The BCAC had a cool game a while back with a simulated gas attack from a munition we had to disable. An engineer had a pair of wire cutters, and we had to get him to the device so he could cut the wire. We failed, the device went off, but there were secondary objectives in the area we had to secure in a time limit, which ended before th gas did. The game admins utilized a large air dropped smoke canister as the chem agent. The thing must have burned for 10 minutes. Those little cheap white dust masks were used as NBC gear, so we could still use PB approved goggles on the field.
As for a game in actual NBC gear, you go right ahead. Ever worn it? I'd be willing to bet if you do, there won't be a second time.
"Anyone with a name like Amanishourbariki should give a few letters to the poor Ng family." - Snarfangel, Fark.com