These fires are of paper, wood, materials, plastics, and rubbish which are in the main organic and contain carbon compounds. They can be suppressed using water, foam, or multi-purpose dry powder, but care needs to be taken in certain circumstances to ensure that smoldering embers do not reignite if and when they again come into contact with oxygen.

Fires involving flammable liquids, such as oil, gasoline, solvents, and other oil-based products like paints used in the home. These liquids tend to have a high carbon content making them highly combustible. The most effective suppressant is normally foam. Water, except in the form of a mist, should never be used against a Class B fire. 

Fires caused by an “energized electrical power source”, and usually provoked by a short circuit, faulty wiring, power extension damage, or overloaded outlets. Water and water-based foams should NEVER be used to suppress this class of fire because it can lead to serious burns and other injuries from electric shock and fatality from electrocution resulting from current passing through the body via conduction. 

You will be hard pressed to find Class D fires in the home as they involve flammable metals, the most common of which include magnesium and titanium, but can also involve other metals such as potassium, zirconium, and lithium. This kind of fire is found in industrial, commercial, and even laboratory environments. Water fire extinguishers cannot be used to suppress these fires. They can, in fact, make them much worse both by intensifying the flames and dispersing the fire to adjacent areas. Extinguishers containing dry powder in the form of graphite (powder) and sodium chloride (granular) are commonly used to fight this class of fire for which people require special training to use them effectively.

This class of fire involves vegetable and animal fat-based cooking oils and greases that are generally found in commercial kitchens. But they can also happen in the home where the kitchen is possibly the most likely place where a fire can start. This is why it is important to have Class K fire extinguishers on hand together with fire blankets.

The extinguishers are able to contain Class K fires involving extremely high temperatures by dispensing a water mist made up of an alkaline mixture that chemically creates a blanket to suppress the flames through oxygen starvation.

 You have to be careful not to mistakenly use a Class B fire extinguisher they are rated for flammable liquids such as petroleum and gases. They cannot deal with Class K fires.