scope:

Description of Driving Event:

The main propulsion system's (MPS) LH2 system operations include the transfer of LH2 from the pad storage tank to the orbiter and pressurization of the external tank during drain operations. A leak/ fire during cryogenic loading or draining operations may result in loss of vehicle and/or life. This risk remains active until shuttle liftoff from the fixed service structure, for a flight readiness firing, or for a countdown demonstration test. LH2 leaks may occur via structure/component failure, purge loss due to flow restriction (clogs, regulator/valve fails closed), or flow diversion (relief valve fails open, flexhose ruptures).