Capt Jim Wyatt
Hanging at the 10 Foot Stop
Staff member
ScubaBoard Business Sponsor
Scuba Instructor
The vast majority of CCR cave divers that I know are not pushing themselves into tiny restrictions where zeroing the vis, getting stuck and accidentally shutting off O2 shutoff valves is likely to occur.
There was a YouTube video made by some guys in the panhandle that claimed the CCR Sidewinder Ginnie fatality could not have happened the way accident analysis conclusions were stated due to the O2 cutoff valve because the diluent was breathable at that depth. But I don’t remember how they claimed that the diluent would have automatically been injected into the loop to prevent hypoxia.
The diver apparently did not know his O2 was off so he could not have known he needed to add diluent. An ADV would not have “fired” at a constant depth. Constant Mass Flow was interrupted due to valve closure. I also do not think and ADV would “fire” due to a loop volume decrease from O2 metabolism, at least not in time to prevent hypoxia. However in the video on YouTube they claim that the ADV would in fact fire due to a reduced volume. I also think most instructors teach to turn off the ADV once at depth to prevent buoyancy problems from adding diluent with very slight depth changes.
I have removed my in-line O2 cutoff valve because I see no value in having it for the type CCR cave diving that I do nor the CCR cave diving techniques that I teach. If I have a solenoid stuck open I shut off the O2 at the O2 tank valve. With CCRs that have the O2 inline shutoff difficult to reach I see even more reason not to have one.
Those that do go into tight places losing visibility may decide to switch off the O2 and run SCR mode since they cannot see their controller. Why not switch off the O2 at the tank valve?
My opinion is also that a CCR should have a HUD. My rationale is that if the loop goes hyperoxic or hypoxic there will be red lights flashing in my face telling me something is wrong. A CCR cave diver should not have to rely on this normally in that they should be looking at their PO2s on their controller every minute or two. However, if things go awry and you are distracted and fail to look then the HUD becomes that critical backup piece of gear.
As cave divers we carry three lights, two safety reels, redundant breathing gas and other redundant pieces of equipment. The saying is “Two is one, one is none”. I don’t see why we should not look at redundant PO2 monitoring via a HUD in the same way.
There was a YouTube video made by some guys in the panhandle that claimed the CCR Sidewinder Ginnie fatality could not have happened the way accident analysis conclusions were stated due to the O2 cutoff valve because the diluent was breathable at that depth. But I don’t remember how they claimed that the diluent would have automatically been injected into the loop to prevent hypoxia.
The diver apparently did not know his O2 was off so he could not have known he needed to add diluent. An ADV would not have “fired” at a constant depth. Constant Mass Flow was interrupted due to valve closure. I also do not think and ADV would “fire” due to a loop volume decrease from O2 metabolism, at least not in time to prevent hypoxia. However in the video on YouTube they claim that the ADV would in fact fire due to a reduced volume. I also think most instructors teach to turn off the ADV once at depth to prevent buoyancy problems from adding diluent with very slight depth changes.
I have removed my in-line O2 cutoff valve because I see no value in having it for the type CCR cave diving that I do nor the CCR cave diving techniques that I teach. If I have a solenoid stuck open I shut off the O2 at the O2 tank valve. With CCRs that have the O2 inline shutoff difficult to reach I see even more reason not to have one.
Those that do go into tight places losing visibility may decide to switch off the O2 and run SCR mode since they cannot see their controller. Why not switch off the O2 at the tank valve?
My opinion is also that a CCR should have a HUD. My rationale is that if the loop goes hyperoxic or hypoxic there will be red lights flashing in my face telling me something is wrong. A CCR cave diver should not have to rely on this normally in that they should be looking at their PO2s on their controller every minute or two. However, if things go awry and you are distracted and fail to look then the HUD becomes that critical backup piece of gear.
As cave divers we carry three lights, two safety reels, redundant breathing gas and other redundant pieces of equipment. The saying is “Two is one, one is none”. I don’t see why we should not look at redundant PO2 monitoring via a HUD in the same way.
