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!
Best Answer
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.