Fire is a familiar concept, but the science behind it, and the speed at which it can develop, is often underestimated. Understanding combustion, how it works, and how rapidly a fire can take hold is essential for effective fire prevention, detection and control. By recognising how fires start, develop and behave, organisations can better protect people, assets and operations.
Everyone knows what fire is, but combustion is often less clearly understood. Combustion is a specific chemical process that underpins all fire. It is the reaction between a fuel, such as wood or coal, and an oxidant, typically oxygen in the air. When a substance is heated and reacts with oxygen, it releases energy. In the case of fire, this energy is usually released as heat, but it can also produce light and sound.
Fire is therefore the visible result of combustion. At its simplest: combustion is what starts a fire, and fire is what happens when combustion has occurred. In a combustion engine, the gases released as a result of combustion apply a force to part of the engine, such as rotors or a piston, eventually resulting in the movement of whatever the engine is attached to.
When combustion occurs, it produces a range of by-products depending on the materials involved. In many environments, particularly those involving fossil fuels, combustion can release gases and particles that are harmful to both people and the environment.
Common products of combustion include :
These by-products highlight the importance of early detection and effective fire control systems, smoke inhalation is often more immediately dangerous than the fire itself, as carbon monoxide in particular is odourless and can incapacitate occupants before they are even aware of the fire.
Combustion can occur in several different ways depending on the conditions and materials involved :
produces heat and light very quickly, as seen when lighting a gas hob.
occurs without an external heat source, when materials ignite due to internal chemical reactions, for example, white phosphorus ignites spontaneously at around 30°C in moist air.
is a fast and intense reaction that produces heat, light and sound, such as in fireworks or certain industrial incidents.
The process of combustion can also occur in two distinct modes. In the flaming mode, solid and liquid vapours are vaporised and ignited, this is what we see as a visible flame. In the non-flaming mode, combustion takes place without an actual flame, in the form of smouldering or glowing embers.
It is worth noting that flaming and non-flaming modes can occur individually or on the same material at the same time. Straw and wood are good examples of fuels that can burn in both flaming and non-flaming modes simultaneously, making them harder to fully extinguish and more likely to re-ignite.
Knowing how fires start and spread is essential knowledge when developing the best means of detecting and controlling them.
There are four recognised stages of a fire :
combustion occurs when heat, fuel and oxygen combine and have a chemical reaction that leads to fire
the point at which a fire becomes self-sustaining
the point when the fire reaches its hottest point and all fuel sources have ignited
when oxygen or fuel sources start to run out and the fire begins to die down and eventually go out
In many regards, the first stage, combustion, is the most important in terms of fire detection and control. The sooner you detect it, the sooner you can control it, and the less chance there is of damage to property or loss of life. This is why early detection systems such as smoke detectors and fire alarms are so critical.
Understanding combustion in theory is one thing, but the reality of how fast a fire can develop is something many people underestimate. A fire can gain speed and begin to spread exponentially in as little as 30 seconds. As long as the three core elements of heat, oxygen and fuel are present and sustained, it is just a matter of minutes before a fire becomes impossible to control without professional intervention.
In fact, it can take just five minutes for a home to become fully engulfed by a fire. A commercial, industrial or non-residential building may take slightly longer due to its size, but this only demonstrates how critical it is to have rigorous fire safety
Understanding the speed at which a fire develops can help you better appreciate what fire protection services your premises require.
It only takes 30 seconds from the start of a fire for it to get out of control.
The temperature of the property will have risen significantly and smoke will be rapidly spreading.
Smoke detectors should be going off, alerting occupants to the presence of the fire.
Smoke will have started spreading into rooms other than the one where the fire originated. The temperature of the room where the fire started may have reached more than 250°C, a temperature no human can survive.
Upper floors will now be covered with smoke as the fire makes its way through the building. Evacuation will become increasingly challenging.
The entire building could be up in flames, including the property's exterior.
As with all fire risks, prevention is the most effective strategy. For commercial, industrial and non-residential properties, fire safety training for staff plays an important role in stopping a fire from breaking out in the first place.
However, preventative measures can sometimes be bypassed. When this happens, it is vital to have appropriate measures in place to slow or contain the fire's spread. Fire doors are one of the most effective tools available, they are designed to stop fire moving from room to room as quickly as it otherwise would. It is also worth noting that lifts in commercial buildings can act like chimneys, providing a passage for fire and smoke to reach upper floors faster than they ordinarily would.
Smoke inhalation is potentially more harmful and deadly than the fire itself. Fire stopping measures, such as sealing gaps, openings and areas where smoke can travel, help to compartmentalise the building and limit the spread of both fire and smoke, buying valuable time for evacuation.
Finally, the fastest way to stop a fire once it has started is to extinguish it immediately. Having fire extinguishers installed and accessible across your property can help quickly and efficiently contain a fire, but remember that different types of fire require different extinguishers. Always consult your fire protection provider about what is most suitable for your premises.
Don't wait for an incident to act. Contact Scutum today to arrange a fire risk assessment, fire alarm installation or fire safety training, and ensure your premises are equipped to detect, contain and respond to fire at every stage, from the first spark of combustion to full evacuation.
