In article , Dave Hinz says...

The real excitement happens when the round penetrates the vacuum
jacket for the heilum dewar. Those are thin, a 9mm round would
go through. At that point all the liquid in the dewar rapidly
changes to gas, one liter of liquid turns into a suprisingly
large volume of STP helium gas....

It'd come out as a "flame", looks _just_ like, say, a propane
flame, but it's white rather than blue. Inner cone & outer
zone and everything. Similar hazards, too.

The best story I heard happened at Brookhaven when they were
testing SSC magnets. They were running them in a vertical
dewar that went down into the floor about 30 feet deep.

The magnets were wound on steel laminations and were about a
foot in diameter.

To test them they were hung from fiberglass straps down into the
bath, off of a top plate.

They were removing one of the magnets when the crane operator
jerked the load, and all of the fiberglass straps parted,
dropping the entire magnet assembly back into the bath.

The blow-off from that setup ran out into a buffer volume in
the parking lot which was a large tank about the size of
a RR tank car, via a 6-inch line. Apparently the line
frosted up all the way out to the tank, and frosted up the
tank too.

They had two liquifiers there for this testing, we were
piggybacking on their system. They were delivering helium
to us in 1000 liter tanks. The boil-off was reclaimed
and then liquified again, it was a closed system - or
at least was supposed to be.

Their helium gas storage consisted of surplus tanks from Lakehurst
which had been brought on site. Because they were in somewhat
rough shape they had been de-rated down to about 500 psi
IIRC. But they had about 20 of them stacked up, each one
was about 3 ft in diameter and about 25 feet long.

Jim


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