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The case for using Gas Blocks by public safety divers

Discussion in 'Public Safety Divers' started by rkinder, Aug 25, 2016.

  1. rkinder

    rkinder Public Safety Diver

    # of Dives: 5,000 - ∞
    Location: Seneca, SC
    41
    44
    18
    I want to start this discussion by looking at the advantages and general features that should be considered when using a gas block.

    In case anyone is not familiar with what a Gas Block is, it is an air manifold that provides the capability of inputting the outputs of 2 or more first stage regulators, and allowing for positive off/on control of at least one of the supply sources while preventing back flow to the other air sources. As an example the inputs would normally be a diver’s Primary Air supply and Emergency Air supply. For the purpose of this discussion the gas block discussed will be the Kirby Morgan style due to several design features that seem to adapt it well to PSD use. I am aware of Omni Swivel as well as others over the years and have used several different models in the past.

    For both teams and agencies that proscribe that the pony bottle must be available for donation to another diver, I do not agree on my primary backup leaving me for another diver, for reasons soon to be revealed.

    1. Each PSD should be equipped with a primary air supply consisting of no less than 20 minutes of usable air with a 15 minute reserve at the operational depth. For the sake of argument an 80 cubic foot tank should suffice for most experienced divers to a depth of 60 feet.

    2. Each PSD should be equipped with a secondary air source providing for 15 minutes of emergency air supply at the operational depth, for most divers this will be a 30 to 40 cubic foot tank to a depth of 60 feet.

    3. Should the diver be using a full face mask that can not be set to free flow in the event of a failure to deliver air such as the EXO-26BR using the dial a breath or a commercial band mask like the KMB-18 or KMB-28 equipped with a free flow valve then the secondary air source must be equipped with a second stage regulator allowing for the diver to bail out of their full face mask.

    4. A gas block should be configured or constructed in a manor that allows air to freely flow from the primary air supply to the divers primary regulator or FFM yet will not allow a back flow or loss of gas back to the primary air source should a hose failure or other loss of gas occur, between the first stage and the gas block. This typically requires the use of a one way valve AKA BACK CHECK.

    5. The secondary air supply (EGS) input to the gas block should be equipped with a multi turn (needle valve) allowing for metering of the (EGS) reserve air supply with the reserve first stage regulator equipped with an over pressure valve or a second stage regulator that will act as an OPV.

    6. At no point should a gas block not allow air flow to the PSD diver, this means that activation of a switch/valve should never fail to supply air flow from the primary gas supply to the diver.

    Pre-dive configuration of the system prior to the start of the dive requires that the reserve (EGS) system be turned on first, air pressure confirmed and that the valve be turned on at the gas block, the diver or tender will breath from the primary regulator or FFM confirming operation and then the EGS valve will then be closed and the Regulator or FFM breathed down or purged, leaving the reserve system turned on at the tank and off at the EGS valve. At this point the primary system is turned on and tested for function and confirmation of air pressure.

    Mounting of the gas block should normally be in what is considered the golden triangle, my personal preference is on the divers chest strap right hand side with all hoses routed under the right arm and back to the first stage regulators, with the second stage hose following the same path or secured up the right front strap allowing for proper hose length to the second stage regulator or FFM.

    Presuming that each diver is equipped with a fully redundant system lets look at several failure modes.

    A. Diver has failed to properly monitor air pressure and runs out of air. Actions: activate the valve on the gas block terminate the dive and ascend to the surface.

    B. Diver has a first stage seat failure and begins to free flow on the primary air supply. Actions: terminate the dive, and begin accent, once the primary air supply is depleted activate valve on the gas block and continue the accent.

    C. Second stage failure, free flow. Actions: terminate the dive, and begin accent, once the primary air supply is depleted activate the valve on the gas block metering the flow as necessary for ease of breathing.

    D. Second stage failure, will not deliver air. Actions: terminate dive, open regulator bypass or in FFM not equipped with the ability to bypass or allowing the diver to free flow air such as the Guardian, AGA, Poseidon, Ocean Reef. Locate the Alternate Second Stage Regulator remove FFM and use the Alternate Second stage.

