Failure of a GH2 tank due to over pressure

During the J-2 engine testing program, the engine start tank was pressurised. The pressure raised to an excess of 1500 psi (ca. 105 bar). The venting of the tank was attempted but remained pressure remained high. It was then assumed that the pressure instrumentation had failed. A blowdown was initiated through engine, but the start tank ruptured and fire engulfed test stand area. The rupture of tank caused damage to engine and test stand facility.
[Ordin, NASA (1974)]

The INITIATING CAUSE was the rupture of a hydrogen tank due to overpressure.

When the tank failed, the internal pressure was probably approximately 2900 psi (ca. 195 bar), far above the maximum allowed 105 bar.
Water was found in the vent manifold where the start tank vent line connects to the manifold. It was believed that an ice blockage prevented the venting as any relief action by the vent or relief valve.

The ROOT CAUSE was a combination of (1) over-pressurisation of the tank, probably due to a wrong (application of the) pressurisation procedure, (2) a system design defect allowing formation of water in the vent, (3) wrong assumption by the operators, who assumed a wrong reading of instrument when the venting failed.

engine start tank

DESCRIPTION of the FAILED COMPONENT:
The start tank assembly system of the J-2 (from Wikipedia: https://en.wikipedia.org/wiki/Rocketdyne_J-2 (accessed August 2023):
"...was made up of an integral helium and hydrogen start tank, which contained the hydrogen and helium gases for starting and operating the engine. The gaseous hydrogen imparted initial spin to the turbines and pumps prior to gas generator combustion, and the helium was used in the control system to sequence the engine valves. The spherical helium tank was positioned inside the hydrogen tank to minimize engine complexity. It held 16,000 cm3 (1,000 cu in) of helium. The larger spherical hydrogen gas tank had a capacity of 118,931 cm3 (7,257.6 cu in). Both tanks were filled from a ground source prior to launch and the gaseous hydrogen tank was refilled during engine operation from the thrust chamber fuel inlet manifold for subsequent restart in third stage application".

DESCRIPTION OF THE ROCKET
The J-2, commonly known as Rocketdyne J-2, was a liquid-fuel cryogenic rocket engine used on NASA's Saturn IB and Saturn V launch vehicles. Built in the United States by Rocketdyne, the J-2 burned cryogenic liquid hydrogen (LH2) and liquid oxygen (LOX) propellants, with each engine producing 1,033.1 kN (232,250 lbf) of thrust in vacuum.

The alarm was called 15 minutes after the explosion, the site was evacuated after approximately an hour, the power shut off and the area was ventilated. Safety barriers were put in place to prevent traffic and firefighters intervened. Measurements of hydrogen concetrations were executed.