The Science of Flammability: Why Some Materials Are More Likely To Catch Fire Than Others

Kim J. Clark
What Makes Something Flammable?

Fire is one of the most dangerous and destructive forces of nature. It is at once beautiful and terrifying. It can bring warmth, light, and a cosy atmosphere to our homes; but it can also destroy everything in its path if left unchecked. The ability of fire to consume almost any material is what makes it so dangerous. Thankfully, many materials are less susceptible to fire than others. 

There are several properties that make some materials more likely to catch fire than others. These properties are flammability, ignition time, flame spread, heat release rate, and flash point. They all have unique variables that determine how prone a material is to catching fire under different circumstances. If you’re working on projects with flammable materials like wood or fabric that require you to know how likely they are to catch fire before using them, this article, as well as the expertise of our team at Capital Fire Doors, will be beneficial to you. Keep reading for explanations of these terms as well as common examples of each category of flammable material.


Flammability is the ease with which a material will catch fire under certain conditions. All materials are flammable to some degree, which means that they can ignite with enough heat or spark. The difference between materials is the amount of heat or spark required to start the fire. Flammability is a laboratory number that quantifies the ease with which a material is likely to catch fire. In order to determine a flammability rating for a particular material, a sample is placed in a furnace and burned at a consistent rate. The amount of heat required to keep the sample burning steadily is measured. This determines the rate at which the sample burns. The amount of heat required to ignite the sample is also measured. This determines the ignition rate. These two numbers are used to calculate the flammability rating.

Materials with a high flammability rating

Materials that have a high flammability rating catch fire easily and burn quickly. Some types of wood, particularly softwoods like pine, spruce, and fir, are highly flammable. So are many types of synthetic fabrics like acrylic, nylon, and polyester.

Materials with a low flammability rating

Materials that have a low flammability rating catch fire less easily and burn more slowly. Some types of hardwood like oak, maple, and cherry are considered to have a low flammability rating. So are some synthetic fabrics like acetate, polyester, and rayon.

Materials with a very low flammability rating

Materials that have a very low flammability rating catch fire very slowly and burn very sluggishly. Some types of natural fabrics like silk, wool, and cotton are considered to have a very low flammability rating.

Ignition Time

Ignition time is the amount of time it takes to catch fire once a material is exposed to sufficient heat or spark. Some materials require higher heat or more spark to catch fire than others. This is why some materials burn more slowly than others. The difference between materials is their ignition time. Higher ignition time means it takes more heat or spark to start the fire.

Flame Spread

Flame spread is the speed at which a fire spreads through the material. This is different from the flammability of the material itself. Some materials that catch fire easily also have a high flame spread. Others that catch fire more slowly have a lower flame spread. Flame spread is determined by how much oxygen the material allows the fire to consume. Materials that allow more oxygen into the fire have higher flame spread. A common example of a material with a low flame spread is concrete. The low flame spread of concrete is a major reason it is used for structural support in buildings.

Materials that are prone to fast flame spread

Materials that are prone to fast flame spread catch fire quickly, thus requiring a greater response time by firefighters. Flammable liquids like gasoline, paint solvents, and alcohol are likely to have a high flame spread. Flame spread can be reduced by sealing the materials in a container that allows minimal oxygen to enter the container. For example, storing gasoline in a sealed container keeps it from being able to catch fire and burning.

Heat Release Rate

Heat release rate is the amount of heat a material generates when it is burnt. Some materials generate more heat than others. Flame retardants and fire-retardant fabrics reduce the heat release rate of the material. This slows the rate at which the fire burns. Fast-burning materials like wood generate more heat than slower-burning materials like concrete. The fire can be controlled and eventually extinguished if the materials are sealed in a container.

Flash Point

The flash point of a material is the minimum amount of heat required to ignite the sample. The shorter the flash point, the more likely a material is to catch fire. Some materials have a higher flash point than others. The flash point of a sample is determined by heating it in a controlled lab setting. The more heat the sample takes before igniting, the lower its flash point.


A wide variety of factors can affect the likelihood of a material catching fire. From the sample’s flammability to its ignition time, flame spread, and heat release rate, there are many variables to consider. The best way to reduce the risk of fire in your home is to be mindful of the materials you use. Make sure they are rated as low-flammability and are treated with fire-retardant materials. If you have children or pets in your home, be extra careful to avoid using high-flammability materials. You can also install fire alarms, smoke alarms and fire doors to give yourself extra warning and safety in case a fire does start.

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