    As to trapped or entangled diver, a donor bottle should be deployed with any responding standby diver. The bottles size should be determined by depth and the maximum SAC rate of the team’s divers. Please remember 15 Minutes of emergency air at depth as a minimum. Should the bottle not be needed then it can be dropped out of the way if necessary for diver safety and recovered at a later time.

    At no point should a standby diver not be equipped with a donor Emergency Air supply as well as their own Emergency Air Supply.

    E. I consider this the most important part of using an emergency air supply. Practice each scenario until it is reflexive. Then make emergency air drills part of your annual first of the year training. Use your experienced divers to mentor the new divers help them build confidence in their equipment and teammates.

    If you don’t agree with me it’s OK, please post your point of view making good arguments for each of the above problems. This way everyone can learn and make informed decisions.

    I thank you in advance for reading this post with an open mind.


    Sincerely,

    Bob Kinder
     
    Lake Hickory Scuba likes this.
  2. clownfishsydney

    clownfishsydney Manta Ray

    # of Dives: 2,500 - 4,999
    Location: Sydney Australia
    1,232
    689
    113
    A very bad idea. On 20 March 1994, a tragic incident occurred on the Sydney wreck Coolooli when a friend of mine, Sydney diver, Paul Cavanagh (then Manager of Sydney's Channel 7 TV station) had this idea. We tried to talk him out of it and one of our buddies who was a fitter and turner refused to make the device. Paul died on a 48 m dive when he breathed a high O2 mix on the bottom. This was supposed to be his deco gas, but either he put the input hoses in the wrong place, selected the wrong mix or accidentally knocked the switch. He had an oxygen toxity attack and drowned.

    Also brings into place an additional potential point of failure.

    Please do not do it.
     
  3. rkinder

    rkinder Public Safety Diver

    # of Dives: 5,000 - ∞
    Location: Seneca, SC
    41
    44
    18
    Dear Clownfishsidney,

    The purpose of this system in PSD is for Emergency Gas Supply, for divers performing Professional Services. The point about accidentally going on a high PPO2 mix by using a gas block violates configuration basics developed back in 1992 when we first started using mix with FFM. To avoid what happened to Paul, had he been using a quick connect for decompression gasses with positive on off for bottom mix then it would have been impossible to inject a High Risk Mix. We saw similar problems with divers using the same model regulator for all of their gasses, and several died as a result of picking up the wrong regulator. As a result Mesh bags where developed and tags on tanks and Second Stage Regulators to avoid this exact problem. I do not remember the exact block but several where made during that time period along with home brew blocks that would have allowed just what you described.

    I am sorry for Paul's death and was aware of it at the time.
     
  4. RainPilot

    RainPilot completey delusional scientology snowflake Staff Member

    # of Dives: I just don't log dives
    Location: UAE
    3,451
    2,706
    113
    I'm diving a KM48 Mod 1 FFM with the UTD Z-system manifold. From what I can see it does address many of your requirements. I have 2 AL80 connected with QC6 to the system with any deco gases staged with a QC6 or a separate 2nd stage. I have my primary reg on an OC pod and any other regs are standard.
     
    northernone likes this.
  5. rkinder

    rkinder Public Safety Diver

    # of Dives: 5,000 - ∞
    Location: Seneca, SC
    41
    44
    18
    Dear Rain Pilot,

    I have looked up the UTD-Z-system manifold, for the intended purpose I feel it is a good product. In fact it offers many fine features for the tech-rec community. In the pure public safety role which in my opinion is closer to commercial than tech-rec My feelings are that based on the original purpose design and the recommended mounting location this manifold may not be ideal for the majority of PSD divers. I must however applaud your efforts to increase your safety and the amount of consideration that you placed in deciding on this purchase and configuration.
    The 48 is a great mask, the first one I ever dove was one of the most comfortable masks that I have ever used. For Military, and Re-breather users along with many other applications it is wonderful. However, due to it's gas flow not defogging the mask it has not been well received in the PSD community much the same as the EXO-26BR. I do like the pod feature and it's ease of use along with the varied choice of pods. .

