Over-pressurisation of a rocket LH2 tank

The second stage of the Saturn V (S-II-T) was under full-duration static test, when one fire near LH2 valves of the LH2 tank and another in the engine area caused the automatic termination of the test. The rest was stopped after 195 seconds, of the total of the planned 350 second firing.
Three day later, when looking for the cause of the leak in the LH2 tank, the second stage of the Saturn was destroyed. Technicians had been trouble-shooting the causes of the fires occurred three days earlier. After the LH2 tank was emptied, pressure checks using helium were in progress. However, during prior tests, the pressure sensors and relief switches of the tank had been disconnected, a fact unknown to the crew conducting the pressure checks. To identify the location of the leak, they closed all valve and pressurised the tank beyond its design limits. Five men of test crew were slightly injured, and two others were hospitalized for observation.

The INITIATING CAUSE was an ignited leak from the LH2 stage tank.
When troubleshooting the leak, a series of errors occurred, which brought to the over-pressurisation of the LH2 tank beyond design limits.
(1) The crew searching for the leak did not know what the previous crew had done (i.e. switching off pressure sensors and pressure relieve systems).
(2) The crew did not perform check of the status of the system before starting working.
(3) Among the members of the crew there was a lack of the knowledge and experience required to understand out-of-specification phenomena.
The ROOT CAUSE was lack of effective control and enforcement of the testing procedures.

valves, sensors, PRD, tank

The event is structured around two dates: the date of the occurrence of hydrogen leak during testing, and the date (three days later) of the catastrophic failing of their troubleshooting.

the whole secod stage of the Saturn had to be disposed.

The test of 25 May was unsuccessful, even though a full-duration test firing had been successfully accomplished five days earlier. It speaks for the complexity of the systems and the difficulty to guarantee stable performance throughout the testing programme.

The fact that “Atwood called von Braun to express his concern about the incident. Together, they discussed the probable cause, closing with discussion about different ways to expedite the program “, witnesses a management pressure to accelerate the end of the preparatory works for the launch.

A third lesson, still valid thill now, is the need to guarantee effective information and enforcing of procedures from one shift crew to the following shift crew. It calls for strong management interventions and controls.