ABC powder extinguisher clean up

[rumple]

Hi there,
I'm hoping someone can give me some reliable advice. My eldest son had a fire in the cabin of his car and used a powder extinguisher to put it out. It was great at killing the flames but we are left with a real mess with the powder getting everywhere. Looking online the recommendation is to clean up with isopropyl then use a weak vinegar solution. We've done this but metal items are still corroding like mad. So are tools that were in the garage at the time. Having looked at monoammonium phosphate which is supposedly the main constituent in the fire extinguisher it seems to have a pH of around 5 which is acid. So it seems odd to me to be advised to use vinegar for the cleanup. Wouldn't a base solution be best? We're in the midst of removing what we can then we plan to use a pressure washer to blast off the residue. If anyone has any experience or knows the best way to deal with the problem I'd be all ears.   I was going to post on the other channel but I've more or less given up on it. Thanks.

[countrypaul]

I remember spending some time when I had a summer job as a student filling dry powder fire extinguishers.
The powder I was using was predominately potassium carbonate, it was very fine and got everywhere - it was done in a dedicated hut with mask goggles on etc. and that was 40 odd years ago.

I don't know where the idea to use vinegar came from, but if the instructions assume all dry powders are the same they are probably wrong.

I would agree that using vinegar with monoamonium phosphate does not appear to make much sense in terms of cleaning it up, after all once it gets wet it is amost equivalent to 2/3 phosphoric acid.  You would need to be cautious if using a strong basic solution as you stand the chance of releasing ammonia if you get it wrong.

Plenty of water to dissolve and wash away may be the other option.

Best bet might be to use something like bicarbonate toif you want to neutralise the phosphoric acid - but test it first in a well ventilated area to make sure there is nothing else likely to cause issues.

[rumple]

Thanks for the reply. I can see why these extinguishers work as the powder finds its way into everything and sticks like the proverbial to a blanket. We've had to clean out the heater matrix assembly, aircon assembly, all the vents etc. etc. You mention ammonia being released, well today I tried a solution of sodium hydroxide in water at around a pH of 9 and dunked some plastic trim parts in. There was a distinct smell of ammonia but I was in a well ventilated area and it soon cleared. I assume it neutralised the monoamonium phosphate but the residue still needed to be brushed/scraped off the trim parts and after drying them, there was still a hint of whiteness on the black plastic. It's difficult to completely remove all trace of it. The inside of the car is pretty much stripped out inside now so we will attempt to clean the bodywork off. I'll go down the bicarbonate route as you suggest. We'll be using a pressure washer to try and dislodge the residue so the car will be outside and fumes shouldn't be an issue. I see that B&Q advertise 500g of bicarb for £1.74 so that'll be a trip for tommorow. Would you suggest a solution of around pH9 would be about right? All done at my risk of course.

[countrypaul]

Both monoammonium phosphate and to a certain degree bicarbonate of soda will act as buffering agents, that means adding some base to the phosphate solution should result in little change to pH, similarly adding a little acid to bicarbonate will make little difference to the pH (though it probably will effervesce). I would not rely on pH to tell you much about the quantity left behind, it would be useful to check if any acid is left behind, but the pH will change little even when significant neutralisation has taken place.

Both ammonium phsphate and ammonium sulphate (the other main constituent of ABC powder) are quite soluble in water, and probably much more so in warm/hot water. It might be worth trying to wash things down with hand hot water once you are down to just a fine white sheen on the plastic parts.

There also appears to be some silicon additives used, but I have no idea what they are or what effect they can have, but silicones can have very significant affects on surface actions. Don't ever use a silicom furniture polish near anything you want to spray paint for example - even in the same room!

[kamaangir]

If it was ABC powder than it was MAP which is acidic, if it was BC powder its bicarbonate of soda which is not. Powder extinguishers are horrible in anything but fresh air, as you have found out unfortunately! They also give you the runs.   

Try and vacuum as much as possible then damp cloth the rest but as its acidic it will eat away at everything.

[rumple]

Hi Kamaanger,
I followed Paul's advice and washed it down with bicarb in warm water. Didn't bother with the pressure washer. It produced loads of smelly ammonia but we pushed the car outside so it was fine. It seems to have been quite successful and the powder's gone from the wiring harnesses, connectors and the inside of the car. I removed all the pedal brackets and various other metalwork and have derusted them using electrolytic rust removal as they were, as you say, badly corroded by the powder. To be honest it's a job we should have done a few months ago when it happened but we did a half *rsed job of it as my son needed it back on the road and only cleaned areas we could easily access. He's off this week so that's why we're trying to sort it. It was that bad that after a small journey you could feel your hands drying up from the powder which was in all the hard to clean areas.
I never realised what a complete mess those extinguishers make and how much corrosion they cause . I've now got a number of CO2 extinguishers on standby for the garage. You live and learn.

[kamaangir]

The reason they are popular is that they have very good knock down power on 3 different classes of fire.
For workshops get a foam 6litre (which does class A and B) class c fires, which are gasses, I wouldn't even try and tackle them in a workshop or domestic environment. Co2 is good for electrical fires and also if you get a diesel runaway. Just blast the air intake and it will put it out in seconds.

Just today I removed a 9kg powder extinguisher from a posh restaurant that have spent a couple of hundred thousand on a refit!!!

Good job on the cleaning though I don't think I would have the patience!