Gas mask bug

[tjockblock]

tjockblock:
Not sure when it is supposed to disappear. The gas mask is needed to enter the machine room and the computer terminal, is that what you mean?

Any idea when the mask disappeared? Are u sure it is not in the inventory?

The walkthrough says:

"Chemical Room:
Put on the gas mask, use a rock to break the rusty pipes, replace the pipes with the good ones scattered around the room go into the airlock"

So im kind of stuck, i guess i didn´t notice the gas mask gone until i were there. But im 100 % sure its not in my inventory. If anyone maybe had a savegame i could use?