Fires – How They Start and How They Spread

Fires are one of the most powerful natural forces that humanity has learned to harness, yet they remain a formidable threat to life, property, and the environment. Understanding the dynamics of how fires start, spread, and can be controlled is not just a matter of curiosity but a crucial aspect of ensuring safety and minimising damage. This knowledge is vital for everyone from homeowners to business operators, from students to professionals in the fire safety industry. It empowers individuals and communities to take proactive measures in fire prevention, management, and response.

The purpose of this article is to demystify the science behind fires. By dissecting the mechanisms of how fires ignite and propagate, we aim to provide a comprehensive guide that enlightens and equips readers with the information necessary to understand fire behaviour and adopt effective strategies to prevent and combat fires.

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    How Do Fires Start?

    At the heart of understanding how fires start is the concept of the fire triangle. A fire needs three elements to ignite and sustain itself: heat, fuel, and oxygen. Removing any one of these components will extinguish the fire.

    The Fire Triangle: Heat, Fuel, and Oxygen

    • Heat: Heat is the energy source that initiates the fire. It raises the temperature of the fuel to its ignition point. Sources of heat can be anything from a small spark to a larger flame or even environmental heat in the case of spontaneous combustion.

    • Fuel: Fuel is any combustible material. It can be solid, such as wood or paper; liquid, like petrol or alcohol; or gas, such as propane. The fuel acts as the sustenance for the fire, allowing it to grow and spread.

    • Oxygen: Oxygen from the air reacts with the fuel in a chemical process called combustion. Most fires require an atmosphere with at least 16% oxygen content to burn, which is readily available in most environments on Earth.

    Fire Triangle

    Types of Ignition Sources

    Understanding different ignition sources is crucial in fire prevention and safety. Ignition sources can be categorised broadly into intentional and unintentional sources:

    • Intentional Sources: These are sources where a fire is ignited deliberately, such as matches, lighters, or controlled burns in forestry.

    • Unintentional Sources: These include accidental or incidental sources such as electrical faults, unattended cooking, spontaneous combustion, or lightning strikes.

    Each type of ignition source has its own characteristics and requires specific strategies for prevention and control. By being aware of these sources and how they can lead to a fire, individuals and organisations can better prepare and reduce the risk of a fire breaking out.

    In the following sections, we will delve deeper into the classifications of fires, how they spread through different methods, and the various techniques and technologies available for fire prevention and control. Our goal is to provide a thorough understanding that not only informs but also empowers action towards greater fire safety.

    Classification of Fires

    Fires are classified into different categories based on the type of fuel that is burning. This classification helps in understanding the nature of the fire and determining the best method for extinguishment. The most commonly used classification system includes five classes: A, B, C, D, and K.

    Class A Fires

    • Description: Class A fires involve ordinary combustibles such as wood, paper, cloth, trash, and plastics.
    • Extinguishing Methods: They are typically extinguished with water or monoammonium phosphate-based fire extinguishers.
    • Examples: A fire in a trash can or a forest fire.

    Class B Fires

    • Description: Class B fires involve flammable liquids or gases such as gasoline, kerosene, grease, and propane.
    • Extinguishing Methods: They are best extinguished by smothering the flames with foam or dry chemical extinguishers to cut off the oxygen supply.
    • Examples: A gasoline spill on a garage floor catching fire or a propane leak in a grill igniting.

    Class C Fires

    • Description: Class C fires involve electrical equipment or installations.
    • Extinguishing Methods: They require non-conductive extinguishing agents, typically CO2 or dry chemical extinguishers. It’s crucial to ensure the electrical supply is turned off before extinguishing these fires.
    • Examples: A short circuit in a home appliance or an electrical panel catching fire.

    Class D Fires

    • Description: Class D fires involve combustible metals such as magnesium, titanium, aluminum, and potassium.
    • Extinguishing Methods: They require special extinguishing agents designed to address the high temperatures and reactivity of metal fires, such as dry powder agents.
    • Examples: A fire in a laboratory where magnesium or other reactive metals are used.

    Class K Fires

    • Description: Class K fires involve cooking oils and fats typically found in commercial kitchens.
    • Extinguishing Methods: They are best extinguished using wet chemical extinguishers that can saponify the oils/fats and create a foam layer to smother the fire.
    • Examples: A deep fryer catching fire in a restaurant kitchen.

    How Fires Spread

    Understanding how fires spread is crucial for effective fire prevention and control. The three primary mechanisms of fire spread are conduction, convection, and radiation.


    Explanation: Conduction is the transfer of heat through a solid material. When one part of an object is heated, the heat travels through the material to other parts.


    • A metal rod with one end in a flame will become hot along its entire length due to conduction.
    • Fire spreading through the structural beams of a building, heating up and igniting adjacent areas.


    Explanation: Convection is the transfer of heat through fluids (liquids or gases). Heated fluids become less dense and rise, while cooler, denser fluids sink, creating a circulation pattern that can spread fire.


    • A room filling with smoke as hot gases rise and spread the fire to upper levels of a building.
    • The rapid spread of fire in a multi-story building as hot air moves upward, igniting materials on higher floors.


    Explanation: Radiation involves the transfer of heat energy through electromagnetic waves. No direct contact or medium is necessary for heat transfer; it can occur through empty space.


