Benzene, C6H6 and Zyklon B (aka HCN) are very different chemicals and I'm not advocating HCN as a delousing agent. The difference is that the body copes with small amounts of HCN very well as small amounts can be naturally found in food whereas C6H6, an aromatic hydrocarbon, isn't. C6H6 does damage in an altogether different way and its effects are cumulative.
Incidentally, as I've mentioned in an earlier post I've always been very careful to avoid exposing myself to C6H6, but less so to HCN. I used to use HCN in photographic processing and as I mentioned once before on HN I was affected by its fumes—and I'm still here to mention the fact (but I'm not for a moment suggesting that people be lax when using the stuff).
Incidentally, as I've mentioned in an earlier post I've always been very careful to avoid exposing myself to C6H6, but less so to HCN. I used to use HCN in photographic processing and as I mentioned once before on HN I was affected by its fumes—and I'm still here to mention the fact (but I'm not for a moment suggesting that people be lax when using the stuff).