On Fri, 06 Jan 2006 03:18:03 GMT, "William Wixon"
wrote:

i figured someone was going to say that. so, if you can use a flammable gas
(carbon monoxide) to displace oxygen, couldn't you purge the oxygen out of
the tank with propane?

Yes, you certainly could.

However you'd then have a problem with the propane igniting too easily
outside the tank, where it's inevitably oxygen rich. CO is harder to
ignite and less energetic than propane, so a leak of CO to the
atmosphere doesn't become a secondary hazard (for typical volumes and
risks).

CO is far from an ideal inerting gas. However it's often commonly
available as engine exhaust (which may contain considerable nitrogen,
CO2, and water vapour too). It's rarely used from choice, but in the
case of oil tanker ships (for example) it was often used simply because
it was the only practical gas to hand. Another risk with exhaust gas
inerting is that diesel exhaust can contain a significant amount of
oxygen under some engine conditions.