cheers guys, that qualification could be a problem, but probably not a very big one. hows about filling times though? and since cheapo air bottles have guages on them, do they break easily?
Air is quicker and more simple to fill, although bottles will have to be filled more often. If installed by someone like hpac, they will provide as many fill stations as required. Most air equipped sites have a safe zone / walkon fill station as well as a safe area / punter fill station.
As a site you will be looking at anywhere between 10-20k depending on the type of compressor, number of hpa bottles and type of install required. But then you are basically sellf sufficient in terms of bottle fills.
In terms of public liability, I am fairly sure it will make little difference to cost. Insurance rates are based on risk assessment. Compressed air is statisticly no more dangerous than co2.