OneAndOneIs2

I've been told that, in smug tones of voice, by various people, and seen it written down in a number of places.

So. To the people who think it's useful advice:

My body has been telling me the same thing for half a decade. It can safely assume that I have heard the message. Message received and understood. Really.

What the body really needs is a "Reply" button. Something along the lines of "Yes, I know something is wrong. So howsabout you stop telling me about the problem and get on with FIXING it for a change??"

I think maybe it's the hot weather. Misalignment apparently causes inflammation, which is worsened by heat.

So I'm going to go and get the frozen peas out of the freezer. Again.

And if it doesn't help, I'm going to sulk.

This weekend, I have to get everything I own packed up into boxes. On Monday, I pack all the boxes onto a van, and on Tuesday, I go to France, where all my worldly goods will be stored whilst I go wandering the world.

Trouble is.. it's always fatal, this sort of thing. You keep coming across stuff you'd packed away. In this case, I've started coming across my scuba gear.

I haven't used it in a while. Rotten weather; seasickness; and a club that insisted on doing its dives in the morning so you had to stagger out of bed at 5am on a Saturday if you wanted to go... all sapped my enthusiasm. And then I got into that year or so of trying to save money to cover me for when I left my job, and that really put a stop to it. One thing scuba diving ISN'T is cheap.

So I put the whole hobby on hold, and packed my gear away in the bottom of a wardrobe. My diving website hasn't been updated in years (still gets several hundred hits a month tho...)

But I came to go through my wardrobe to have a clear-out, and there was all my dive gear... as described here if you want to see it.. Ahh, the nostalgia! If not for the fact that the cylinders are out of test and can't be filled, and solo diving is generally banned at most diving sites, I'd probably have gone for a splash-around in all this hot weather.

Ah well. Maybe in a year or two's time, when I'm back from backpacking and have a job and everything.

Trouble is.. when you start thinking about diving in the future, you start thinking about buying new stuff... and the bit of gear I always wanted to get was a rebreather.

About 90% of diving practice is about managing gas: Having enough to breathe, keeping insulated from the colder water, not letting it cause the bends, etc.

Conventional scuba gear, you breathe in from the cylinders full of compressed air on your back, and breathe it out into the water.

As you probably know, the air is roughly 20% Oxygen and 80% Nitrogen. When you breathe out, it's generally in the region of 80% Nitrogen, 17% Oxygen, and 3% Carbon Dioxide.

So there's a lot of useful gas gets wasted when you breathe out if it just bubbles away.

What's more, because pressure goes up by one atmosphere every 10 meters (30 foot), the gas is twice as dense and therefore you waste twice as much at 10 meters. You waste three times as much at 20m, and four times as much at 30m. Etcetera etcetera.

So if, instead, you were to breathe in and out of a bag, you wouldn't lose the gas. Much more efficient.. except you'd die when you used up the Oxygen. But if you plug in a supply of pure Oxygen to keep it topped up, then you would die of CO2 toxicity instead. Unless you put in a scrubber to remove the CO2.

What you have if you do this is a rebreather: You keep breathing the same gas, removing CO2 and adding O2 to keep it at a breathable level. This can make a huge difference: A 30m dive at 20m could use up some 2000 litres of air with a conventional scuba setup; whereas you would use barely 30 litres of Oxygen and the odd few litres of air on a rebreather.

Advantage one: Smaller cylinders and longer dive times.

Your body does nothing with the Nitrogen. It just takes up space in the air supply. What's more, Nitrogen is narcotic, and makes you start to feel drunk from 30-ish meters down. Additionally, Nitrogen is what gives divers the bends: It dissolves into your body fluids at the higher pressures, then comes out of solution as pressure decreases. Just like a bottle of coke starts to fizz when you open the lid. Come up slowly, that excess gas comes out slowly enough to be gotten rid of safely. Come up too fast, and it's like shaking that bottle of coke before opening it.

You might think that breathing pure Oxygen instead of air would therefore be a great idea: No bends and no narcosis.

And it would, if only Oxygen weren't toxic in high concentrations. You can't breathe pure Oxygen deeper than six meters within recreational diving limits.

But you can increase the amount of Oxygen in the mix you breathe, so instead of air at 20% you have Nitrox at 32% or 36% - it'll cut down on the amount of Nitrogen in your body.

You can also breathe higher-Oxygen mixes as you ascend. 50%, 80% and 100% Oxygen are popular for this. After all, if you have too much Nitrogen in your body, breathing in more of the stuff is going to make it harder for your body to get rid of it than breathing pure Oxygen.

Trouble is.. if you want to breathe 32% at the bottom, and then 50% followed by 100% on the way up, you've got to take at least three cylinders. That's getting heavy!

Unless you're on a rebreather, where you can simply add Oxygen to the air until you have whatever Oxygen percentage you want at any time in the dive.

Advantage 2.

Also, you can replace Nitrogen with some other inert gas to stop it being so narcotic. Helium is used here. It's much less narcotic, but sadly it's a lot more expensive.

A rebreather diver uses much less gas per dive: It's a lot cheaper & easier to use Trimix (Helium/Nitrogen/Oxygen) with his equipment.

Advantage 3.

The downsides?

Well, rebreathers are a lot more expensive. They require a completely different skill set. They can go wrong 'silently'. They require more attention and setting up. And so on.

The first rebreather to make it big in the UK was the Buddy Inspiration: The first rebreather to get CE approval. It has three Oxygen sensors to keep track of your breathing mix, and a computer to keep it at the right amount. If the sensors start to disagree, it uses 'voting logic' to decide which to believe. You're supposed to monitor your Oxygen at all times in case the computer gets it wrong.

I wouldn't buy an Inspiration. It'd be too easy to get used to the computer thinking for me, and stop bothering to monitor it. I know I would get complacent.

I'd buy a KISS. This has three sensors, but no computer. It has a valve that puts in Oxygen at roughly the same speed as your body will use it up, and you handle anything else yourself, manually.

Unlike the Inspiration, then, you can't get complacent and leave it to it. You have to monitor it regularly, because your gas WILL go wrong if you don't.

I like that. I like the way the counterlungs (the bags the gas go into when you breathe out) are on the back instead of the front. I like how simple it is, and how many clever features it's got.

When I finally have the time and opportunity to get back into diving, I'll probably buy a KISS and relearn to dive using a rebreather instead.

If nothing else, that plan guarantees it'll be a few years before I start splashing out on dive gear again :o)