[hermitcrab]

Water extinguishers are almost completely useless.

I once had a go at putting out a fire in a waste paper bin with a water extinguisher, as part of a fire safety course. The burning paper just floated on the water as the bin filled up.

CO2 extinguishers are more effective. But I believe you have to be careful where you hold it or your skin may freeze onto it.

Get a fire blanket for your kitchen.

[michaelt]

The time you want water is when something that water can soak into is on fire. Sofas, curtains, bedding, bookshelves, carpets, filing cabinets full of paper, etc.

The water soaks in and prevents the fire re-igniting. 30 years ago, workplaces contained a lot more filing cabinets and bookshelves, and smoking was more common.

CO2 is non-conductive, and less messy. It's also great at flowing around things, making it good for spraying through vents into electrical cabinets and car engines. Downside is the CO2 dissipates within a few seconds, so if the material is prone to re-igniting it's not such a good choice.

Dry powder is in between - the powder stays around, but doesn't soak in. It's a good choice if you're only going to get one extinguisher.

[potato3732842]

Water extinguishers are incredibly useful for putting out small incidental fires that can result from hot work without making a big mess. The kind of stuff you'd just move outside or let burn out rather than discharge a powder extinguisher over.

Nobody is whipping out a dry-chem extinguisher because the leaves under the workbench caught on fire from welding sparks.

[avhon1]

Water mist fire extinguishers are nice. They are much more able to cool lightweight, flammable objects, and pose less risk of causing electrical arcs.