This is a follow up article from a couple of weeks ago which covered the correct fire extinguisher to use for which type of fire.

In brief, stripping out all the technical jargon. With Aqueous Film, Forming Foam (AFFF or just plain foam) extinguishers there is a problem with the extinguishing agent. This is primarily water but the additive which forms the foam has now been proved to be harmful. Even the more "environmentally friendly" extinguishers that became popular in recent years is also harmful and engineers are being instructed that we need to start replacing them except in certain circumstances.

So we need an alternative. 

Water fire extinguishers are all that are needed in the majority of cases where foam extinguishers have been installed which became popular over the last couple of decades. Not for their class B fire rating which relates to Flammable liquids, but because they were more compact and lighter than then equivalently, heavy and cumbersome 9ltr water extinguishers.  6ltr water spray/mist extinguishers now provide 13A and in some cases 21A ratings with no environmental consequences during use or at end-of-life disposal.  In the situations where a contained class B fire risk exists, more environmentally 14 friendly foam extinguishers are available from your usual service provider.