A around 9:45, during the hydrogen pressure pre-setting phase, a hydrogen leak caught fire on an experimental testbed designed to study the lift-off of launch vehicles. The installation was located in a university research building. A technician gave the alert after seeing on the CCTV screen a flame on a pressure-reducing valve on the line located on the gangway above the test hall. One of the technicians shut off the power to the line and initiated a purge. The technicians present contained the fire. The staff called emergency services. The main power supply was cut off. The six people present in the remote control room were directed to the assembly point. One hour and 15 minutes later, access to the testbed was allowed so that the rest of the hydrogen supply line could be purged.

The fire was caused by the combination of two equipment failures:

• a hydrogen leak on the pressure-reducing valve;
• an electrical short-circuit on an item of equipment near the pressure-reducing valve. This short-circuit was caused either by faulty equipment in a system temporarily installed on the gangway for the experiment or by the voltage surge due to the build-up of moisture in one of the components of the electrical circuit following a water leak the day before.

The operator implemented the following measures:

• the electrical connection that may have caused the short-circuit, as well as the electrical cables damaged by fire, were replaced;
• the seeding system that may have caused the short-circuit was moved to an area away from the hydrogen line;
• part of the control command board was re-energised to carry out leakage tests and check for short-circuits;
• the valves and the seals on the defective hydrogen pressure-reducing valve were replaced and the other pressure-reducing valves and pressure sensors were checked;
• the line was tested for leaks using nitrogen and then hydrogen;
• the control command board was fully re-energised to test the operation of the combustion furnace at low hydrogen flow rates and then at the nominal flow rate.