What is Fire Triangle and How Do Fires Spread

What is Fire Triangle and How Do Fires Spread

Fire Triangle

The Fire Triangle is a model used to understand the elements necessary for a fire to occur. The model consists of three elements: heat, fuel, and oxygen. All three of these elements must be present for a fire to occur.

A fire will start when all three elements are present in the right proportions. If one of the elements is removed, the fire will go out. For example, there can be no fire if there is no fuel. If there is no oxygen, the fire will eventually suffocate. And if the heat is removed, the fire will cool down and go out.

The type of fire that results from a particular combination of fuel, heat, and oxygen depends on the proportions of each element. A fire with more fuel will burn hotter and produce more smoke. A fire with more oxygen will burn hotter and produce less smoke. And fire with more heat will burn hotter and produce less smoke.

Fire Triangle

Principles of Fire

The fire triangle represents the basic principles of fire and combustion.

For a fire to exist, three things must be present:

  • Heat
  • Fuel
  • Oxygen

Sources Of Heat

Workplaces have numerous sources of ignition, some of which are obvious, but others may be hidden inside machinery. Most of the sources may cause an accidental fire from sources inside. Still, in the case of arson (about 13% of industrial fires), the source of ignition may be brought from outside the workplace and will be deliberately used. The commonest type of fire in the workplace is caused by heat or light energy igniting materials like paper, wood, cloth, or chemicals. Other types of ignition include electricity, static electricity, friction, and enzymes.

The control of ignition sources is a key element in preventing fires in the workplace. Employers should conduct a fire risk assessment and place appropriate controls to minimize the fire risk. Employees should be trained to identify and control ignition sources in their workplace. In the event of a fire, everyone should know what to do to ensure their safety.

The following are potential sources of ignition in the typical workplace:

  • Naked Flames: Naked flames are the leading cause of ignition for fires in the home and workplace. They can come from smoking materials, cooking appliances, heating appliances, and process equipment. Naked flames can ignite flammable materials and start a fire very quickly.
  • External Sparks: External sparks are also common sources of ignition for fires and explosions. They can come from various sources, including grinding metals, welding, impact tools, and electrical switchgear. These sparks can easily ignite a fire or explosion when they come into contact with flammable or combustible materials.
  • Internal Sparking: Internal sparking is a significant ignition source for many fires. It can come from electrical equipment, machinery, and lighting. While some sources are faulty or normal, others may be due to poor maintenance or improper installation.
  • Hot Surfaces: Hot surfaces are one of the most common sources of ignition for fires. They can come from many sources, including lighting, cooking, heating appliances, process equipment, poorly ventilated equipment, faulty and/or inadequately lubricated equipment, hot bearings, and drive belts. These can create a fire risk if they are not properly used or maintained.
  • Static Electricity: One of the most common sources of ignition in industrial settings is static electricity. This can occur when materials such as unwinding plastic, pouring highly flammable liquids, walking across insulated floors, or removing synthetic overalls come into contact and then separate. The resulting sparks can be enough to ignite nearby combustible materials.

Sources Of Fuel

If it burns, it can be fuel for a fire. The things which will burn quickly are the most likely to be the initial fuel, which then burns quickly and spreads the fire to other fuels. The most common things that will burn in a typical workplace are:

  • Solid: When it comes to fires, solids are often the source of fuel. That’s because they can easily catch fire and spread quickly. Wood, paper, cardboard, plastics, rubber, and foam are all examples of solid materials that can easily ignite. Even textile materials like furnishings and clothing can be flammable if not properly taken care of. In addition to being the source of ignition, solids can also be the fuel that feeds a fire. That’s why it’s essential to be careful with materials like wood shavings, dust, and paper. If they’re not properly disposed of, they can quickly become a fire hazard.
  • Liquids: Liquids are often the source of fuel for fires. This is because they can easily catch fire and spread quickly. Common flammable liquids include paint, varnish, thinners, adhesives, petrol, white spirit, methylated spirits, paraffin, toluene, acetone, and other chemicals. Most flammable liquids give off vapors that are heavier than air, so they will fall to the lowest levels. If there is a spill, the vapors will settle in low areas and can easily be ignited by a spark or flame.
  • Gases: Flammable gases are a significant fuel source in many industrial accidents. The most common flammable gases include LPG (liquefied petroleum gas in cylinders, usually butane or propane), acetylene (used for welding), and hydrogen. An explosion can occur if the air/gas mixture is within the explosive range.


