I was surprised at how long it took before the can exploded. I would have
expected the plastic valve near the nozzle to melt quicker than that, and
maybe to cause an impressive jet of flame for a while before the whole can
If you watch videos of fires on the news, something normally "blows" on
LPG cylinders and you get a jet of flame, insufficient to turn it into a
rocket, and the cylinder itself doesn't explode. It *might* be that the
same happened in this case and that it was the containment provided by
the woodburner, probably the windows or the lid, which "blew".
Yes, that's what I'd expect to happen with an aerosol can: that the valve in
the nozzle would melt and release the contents, rapidly rather than
explosively, long before the pressure built to the point where the metal of
the can sheared at its weakest point and dumped its contents explosively.
Even an inert propellant will increase in pressure enough to make the can
rip open; if the propellant or payload is flammable, then that makes things
even more dramatic - which is what you'd think they'd want to avoid with
Good thing they weren't acetylene cylinders. Apparently they are even more
dangerous. When roads and railway lines are closed due to a fire and a
several-hundred metre exclusion zone, it's usually acetylene (and associate
oxygen) cylinders from oxy-acetylene welding kit.
There was a fire at a garage just down the road from me about 8 years ago
and that started in welding equipment - and then spread to the underground
luckily I lived just outside the exclusion zone so I wasn't evacuated, and I
managed to work my way round to the other side (driving several miles to do
what was about 1/4 mile) and took some of the photos in the article. The
noise of the explosions was *very* loud. The fire brigade set up a "paddling
pool" of water into which they could dump any hot acetylene cylinders that
had not exploded, which is not a job you'd get me doing: transporting a
cylinder that could explode at any moment. The garage site was a mess for
several years until insurance and liability was finally sorted out and the
place was rebuilt. A friend's car had a lucky escape: he was due to leave it
there overnight to have a new tyre fitted but decided instead to call back
with the car in the morning, so it escaped going up in flames.
Mind you, even inert compressed gas is dangerous. My A level chemistry
teacher had taught "in industry" before becoming a teacher and he worked in
a building near Heathrow. One of the young engineers (who should have known
better) tried to unscrew the main valve-plus-gauge unit from a big 4-foot
nitrogen cylinder, possibly when he should have been unscrewing a hose from
it. The valve blew off, shot through the ceiling and was found several miles
away just inside the perimeter fence of Heathrow by a routine security
patrol. The cylinder was pushed through the floor and buried itself in the
concrete floor below. No trace of the engineer was found. And that's due to
pressure alone - nitrogen is not flammable.
Many years ago, about 1960, coming back from school of a winter evening I
witnessed a fire in one of my fathers rented artisan workshops.
A cylinder of dissolved acetylene went up, and I do mean up. As in a rocket.
The cylinder went through the roof and continued skyward. DA cylinders are
bl**dy heavy. It was found the next morning about 50 yards away.
Gutted the workshop and those adjoining it. Nobody hurt fortunately. Fire
brigade sorted the fire. Roof gone but structure sound.
Re-roofed and refitted. Workshops still in use today