Dry Powder extinguishers carried on road vehicles

[John Webb]

In another thread there is mention of problems regarding handles dropping off DP fire extinguishers being carried on lorries.

This reminded me that when I carried a 6kg DP in my old HA van in the 1970s, I noticed that the contents seemed to pack down in the extinguisher.
About the same time colleagues of mine at Fire Research were looking at the effect of vibrations on DP extinguishers, and as a result suggested that where such extinguishers were subject to vibration, particularly on road or rail vehicles, the extinguishers should be regularly inverted and shaken to loosen up the contents to ensure a full and proper discharge.

I wonder if this advice was made public and if it is still followed?

[kurnal]

We had the same problem in the 1970s when we first started carrying dry powder on fire appliances. I think this was before the days of multi purpose dry powders and I have a feeling they may even have been gas cartridge operated - but dont quote me on that. We were told to tip them upside down and give them a good shaking during the weekly standard tests.

I just have at the back of my mind an idea that stored pressure were less susceptible and the caking may have been partly due to vibration and partly due to damp in the extinguisher body.

I always carry a 2kg multi purpose in my car - a gloria- and I discharged it recently with no problem at all on a training course as it was due for a periodic discharge test.

I bet Anthony B wont have heard of this phenomenon.

Bedford HA vans- now that takes me back. Quite nice looking at the time but rattletraps and no go. I preferred the Anglia (Thames) for performance, minivans for handling and the Imp for looks- but they were always in the garage.

[AnthonyB]

Compaction was a major problem in older powder extinguishers mainly because they were cartridge type. The powder was able to compact due to vibration to such an extent that it couldn't be fluidised by the CO2 when set off, so little or no flow came out. Free flow additives helped a bit, but the problem was such that in the 1970's after a critical failure of a powder extinguisher on an agricultural vehicle questions were asked in the House of Commons. Regular shaking and inversion was indeed required.

The need for a dry environment for charging was critical too as dampness also caused caking. Mixing powder types generated CO2 & water leading to a pressure build up & caking as well- very dangerous.

The use of stored pressure technology cured the problem - this kept the powder permanently fluidised and thus unable to compact. In the UK Nu-Swift were one of the first to use this technology with CO2 as the propellant, followed by Pyrene and then others using nitrogen and/or dry air.

The need to fluidise the powder and discharge it on a stream of propellant is why powder extinguishers need bigger gas cartridges mass for mass than water based agent which are 'pushed out' by the propellant without mixing.

Another vibration problem was observed on a ship by Angus Fire Armour with reports of some cartridges in powder extinguishers unscrewing themselves.

[John Webb]

Thanks - yes, mine was a CO2 cartridge operated one. I don't have any of the FRS papers regarding their tests on DP, so I just could not look it up in my effort to remember!