Plastic Bodied Powders

[Guest Steve B]

Hey Guys

bit of a weird one, someone mentioned the Plastic bodied powder extinguishers from the 70s / 80s ceased to be serviceable years ago because of something called Osmosis / reverse osmosis that affected the plastic bodies?? anyone able to shed any light on that and what its about,  ? 

Ta lots :) 

[AnthonyB]

The Fireward brand of plastic bodied cartridge operated powder extinguisher was very popular in both the commercial and domestic/leisure/motoring markets with tens of thousands sold under various distributor brands including Betterware, Chubb, Angus and many more.

However the natural decay and aging of plastic, particularly where subject to external factors including UV from sunlight, was found to make the shell brittle - furthermore impact damage could cause tiny fractures that could not be readily visually detected. Thus they could sit there fine until operated when they would be subject to a rapid rise in pressure and if the shell or headcal/valve was in any way compromised then there could be a rupture or ejection of parts.

Pressure testing could not be carried out readily unlike with steel & aluminum cylinders - also with steel cylinders degradation is readily seen (rust!), so ultimately the model was discontinued (there was also a move away from cartridge extinguishers to stored pressure extinguishers which helped push things along) and for the last 20 years or so servicing standards have required non metal bodied extinguishers to be declared obsolete, not serviced and replaced unless made after 2002 (when more modern synthetic materials such as Kevlar had been developed for pressure vessel use)

 

 

 

[Guest Steve B]

Excellent knowledge and explanation Anthony, but where does the Osmosis come in ? I always thought Osmosis was something to do with Water, not sure how its applied to a plastic bodied extinguisher ? 

[AnthonyB]

Simple answer - it doesn't! 

If you immersed the plastic extinguisher in reverse osmosis filtered water, especially warm water, and left it there in the water then gradually tiny amounts of plastic would 'leach' into the water (why you are only meant to use most plastic bottles once) but this has nothing to do with a plastic extinguisher in service.