Fire on a CHG2 tube trailer in filling area

Safety slug in the vent pipe of a hydrogen trailer failed, damaging the pipe and causing a hydrogen leak. The following fire damaged several other trailers.

[Zalosh and Short, 1978]

Despite the lack of details, INITIATING CAUSE was a damage of the safety valve, causing a leak.
The fact that the fire damaged additional trailers hint at a ROOT CAUSE related to a lack of proper risk assessment when designing the operations, which did not consider the possible escalation from too nearly parked trailers without fire barriers.

vent pipe

The meaning of the term 'safety slug' is unclear. A slug flow, in liquid flow engineering, is a "is a phenomenon that occurs in pipelines carrying gas and liquid mixtures. It involves the intermittent movement of slugs—large pockets of liquid—that can lead to pressure fluctuations, flow disruptions, and potential equipment damage... Slug catchers are specialized devices designed to capture and manage liquid slugs in pipelines." Source: https://www.everyeng.com/blog/ff4ac270)
It can only be hypothesised that a safety slug is a system preventing slug to further block the gas flow in the vent piping. However, why a safety slug would be necessary on a pipe of a hydrogentrailer is unexplicable.