Class D fires involve combustible metals, especially alkali metals such as lithium and potassium, alkaline earth metals such as magnesium, and group 4 elements such as titanium and zirconium.[2]​.

Metal fires present a unique danger because people are not aware of the characteristics of these fires and are not adequately prepared to fight them. Furthermore, it is not always clear what type of metal is burned. Therefore, even a small metal fire can spread and become a larger fire, spreading to surrounding common combustible materials. Certain metals ignite on contact with air or water (for example, sodium), which exacerbates this risk. Monolithic masses of combustible metals typically do not pose major fire hazards because heat is carried away from hot spots so efficiently that the heat of combustion cannot be maintained. Consequently, a significant amount of thermal energy is required to ignite a mass of combustible metal. Generally, metal fires are a hazard when the metal is in fragmented form or in machine shavings or other fine metals, which burn more quickly than larger blocks due to their greater surface-to-volume ratio. Metal fires can be ignited by the same ignition sources that would cause other common fires.

Special care must be taken when extinguishing metal fires. Water and other common firefighting agents can exacerbate metal fires and make them worse. The National Fire Protection Association recommends that metal fires be fought with dry powder extinguishing agents that act by smothering and absorbing heat. Furthermore, depending on the metal, an extinguishing agent is needed and, for a particular metal, the agents cannot necessarily be substituted for each other. The most common agents are sodium chloride granules and graphite powder. In recent years, copper powder has also begun to be used. These dry powder extinguishers should not be confused with those containing dry chemical agents. They are not the same and only dry powder should be used to extinguish a metal fire. Using a dry chemical extinguisher by mistake instead of dry powder can be ineffective or even increase the intensity of a metal fire.

Fires caused by electricity have different classifications in each of the three systems. They are classified as a "Class E" fire in the Australian system, "Class C" in the American system,[3]​ and according to the type of fuel ignited according to the European system (which previously shared the "Class E" classification with the Australian system). Electrical fires are fires involving potentially energized electrical equipment. This type of fire can be caused by a short circuit in machinery or overloaded electrical cables. These fires can pose a serious danger to firefighters using water or other conductive agents, as electricity can conduct from the fire, through the water, to the firefighter's body and then to the ground. Electrical shocks have caused many firefighter deaths.

Fires related to cooking oils and greases are classified as "Class F" according to the European and Australian systems and "Class K" according to the American system. Although these fires are technically a subclass of the flammable liquid/gas class, the special characteristics of these types of fires, i.e., higher flash point, are considered important enough to be recognized separately. Some special extinguishers designed for this use smother the fire by turning the oil into foam. As with Class B fires, a solid stream of water should never be used to extinguish this fire, because it can cause the fuel to disperse and spread the flames. Commercial kitchens may also have a fire suppression system built into the range hood to release an extinguishing agent onto the source of the fire, releasing it automatically via a fuse or manually using a pull station. Fire blankets are sometimes used to put out a fire in a frying pan or kitchen oven.

Fires where the fuel is flammable or gaseous are classified as "Class C" in the European/Australian system, but are "Class B", along with liquids, in the US system. Due to the gaseous nature of the fuel, these fires are difficult to extinguish. The most effective techniques for controlling a flammable gas fire are to stop the flow of fuel (by closing gas taps or valves) or to displace the oxygen. Control of fires involving flammable gases when the gas source cannot be controlled must be done carefully. If the flames are extinguished, but the gas remains open, an explosive atmosphere can be created and the gas can find a source of re-ignition away from its origin. Strategies used to control these fires may include attempting to direct or contain the fire to prevent ignition of other fuels while working to control the fuel supply.

Class D fires involve combustible metals, especially alkali metals such as lithium and potassium, alkaline earth metals such as magnesium, and group 4 elements such as titanium and zirconium.[2]​.

Metal fires present a unique danger because people are not aware of the characteristics of these fires and are not adequately prepared to fight them. Furthermore, it is not always clear what type of metal is burned. Therefore, even a small metal fire can spread and become a larger fire, spreading to surrounding common combustible materials. Certain metals ignite on contact with air or water (for example, sodium), which exacerbates this risk. Monolithic masses of combustible metals typically do not pose major fire hazards because heat is carried away from hot spots so efficiently that the heat of combustion cannot be maintained. Consequently, a significant amount of thermal energy is required to ignite a mass of combustible metal. Generally, metal fires are a hazard when the metal is in fragmented form or in machine shavings or other fine metals, which burn more quickly than larger blocks due to their greater surface-to-volume ratio. Metal fires can be ignited by the same ignition sources that would cause other common fires.

Special care must be taken when extinguishing metal fires. Water and other common firefighting agents can exacerbate metal fires and make them worse. The National Fire Protection Association recommends that metal fires be fought with dry powder extinguishing agents that act by smothering and absorbing heat. Furthermore, depending on the metal, an extinguishing agent is needed and, for a particular metal, the agents cannot necessarily be substituted for each other. The most common agents are sodium chloride granules and graphite powder. In recent years, copper powder has also begun to be used. These dry powder extinguishers should not be confused with those containing dry chemical agents. They are not the same and only dry powder should be used to extinguish a metal fire. Using a dry chemical extinguisher by mistake instead of dry powder can be ineffective or even increase the intensity of a metal fire.

Fires caused by electricity have different classifications in each of the three systems. They are classified as a "Class E" fire in the Australian system, "Class C" in the American system,[3]​ and according to the type of fuel ignited according to the European system (which previously shared the "Class E" classification with the Australian system). Electrical fires are fires involving potentially energized electrical equipment. This type of fire can be caused by a short circuit in machinery or overloaded electrical cables. These fires can pose a serious danger to firefighters using water or other conductive agents, as electricity can conduct from the fire, through the water, to the firefighter's body and then to the ground. Electrical shocks have caused many firefighter deaths.

Fires related to cooking oils and greases are classified as "Class F" according to the European and Australian systems and "Class K" according to the American system. Although these fires are technically a subclass of the flammable liquid/gas class, the special characteristics of these types of fires, i.e., higher flash point, are considered important enough to be recognized separately. Some special extinguishers designed for this use smother the fire by turning the oil into foam. As with Class B fires, a solid stream of water should never be used to extinguish this fire, because it can cause the fuel to disperse and spread the flames. Commercial kitchens may also have a fire suppression system built into the range hood to release an extinguishing agent onto the source of the fire, releasing it automatically via a fuse or manually using a pull station. Fire blankets are sometimes used to put out a fire in a frying pan or kitchen oven.