Larry Jaques wrote:

On Tue, 14 Mar 2006 14:16:05 GMT, with neither quill nor qualm,
Michelle quickly quoth:

In talking to our local plumbing supplier about that very subject....
Black copper or PVC is fine.
I went with PVC. easiest to work with and cheapest.

Michelle, I worked with PVC air lines for years and nobody got shards
imbedded in their eyes (skulls, or anything else) BUT, PVC isn't rated
for air pressures and can explode. I no longer recommend its use after
reading the official stance. OSHA has _kittens_ upon its mention in
that usage.

http://www.osha.gov/dts/hib/hib_data/hib19880520.html

I now recommend black pipe or copper tubing or air, though there are
some plastics now used in air lines: Nylon, polyurethane, and ABS.

http://www.cbs.state.or.us/osha/interps/1989/im-89-06(rr).pdf
http://www.newageindustries.com/sprthncl.asp
http://www.colexint.com/pneumn.htm

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That brings up an interesting possibility, how about the PEX tubing that
is pretty cheap and easy to crimp together? I would imagine that unlike
PVC the failure mode if it were to fail would be a startling but
harmless split and air release with no flying shards.

Pete C.