explosion on a turbopump at an aerospace testing facility

A special test was being executed to evaluate a high-pressure fuel turbo-pump lift-off seal.

During the test, an open-air explosion took place on the test stand. There were no injuries, but non-structural damage occurred.
It was concluded that structures or other barriers erected for weather protection tended to minimize hydrogen dissipation and may have contributed to the extent of the damage by partial containment of the explosion to the damaged areas.

The INITATING CAUSE was probably the failure of the lift-off seal of the turbopump. This is not explicitly stated in the source, but it can be deduced by knowing that the ongoing test aimed at testing exactly the seal.

The ROOT CAUSE was the unavailability of measures mitigating hydrogen releases, worsened by a design which created structures around the testing device, what made possible deflagration or detonation in (semi-)confined environment.

rain shield, wind barrier

THE TURBOPUMP
The aerospace turbopumps is a components in rocket engines, where fluids like liquid hydrogen must be pumped at high pressures and temperatures before entering the combustion chamber. The liquid hydrogen pressure varies depending on the rocket engine's turbopump, for example in the J2 engine the inlet pressure was 0.2 MPa and was brought to 8.5 MPa. The final pressure in the LE-9 engine reached 19.1 MPa.

WHAT IS A LIFT-OFF SEAL?
A turbo-pump lift-off seal is a non-contacting mechanical seal that uses engineered grooves to create a pressurized fluid film, causing the seal faces to separate during operation. This "lift-off" action prevents wear and heat generation, making it ideal for high-speed, high-pressure environments like turbopumps in rockets, where it can reliably seal fluids like liquid hydrogen and kerosene while also functioning as a static seal when the system is not running.
Lift-off seals are basically consisting in two metal sealing faces that are lapped to a very smooth finish and are pressed together during assembly. The faces develop a thin microfilm of leakage fluid between them during operation that minimises friction between the static and rotating face.
[Turbopump - Wikipedia]
[NASA lesson learnt at https://llis.nasa.gov/lesson/750]
(accessed November 2025)

WHICH TESTING FACILITY WAS BEING USED?
The A-1 engine installation was used for the static testing of rocket engines, at the National Space Transportation Laboratory (now NASA's Stennis Space Centre). The tests involved attaching engines to the stand to fire and measure their performance, power, and durability before their installation on a launch vehicle.
Propellants for engine tests are supplied by a 40,000-gallon liquid oxygen run tank and a 110,000-gallon liquid hydrogen run tank (420 m3, 30 tons). Fully loaded, the tanks can supply enough propellant for a 350-second test.
[https://www.nasa.gov/wp-content/uploads/2021/09/a-1_test_stand_v1.pdf]

The damage was limited to non-structural component of the testing facility, such as shields and protection/insulation pipe jackets.

The main lesson learnt was that the role of structures in impeding hydrogen effective evaporation and/or dissipation must be considered in the overall risk assessment and the safety-design. Non-structural elements must be considered as well in the risk analysis, such as those used to minimise damage from or influence by environmental factors such as rain and wind. This is especially important in testing facility where hydrogen release cannot be prevented or excluded due to the sheer nature of the tests.