rkinder
Registered
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
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
