A hydrogen leak took place on a trailer carrying compressed hydrogen, located inside the fenced perimeter of a hydrogen station. According to the company managing the hydrogen delivery and refuelling station, the leak did not pose any risk to people or the environment. A preliminary assessment identified a faulty valve s source of the leak, but t was unclear a that time if it was a single defect or a systemic (i.e. design) problem. Following a detailed investigation in close cooperation with the trailer and valve suppliers, the company determined that the root cause of the valve malfunction was due to a set of improperly tightened bolts, causing an O-ring to burst.