I have been told of this issue a few times, and its also the main reason they no longer use OFN to purge silo's on large petro-chem sites.
I did once raise this issue on the forum but i was imediately shot down by another member, maybe as a more respected member is now raising this it might be noted.
Just to add to the vetenry use, it had been rumoured that some states in the US were researching it as an alterintive gas for execution's as it's apparently more humane,