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.
Juhani Jokinen: Associate Lead Concept Artist at Ubisoft Redlynx - Concept Art - Juhani Jokinen is a Concept Designer and Illustrator from Finland. Juhani works in the Entertainment and games industry for over 8 years.