Oxygen is required for a fire to burn. The air around us is the most common source of oxygen in a fire. However, other sources of oxygen can be used to make a fire burn hotter and faster. These include compressed oxygen cylinders (used for welding), liquid oxygen tanks (used in some chemical processes), and oxygen-enriched air (used in some industrial processes).

In addition, some chemicals such as nitrates, chlorates, chromates, and peroxides can release oxygen as they burn and therefore need no external source of air.

Heat Transfer Methods

How Do Fire Spread?

There are several ways that fire can spread, each of which needs to be understood to prevent and fight fires effectively. Heat can be transmitted by convection, conduction, radiation, and direct burning.


Convection is the process of heat transfer by the movement of fluids. The heated fluid rises, and the colder fluid sinks, causing a continuous circulation. This process transfers heat from the Sun to the Earth’s surface and moves heated air or water in a room or body.

Convection can be either forced or natural. Forced convection occurs when a fluid is moved by an external force, such as a fan or pump. Natural convection occurs when the fluid is moved by buoyancy forces, which occur when the density of the fluid decreases with increasing temperature.


Conduction is the transfer of heat through a material by direct contact between particles. This process of heat transfer occurs without the material actually changing phase. In other words, the conduction rate depends on the material, its temperature, and the area of contact between the particles.

For example, metal is a good conductor of heat, so if you touch a hot metal object, you will feel the heat immediately. This is because the heat is being conducted directly from the hot metal object to your skin. Other materials, such as concrete and brickwork, have a low thermal conductivity. This means that they are not very effective at conducting heat. As a result, these materials are often used to insulate buildings. Insulation materials have a very low thermal conductivity, which makes them excellent at preventing heat from escaping.

How Do Fire Spread

When it comes to fire protection, it is important to use materials that are either poor conductors or good insulators. This helps to prevent the spread of fire by slowing the transfer of heat. Asbestos is one material that fits this description, as it is an inferior heat conductor and incombustible. However, asbestos can cause serious health problems, such as lung cancer, so it is no longer used as a fire protection material. 


Radiation is the transfer of heat by electromagnetic waves. This process does not require a material to be in contact with the object emitting the radiation. Radiation can travel through a vacuum, which makes it very efficient at transferring heat over long distances.

The Sun is an excellent example of how radiation can be used to transfer heat. The Sun emits electromagnetic radiation, which travels through space and is then absorbed by the Earth’s atmosphere. This absorbs the heat, radiating back towards the planet’s surface. This process warms the Earth’s surface and makes it habitable for life.

Fire also spreads by radiation. Hot gases radiate heat, which can then ignite nearby combustible materials. This is why keeping flammable materials away from heat sources is essential.

Direct Burning

Direct burning is the fire spread by direct contact between the flame and the material. This is the most common form of fire spread, as it only requires a small amount of heat to ignite most materials.

For example, paper is a very flammable material; it only takes a small flame to set it alight. Once the paper is burning, the heat from the flame will cause it to ignite other nearby materials. This can create a chain reaction, with the fire spreading rapidly through a room or building.

Common Causes of Fires in Workplaces

There are many different causes of fires in workplaces, but some of the most common include:

  • Electrical equipment: Faulty or poorly maintained electrical equipment is a common cause of workplace fires. This includes items such as electrical cables, plugs, and sockets.
  • Smoking: Smoking is the leading cause of fatal fires in the home and a significant cause of workplace fires.
  • Heating equipment: Faulty or poorly maintained heating equipment, such as radiators and boilers, can also be a fire hazard.
  • Arson: Arson is a common cause of fires in commercial premises, such as shops and offices.

The consequences of fires in workplaces can be devastating. They can cause injuries, death, and damage to property. In addition, fires can also disrupt businesses and lead to financial losses.


The conclusion is that the three main ways fires spread are convection, conduction, and radiation. Direct burning is also a common way for fires to spread. All of these methods require some form of contact with an ignition source to start the fire. Once the fire has started, it can quickly spread through a room or building, causing extensive damage. It is essential to be aware of these methods of fire spread to help prevent the spread of fire.

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