One of the most commonly asked questions when divers with experience diving the classic North Florida Cave Diving setup (backplate, wing, long hose, etc.), and who are switching to technical sidemount, centers on donating the long hose in an Out of Air (OoA) scenario.
And, here’s the answer I give them.
First let’s look at a common sidemount setup — at least here in North America — which is a configuration with the long hose on the right-side bottle, and a shorter hose to the diver’s left. This configuration almost certainly owes its popularity and its genesis to North American cave divers who converted from wearing doubles to sidemount. These folks almost certainly brought the longhose with them, since the traditional SM rig had NO long hose at all!
OK, so we are considering then, a SM diver with one long hose… on his or her right, very similar to their backmounted cousin.
Now, any discussion of an OoA situation by definition is one about risk management, so first steps are to consider when (if) the requirement to share gas with a buddy becomes necessary. In other words, how likely is it… how often does this happen?
I may have been lucky but after more than a thousand cave dives and several thousand open water decompression dives, I have never been in a situation where gas sharing was required. Certainly never in a panic situation.
Before you start a letter-writing campaign, let’s be clear, I am NOT suggesting it (an OoA situation) does not happen, just that it is a rare occurrence: especially among technically trained and experienced divers. One might argue that it is so unlikely in this community that planning for it should be approached with a different mindset to the one that is taught, but let’s leave that debate for a later date. Instead let’s say that it seems far more likely in a technically trained and practiced team that a team member would realize an “OOA” situation is being APPROACHED rather than suddenly discovering that it has ARRIVED.
In these situations, handing off a regulator would be controlled and simple to manage, almost regardless of which regulator was being breathed from.
Real-world experience tells us that the VAST majority (one might say almost ALL), panicked divers grabbing at working regulators are novices who have been poorly trained, do not follow safe gas management rules, and have poor skills.
However, let’s err on the side of convention and ultra-conservatism and say that OoA scenarios are common enough to require special kit considerations. And let’s look at times during a dive when a team of well-trained, and similarly configured sidemount divers are most likely to experience a mildly emphatic need to donate a regulator. This may help to inform us how best to train/prepare for this type of event.
A list of the most likely times to share gas would certainly begin during the very first stages of a dive. This is the most likely time for a regulator to malfunction, or, if pre-dive tests have been cursory, for things like a leaking second-stage mushroom valve to make its presence known or an incorrectly opened valve to stop delivering gas at depth.
Second on the list would be around the point of “maximum penetration” either approaching the turn-around or immediately following. (For the sake of simplicity, let’s apply the maximum penetration label to an open-water or soft-overhead environment where TIME is often the controlling factor influencing when a dive team turns.)
A third situation is during the final stages of a dive… essentially when a diver switches to his/her decompression gas or during the later stages of a decompression obligation.
It would be beneficial or prudent perhaps, for a diver to PLAN to be breathing from his/her long hose during these periods when the likelihood of needing to donate a regulator is at its highest. It’s not a coincidence that when one follows the method commonly taught to sidemount cave divers (described in an article I wrote for X-Ray Dive magazine last year), this is exactly the case!
Very briefly, the suggested method begins with the diver breathing from the right-hand bottle for one-sixth of the available volume, then switching to the left-hand bottle until one-third of the starting volume has been consumed. At this point, they switch back to their RH bottle and breath IT until a further one-third of its starting volume has been used. Note well that the dive will have been turned about halfway through this second spell breathing from the RH tank. When the RH tank pressure gauge indicates the switch point has been reached (one half of the starting volume gone… one sixth plus one third is one half), the diver switches to their LH cylinder and exits on it.
An added advantage to this method is that there is ALWAYS at LEAST half the starting volume of gas in the RH bottle… the one with the long hose.
Of course, there are a couple of refinements to this method that one can employ.
Firstly, use a long hose on both left and right cylinders. Secondly, attach boltsnaps to regs on the long hose with breakaway fastenings.
Most of all, while there are many alternatives to the methods outlined above, it is worth reminding oneself that putting a lot of effort (and circular debate) about gas-sharing should begin with a full and frank analysis on HOW MANY TIMES GAS SHARING INCIDENTS OCCUR in well-trained, properly equipped teams. The response to this may shock you.
You may also be interested to investigate what actually happens in a panicked OOA situation and how well WHICHEVER technique you have been trained to employ will serve you in that particularly challenging situation.
Hope this helps.