Liquid N2 is held in a dewar, consisting of an internal and an external tank with vacuum in between. In case of overpressure, there are blowout valves, designed to relieve pressure in a large hole rather than a small one. You'd rather have a large hole because a high pressure tank with a small hole is basically a rocket. Or a grenade. Also, the N2 liquid to gas expansion factor is roughly 1:700.
In any case, some special person at Texas A&M noticed a N2 dewar with a presumably damaged overpressure blowout valve and fucking welded a brass plug in place. Eventually, the tank catastrophically failed, most likely due to corrosion of the internal tank, leading to temperature increase and the aforementioned 1:700 volume increase. According to I believe the tank manufacturer, the tank mechanically fails at 1200 psi. When it finally went boom, it shredded the room it was in, put a 24-in hole through a concrete floor, significantly damaged a concrete/steel support beam, and was eventually stopped by a 3-in water main and other stuff in a mechanical room. Miraculously it went at 3-am or so and no-one was present.
When people determined what had happened, some unlucky dude who didn't get paid nearly enough got to frantically inspect every tank in the chemistry building to see if the mystery welder had "upgraded" any others.
There's a report pdf somewhere on the internet that I can't find at the moment.
I may have some details wrong but the boom part is definitely right =P
edit: https://web.archive.org/web/20060901094515/http://finance.ta...
it's worth looking at the pictures in the pdf