This is the failure mode that catches out competent people, because it happens in the pipework rather than in the vessel.
The mechanism
Close two valves with liquid nitrogen between them and you have sealed a liquid that is already 200 degrees below room temperature into a fixed volume. It warms. One litre of liquid becomes roughly 683 litres of gas at ambient conditions, and in a sealed section that expansion has nowhere to go, so it appears as pressure instead.
Why the pipe loses
Pipework and fittings are specified for the system operating pressure, not for the pressure a trapped cryogenic liquid can generate as it warms. The failure is sudden and the release is a large volume of cold gas at head height.
The control
Any section of line that can be isolated at both ends and can contain liquid needs its own pressure relief. This is a design requirement rather than an operator habit, so it belongs in the installation review, not the daily checklist.
What to check on your own system
Walk the line and look for any pair of valves that can be closed independently. Each isolated section between them needs a relief path, and that path needs to be unobstructed.
