The Different Types of Fires

There are different types of fires and they can be caused by a variety of different things and may take place in any business or home. All companies must be aware of fire safety and even if you are not working with clearly flammable materials, there is still a risk that fires can start.

A hazard is something which may cause you or someone else harm. Fires can cause a lot of harm to people and some examples of the hazards are –

• Heat – The most obvious hazard from a fire is the actual flames. These flames can burn your skin as well as your eyes and lungs. Burns are life threatening to a large extent and extremely painful.
• Smoke – When a fire burns, smoke is often given off. This smoke can be inhaled and cause serious harm to the lungs. It is a well-known fact that the majority of fires which result in death actually come about from smoke inhalation rather than burns.
• Lack of oxygen –Since oxygen is one of the three components needed for a fire, it is used up quickly. This means that the fire can burn through the oxygen in a room and leave none for people in the vicinity to breathe.
• Damage to the environment – As a fire burns it will cause damage to the surrounding building or other things in the environment. This has the potential to cause harm if the surroundings collapse.

Fire behaviour

There are a number of different behaviours that fire can show. Each one will work in a distinct way to spread the flames and heat from a fire to new areas. Heat is passed from one area to another through different objects and principles.

The main principles of heat transfer are –

• Direct contact.
• Conduction.
• Radiation.
• Convection.
• Flashover.
• Backdraught.

We will look at each of the main principles in more detail.

Direct Contact

The first way that a fire will spread is through direct contact.

This means that the flames themselves come into contact with other fuel sources which also catch fire. The fire will travel along the other source of fuel as long as it is combustible. This is seen very often and a good example is when paper or cardboard is set alight – the flame will travel down the fuel and spread.

Combustible – able to catch fire or burn easily.

Conduction

Some materials may not be combustible themselves but could allow fire to spread through conduction.

This is when the material does not burn but instead heats up to a high temperature when in contact with fire. This high temperature passes to the other side of the material. If there is a fuel source on the other side and the temperature is high enough, this can set on fire.

An example of conduction is through metal. If you heat a metal rod it is unlikely to catch fire. However, it will heat up to high temperatures and could set fire to something at the other side such as paper.

Radiation

Heat is transferred through electromagnetic waves and not just through contact.

This is why we feel heat from objects even if we do not touch them. If an object is simply too close to a fire, it could pick up so many waves that its temperature reaches a point that allows it to set alight.

An example of this could be if you place a magnifying glass on to paper on a hot day. The heat (in the form of radiation) from the sun is magnified and can set the paper on fire.

Convection

Fire causes the air around it to heat up and smoke to be produced.

Warm air rises above cool air and therefore the air that is heated by flames will rise up to the roof or ceiling in a building. This process is known as convection.

When convection takes place, the heat from the air can become trapped on the ceiling and, as the fire continues to burn, the heat will continue to rise. This build of heat can start new fires if there is enough oxygen and a fuel source. For example, a lot of offices have suspended ceiling tiles which may set alight if enough hot air rises during a fire.

Flashover

This method of fire spreading is closely linked to convection.

Flashover happens when hot air from a fire rises to the top of a room which then radiates enough heat for objects in the room to heat up. As furniture and other objects get hot, they will begin to give off flammable gases. This gas can result in the materials in the room quickly catching fire simultaneously.

Flashover is what makes a fire spread very quickly. One minute, a fire can be seemingly small but, if the surrounding objects have been heated up, they can quickly ignite into a large-scale blaze.

Backdraught

When a fire is not well ventilated, it can start to use up the limited oxygen that is available.

This will cause the fire to die down and the flames to reduce. This can result in a large number of areas where flammable gases are present but there is no actual fire due to oxygen being limited. A sudden introduction of oxygen such as a door opening or window breaking can then result in the fire starting again. These restarts will often be very explosive as oxygen rushes back into the mix.

The risk of backdraught is the reason why people should never re-enter a building that has been on fire. The opening of a door will allow oxygen to get back to the flames and could easily end in an explosion.

Classes of fire

Fires can be placed into different classes depending on what material is burning. This classification then gives us information on the type of fire extinguisher we should use to put out the flames.

Not all fires require the same type of extinguisher and the correct type has to be used for each blaze.

Class A

A class A fire is burning flammable solids as fuel. Examples of these include paper and wood.

Extinguishers that can be used: Water, Foam, ABC Dry powder, Wet chemical

Class B

Class B fires are burning flammable liquids. Examples include petrol and paint.

Extinguishers that can be used: Foam, CO2 Gas, ABC Dry powder

Class C

Class C fires burn flammable gases. A couple of examples are propane and butane.

Extinguishers that can be used: ABC Dry powder

Class D

Class D fires are burning flammable metals. These may include lithium or magnesium.

Extinguishers that can be used: Dry Special Powder

Electrical

Any fire involving electrical equipment is classed as an electrical fire.

Extinguishers that can be used: CO2 Gas, ABC Dry powder

Class F

Class F fires are burning cooking oils or fat.

Extinguishers that can be used: Wet chemical

Checkout our quiz to test your knowledge on fire extinguishers.

How can we prevent fires?

Fire protection

Protection is about reducing damage and saving lives when a fire occurs. This can be done using a lot of methods which we will explore in this section of the course. Protection measures can be split into active and passive.

