In Black River Falls the non infected people could be around the infected people but if they were too close to them they could get it. So they used gas mask to be close to the infected people. It was an air born illness so that why they used gas mask.
inBoil remarked "You people don't know about iDeath. Not a damn thing, you're all at a masqerade party." "Ar you afraid to find out about iDeath?" "what it really means?". "Come, then" Charley said "Show us iDeath ",