Abstract: A leak test apparatus for leak testing a tank including a gas supply system configured to provide to the tank a leak detection gas mixture including hydrogen, a test chamber having a cavity for sealably enclosing the tank such that dead space exists outside the tank and within the cavity, and a gas conduit configured to interconnect the gas supply system and the tank, a control system including a controller programmed to pressurize the tank with the leak detection mixture by flowing gas from the gas supply system through the gas conduit, and a leak detector to determine the presence or absence of a leak in the tank by measuring a concentration of hydrogen in the dead space.