JamesC
Fishaholic
My last word on this is DONT DICE WITH DEATH. High pressure cylinders should not be messed around with by unqualified people.
I'm afraid to say but gowing238 is correct in what he has said, if a little alarmist. CO2 cylinders are highly dangerous pieces of equipment and must be treated with extreme care. If the top is knocked off or regulator comes off they can quite easily kill and even go through brick walls. Fire extinguishers are more dangerous than aquarium and pub cylinders due to the fact that they use syphon tubes. These are incorporated into extinguishers to enable the release of CO2 as quickly as possible so to put out the fire. Because the syphon tube draws the CO2 from the bottom it means that liquid CO2 is expelled rather than gaseous CO2 in aquarium and pub cylinders.
All cylinders should be safely secured so they are not able to be knocked over. I have a 6.35KG pub bottle that is secured to the wall by a chain and also has protection around the regulator to prevent any accidental damage. I used to work in a lab for many years and have seen the damage that a gas bottle can do. Somebody I know of in the States used to get his CO2 cylinder refilled from a filling station. One day he went to get a refill and it was gone - including the bloke who was filling a cylinder at the time.
Just be careful folks
James