Bobby
Contributor
With the recent incident I want to post on the topic of stage diving. How I learned to stage dive and how I have managed my stage diving for the last couple of decades are very different. There are multiple ways to approach stage diving and I won?t attempt to discuss them all. I?ll discuss the two methods that I learned and the reason I don?t use them. I will then present my method to stage diving with an explanation of why I do it the way that I do.
The first method of stage diving, that I have not used, is half plus two. This approach to stage diving leaves the majority of reserve (emergency) gas in the primary cylinders which we will call back gas (BG) regardless of a diver?s actual configuration. ?+2 is simple in its approach however leaves the real possibility of a simple math error opening the door for a diver or team to miscalculate with the possible result of death. ?+2, for stage diving, simply takes a stage cylinders start pressure divided in half with 200 psi added to that number. This is the pressure that the stage is breathed to before shutting off the stage and dropping it. The extra gas that is used from the stage, in relation to thirds, is then kept as reserve in the BG. To do this the pressure of the gas needs to be converted to cubic feet in both the BG and the stage. Then the extra cubic feet of gas is added back to the BG resulting in less gas used or to put it another way, a higher turn pressure than the thirds turn pressure. The reason that I have not used this method personally is that I have always approached my diving with the mind set of keeping everything as simple as possible, I subscribe to the KISS methodology. Converting back and forth between psi and cubic feet between different cylinder sizes is simple math however it also opens the door to making simple math errors. Even if the same cylinders are used for both BG & stages the turn pressure numbers, when using ?+2 are very different opening the possibility for a simple mistake. This most recent incident fits this scenario. I?m not saying that this is what happened in this situation however it is a possible factor.
The second method is simple thirds. Breath a stage down to a third, shut it down, and drop it. This is a simpler approach that requires less math resulting in less opportunity for simple math errors. The issue with this approach is that 2/3?s of the gas required for a normal exit, for where the stage is dropped, is left in the cylinder. There have been multiple fatalities that the diver was very close to reaching a dropped stage when they ran out of gas.
My approach to stage diving is to use time and thirds to control when I shut down a stage and when I drop it. The stage is breathed down to a third and shut down, if it took 20 minutes to breath that third then the stage is swam another 20 minutes before it is dropped and a minimum of 100 psi is added to the reserve of back gas. This puts the stage at the farthest point of penetration to be useful and adds reserve to the back gas. When the stage is reached it is used at the point it is picked up to keep the reserve of back gas. If there are no problems then the stage will be shut down at 200 psi and back gas is used for the rest of the exit. If there has been an issue that puts the exit in question, then the stage is breathed until empty and discarded to preserve back gas as much as possible, which will also contribute to maintaining buoyancy and not becoming over positively buoyant. When there is a question regarding having enough gas to exit, discarding an empty stage reduces work load improving the odds of reaching the exit. Empty stages can be recovered at a later date and the cost of a stage is not worth dying over, IMHO.
Real application of this method results in added conservatism and safety for the stage dive. By swimming the stage farther than it is breathed the slight amount of added drag (not considering a siphon dive) gives a larger reserve of gas and ads to the conservatism. Actual dives normally result with gas left in the stage, with it being breathed all the way to the exit or arriving at deco where a switch to decompression gas happens. Multiple stage dives result in increased reserve gas and conservatism. For each stage a minimum of 100 psi is added to reserve gas and each stage is dropped at the maximum useful penetration. I have had situations where the dive did not go as planned and reaching the stage sooner rather than later makes a positive psychological impact, which alone can be the difference between just a dive that didn?t go well and a catastrophic incident.
The same as with any dive there are a lot of factors that may impact conservatism. It is simple to add another 100 psi to BG or stages to increase reserves for added conservatism. Thirds is only a method for calculation, for me, actually using an entire third is something that I don?t do. Every dive is turned with extra reserve even if I have done the particular dive hundreds of times and know the system thoroughly. If 3600 psi is my fill pressure and 2400 psi is my 1/3 turn pressure then 2500 psi is a bare minimum turn pressure, for me, with 2600 being my usual turn pressure, in systems that I know very well. Add a stage and a second 100 psi is added to my normal turn pressure.
Some will feel this is overly conservative and I?m fine with that. I?ve found that conservatism in overhead diving has been good for me and I?m OK with turning a dive earlier than others would. I have over the years pushed things to, what I consider, my limits. I?ve had things go wrong and have had to deal with and sort through issues. My conservative approach has gotten me through those situations. Divers with a lot of skill and experience have also not survived situations and some of them were very close to reaching their staged gas. However anyone decides to approach their stage diving, please evaluate and consider reserves and your level of conservatism.
