Section 154.1828 - Spaces containing cargo vapor: Entry(a) No person may enter a cargo handling space without the permission of the master or without following a safety procedure established by the master.(b) Before allowing anyone to enter a cargo handling space, the master shall ensure that: (1) The space is free of toxic vapors and has an oxygen concentration of at least 19.5 percent oxygen by volume; or(2) Those entering the space wear protective equipment with breathing apparatus and an officer closely supervises the entire operation in the space.