What Is Fire & How Does It Spread?

Originally Published December 30, 2014

Fire is a chemical reaction that occurs when fuel combines with oxygen and produces heat and light.

Fire is a chemical reaction that requires three things to occur: oxygen, fuel, and a heat source. This process is also known as combustion. Without one of these factors, a fire can’t start or sustain itself.

Most home and business fires start within the building. For example, a smoldering cigarette dropped into a trash can full of paper could ignite into flames. The cigarette is the heat source, and the paper is the fuel or substance that burns. If the fire is not extinguished while in this early phase, it could spread throughout the structure.

So, how do the flames spread beyond the confines of the trash can to the rest of the building? This guide explains what fire is and how it spreads to help better understand how to prevent fire damage to homes and businesses.

Fire Definition

Fuel, oxygen, and heat work together to produce fire. This is often referred to as the fire triangle:

• Fuel: materials that can burn and undergo combustion, like paper, wood, and gasoline.
• Oxygen: the gas in the air, which combines with fuel during combustion to release heat and light.
• Heat: the initial heat source needed to raise the temperature of the fuel; once the fuel reaches a certain temperature, it ignites and burns.

In all chemical processes, molecules rearrange themselves, and energy is either absorbed or expelled. When a fire burns, a process called oxidation occurs, the same process that causes metal to rust.

Oxidation is when oxygen atoms combine with carbon and hydrogen to form carbon dioxide and water. When metal rusts, the process happens very slowly, but when a fire burns, heat and energy are released very quickly.

The rate of oxidation is faster with fuel sources such as paper and wood. When heat can’t release faster than it’s created, combustion occurs. This is what creates the flame and heat known as fire.

Smoke comprised of unburnt particles, evaporated water, and carbon dioxide is also produced, though the cleaner the burning process, the less smoke that is produced and visible.

How Does Fire Spread?

Once started, a building fire is likely to spread until the fuel is depleted— which could have devastating consequences for homes or businesses. Without fuel and oxygen, a fire cannot sustain itself. According to the National Fire Protection Agency, fire departments respond to fires approximately every 22 seconds in the United States.

By understanding how fire spreads, individuals may be better equipped to extinguish it early on to avoid significant damage. A fire can spread due to the following factors:

• Chemicals and combustibles: When fire comes in contact with lab chemicals, household cleaners, paint, and other chemicals, it burns hotter and more aggressively, encouraging it to spread. Other combustibles commonly found in homes and businesses include mattresses, sofa cushions, magazines, newspapers, and various textiles.
• Open space: A building with a limited interior structure burns much faster than one with hallways and closed doors. Walls and doors trap the fire and prevent the flames and smoke from spreading as quickly.
• Construction materials: While a fire can burn through just about any modern building, fire-resistive buildings made of concrete and steel curb the spread of fire better than wood-frame structures.
• Ventilation: Buildings with central heating or air conditioning have ductwork, which provides a way for flames and smoke to spread between floors of a building, even when the structure is comprised primarily of concrete and steel.
• Water: In some cases, water is not the best fire extinguisher. For example, grease fires can spread faster when doused with water. A class B fire extinguisher, salt, baking soda, fire blanket, or a pan lid can be used to suffocate and stop the spread of a grease fire.

How Do House Fires Spread?

House fires can spread quickly due to the amount of synthetic materials in homes. For example, furniture, curtains, and certain articles of clothing made with synthetic materials burn faster and hotter. Synthetic fibers, like nylon or polyester, burn eight times faster than natural materials, like cotton or wood.

How Do Fires Spread in Commercial Buildings?

Fires in commercial buildings with an open concept can spread faster since there are no structural barriers, like walls or doors, to stop the fire from spreading. While a fire will eventually burn through the structure and continue to spread, it's easier for firefighting teams to contain flames in a building with more walls and doors, especially if those structures are built to withstand the heat and damage caused by a fire.

How Fast Does Fire Spread?

Fires can spread within 30 seconds, and an average-sized building can become engulfed in flames in as little as five minutes. Fires can spread at different rates, depending on factors like the type of fuel, the amount of moisture in the air, the layout of the building, and the presence of combustible materials.

Because fires can spread so rapidly, it’s important to prepare for the unthinkable. For businesses, developing an emergency response plan can ensure a plan is in place and company protocols are followed in the event of a fire.

FAQ About Fire and How It Spreads

Is Fire a Chemical Reaction?

Yes, a fire is the result of combustion, which is a chemical reaction. Combustion occurs when fuel combines with oxygen to produce heat and light, creating fire.

What Is Fire Made Of?

Fire is made of oxygen, heat, and fuel. As mentioned above, when fuel combines with the oxygen in the air, it produces hot flames.

Does Fire Travel Up or Down?

Though heat naturally rises, fire can travel upward, downward, and horizontally depending on different factors, such as the materials involved, ventilation within the building, or the layout of the property.

For example, a home fire may start by traveling upward but spread horizontally once it reaches the ceiling. When heat becomes trapped in a confined space, it’s forced to move horizontally or downward.

How Can a Fire Start?

A fire can start in many different ways, but some common fire-starters include:

• Unattended candles
• Matches and lighters
• Unattended kitchen appliances
• Unsafe cooking methods
• Fireplaces or wood stove
• Flammable products
• Worn-out electrical cords

What Are the Four Ways Fire Can Spread?

Fire can spread in four ways through different methods of heat transfer:

• Conduction: This process occurs when fire spreads from direct contact between materials and objects. Objects that are good heat conductors, like metal, can cause a fire to spread when they come in contact with a combustible material.
• Convection: This happens when heat is transferred through the movement of liquid or gas. The hot gases and smoke from a fire rise upward and can heat the materials it comes in contact with, causing them to ignite.
• Radiation: This process involves heat traveling through electromagnetic waves. The heat can radiate in different directions and ignite a fire once it comes in contact with combustible materials.
• Direct burning: This happens when a direct flame comes in contact with a combustible material and ignites it, starting the spread of fire.

What To Do After a Fire

If a home or business has fallen victim to the destructive forces of a rampaging fire, professional restoration services from Rainbow Restoration can help restore order. Contact Rainbow Restoration® today to begin the recovery process.

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This article is intended for general informational purposes only and may not be applicable to every situation. You are responsible for determining the proper course of action for your property. Services should be performed by licensed and experienced professionals. Rainbow Restoration is not responsible for any damages that occur as a result of this blog content or your actions. For the most accurate guidance, contact a Rainbow Restoration professional for a custom, on-site assessment.