Fires occur when we least expect them to. They have the capacity to cause utter and complete destruction. When they occur, a quick reaction can not only save property but also lives.

But to react in the right way, we must first learn what it is. A wrong reaction can cause much more destruction than would have originally occurred.

For instance, if someone pours water on an oil fire, they will end up spreading the fire even more. Watch the following video to understand what we mean.

This is why the first step in combating fire is always to understand the type or class of fire. The different classes of fire need different types of extinguishing agents.

By the end of this article, you will not only be able to understand the different types of fire but also what extinguishing agent to use for a type of fire. Let us begin!

Classes of fire

Different organizations define fire classes differently. Two of the most popular standards are the ISO (International Organization for Standardization) and NFPA (National Fire Protection Association) standards.

Both standards find use in the marine environment and hence, all seafarers must be familiar with both of them.

The ISO has its headquarters in the UK and is also known as the European standard. On the other hand, the NFPA has its headquarters in the United States making it the US standard.

There are also other standards such as the Australian standard but that is beyond the purview of our article here.

We shall explain the ISO standard in this article and then diverge where the NFPA differs from the ISO. As per ISO Standard 3941, there are 5 main classes of fire depending on the fuel source. These are:

  1. Class A Fire
  2. Class B Fire
  3. Class C Fire
  4. Class D Fire
  5. Class F Fire

Let us look at each of these classes of fire in detail.

Class A Fire

As per ISO as well as NFPA, Class A fires are fires caused by solid fuels. Solid fuels mean any combustible materials such as wood, paper, rubber, plastic, cardboard, fabric, etc.

Solid fuels may be in the form of dunnage, doors, cardboard, fixtures, fittings, and even the structure of the building itself.

Since solid fuels are all around us, these are the most common type of fires. They also have a low ignition temperature which increases their likelihood.

The best agent to douse a Class A fire is water. Water removes the heat from the fire reaction and prevents the fuel from reigniting.

You may also use dry powder fire extinguishers that cut off the oxygen supply. The lack of oxygen suffocates the fire and puts it out.

Class A fire example - Wood fire
A wood fire is an example of Class A fire

Related read: The Fire Triangle and The Fire Tetrahedron: A Beginner’s Guide

Class B Fire

As per ISO (Europe), Class B fires are fires that involve combustible liquids. In NFPA (US), Class B fires refer to fires involving flammable liquids as well as gases.

Combustible liquids such as fuels, oils, cleaning liquids, solvents, inks, alcohols, coolants, etc. are capable of starting and sustaining a fire when the right conditions are present.

Some examples are gasoline, diesel, kerosene, lubrication oils, greases, tars, lacquer, paints, etc. which are available in industrial and residential facilities as well as on ships.

These fires come with the risk of explosion and are relatively trickier to combat. A careful assessment and execution of firefighting operations are essential for quick and effective results.

We need specific agents to combat a Class B fire. Agents such as foam, powder, and carbon dioxide are effective against these fires. They work by cutting off fresh air and smothering the fire.

The firefighter must never use water on a Class B fire. Using water only exacerbates the situation by spreading the flaming material instead of extinguishing it.

Another important point to note is that Class B fires can reignite when fresh air is introduced into the chamber smothered by foam or carbon dioxide. Thus, we must cool the chamber down to acceptable levels before opening it for verification purposes.

Fire teams typically use water for boundary cooling and thermometers for continuous monitoring of chamber wall temperatures.

Oil fire Class B fire
An oil fire is an example of Class B fire

Class C Fire

According to ISO, a Class C fire refers to a fire caused by flammable gases.

Flammable gases refer to fuel vapors, natural gas, LPG, methane, hydrogen, and any other gases that can form a combustible/explosive atmosphere with the surrounding air. Such an atmosphere can lead to large-scale fires and explosions that are very difficult to tame. For ISO Class C fires, a dry powder fire extinguisher works best.

NFPA Class B fires cover flammable gases along with flammable liquids. Class C in NFPA is dedicated to electrical fires. Any fire involving energized electrical equipment is termed a Class C fire. Once the equipment is isolated, Class C fires can be doused using the same type of fire extinguishers as Class A and Class B fires.

But in cases where the electricity has not been cut off, it is crucial to only use an extinguishing agent that does not conduct electricity. You must never use water or foam fire extinguishers on a live electrical equipment fire.

Carbon dioxide fire extinguishers are best for such electrical fires. But they must not be used in tight spaces as carbon dioxide creates a suffocation risk for persons in the vicinity.

Flammable gas fire Class C fire
A flammable gas leak from pipe is a Class C fire (ISO)

Class D Fire

In ISO as well as NFPA, Class D fires are fires involving combustible metals. These types of fires are not so common. They occur when metals melt at high temperatures. Metals are also good conductors of heat and electricity which helps the fire spread more quickly.

Some examples of combustible metals are aluminum, calcium, lithium, magnesium, potassium, plutonium, sodium, titanium, uranium, and zirconium.

Dry earth and sand work well enough for extinguishing small metallic fires. Powder extinguishers are recommended for larger fires. Fire extinguishers meant for metallic fires contain special dry powder depending on the metal at risk.

One point to note for metal fires is to never use water fire extinguishers. Water acts as an accelerant for metal fires and dousing a metal fire with it will make the situation worse.

Metal Fire - Class D fire
Aluminum metal set alight by an oxy-acetylene torch

Class F Fire

ISO categorizes Class F fires as those that are fueled by cooking oils and fats. Cooking oils, when they get too hot, can catch fire damaging people and property. Such a fire is also known as a grease fire.

Cooking oils are often an overlooked fire source and may be stored or handled carelessly. But these fires can spread very fast and cause high amounts of damage. This quality makes them one of the most dangerous types of fires.

Combustible materials in Class F fires include combustible cooking media in the galley such as cooking oils, grease, and vegetable and animal fats.

The best way to put out a Class F fire is to cover the cooking appliances with a metal lid. We also have special wet chemical type fire extinguishers that are very effective against Class F fires. They form a foam blanket over the fire and prevent reignition.

Just like oil fires, Class F fires become worse when attacked with water except when sprayed as a fine mist. You may also use a fire blanket to smother small kitchen fires.

When it comes to NFPA, there is no Class F. Cooking oil fires are classified as Class K fires. The same rules apply to Class K fires as Class F fires.

Cooking oil fire - Class F fire
Cooking oil fire in a kitchen – Class F fire (ISO)

Electrical Fires

Electrical fires do not have their own class in ISO as electricity is not a fuel source. Instead, it only sets alight combustible materials in its surrounding.

There is no Class E in ISO. When denoting an electrical fire, a “spark” symbol is used without the letter “E”.

In NFPA, fires involving energized electrical equipment are known as Class C fires.

As discussed above, electrical fires involving energized equipment must only be attacked with non-conducting media such as carbon dioxide.

If you are able to de-energize the equipment, you may deal with it in the same way as an ordinary solid fire.

Electrical fire
Electrical fire starting at the plug


Let’s do a quick recap of the types of fire according to ISO and NFPA to further improve our comprehension of the topic.

ISO and NFPA fire classes and types of fire extinguishers


Sufficient knowledge of the different classes of fire is necessary to choose the right type of extinguisher when a fire occurs. If you happen to notice a small fire that can be extinguished using a portable fire extinguisher, just ensure that the class mentioned on the extinguisher is the same as that of the fire under attack.

This small thought before operating the fire extinguisher only takes a second. But it can be the difference between an extinguished fire and one that gets out of control.