Release at a dispenser of a HRS

Event

Event ID: 463
Quality: 3
Description: Minor leak in the break-away coupling for 35MPa dispenser of a refuelling station for buses.
The leak developed in the break-away coupling during a controlled test refuel. The test was attended by the station operator’s staff. The leak occurred as the temperature was decreasing (the hydrogen is pre-chilled to between -33oC and -40oC prior to entering the dispenser).

The dispenser was taken out of service until a replacement break-away coupling was installed by the manufacturer. The 70MPa dispenser remained operational.
The dispenser system had been leak-tested during the installation/commissioning phase, however this had only been carried out at ambient temperature. It is believed that the leak was only present at low temperature.
Event Initiating system: Non-Hydrogen System Initiating Event
Classification of the physical effects: Unignited Hydrogen Release
Nature of the consequences: Leak No Ignition (No additional details provided)
Macro-region: Europe
Country: United Kingdom
Date: 25/05/2016
Main component involved?: Dispenser (Breakaway)
How was it involved?: Leak & Formation Of A Flammable H2-Air Mixture
Initiating cause: Material Degradation (Cryogenic)
Root causes: Job Factors
Root CAUSE analysis: Shortcoming in the testing procedure did not allowed for the detection of a small leak.

Application: Hydrogen Refuelling Station
Sub-application: HRS
Hydrogen supply chain stage: Hydrogen Transfer (No additional details provided)
All components affected: break-away
Location type: Open
Operational condition: Normal

Number of injured persons: 0
Number of fatalities: 0
Post-event summary: The 35MPa dispenser was taken out of service until a replacement break-away coupling was installed by the manufacturer. The 70MPa dispenser remained operational.
No injury or harm to any people.

Lesson Learnt: Leak test at ambient temperature may not be sufficient to identify leaks within systems cooled during normal operation. It is proposed that a leak test is conducted during commissioning at the minimum temperature expected during operation.
A more refined automated leak detection logic needs to be developed and is under discussion with the manufacturer in order to capture this type of leaks when trained personnel are not present.