Kenneth Anderson has an excellent article on modern gas warfare at Lawfare. He explains why it is especially useful against civilians, something I’d be wondering about. It’s rather like the effect of randomly distributed land mines or IED’s:
Having taken testimony from civilians in civil wars ranging from Central America to central Asia, I can say simply that the panic described by survivors in the interviews I conducted in Kurdistan were qualitatively different from that induced by ordinary weapons. This is partly because – from the victims’ and survivors’ standpoint, as they expressed it to me – poison gas free-floating in the air, blowing wherever it blew, invisible and deadly, was “indiscriminate” in some way beyond that term’s usual meaning in the law of armed conflict.