    • A fire spreading from one building to another across a street due to the radiant heat.
    • People feeling the warmth of a fire from a distance, as the radiant heat travels through the air.

    Fire Prevention Techniques

    Preventing fires is always preferable to fighting them. Effective fire prevention involves a combination of using the right materials, designing buildings intelligently, and ensuring that occupants are prepared and knowledgeable. Here are some key techniques:

    Fire-Resistant Materials and Building Design

    • Materials: Use of non-combustible or fire-resistant materials in construction can significantly reduce the risk of fire. This includes fire-resistant glass, fire-retardant paints, and treated wood.
    • Building Design: Smart design includes creating fire barriers, compartmentalisation to prevent the spread of fire, and ensuring that buildings have proper escape routes and fire doors.

    Fire Suppression Systems

    • Sprinklers: Automatic fire sprinkler systems are one of the most effective fire protection measures. They detect the heat from a fire and activate, spraying water over the flames and nearby areas.
    • Extinguishers: Different types of fire extinguishers should be available and easily accessible in a building, with the appropriate type used for specific classes of fires.

    Fire Safety Planning and Drills

    • Evacuation Plans: Clear and well-communicated evacuation plans are crucial. These should include multiple escape routes and designated meeting points.
    • Drills: Regular fire drills ensure that occupants are familiar with evacuation procedures and can exit the building quickly and safely in the event of a fire.

    The Role of Technology in Fire Safety

    Technological advancements have significantly improved fire safety, making buildings safer and fire management more effective. Here’s how technology plays a role:

    Advances in Fire Detection and Suppression

    • Early Detection: Smoke detectors and heat sensors can provide early warnings, often before a fire has spread significantly. Advanced systems can pinpoint the location of a fire, improving response times.
    • Automated Suppression: Beyond sprinklers, there are systems that use gases or chemicals to suppress fires without damaging sensitive equipment, suitable for data centers or laboratories.

    Future Trends in Fire Safety Technology

    • Smart Buildings: Integration of fire safety systems with other building management systems allows for smarter, more coordinated responses to fires. For example, a fire alarm can trigger building ventilation systems to control smoke spread.
    • Drones and Robots: These can be used to enter areas that are too dangerous for human firefighters, providing reconnaissance and even delivering fire suppression agents.

    Passive Fire Prevention Software like FireArrest

    • Software Solutions: Software like FireArrest provides tools for managing and documenting fire prevention measures. It can track the installation of fire safety equipment, ensure regular maintenance, and provide training modules for staff.
    • Integration and Accessibility: Such software can integrate with other building systems and be accessible on various devices, ensuring that up-to-date information about a building’s fire safety status is always available.


    Fire remains one of the most significant risks to safety, property, and the environment. However, our understanding of how fires start, spread, and can be extinguished has grown immensely, leading to more effective methods of prevention, detection, and suppression. The classification of fires into different categories (A, B, C, D, and K) provides a foundational understanding that informs appropriate response strategies. By understanding the mechanisms of fire spread — conduction, convection, and radiation — we can design safer buildings, develop better fire suppression systems, and implement more effective fire safety protocols.

    The role of technology in fire safety is increasingly prominent, offering advanced solutions for early detection, suppression, and management of fire-related incidents. Innovations like smart building technologies, drones, and sophisticated software like FireArrest are pushing the boundaries of what’s possible in fire safety management. These tools not only enhance our ability to respond to fires but also improve our capacity to prevent them.


    The fire triangle consists of three elements: heat, fuel, and oxygen, all of which are necessary for a fire to ignite and sustain itself. Understanding the fire triangle is crucial because removing one of these elements can extinguish a fire, making it a fundamental concept in fire prevention and fighting strategies.

    Fires are classified into five main categories: Class A (ordinary combustibles), Class B (flammable liquids and gases), Class C (electrical equipment), Class D (combustible metals), and Class K (cooking oils and fats). Classification is important as it determines the best method for extinguishing a fire, ensuring safety and minimizing damage.

    Conduction is the transfer of heat through a solid material. In a fire, this means that heat can travel through walls, floors, and other structural elements, spreading the fire to new areas. Understanding conduction helps in fireproofing buildings and materials to slow the spread of fire.

    Convection is the process of heat transfer through fluids (gases and liquids). In a fire, hot gases rise and cooler air descends, creating a cycle that can rapidly spread flames upwards and throughout a building, especially affecting higher floors and enclosed spaces.

    Common fire suppression systems include water sprinklers, which are activated by heat; foam systems, used for Class B fires; CO2 systems, often used for electrical fires; and dry chemical extinguishers, which can be used on a variety of fire types. Each system has specific applications based on the fire class and setting.

    Radiation refers to the transfer of heat through electromagnetic waves. In a fire, radiant heat can ignite combustible materials without direct contact, allowing the fire to jump across gaps and spread between objects and buildings.

    Technology has greatly improved fire safety through advanced detection systems like smoke and heat detectors, automated suppression systems, smart building integrations for coordinated responses, and software for managing and documenting fire safety procedures.

    Some effective fire prevention tips include regularly testing smoke alarms, keeping flammable materials away from heat sources, never leaving open flames unattended, maintaining electrical wiring, having fire extinguishers accessible, and practicing fire evacuation drills. These measures can significantly reduce the risk of fire and enhance safety.