The first method of stage diving, that I have not used, is half plus two. This approach to stage diving leaves the majority of reserve (emergency) gas in the primary cylinders which we will call back gas (BG) regardless of a diver?s actual configuration. ?+2 is simple in its approach however leaves the real possibility of a simple math error opening the door for a diver or team to miscalculate with the possible result of death. ?+2, for stage diving, simply takes a stage cylinders start pressure divided in half with 200 psi added to that number. This is the pressure that the stage is breathed to before shutting off the stage and dropping it. The extra gas that is used from the stage, in relation to thirds, is then kept as reserve in the BG. To do this the pressure of the gas needs to be converted to cubic feet in both the BG and the stage. Then the extra cubic feet of gas is added back to the BG resulting in less gas used or to put it another way, a higher turn pressure than the thirds turn pressure. The reason that I have not used this method personally is that I have always approached my diving with the mind set of keeping everything as simple as possible, I subscribe to the KISS methodology. Converting back and forth between psi and cubic feet between different cylinder sizes is simple math however it also opens the door to making simple math errors. Even if the same cylinders are used for both BG & stages the turn pressure numbers, when using ?+2 are very different opening the possibility for a simple mistake. This most recent incident fits this scenario. I?m not saying that this is what happened in this situation however it is a possible factor.
The second method is simple thirds. Breath a stage down to a third, shut it down, and drop it. This is a simpler approach that requires less math resulting in less opportunity for simple math errors. The issue with this approach is that 2/3?s of the gas required for a normal exit, for where the stage is dropped, is left in the cylinder. There have been multiple fatalities that the diver was very close to reaching a dropped stage when they ran out of gas.
My approach to stage diving is to use time and thirds to control when I shut down a stage and when I drop it. The stage is breathed down to a third and shut down, if it took 20 minutes to breath that third then the stage is swam another 20 minutes before it is dropped and a minimum of 100 psi is added to the reserve of back gas. This puts the stage at the farthest point of penetration to be useful and adds reserve to the back gas. When the stage is reached it is used at the point it is picked up to keep the reserve of back gas. If there are no problems then the stage will be shut down at 200 psi and back gas is used for the rest of the exit. If there has been an issue that puts the exit in question, then the stage is breathed until empty and discarded to preserve back gas as much as possible, which will also contribute to maintaining buoyancy and not becoming over positively buoyant. When there is a question regarding having enough gas to exit, discarding an empty stage reduces work load improving the odds of reaching the exit. Empty stages can be recovered at a later date and the cost of a stage is not worth dying over, IMHO.
Real application of this method results in added conservatism and safety for the stage dive. By swimming the stage farther than it is breathed the slight amount of added drag (not considering a siphon dive) gives a larger reserve of gas and ads to the conservatism. Actual dives normally result with gas left in the stage, with it being breathed all the way to the exit or arriving at deco where a switch to decompression gas happens. Multiple stage dives result in increased reserve gas and conservatism. For each stage a minimum of 100 psi is added to reserve gas and each stage is dropped at the maximum useful penetration. I have had situations where the dive did not go as planned and reaching the stage sooner rather than later makes a positive psychological impact, which alone can be the difference between just a dive that didn?t go well and a catastrophic incident.
The same as with any dive there are a lot of factors that may impact conservatism. It is simple to add another 100 psi to BG or stages to increase reserves for added conservatism. Thirds is only a method for calculation, for me, actually using an entire third is something that I don?t do. Every dive is turned with extra reserve even if I have done the particular dive hundreds of times and know the system thoroughly. If 3600 psi is my fill pressure and 2400 psi is my 1/3 turn pressure then 2500 psi is a bare minimum turn pressure, for me, with 2600 being my usual turn pressure, in systems that I know very well. Add a stage and a second 100 psi is added to my normal turn pressure.
Some will feel this is overly conservative and I?m fine with that. I?ve found that conservatism in overhead diving has been good for me and I?m OK with turning a dive earlier than others would. I have over the years pushed things to, what I consider, my limits. I?ve had things go wrong and have had to deal with and sort through issues. My conservative approach has gotten me through those situations. Divers with a lot of skill and experience have also not survived situations and some of them were very close to reaching their staged gas. However anyone decides to approach their stage diving, please evaluate and consider reserves and your level of conservatism.
