathing loop onto ABS and surface.

Sensor failure:
Severity: low
Detection: high
Occurrence: low

Old sensor, sensor premature failure, millivolt limited, failed in the high, moisture on sensors, poor electronic design grounding out sensors or influencing sensors to act unreliably or unpredictably. Sensor acting slow, leaking KOH from sensor, sensor connector damage, connector corrosion, damaged wiring, sensor reading high mV and low displayed PO2.

• Preventive action: Replace sensors every year from date of installation unless sensor is outside the 18 month storage life in original bag then discard and replace with sensor inside the 18 month package date or use recommended use dates by sensor manufacturer.
• Corrective action: Calculate sensors mV in air and annotate on tape on side of handset. Use information to determine sensor real time output. Watch voting logic and see if both independent handsets agree. Bailout to ABS if diver in unsure of what they are breathing in the breathing loop.

Increased WOB:

Severity: moderate to high
Detection: high
Occurrence: low

Exceeding the breathing design and standard of CCR or O/C ABS bailout system, positional attitude in water column for optimum breathing for too long, pinched or collapsed breathing hose, DSV not fully open, inappropriate canister design such as after market, incorrect check valves installed or by design in DSV, excessive exhalation pressure in breathing loop or on ABS second stage due to incorrect exhaust valve or excessive breathing loop pressure, excessive tortuous breathing path in breathing loop. Diver not exhaling from nose.

• Preventive action: Use the CCR within tested parameters. Follow operational manual instructions. Avoid condition.
• Corrective action: Diver experiences excessive exhalation effort diver should vent out nose and/or use vent valve to decrease breathing loop pressure.

Loss of Oxygen from cylinder:

Severity: high
Detection: high
Occurrence: low

First stage failure.

L.P hose/HP hose failure, free flowing bypass or solenoid, Frangible burst disk failure, O-ring failure, Plumbing failure or fittings. First stage failure.

