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Ill start by saying that I found this question, which is extremely similar to my line of thought: Can a class A fire be extinguished with a class BC fire extinguisher?

I am trying to consider the right mix of extinguishers for my home and detached garage. While the ABC dry chemical seems to be a good base extinguisher that is ubiquitous, it appears that they can make a big, acidic mess, and other options may be better.

So my curiosity is that many places say DO NOT USE an extinguisher on a fire other than what the extinguisher is rated for. Sensible for a type A water extinguisher on a flammable liquid or on an electric fire. In a garage or basement, where a solvent or fuel fire may be the principal consideration, other items may get engulfed (vehicle interior, lumber stored nearby, building structure, etc) it makes the question more relevant. You want the best agent for the actual risk at hand (say, stored flammable organic liquids), but need to know the effect if the extinguisher is applied to other materials. This is not defined anywhere that I know of!

But what would happen if one used a different dry chemical, say a standard BC or purple K extinguisher on a Class B fire that also had some wood or other Class A materials in the mix. Ive not seen any real data on the efficiacy of this, though I have to imagine there is some.

I get it that some types must NEVER mix. Im not asking that for the dumb, obvious ones. Instead, for how dry chemical applications overlap.

Thanks!

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    "Big acidic mess" is relative to "watch the house burn down" - if you have to actually use a fire extinguisher, what sort of mess you are going to have to clean up is a very low consideration outside of museums and data-centers. As already explained in that answer, the general concern with Class A fires and non-class-A extinguishers is that they may re-ignite from embers. AC water (ultra-pure non-conductive with a droplet nozzle) offers a minimal clean-up halon-free solution to flaming computers; the old-fashioned fire bucket full of sand may also prove useful for putting those embers out. – Ecnerwal Jul 20 '16 at 14:12
  • Usual solution is to get something like a 1A10BC mixed-use extinguisher. Messes can be cleaned up later, damaged appliances and electronics can be replaced, if you have a fire first priority is safety, putting it out quickly or getting out of the building and getting the fire department on the job quickly. Second priority is saving the house and as much of the House's contents as possible, and you may have to accept some sacrifices. – keshlam Jul 20 '16 at 15:59
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    I use ABC in my home a water extinguisher will make a grease fire worse. My oldest daughter started a grease fire on the stove and first dumped water on it causing it to spread, Then my son put it out with the ABC, It was a mess to clean up but other than some scorched paint everything was able to be cleaned up with lots of soapy water, then some paint. – Ed Beal Jul 20 '16 at 16:28
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This is a layman's view, but with some logic behind it as well as experience.

Choose an extinguisher for the major threat first. A second extinguisher might be nice to have but as residual smouldering of things like wood is probably the most likely secondary threat, a ready supply of water should be sufficient backup. If you've still got a fire after using an extinguisher, you should be well on the way out of the door by that point.

The experience I mentioned: we had a small electrical fire, by the time we got the CO2 on it there was paper/card burning nicely and a wooden bench getting going. Once the fire was out and the power off it became obvious that the bench wasn't completely out. CO2 isn't much use on smouldering wood but less than a litre of water dealt with that. For liquid fuels this may not translate directly, but then it's even more important to keep your exit clear and/or use the extinguisher to help you get out, as the spread may not be what you expect.

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