I don't like the gas mask idea..
Be very careful, depending on how old your gas mask is you may actually be poisining yourself. And even if it looks brand new it may not be protecting you from shit.
Check out the provided link, if your mask resembles any ot the ones on the page, it can be considered useless. This is by no means a complete list, I think you would be safer applying yourself to other means of protection. I would hate to hear that you are suffering from chromium toxicity, just because you were trying to protect yourself by wearing a gas mask...
http://www.approvedgasmasks.com/defective-masks.htm (http://www.approvedgasmasks.com/defective-masks.htm)
Ventilate, Ventilate, Ventilate.....