Thanks, Davros, though we've derailed the thread. I looked into it further and the Drano Foam MSDS does not say Drano Foam is a DOT-classified "oxidizer" but does mention that it contains "strong oxidizers." Specifically, though not noted on the MSDS, the culprit in this case is sodium dichloroiscyanurate - which has its own MSDS stating lots of nastiness. Given that the Drano MSDS was provided to the storage facility that mixed the shite w/ water I think it's their fault. Course, they pay me a lot to think that.
Look, now I've even bored the crap out of myself.