On Thu, 26 Jul 2018 14:33:30 +0100
Clive Arthur wrote:

On 26/07/2018 11:38, Bert Coules wrote:
Tim,

Many thanks for your thoughts.Â* The collapse has to be pretty much
instant, so any release of pressure on an inflatable dummy would
need to take immediate effect or nearly so.

snip

Inflate the 'balloon' with ammonia gas. To deflate quickly, squirt
some water in - ammonia dissolves in water very well and rapidly.

(Ok, maybe not, a bit dangerous, but it might provoke some other
ideas.)

I was thinking more of constructing the dummy from balloons filled with
hydrogen and oxygen. :-)