Under Pressure

Have you ever lifted a bucket full of water?

Heavy, isn't it? Imagine what's required to lift a diving pool full of the stuff, or what it would feel like to lie underneath it.

Because that's exactly what happens when you dive. Gravity pushes the weight of the water downwards onto you. What's odd is that you're not aware of it. This is where it gets all scientific and beyond my limited comprehension - somehow the interplay of forces on your body prevents you from feeling the weight, or from being crushed by it.

At least, it seems that way. In fact the air inside your body does get squashed as you dive, and you don't need to go very deep before you feel the effects. If you've ever dived into a pool and swum down to about three metres (or ten feet) you'll probably have experienced pain in your ears. That's caused by the air inside you being squashed - or by the change in pressure, to be more technical.

Even when you're not beneath the water your body is under pressure from the air. The invisible stuff around you, that you breathe in and out, has a weight. It's not very much, but when you're standing on the beach you're underneath about 35 kilometre of air (that's around 21 miles). That's a lot of air and it weighs about 2kg per square centimetre. All that weight is pushing down on your body all of the time - but you don't notice because you're designed to live in it.

Because water is a lot heavier than air, you don't have to go very deep before it begins to affect you - remember that pain in your ears when you dived to three metres? In fact, the pressure on your body doubles when you reach about 10 metres. Which means all the air in your body is squashed into half the space it usually takes up when you're on the surface.

Those first 10 metres are where you get the most dramatic change, as pressure doubles (or increases by 100%) from sea-level. At 20 metres the pressure is triple the pressure at sea-level, but it's only 50% more than the pressure at 10 metres. And so on downwards. Eventually, of course, it becomes unsustainable our bodies to cope, but by then we'd also be dealing with lots of other problems.

These changes have all sorts of implications for divers which is why training and practise is so important. At about three metres you might have a pain in your ears because of the change in pressure, but at 10 metres it could get much more serious.

For me, dealing with the pressure changes in my ears is the next serious hurdle to overcome. My first was being able to jump into the water and now I need to find a way to equalise the air pressure in my head as I dive. During both of my lesson my ears have hurt at the bottom of the diving pool (3 metres) and this week I still had minor ear problems over 24 hours after coming out. They've cleared now.

You're probably used to handling changes in air pressure - it happens when you come down from a hill or if you're in a descending aeroplane. I usually find that yawning or swallowing hard helps my ears to 'pop' or equalise. But you can't yawn under water and even swallowing is tricky. So I need to find another way.

I'm sure I'll find a way of dealing with it, and I'll have to if I want to dive deeper. But for the moment I do feel under a little more pressure than usual!