The gas mask on the Breach Response outfit doesn’t actually protect against gas either. I went to Hawke’s Bay and did the sedative poison in the bathroom vent and failed. Then I went to Whittleton Creek and put the lethal poison into the fumigation machine. Died when I entered the house.
Seems like a gas mask should actually, you know, mask gas…
Also, credit to @silvereaper who discovered this a couple days before I did and posted in another thread. Things About Hitman You Just Found Out - #6816 by silvereaper