A Pressure vessel for human occupancy is a container that is intended to be occupied by one or more persons at a pressure which differs from ambient by at least 2 pounds per square inch (0.14 bar). Since 1977, the American Society of Mechanical Engineers PVHO committee has published standards governing the construction of a number of structures which are defined as Pressure Vessels for Human Occupancy. The current standard is PVHO-1-2019.[1] Similar standards are published by a range of national and international standards organisations.
Nuclear reactor containments, aerospace cabins, caissons or mild hyperbaric chambers[clarification needed] are not considered to be PVHOs according to the standard.[citation needed]