I thought I'd share by exerience of making a foolish and potentially
dangerous mistake. I am replumbing the house at the moment and there
are some 'dead end' pipes that lead up to the bathroom but are
presently capped off with compression stop-end fittings like this:

http://www.screwfix.com/prods/50419/...22mm-Pack-of-5

Anyway, these pipes were pressurised at mains pressure but had a lot
of air in them. I thought it would be a good idea to bleed the air
out. So I thought: "I'll just slacken the stop end compression nut a
tiny bit and let the air hiss out, then tighten it up again."

Well, as soon as I slackened the nut a little there was a loud BANG
and the whole fitting shot off at high speed. Luckily it did no
damage. This was followed by a lot of water!

I now realise of course that once the fitting was slackened it did not
take much force to slide the olive off the end of the pipe. The loud
bang was because of all the compressed air in the pipe -about 1 litre
of air at 70 Bar.

I felt really foolish. Learn from my mistake!

Robert