Thursday 18 March 2010

Rocket Guy

Well, just over a week ago I did a refresher dive in Benfield pool, and thankfully it turned out not to be a case of "all mouth and no wetsuit". We practised standard skills: mask removal and clearing, taking the scuba unit (BCD+, tank and regs) off*, breathing from a free-flowing regulator++, hovering, fin pivot, and CESA**.

I was slightly dreading the mask removal. This is the one skill that a lot of divers HATE having to do on their training dives, although some say they don't mind it. No-one likes losing their vision under water, and getting cold water straight in your face (I did my training dives in the Firth of Clyde off the west Scottish coast) is no-one's idea of a fun time. It is, however, essential to master since it's not completely unknown to have a mask strap break, or a mask knocked off whilst diving. I was actually quite relieved when the instructor indicated we'd do that first, and pointed at me to go first. I took one breath, then pulled the mask off and shut my eyes.

My first thought was "Damn, I hate breathing through a regulator without having my nose covered by the mask" (diving masks cover your nose). It sounds daft, but the bubbles go right up your nose and it's no fun. I breathed maskless for a minute. This is also a skill, since if you lost your mask completely on a dive you'd have to be able to breathe through the reg without it until you made it safetly up to the surface. I then pressed the mask back on my face, slid the strap over the back of my head, tipped my head back a little and held the top of the mask against my forehead with the palm of my hand. Breathe in, blow out smoothly through nose, let the air force the water out and... open eyes.

I looked out through a perfectly-cleared mask, and had to resist the urge to do the Underwater Victory Dance. (There wasn't enough room - it's a small pool.) Go, me!

Here is a video of a PADI Course Director doing this with much more grace than me:

We next practised buoyancy skills. A skilled diver can sit on the bottom of the pool, inflate their buoyancy jacket just enough to rise off the bottom as they breathe in, then hover almost motionless in the water, controlling their buoyancy as they breathe in and out.

I'd like to think I'm a skilled diver. Unfortunately, I was wearing my own fins, meaning that I was wearing my neoprene diving boots. (I have open-heel fins which fasten with a strap at the back to allow you to wear boots underneath them, meaning that you have to wear the boots, otherwise the fins don't fit.) Neoprene is buoyant in water, meaning that my feet are more buoyant than the rest of me. I can hover in the water, but, alas, only in a position where I'm on my back with my feet floating above me, like an upturned and possibly dying turtle. Hilariously funny for anyone watching. Next time I do this I'm going to try wearing little weights around my ankles, and see if this fixes the problem.

At least I was doing better than Rocket Guy. I probably shouldn't call him that, but it's hard to resist. He was one of the other refresher students, and could not seem to quite grasp the concept of "you put SMALL amounts of air in your jacket, because BIG amounts of air will make you so buoyant you float to the top", despite the instructor's increasingly insistent hand signals. Ah well. After he'd gone from the pool bottom to the surface a few times he seemed to get it.

Towards the end, we practised our CESAs (see below). CESA is meant to be done on one lungful of air, since that's what you'd have in a real OOA (out-of-air) emergency. You swim from one side of the pool to the other, beneath the water, keeping the regulator in your mouth and exhaling as you go.

Rocket Guy didn't seem to get this, either. We know this because, when you exhale underwater, you blow bubbles.

Rocket Guy had a string of bubbles coming from his mouth... until about halfway across the pool, when they stopped. He was obviously breathing through his regulator!

He seemed a bit surprised when the instructor finally signalled "Go Up" and explained it to him on the surface.

Ah well. As I hauled my dripping self out of the pool, I was grinning like a idiot. Truly, I love diving. Maybe I was a fish in a past life.

+ BCD = Buoyancy Compensator (or Controlling) Device. For most sports divers, an inflatable jacket like a lifejacket, which has a valve attached to the air tank and inflates and deflates. Fish have swim bladders, divers have BCDs. It also holds the air tank on your back. Utterly essential to diving as it's used to control your buoyancy both at depth and on the surface, where having something that keeps you afloat without you having to kick to keep your head above water is essential. You sometimes see "backmounted" BCDs, or "wings", where the air cell (which inflates) is on the diver's back. These are more usually favoured by technical divers, who typically dive with two or more tanks of gas.

* If you're wondering why on earth you'd do this, it's sometimes necessary if you're unlucky enough to get entangled in something and need a bit more wriggle room to get yourself free. And yes, the regulator mouthpiece stays in your mouth throughout.

++ Free-flow: when the valve in the regulator sticks open, meaning that the air flow doesn't shut off. This is a "fail-safe" feature. If the regulator fails, better it fails in a way that means you can still get air from it, albeit you are losing air very fast and need to head for the surface at the safest possible rate. Breathing from a freeflowing regulator is often described, accurately, as being like trying to drink from a fire hose.

** CESA = Controlled Emergency Swimming Ascent. Technique of near last-resort if a diver runs completely out of air and there is no-one around them to give them their spare regulator for their air tank. (Avoiding this situation is why divers are supposed to dive in pairs and stick close together. Also why you're meant to check your air gauge, often.) You keep all your gear on and swim directly up to the surface exhaling all the way. The exhalation, usually done by going "AAAAAHHH" like you're at the dentist's, is to ensure that the pressurised air in your lungs can safely escape as it expands on the ascent, so no lung damage should be caused. You can do this from anywhere up to about 9m depth. Beyond that depth, you are in (even more) serious trouble if you run out of air.

CESA is in the same category as wearing a car seatbelt. You don't ever plan to need it, and you should always do everything you can (drive carefully / stick close to your buddy and check your air gauge) to avoid it. But if ever you do need it, then, like a seatbelt or a parachute, you'd better hope it works first time, because if it doesn't, odds are you won't be in a position to use it again.

Diving does not have to be dangerous. Driving a car is probably more dangerous, and I don't fear for my safety when I get in my car. But equally, it would be stupid to pretend it has no risks, which is why driving / diving instructors train their students to do emergency stops / CESAs (and other safety techniques), and, most importantly, THINK.

No comments:

Post a Comment