• Preventive action: Perform scheduled maintenance and follow pre dive check sheet. Check IP of first stage.Corrective action: Boom scenario. Shut down both gases unless diver knows what offending gas is leaking and check H.P. gauges and then handset to determine if they have a safe breathing able loop. The diver will open none afflicted valve and also try to feather effected gas valve if possible to maintain a operational PO2. If gas is totally lost the diver will look for other sources of oxygen and plug into the manual bypasses and manually add oxygen. Semi-closed is one option but bad for decompression. Best alternative is to use ABS with planned profile.
  Loss of diluent from cylinder:
  Severity: moderate to high
  Detection: high
  Occurrence: lowLP/HP hose failure, free flowing bypass or ADV, Frangible burst disk failure, O-ring failure, and fittings failure.
  Preventive action: Perform scheduled maintenance and follow pre dive check sheet. Check IP of first stage.Corrective action: Boom scenario. Shut down both gases unless diver knows what offending gas is leaking and check H.P. gauges and then handset to determine if they have a safe breathing able loop. The diver will open none afflicted valve and also try to feather effected gas valve if possible to maintain a operational breathing loop volume. If gas is totally lost the diver will look for other sources of diluent and plug into the manual bypasses and manually add diluent. Diver may breathe off of an alternate breathing source as long as it meets the dive plan and exhale into breathing loop to maintain safe PO2 levels and breathing volume.Electronic failures:
  Severity: High to low
  Detection: high
  Occurrence: lowPrimary battery failure or flood, secondary battery failure or flood, primary display failure or flood, secondary display failure or flood, HUD failure or flood, cable damaged on any display, flooded/ moisture in electronics brain box, system shorts, damaged wiring, dissimilar electronics protection, ESD, EMI, Radiated RF, EMP, damage from unauthorized intrusion into electronics package.Main Electronics failure:
  Electronics board(s) component failure, bad connections with external wiring due to bad solder joints, broken wires due to external causes, solenoid control circuit failure, HUD control failure, internal temperature sensor failure, oxygen sensor operational amplifier failures, container flooding problems causing board failures, and improperly potted containment allowing moisture to short out board circuits. May be confused with battery or battery box failure.Recovery action during dive:
  If flooding of canister occurred and electronics effected, switch to ABS and abort the dive.
  If only one subsystem affected, use alternate subsystem and abort the dive.
  If both subsystems affected, switch to ABS and abort the dive.
  Preventive action:
  Use quality components.
  Factory assembly processes and quality control shall be followed.
  Follow operational manual and pre and post dive check lists.
  Diver observes electronics every 1-4 minutes.
  Corrective action:
  Design for more robust electronics to fully automotive system with two independent solenoids and oxygen supply connectors. Electronics may have operational replaceable components such as handsets and HUD.Handset failure:
  Primary or secondary handset flood failure due to o-ring failure, lens mounting hole stress cracks, case structure cracks originating from threaded fittings or screws, hermetic reed switch failure, weak magnetic push buttons not activating hermetic reed switches, display electronics failure, internal wiring solder joint failure, water temperature sensor component failure, handset cable damage causing shorting by water or cable break resulting in no connection, and electronics protection (ESD, EMI, Radiated RF).Symptoms –
  Display not functioning (appears dead)
  Magnetic switch(es) not functioning
  Water visible through lens indicating flooded handset
  Display affected when near high radiated RF source such as high performance movie lighting causing intermittent, but recoverable, display errors or display failure.
  Detection –
  Visual only
  Preventive action:
  Assembly quality checks on materials used.
  Lens and case construction and quality checks performed before final assembly.
  Proper following of factory assembly process.
  User training on care and maintenance of handset, handset switches, handset cable.
  Keep unit away from high power RF emissions.
  Corrective action:
  Dive observes loss of handset and switches to alternate displayed system and abort dive.
  HUD failure:HUD potting leak failure – seawater entering and shorting the LED, HUD cable damage causing shorting by water or cable break resulting in no connection, bad soldering of leads at LED in HUD or on electronics board (cold solder joints), and failed components on electronics board that drive the HUD. Solder station temperature set to high.
  Symptoms – One or more LED colors not displaying when HUD is enabled. No HUD warning flash sequence when PO2 is too high or too low.
  Detection – Visual only.
  Preventive action:
  Observe power-on HUD diagnostics during power up to insure HUD performs prior to dive.
  Observe HUD performance during dive. If HUD fails, isolate cause, insure HUD is enabled, and use Primary or Secondary Handset for PO2 information.
  Corrective action:
  Factory or authorized service center can repair/replace defective HUD or correct the problem.
  Battery Box failure:Primary or secondary battery box floods due to improperly maintained lid o-ring, magnetic reed switch failure, electronic protection board component(s) failure, bulkhead cable connector failure, solder joints improperly soldered (such as cold solder joints), and battery box structure failure/damage.Causes:
  Structure damage to box, lid, or bulkhead cable connector.
  Battery box or lid component material failures (rare)
  Component failures for reed switch and electronic protection board.
  Battery box lid o-ring seal compromised, then battery box floods if the surrounding unit floods.
  Preventive action:
  Use quality electronic components.
  Quality check on all components before factory assembly.
  User pre-dive checklist properly followed.
  User inspection of head assembly o-rings as part of pre-dive process
  Corrective action:
  Factory or authorized service center can repair/replace defective HUD or correct the problem.
  Battery Low:Cause: Over-use or internal failure.Symptoms: Indicated by low battery visual warning on the handset on affected primary or secondary subsystems or total shutdown on affected display, O2 injection solenoid not functioning when PPO2 is lower than selected set point due to battery voltage below injection solenoid minimum voltage threshold, cannot maintain set point on primary subsystem, HUD no longer blinking due to under voltage. Warning appears any time system measures the battery voltage to be less than 5.2 volts DC.Preventive action:
  Using pre dive checklist, user is required to log the measured voltage as shown by both subsystems display system monitor pages identifies weak batteries and provides stimulus to change batteries before proceeding to dive.
  Display backlight draws the most power on each subsystem. Frequent menu selections during dive operations turn on backlight for 5 second intervals. Reducing the backlight usage will conserve power. Menu option available for disabling the backlight when lighting conditions warrant doing so. Keep backlight option on menu selection uses a lot of power and drains battery faster. This option’s use should be limited to short dives and start with fresh batteries installed.
  Corrective action:
  Design for higher load capacity batteries. Use C-Cell Lithium battery packs for higher milliamp hour capacity.
  Design for alternate power supply, if practical.
  Battery Failure:Caused by over-use or internal failure of battery or battery box protection circuitry.Symptoms – No handset display functionality, menu switches dysfunctional, O2 injection solenoid not firing resulting in not maintaining selected PPO2 on primary subsystem, HUD not functioning on secondary subsystem. Isolate which subsystem has the battery failure by observing and isolating specific subsystem functions.Detection – Handset display no longer displays, diver notices O2 injection by primary ceases by not hearing the injection (if he can hear it at all), diver observes HUD not displaying PO2 when HUD is enabled.Recovery action during dive:
  Rely on the remaining functioning subsystem. If primary battery failed, then diver manually injects O2 for the remainder of the dive, monitoring PPO2 using HUD and/or secondary display. If secondary battery failed, then diver monitors PPO2 using primary display.
  Preventive action:
  Using pre dive checklist, user is required to log the measured voltage as shown by both subsystems display system monitor pages identifies weak batteries before the dive and provides stimulus to change batteries before proceeding to dive.
  Corrective action:
  User change batteries when battery voltage level is too low to dive.
  User follows pre-dive checklist and acts on low batteries by replacing them.
  Design for alternate power source, if practical.
  Power Drop-out or Battery Bounce:

