Any user of a pressure vessel or pressurised system shall cause every such vessel or system which for operational purposes is equipped with a removable or hinged door to be provided with an interlock or other effective means for preventing -
a. a rise of pressure inside the pressure vessel or pressurised system before the removable or hinged door is in the fully closed and locked position; and
b. the release of the removable or hinged door from the locked and closed position before the pressure inside the pressure vessel or pressurised system has been reduced to atmospheric pressure.