One of the most important things every firefighter or person trained in fire safety must learn is the fire tetrahedron. If you’re looking to learn more about the fire tetrahedron, you’ve come to the right place. We’ll explain everything you should know about it below!
The Four Elements of the Fire Tetrahedron
The gist of the fire tetrahedron is that there are four elements that a fire needs to ignite and continue to burn—heat, fuel, oxygen, and a chemical chain reaction. For many years, it was only a fire triangle of heat, fuel, and oxygen until further research determined the fourth element of chemical reaction was needed—thus making the triangle a tetrahedron.
We’ll explain everything you should know about the elements of the fire tetrahedron.
Heat
What’s the one thing we all know about fires? They’re hot! Naturally, a fire needs heat to combust. The heating element of the tetrahedron refers to the heat source necessary for ignition.
Every material has a flash point—the lowest temperature at which that material can ignite and produce flames. The heating element of the fire tetrahedron is responsible for raising the material’s temperature to or above its flash point, making it susceptible to combustion.
Fuel
A fire can’t erupt from thin air—it needs a material to fuel the chemical reaction. While gasses can certainly ignite, they combust and extinguish quickly if no continuous fuel source exists. We’re all familiar with common flammable materials:
- Wood
- Oil
- Paper
- Certain fabrics like cotton
Some materials burn more easily than others because they have lower flash points, and some burn at different speeds than others. A fire can’t produce its own fuel, so if this element is removed, the fire will extinguish.
Oxygen
Oxygen was, for many years, the final piece of the fire triangle before the chemical chain reaction was added to make it a tetrahedron. To sustain the combustion reaction of fire, oxygen reacts with the burning fuel to release carbon dioxide and heat.
This reaction of oxygen to release carbon dioxide and heat is known as oxidation. As we all know, Earth’s atmosphere is full of oxygen, so this combustion element is almost always available. However, there are methods of removing oxygen from the equation to extinguish the fire.
Chemical Chain Reaction
After further researching the parameters of combustion and fire, a fourth element was added to the triangle—a chemical chain reaction. Now, the triangle is a tetrahedron (also called a fire pyramid), a large triangle with four elements making up four triangles within with the chemical chain reaction in the middle.
Adding the chemical chain reaction gives us a fuller picture of how fires start and burn. After all, oxygen, fuel, and heat alone can’t create a fire—they need to produce a chemical reaction to connect and produce fire.
Understanding the Fire Tetrahedron Helps Extinguish Fires
By learning the core elements of the fire tetrahedron, we can learn more methods for preventing and extinguishing fires. Removing the heat, fuel, oxygen, or chemical reaction can safely extinguish a fire.
For example, a natural gas fire can be extinguished quite easily by simply removing the gas supply. Anyone who has used a gas stove or propane grill knows this. Many of us throw water on a fire to remove heat from the equation, but this doesn’t always work and can make the fire spread. In such cases, we can develop other extinguishing methods, like smothering the fire with fire blankets to remove oxygen or introducing halon gas to disrupt the chemical reaction.
The Five Fire Classes
Our understanding of the fire tetrahedron helps us classify fires into five separate categories: A, B, C, D, and K. These classifications are based on the fuel element of the fire or, in some cases, the setting of the fire.
We’ll explain and define these classes of fires and give examples of extinguishing methods.
Class A
Class A fires are also called “ordinary fires” because they are the most common. Class A fires come from everyday flammable materials we’re all familiar with, like wood, paper, and certain fabrics.
Practically every adult has started a Class A fire at some point in their lives—intentionally in a controlled setting like a fireplace or accidentally. While they may be deemed “ordinary,” class A fires are no less dangerous. They’re typically the easiest to extinguish with water or monoammonium phosphate.
Class B
Class B fires come from flammable liquids and gasses:
- Gasoline
- Paint
- Kerosene
- Alcohol
- Acetone
- Propane
Class B fires are significant concerns in industrial settings, as many industrial workplaces have these flammable liquids and gasses in abundance. Their low flashpoints make them capable of igniting at a moment’s notice. These liquid and gas fires also spread quickly, as liquid and gas can travel easily and interact with other fuel sources to start other fires.
Water will not extinguish a Class B fire—it’ll only spread it by splashing the fuel to more places. To extinguish a Class B fire, dry chemical agents are needed to suffocate the fire and remove oxygen.
Class C
Otherwise known as electrical fires, Class C fires feature live electrical currents or use electrical equipment as a fuel source. As we all know, electronics can generate a lot of heat, and if they overheat, they can reach the point of igniting surrounding materials like plastics.
While class C fires are feared mostly in settings with lots of electrical equipment (like data centers), they can still happen in residential and old buildings due to faulty wiring. Many data centers combat class C fires with a clean agent suppression that removes the chemical chain reaction without harming the electrical equipment.
Class D
Class D fires are known as metallic fires; they are rarer than the other four classes but no less dangerous. These fires occur from flammable metallic materials like:
- Titanium
- Magnesium
- Aluminum
- Potassium
These materials don’t exist everywhere, so laboratories are the most common setting for these fires. The preferred method for extinguishing a class D fire is typically with a dry powder agent to remove the oxygen from combustion.
Class K
Finally, we have class K fires, otherwise known as kitchen, grease, or cooking fires. Class K fires are the same as class B but specific to food service, as they combust grease, oils, and animal or vegetable fats.
Class K fires are incredibly dangerous because of the fuel’s low flashpoint, the wealth of heat in a kitchen, and the proximity of people in a small space. As with class B fires, never use water to extinguish a class K fire—a fire extinguisher with chemical agents is the safest and best method for quick extinguishing.
We hope our explainer of the fire tetrahedron has been enlightening! If you need protective, fire-resistant clothing, remember us at FR Outlet. We have garments like men’s FR shirts and much more! Contact our helpful staff to learn more about our wide inventory of products today!
