by B. N. Sullivan
Basic diver certification courses all include instruction on air sharing. (For our non-diving readers, 'air-sharing' refers to more than one diver using the same air source.) This is a very basic and essential skill, and these days it is also quite easy, in principle.
Back in the day when I first learned to dive, SCUBA regulators only had one second stage, i.e., the part of the regulator that includes the mouthpiece. In order to share air, one diver had to take the regulator out of his/her mouth and hand it to the other diver. The second diver would take a breath or two, and then pass the regulator mouthpiece back to the first diver. This alternating pattern would continue until the divers could surface. The procedure worked, of course, but it could be quite awkward. Also, since neither diver could breathe continuously, both divers could end up experiencing considerable anxiety.
These days, most divers use regulators that have two second stages, each attached to its own low-pressure port on the regulator's first stage, i.e., the part that connects to the valve of the air cylinder. Look at the photo of our friend Dan on this page. You can see that his regulator has two second stages. The hose of the primary one passes over his right shoulder, and he is breathing through the mouthpiece. The hose of the secondary one passes under his arm, with the mouthpiece attached to his vest with a quick-release clip. This is a standard sport diving configuration.
In a popular alternative configuration, the inflator hose for the diver's buoyancy compensator has a mouthpiece on it so that it can double as a breathing device.
The advantage of using regulators with two second stages should be obvious: two divers can share the same air source simultaneously and continuously, without the need to pass the mouthpiece back and forth between them. This makes air sharing much easier, and is less anxiety-producing.
Divers are taught how to signal to each other that they need to share air, and the procedure of handing off the secondary regulator to the diver in need of air is practiced during training. They are taught that as soon as air sharing begins, the divers should begin their ascent together.
I take issue with this aspect of diver training. It seems to assume that the divers are right underneath their boat, or near to their exit point if they are shore diving. In real life, things are not often so tidy.
What happens if the divers are a good ten minute (or longer) swim away from their boat or exit point? What if they are near the deepest point of a deep dive? What if it is not prudent to surface immediately because of some other hazard -- e.g., boat traffic, or a strong surface current.
Over the years we have been in a few situations when we had to share air, and we have witnessed many other divers in such situations. Rarely, if ever, have these events happened right under a boat or very near to our exit point. Divers need to understand this and prepare for it, or they may find themselves in deep trouble (pun pointedly intended).
If the diver always stays very near to the boat or exit point, and doesn't go very deep, air sharing using the procedure taught in initial training, which I described above, probably will be sufficient. Otherwise, divers need to plan for -- and practice -- sharing air during a long swim, and during an ascent that may have to include a five minute 'safety stop' at 5 meters.
In order to facilitate swimming a longer distance while sharing air, one of the regulator's second stages should have a long hose. When divers are sharing air via a regulator with a 'standard' hose length of, say, 27 inches, they necessarily have to be very close to each other. It's difficult to swim while physically close to another diver, but that is what's required when both are sharing air and both are attached to the same air cylinder by relatively short hoses. It is much better to have a much longer hose on one of the second stages -- say 40 inches or even longer.
Won't a longer hose be a nuisance when not sharing air? Not really. You can do what cave divers do: bundle it and secure the bundle with a bungee cord. Alternatively, you can feed the longer hose under your right arm and across your front, securing the mouthpiece somewhere on the left side of your gear, instead of the right side where most divers stow their secondary reg mouthpiece. (Just be sure you show your buddy where it is before you begin the dive!)
By the way, if you do need to share air from a regulator using two shorter hoses, and you have to swim any distance, we figured out that it is easier to swim with one diver positioned above and a little behind the diver with the air supply. Imagine that the diver with the air source is going to give the air-sharing diver a piggy-back ride -- except the two divers swim, one a bit above the other. The 'top' diver can hold on lightly to the other diver's shoulder to maintain position and stay in place.
Now, a final note, but a very important one: practice. Practice air sharing while swimming longer distances. Practice air sharing while hovering at a depth of five meters as you would for a safety stop. (This is much easier to do if you have a regular dive partner, but even if you don't, get someone to practice with you from time to time.)
Ever since we began diving together, we have occasionaly practiced swimming at least ten minutes while sharing air. We also have practiced sharing air while hovering in place for a safety stop. We have done this exercise three or four times a year. Then one day, while we were more than a 10 minute swim from our exit point, and at a depth of about 120 feet (37 meters), a high pressure hose on my regulator popped. Oh the bubbly froth that instantly ensued! But there was no panic. Jerry passed his secondary reg mouthpiece to me right away, and turned off the valve on my air cylinder. The two of us set off toward our exit point, swimming easily together -- side by side, but with enough space between us that it was not at all awkward or cumbersome, thanks to a longer-than-standard hose length on Jerry's secondary reg. We even did a five minute safety stop before surfacing. Our practicing had served us well.