On 05/07/2019 17:11, NY wrote:
"Steve Walker" wrote in message
...

I've been on company fire training courses. Interestingly they were
suspended for a while when one of my colleagues set off a CO2
extinguisher that turned out to have a leak from the pipe that joined
the horn and he suffered a cold-burn.

I remember being told that we mustn't touch the horn itself, only the
handle that's attached to it, because of the risk of cold burns.

The most memorable thing I remember was the demonstration of why you
shouldn't pour water on a burning-liquid (petrol or chip pan) fire. The
demonstrator set up two wide, shallow trays. One was filled with petrol,
the other with diesel. The petrol ignited as soon as a flame (on a long
pole!) was brought near the vapour. The diesel could not be ignited, and
put out the flame if it was touched onto the surface.

When the petrol fire was burning away nicely, the demonstrator poured a
few millilitres of water (again, on a long pole) onto the fire and the
whole thing exploded and shot burning petrol over a wide area. He then
tried with a CO2 extinguisher - that blew the petrol out of the tray
onto the grass, but the tray remained alight because the hot combustion
gases heated the CO2 so it didn't lay as a blanket over the fuel. Foam
or dry powder for liquid fuel fires, IIRC.

I've never had to use the approved method of holding a fire blanket, but
I can still remember it: hold the blanket so the top edge faces towards
you, curled round so it's covering your fists which are facing palm
towards you, and lay the blanket gently *from front to back* (never the
other way round) over the chip pan until it covers the pan, when the
flames will very quickly go out because the fire is starved of oxygen.
Leave the pan where it is until the fire brigade arrive: don't move it
*even after the flames have gone out*. Obviously don't try to move it
while it's on fire.
I did a few company fire courses too, with similar demos. Sometime in my
past (no idea when or where) I saw a demo of what not to do with a hot
oil fire - a spectacular demo that sticks in the memory quite well.
I once set-off a CO2 extinguisher as a test in a small electronics lab -
the temperature change was surprising but shortly afterwards I had to
rush out because of a feeling of lack of oxygen - obvious really, but I
hadn't thought of that effect beforehand.