Date: Mon Oct 12 11:29:27 2009
Author: Richard Flarend
Subject: DANGER: Fire-extinguisher on a turntable/stool/hoovercraft
We did our demo show saturday to a standing room only crowd. All went
great except for a really dangerous accident which very easily could
have broken an arm, leg, or something like that for either a
participant or even an audience member.
We did two roller carts with CO2 extinguishers racing across the stage
(with two people of very different masses). This worked fine. Both
people sat on 24" x 24" platforms mounted on roller skate wheels.
Each person held the extinguisher in front of them without the
extinguisher strapped down or otherwise fastened. This did not have
any problems, but I'm now thinking that perhaps we should have the
extinguisher fastened to the cart.
The next demo was to use the Pasco hoovercraft with the extinguisher.
The extinguisher was held (by myself) in my lap and over my feet so
that it was directed tangentally. I pulled on the lever and started
spinning in circles on a cleared stage. Since this was near the very
end of the show, we had cleared the stage of everything so there was
nothing to hit. We also had 'spotters' along both sides of the stage
and off the front of the stage if the hovercraft drifted too far so I
wouldn't fall off the stage or hit something off stage. But what
happened was the the centrifugal force of the extinguisher somehow
pressed against my hand, and I could not let go of the trigger. At
least that is the feeling I recall. I spun faster and faster (all
within what must have been just seconds). I could then not even hold
onto the extinguisher any more (too great a centrifugal force), and it
took off skipping across the stage with me just sitting on the
spinning hoovercraft. Fortunately the entinguisher went straight into
a barrel off stage which absorbed the impact. The extinguisher was
not still spewing after it left my hands. If it had skipped off a
moment sooner, it would have landed in the audience, and maybe (but
doubtful) would have had enough speed to skip over the blocked off 1st
row and then go into the second row where people were sitting.
So I am thinking that this type of a spinning demo is inherrently
unsafe unless the extinguisher is fastened down to the cart and
positioned in the center of the cart so that it cannot obtain any
translational kinetic energy. This is what I plan on doing for future
years. I am also going to go a bit further and also remake the linear
carts so that the extinguisher is fastened into them too.