The Big Deal About Deep Diving

Some of us are depth junkies.

We just like the idea of going deep. Not me personally, but I’d say about 10% of those I meet want to go deeper for no other reason than to do it, or perhaps to be able to tell others that they’ve done it.

Not that there’s anything wrong with that, except when you’re not actually prepared to go deep.

Being prepared to go deep means a number of things, but above all, going deep requires an independent alternate air source.

Here’s a real scenario that actually happened recently and which prompted me to write this post.

Two divers go on a 130′ dive in a cold-water lake. They’re fairly experienced with the diving conditions and are frequent divers. At their maximum depth, one of the divers’ regulator free flows. He connects with his buddy for immediate ascent to the surface. He doesn’t get far with the free flowing reg before it drains his 80 cubic foot tank and switches to his buddy’s octopus.

Nothing extraordinary here, except that during the ascent, the diver with the free flowing reg experiences a second issue: the air in his drysuit begins to expand rapidly. Being task loaded with managing the free flowing reg, the octopus, the ascent,and the speed of the event, our diver wasn’t able to get to the air in his drysuit fast enough. In most instances, this wouldn’t be an issue since the majority of dry suit dump valves will self-purge if the valve is kept open. Unfortunately in this incident, our diver’s dry suit featured a valve that must be manually depressed to release air from the suit.

Compounding the issue of the manual dry suit dump valve is the integrated hood on the suit. In a dry suit course, one of the emergency procedures in the event of a dry suit valve malfunction is to open the neck or wrist seals to release the air from the suit. Our diver’s suit featured an integrated hood that makes it just about impossible to open the neck seal with hands that are encased in thick gloves. In addition, the wrist seals are also hidden under the gloves and an overflap, rendering quick access to the inner dry seal impossible.

So, with the air in his dry suit quickly expanding, our diver is rapidly ascending…while still attached to his buddy’s octopus and taking his buddy with him on a dangerously fast ride to the surface.

There are lots of issues in this incident, but in the context of deep diving, the most critical one centres on what qualifies as an appropriate alternate air source for a deep dive. On a deep dive, your buddy’s tank does not qualify as an alternate source of air, especially if the tank’s capacity is 80 cubic feet or less. If our divers each carried a pony bottle with a capacity of at least 20 cubic feet, there would have only been one diver going on a rapid ascent, not two. Our diver with the free flow would have had an independent alternate air source that he can access. With an independent alternate air source, our diver wouldn’t have had to involve his buddy in a rapid ascent, creating a DCS risk to both of them.

It’s true: an independent alternate air source wouldn’t have prevented our diver with the free flow from a rapid ascent. What it would’ve prevented, however, is the second diver going on the rapid ascent because the diver with the free flow would’nt have had to physically tie himself to his buddy. He wouldn’t have had to raise his buddy’s DCS risk.

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