The clean room work environments I saw didn't have people wear masks. They had special suits though, that made them look a bit like people in the old Star Trek

The clean room work environments I saw didn't have people wear masks. They had special suits though, that made them look a bit like people in the old Star Trek movies. The reason that was explain to us was that working several hours every day in an environment with high volume vertical air flow was uncomfortable without padding in the shoulder parts.