A Dewar-type cylinder filled with liquid nitrogen burst at 3 am in a university chemistry laboratory. The accident occurred during the night and no one was injured, but substantial material damages were observed. The overpressure blew off the bottom of the cylinder which was propelled into the air. An unidentified person had in the past replaced the cylinder’s safety relief valve and the rupture disk with 2 brass plugs. Before bursting, the cylinder was apparently leaking through an old static seal thus preventing any overpressure in the chamber. This seal had been replaced 12 hours before the explosion, then the cylinder had been refilled with liquid nitrogen. With this new leaktight seal, the internal pressure progressively rose eventually exceeding 1,000 psi (69 bar) and causing the cryogenic tank to rupture.

Cryogenic equipment must be properly refrigerated in order to maintain low temperatures and pressures, or designed to allow enough vapours to escape thereby maintaining the chamber’s pressure and cooling. The explosion and the projection of cylinder parts could have damaged other recipients and pipes containing dangerous substances. The equipment, which should not have been modified by removing its safety mechanisms, does not seem to have undergone sufficient regular inspections. The exact date and location of the accident was unknown.