Poison gas is a destructive device for purposes of "firearm" deportability under 8 U.S.C. 1227(a)(2)(C) because it is included in the definition under 18 U.S.C. 921(a)(4). California Penal Code 16460(a)(6) lists dry gas (co2) as a destructive device for state purposes. Other Penal Code sections make it a crime to possess a destructive device unlawfully. California Penal Code 18710, 18715. This apparently means that if co2 is a poison gas under federal law, then a person could be deported as a firearm offender for having a California conviction for unlawfully possessing dry gas. Thanks to Dan Kesselbrenner.