Causes – Poor battery pack assembly of wiring and power connector pins. Power connector pins with loose crimps of pins on wires. Movement of the unit or jarring of the system may provide intermittent power and/or full battery failure.

Symptoms – subsystem display shows frequent restarts and startup screen cyclically redisplaying. HUD or solenoid diagnostics cyclically restarting. Can occur in or out of water.

System restarts retain calibration data, last selected PO2 set point, and most menu options.

Preventive action:
Check for system stability during pre-dive, pre entry into water, and during the dive.
Corrective action:
Use alternate display and abort dive.
Open circuit systems and bail out failures:
Severity: high
Detection: low
Occurrence: high

Breathing gas volume inadequate, breathing gas supply non existent, free flow of second stage, IP incorrect, poor performing O/C system by design (Not class A, inadequate/improper placement of second stage, failure of exhaust diaphragm inducing flooding, failure of primary diaphragm inducing flooding, cut or damaged mouth piece inducing flooding, cable tie on mouth piece inadequate, flooded second stage hose and other LP and HP hoses, flooded first stage, inadequate. HP gauge not calibrated, leaks in HP and LP o- ring fittings from valve to all sub assemblies, breathing hose on second stage not long enough to share gas with another diver, or lack of another second stage to offer to another diver.

Improper training:
Severity: high
Detection low
Occurrence: high

Lack of training induces any of the above on this FMCA list.

Preventive action:
Stress the use of operational training procedures and validate by testing.
Corrective action:
Diver refers to refresher testing by manufacturer or training agency.
Failure to use training and good judgment:
Severity: high
Detection: low
Occurrence: high

Lack of good judgment and proper use of product will induce many problems on this FMCA.

Preventive action:
Stress the use of operational training procedures and validate by testing.
Corrective action:
Diver refers to refresher testing by manufacturer or training agency.
Blow up:

Loss of weight belt and excessive buoyancy, vent valves fails in closed position on Dry suit or CCR, B.C. fails closed, and Diver fails to vent gases from appropriate gas reservoirs fast enough if at all, free flow of ADV, manual bypasses, solenoid, plumbing inside loop to solenoid, dry suit, B.C.

Preventive action:
Follow instructional manual for maintenance and operation. Perform pre dive checks.
Corrective action.
Double buckle weight belt or use non disposable weights or multi positional weights that cannot all be ditched at once by mistake. Vent any excessive gas in closed system early and often before buoyancy gets excessive. Vent gas from valve or use alternate method of gas expulsion such as breathing out your nose for excessive gas in breathing loop. Shut down any free flowing gas immediately and check PO2 on handset if gas was flowing into the breathing loop.
Loss of buoyancy neutral buoyancy to the negative:

Diver is over weighted due to lead weight, flooded dry suit, flooded breathing loop, compression of neoprene dry suit, failure to add gas to the B.C. and or dry suit, inadequate volume in B.C. failure of vent valve in open, damage of separated couplings, torn bladder, torn hose, B.C. inflator fails closed, no gas to inject into buoyancy systems, gas does not inject fast enough, no back up system to primary system.

Preventive action:
Follow operational manual to maintenance and safe operation. Check weighting with breathable loop and do not add any more. Use redundant means for buoyancy control and have multi use connectors for gas addition if loss of primary buoyancy gas. Do not flood any system that contains any gas.
Corrective action:
Dropping primary weights is not an option if dives are staged decompression profiles so use redundant buoyancy system to achieve lift and trim.