The govorning regulation is DOT CFR 49, Subpart D, 173.115(b).

Basically, if a tank is above 41psia, its a restricted HAZMAT, but if its below 41psia, its completely unregulated.

For international flight rules, the DOT referred me to International Civil Aviation Organization (ICAO) 1995-1996 edition, chapter 2 on page 2-2-1, which is pragmatically identical to the above. This does not guarentee that each country doesn't have their own rules, but is a general guide.

I have the complete text of DOT CFR 49, Subpart D, 173.115(b). online at URL:

This page also contains a DOT 800# to verify if its still current.

-hh ( H NED Huntzinger )