It is a good idea to always have a fire extinguisher nearby, and of course, testing them regularly to make sure they are working is also a good idea. Most businesses have fire extinguishers as well as warning systems of some kind. Most people have fire alarms in their homes as well, which are really smoke alarms, and testing those regularly as well is also a good safety precaution.
The Fire Equipment Manufacturers Association lists five kinds of fires and as many as eight kinds of extinguishers. There is some crossover as some extinguishers can be used on different kinds of fires. It is important to know what kind of fire you are confronting, as well as what different extinguishers do. Some kinds of extinguishers can actually make a certain kind of fire worse, or cause other safety hazards.
The most common type of fire in homes is Class A fires, which involves wood, paper, cloth, and other basic household items. A basic water and foam extinguisher is effective for this kind of fire, and it is the extinguisher found in most homes. They should not be used on other kinds of fires though. The spraying of the foam could spread a liquid, like gasoline, and make the fire worse. It could also create a shock hazard if there were electrical wires involved in a fire.
Another class of fire is for liquids that are burning, like gas or oil. A similar type is fires involving electronic equipment. these are called Class B and C fires respectively. A carbon dioxide extinguisher is best for this kind of fire as it removes oxygen from the fire, and does not make it spread. This type of extinguisher is not generally effective for the basic Class A fire.
There are also wet and dry chemical extinguishers. Dry chemical extinguishers interrupt the chemical reaction going on in a fire while a wet extinguisher removes the heat and prevents the fire from restarting. These are good for cooking accidents and are used in commercial kitchens.
Water mist extinguishers are for Class A fires and can be used on some other types of fires. A dry powder extinguisher is best for fires involving metals, and are used almost exclusively on that kind of fire. A clean agent extinguisher uses halon agents and interrupts the chemical reaction in the fire. These also come in smaller sizes and can be handheld.
It is important to have the right kind of extinguisher, but no matter what kind you have, regular testing is essential.