Active control measures

Active control measures are safety measures that require action from a person or situation. This means that active protection measures are either used or react when a fire takes place. Examples include fire extinguishers and blankets which are used by people. Other examples include sprinkler systems and emergency lighting as these are triggered when a fire happens.

Passive control measures

Passive control measures are physical features that do not require any action in protecting life. They are usually built into a building and are no different when a fire takes place to any other day. They include fire exits, signs leading to the nearest exits and any special fire safety equipment built into the location (such as fire resistant walls and doors).

How we react to fire

Once a fire has taken hold, it is important that we react calmly and quickly.

Obviously, it is a lot easier to say this than do it in practice but carrying out regular fire drills and having a good understanding of how fire spreads is a huge help. This knowledge will result in you knowing what to do in situations where fire is present and help you to avoid some of the common mistakes people make.

When no training is taken, people that are caught in a fire can make mistakes such as –

• Not knowing how long an evacuation takes.
• Reacting slowly.
• Not knowing the correct procedure.
• Underestimating the way in which fire spreads.
• Underestimating the time it takes for fire to spread.

What to do when you hear the fire alarm

If you ever hear a fire alarm you should stay calm and act according to the procedures set out in your workplace.

Always

• Stay calm and act quickly.
• Leave near the nearest fire exit.
• Close doors and windows behind you.
• Assemble at the nearest designated assembly point.

Never

• Spend time collecting belongings.
• Use lifts unless they are part of a specific personal evacuation plan.
• Attempt to tackle a fire without correct training.
• Go back into the building unless you are told it is safe to do so.

When evacuating a building due to an alarm being raised, you should stay calm and not take any risks. All belongings should be left as fire can quickly spread and the most important thing is to get out of the building as quickly as possible.

Lifts should not be used unless they are part of a Personal Emergency Evacuation Plan (these will be covered soon). This is due to the risk of the lift mechanisms being damaged by fire as well as the elevator shaft being able to fill with smoke very easily.

The nearest fire exit should be taken as long as this is safe to use. If it is smokey, stay low to the ground and always remember to shut any windows and doors after you.

What to do if you cannot get out

At all times in the workplace, you should have access to an emergency exit. These exits should never be blocked as you do not know if these will be needed at any point.

However, if you do become trapped in a building with no means of escape you must carry out certain steps.

Firstly, if the emergency services have not yet been informed you must call them. If the fire is not in the same room as you, make sure that the doors and internal windows are shut. This will create a barrier between you and the fire.

Grab any fabric that is available and place this in cracks around doors and windows to stop any smoke or flames from entering. If possible, it is also best to wet this material first. If an external window is present, open this and shout ‘Fire’.

If any smoke does start to get into the room, use some material to cover your nose and mouth and try to only breath through your nose.

• Contact the emergency services if they have not already been informed of the fire
• Close any internal doors and windows
• Block gaps in doors and windows with damp cloth
• Open external windows and shout ‘Fire’
• Use a cloth or other material over your mouth and nose to block smoke.

If you are ever too close to a fire and your clothes catch alight, you can carry out the stop, drop and roll technique.

STOP – the first thing to remember is to never run if your clothes catch fire. This will add more oxygen to the flames and make the fire burn faster.

DROP – drop to the floor and lie down. This will stop the flames from moving up your body vertically and burning your head and face.

ROLL – Once on the floor, place your hands over your face and roll back and forth to smother the flames. This will reduce the oxygen to the fire and work to extinguish the flames.

DON’T STOP – Do not stop until the flames are out.

If someone else is present, they can use something like a rug or thick blanket to smother the flames. If possible, this should be soaked in water first.

When to use a fire extinguisher

Fires should only ever be tackled if it is safe to do so. Without the correct training and equipment, attempting to tackle a fire is extremely dangerous and should never be done.

Fires should only be extinguished if –

• Someone has raised an alarm.
• Someone has called the emergency services already.
• There are the right types of extinguishers available.
• You have undergone training to use an extinguisher.
• The fire is small and not growing.
• A safe route to an exit is available.

Fires should not be extinguished if –

• The room is filling with smoke.
• The fire is spreading.
• There are other flammable hazards around (such as gas canisters).
• More than one fire extinguisher is needed.

How to use a fire extinguisher

Different types of fire extinguisher can have different instructions for use so these should be checked. However, in the case of a fire, it is unlikely that you will have time to read these instructions fully so you can follow general advice with the PASS method.

The PASS method –

PULL – Firstly pull the pin from the fire extinguisher. This may have a small plastic seal around it (known as a tamper seal) which will break when the pin is removed.

AIM – Aim the nozzle low at the base of the fire and not at the flames.

SQUEEZE – Squeeze the handle slowly until the fire extinguisher discharges.

SWEEP – Sweep the nozzle from side to side in small motions at the base of the fire. This will act to cover the base of the fire and should be continued until the fire is out.

If the fire reignites afterwards, repeat steps 2 to 4.

Good fire safety housekeeping practices

The ways to minimise and prevent the risk of a fire breaking out is to follow good house keeping practices, at home and at work.

Here are some of the best tips –

• Install at least one smoke alarm on every floor in the property and ensure they are tested often.
• Ensure all appliances are switched off before you go to bed.
• Do not leave candles unattended.
• Equip your home with fire safety equipment.
• Ensure all cigarettes are extinguished in an ashtray.
• Do not leave anything close to an electric heater.
• Do not over load plug sockets.