Info needed: Foam extinguishers fitted on trucks

[Tony Smith]

Originally Posted by Jacques Reed

The other question is colour. I water blasted .. paint off to reveal a lot of the original dark blue colour which is the colour used to denote foam extinguishers. Water type ones are painted red.

Cheers,

Rather than Water, the Red ones are actually Soda Acid. They contained 2 Gal solution of Bicarb Soda dissolved in water. There was a glass bottle of 50% Sulphuric Acid in the top, which when upturned reacted with the Soda solution to produce Hydrogen Gas and this expanded to expel the water under pressure. I'm not sure of the chemistry that was used with the foam types.

Richard's experience of the non-working extinguishers was a lucky one. The extinguishers were supposed to be emptied, cleaned and refilled every 12 months, as vapours off the sulphuric acid could corrode the copper internals, resulting in big green flakes of crud blocking the hose. If not cleaned out and left sitting for long periods, when activated the expanding Hydrogen gases would have no route of escape past the crud blockage and the cylinder would rupture explosively. The Cylinders were tested to 300psi.