Bob Bownes said:
>->There's a discussion of this over on rec.crafts.metalworking, started
>->by the usual question of "is PVC OK". The concensus is still no,
>->but a new reason or three have cropped up:
>->* PVC brittles with age; the plasticizer evaporates over time
>->* Oil in the compressed air attacks the plasticizer
>->* Compressed gasses store much more energy than uncompressed liquids,
>-> so failure is much more catastrophics (the "grenade" effect)
>->* PVC pipe melts in a fire, leading to hazardous conditions for firefighters
>->This last reason is apparently why it is against many local, business
>->and OSHA regulations.
>Then why is is legal for h2o? This doesn't make sense....(and if you
>think it won't melt with h2o in it, I can assure you from personal
>experience, it does. Lead pipes full of water melt. Copper pipes full
>of water melt. Iron ones seem to hold up a bit better, though they'll
>usually still bend some...Of course it depends on the severity of a fire.)
>I'll buy it's against OSHA, but more likely for the explosive failure mode.
Well, think about this for a second. Fire breaks out and your
PVC pipe filled with water melts and bursts. Big deal - there's
now a bunch of water helping put out the fire. Fire breaks out
and your PVC pipe filled with compressed air melts and explodes
into shrapnel. There's now a bunch of hot plastic being splattered
on the firefighters, and a high pressure source of oxygen turning
your fire into a blast furnace.
I'd never considered this before, but now I notice that plumbing lines
for water may be copper, but sprinkler lines are *always* black iron
with threaded fittings. And I think this is why - the joints don't
come apart when things get hot.