Cozumel, 2006: I was leading a small group of divers from a midwest dive center on a four-day trip to one of my favorite dive destinations. One of the group members was a newly certified diver whom I knew, but had not taught personally.
The location was Palancar wall. This would be our group’s first deep dive of the trip. The plan was to drift the face of the wall at 80 feet, until it was time to return to shallower water and ascend.
The group was being led by a very capable local divemaster. I would bring up the rear, where I could more easily keep an eye on people.
I sensed early on that this diver was going through air faster than everyone else. This being the case, I started checking his pressure gauge on a regular basis.
When he hit 1,200 psi, I offered him my alternate, so that I could use my extra gas to get him to a place where he could ascend on his remaining air and surface next to the boat. To my surprise, he refused the offered second stage.
Immediately I started looking for a place where he and I could safely cut through the reef and return to shallower water, under the boat. While doing so, I offered him my octopus two more times yet, despite my insistance, he kept refusing.
At this point, a group of divers from another boat decided to cut right between us, as though we weren’t even there. By the time I got around them, my diver was gone.
I finally caught up with him on top of the wall. By now he was breathing fumes and was more than happy to take the offered alternate. Unfortunately, by the time we hit 20 feet, his empty tank was so light he ended up dragging us both to the surface.
On deck, I asked him why he didn’t take my alternate when offered. His response? “I wasn’t out of air yet.”
As it turned out, both his instructor and the training materials he watched and read presented alternate-air-source use as something you did only after running out of air.
I patiently explained that, had he taken my octopus when offered, I could have gotten him to a point where he could have easily ascended on his remaining gas, and we both would have been able to make a slow ascent and safety stop.
“I didn’t know you could do that,” was all he said.
Since first being introduced in the early 1970s, alternate air source second stages have been largely presented as something you use only after a diver has run out of gas. The idea that you can use them to prevent a diver from running out of air is almost never discussed.
So why not simply have a low-on-air diver ascend before running out of air? That would generally be the best response, but not always.
In the case of the diver I tried to help, an immediate ascent would have involved coming up directly from 80 feet and not 40, and surfacing some distance from the boat in heavy traffic. And while new divers generally associate the surface with safety, more experienced ones know that the surface is where most accidents happen.
Long surface swims in waves and current — and especially following a deeper dive — are something to avoid.
Since that time, I’ve made a point to teach beginning divers alternate-air-source use, not only while stationary and ascending, but also while traveling. Coupled with this has been a detailed explanation of when and why this could be beneficial.
Obviously, the best response to this type of situation is preventing it in the first place, by establishing turnaround or “take action” pressures and Minimum Gas Reserves (MGRs). We cover those in a separate article.
The bottom line is, if you teach students that an alternate-air-source is something they can only use after running completely out of air, you may be teaching them to run out of air.
Is that really what you want?
Reposted from cavediverharry.com