Hydrogen explosion in a rocket fuels laboratory

In a laboratory, tests with hydrogen as aerospace rocket propellants were carried out.
One of the experiments consisted in the generation of a vertical jet (turbulent regime) to determine the sound levels emitted by jets of H2 gas. It consisted in the intentional venting of 1000 kg of hydrogen at 23 MPa within 30 s.
The discharge flow was uniformely increased upt to 55 kg/s, maintained for 10 seconds and then reduced to zero, After 26 s, while decreasing the flow, the hydrogen unintentionally ignited. A fireball was formed followed immediately by an explosion.

The Vapour Cloud explosion VCE caused damage to structures of the surrounding buildings (walls, doors, roofs).
The over-pressure was estimated at 0.035 bar to 45 m. The burning gas cloud of approx. 9 m diameter and 45 m height containing 9 to 10 kg of hydrogen.
According to the some sources, the cause of the ignition could have been static electricity or a spark of mechanical origin. Other sources concluded that at the release conditions of the experiment, auto-ignition can occur.

[Note of HIAD Validator: on the quantity of hydrogen involved in the explosion, the sources diverge (see reference): for ARIA it was 90 kg, for PRESLHY it was 9 kg, for Lee it was 10 kg, for ICHEME was 71 kg. ]

The INITIATING CAUSE was the unplanned ignition of a hydrogen flow during an experiment.
IGNITION was probably due to static electricity and / or a spark of mechanical origin.
The ROOT CAUSE was probably a shortcoming in the design and execution of the experiment, which did not consider the possibility of ignition and detonation.

laboratory, vertical jet experiment

According to the Wikipedia page dedicated to the testing facility, previous accidents with hydrogen had already taken place in the year 1960-64.
This is not surprising, because the laboratory was one of the first in the world studying hydrogen properties.

For abackground information regarding this NASA project, see Wikipedia page https://en.wikipedia.org/wiki/Project_Rover#CITEREFFinseth1991 (accessed November 2025)

VCE (mainly negative overpressure) causes damage to structures (walls, doors, roofs) of buildings. The overpressure is estimated to be 0.035bar to 45 m and the amount of H2 involved in the explosion is 90 kg (othe source says 10 kg).
Explosion was heard 3.2 km away. TNT equivalent of 8%.