Abstract: A protective enclosure device for filling tanks with compressed gas provides a cylindrical enclosure within which a tank may be placed and connected to a filling line, and which can, thereafter be closed by a closure arrangement that is equivalent in design to a cannon breech block from the standpoint of its ability to resist the explosive forces of an uncontrolled tank rupture. The walls of the enclosure are not only sufficiently thick to resist rupturing thereof, but are sufficiently heavy to absorb all of the dynamic reaction forces of an explosive tank rupture. Venting of the enclosure is provided at a rate which will prevent room over-pressurization and a resulting potential damaging of windows, doors, and other structures. The device is constructed to function in a fully automatic manner employing electromechanical and pneumatic devices.