    Thank you for your reply and safe diving.

    Sincerely,

    Bob Kinder
     
  6. kelemvor

    kelemvor Big Fleshy Monster ScubaBoard Supporter

    # of Dives: 100 - 199
    Location: Largo, FL USA
    4,909
    2,380
    113
    Does a FFM mitigate the risk of drowning due to unconsciousness (e.g. oxygen toxicity)?
     
  7. rkinder

    rkinder Public Safety Diver

    # of Dives: 5,000 - ∞
    Location: Seneca, SC
    41
    44
    18
    Yes, it does increase your chance of survival. Even with in water cardiac arrest a dry set of lungs and clear airway gives you a much better chance of survival.
     
  8. RainPilot

    RainPilot completey delusional scientology snowflake Staff Member

    # of Dives: I just don't log dives
    Location: UAE
    3,451
    2,706
    113
    Hi Bob

    I am curious about some of your points. This is genuine curiosity as I have next to no knowledge of PSD operations. What would be a better mounting location for a manifold in your application? I have been looking at several gas block options for plumbing in various gases for my bailout on the rebreather.

    The defogging issue makes total sense in a dirty water environment. I guess an AGA type mask with p-ported 2nd stages makes more sense for that environment.

    For what it's worth UTD is very keen to move into the PSD environment. There is a course in the works and I know AG is working on some specialised equipment. Most of the existing wings etc come in a PSD variant for heavy wear and contaminated water applications.

    I'll drop him a link to this thread maybe he has some things in the works that may be of use.

    Best regards
    Brendon Allen
     
  9. 73diver

    73diver Solo Diver

    # of Dives: 200 - 499
    Location: Milwaukee, Wisconsin
    98
    44
    18
    Our team uses the Apeks-switch block-non-return AP0281 (also Aqua Lung) There are options for surface-supplied air, back-mount air and different FFM. Points 4 & 6 from the OP are affirmative. Point #5 is negative (i.e. no OPV for pony first stage) as we mount an octopus directly to the pony first stage. Our team uses the back-mount option AP0281/PS. The back-mount air cannot be turned off; but, a safety diver can descend with an additional bottle to 'quick connect' into the block if necessary. This requires prior coordination with the diver to open the pony hand wheel valve. We practice this regularly. One feature that I don't care for: The hand wheel to admit pony air to the manifold is very easy to turn. It is prudent to regularly check that brushing up against things has not allowed it to become open, for example checking it when performing each turn in a search pattern. The failure mode would be, if the pony regulator IP is set higher than the main regulator IP and the hand wheel valve is open, one could consume the pony air prior to using back gas. The in-line one-way check valve between the back-mount bottle and the manifold has a 0.5 PSI cracking pressure. It is also recommended that the drysuit inflator not be attached to the manifold without a flow restrictor.
     
  10. kwinter

    kwinter Rebreather Pilot

    # of Dives: 500 - 999
    Location: South Jersey
    1,563
    755
    113
    I am a proponent of several different issues. FFM use, especially in conjunction with comms, has the potential to save many lives. A gas switch block used with the FFM is another great safety feature, but does require diligence in making sure the active gas is appropriate for the depth. Quick disconnects on all gasses facilitate switching gasses to the block. These things should really be standardized for PS divers.

    Someone that dies from OxTox because they had the wrong gas active does not mean the method of delivery is faulty. Yes, there is a greater risk. But especially with the KM type of gate valve, it is a matter of whether the emergency supply is on or off. If a beginner scuba diver jumped in the water with his tank shut off and died, would you say that having valves on scuba tanks is dangerous? Of course not. The risk is slightly higher with a ball valve like the Omniswivel, but I find the convenience worth it.

    If anyone needs a KM bailout valve, I happen to have a couple of extras that I picked up.
     

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