One of the best insights I received about masks was from my son who went through the Federal Law Enforcement Training Center (FLETC). He was instructed that the N95 mask could be used in environments where they were likely to encounter chemical and/or biological hazards. They received instruction on a three-step procedure to follow to ensure a proper seal. After one half hour, they needed to leave the environment and put on a new mask. They were instructed that any other masks would only protect from agents carried by droplets the size of water vapor.