Understanding The Classification of Fires – A Comprehensive Guide
Several fire classification systems are used worldwide, typically categorising fires into five or six classes using letters of the alphabet. The Classification of Fires identify the fuel or energy source involved, helping to determine the root cause of the fire, the appropriate fire extinguisher and the most effective restoration methods.
In this guide we provide everything you need to know about the classification of fires, explaining the key differences and common examples for each class.
Understanding Fire Classification Systems
There are several globally recognised fire classification systems, each with slight variations: The European Fire Classification (EN2) and Australian Fire Classification (AS8151) both use letters A to F, whilst the North American Fire Classification (NFPA) uses the letters A, B, C, D and K.
Although the UK doesn’t officially recognise any one system, the Government and other reputable fire safety resources most often adopt the European Fire Classification system, which categorises fires into groups A, B, C, D, E and F. This system was introduced to standardise responses to fires based on the specific characteristics and risks of each type of fire.
It is important to note fires can have multiple classifications, as they may involve a variety of different materials. The classes are as follows:
Class A – Solid Combustible materials.
Class B – Flammable liquids.
Class C – Flammable gases.
Class D – Burning metals.
Class E – Electrical fires.
Class F – Cooking oils and fats.
The chart below shows an example of what the symbols for The Classification of Fire may look like when adopted in the UK and Europe, although there may be slight variation from label to label.
‘Combustible’ vs ‘Flammable’
‘Combustible’ and ‘Flammable’ are two terms often used interchangeably in everyday language, but their scientific definitions outline some distinct differences. To understand this, first you will need to understand the definition of ‘Flash point’.
What is Flash Point?
The Flash Point of a material is the lowest possible temperature at which it emits enough vapour to form an ignitable mixture with air. Below this temperature, the material does not release sufficient vapour to ignite.
It is important to note that reaching the flash point does not guarantee ignition; it simply means that the conditions are favourable for ignition if an ignition source is present.
What Makes a Substance Flammable?
A liquid is considered flammable when its flash point is below 37.8 degrees Celsius, making it more likely to ignite at typical working temperatures. Flammables are considered a greater hazard to safety than other substances due to their susceptibility to ignite under everyday conditions.
What Makes a Substance Combustible?
These materials ignite easily, hence the term ‘combustibles’. However, unlike flammable materials, combustibles are less volatile, with a flash point above the standard working temperature of 37.8 degrees Celsius.
In our blog, ‘How Does Fire Spread’, we delve deeper into the science of fire ignition and spread, exploring fundamental concepts like the Fire Triangle and more. Now that you understand the basics of The Classification of Fires, we can explore more examples and discuss the most appropriate agents for extinguishing each type of fire.
Extinguishing a Fire
There are five different fire extinguishers used in the UK. Each extinguisher will have a red body and a coloured label to easily identify which type of fire they can be used for.
The categories are as follows:
- Red – Water (Spray and Mist)
- Cream – Foam.
- Blue – Dry Powder.
- Black – Carbon Dioxide (CO2).
- Yellow – Wet Chemical.
Each fire extinguisher provides specific instructions for its use. The ‘PASS‘ technique is often followed.
Use ‘PASS’ to extinguish a fire:
Pull: Pull the pin to break the tamper seal.
Aim: Aim the discharge hose at the base of the fire.
Squeeze: Squeeze the lever to release the extinguishing agent.
Sweep: Sweep the nozzle from side to side, covering the fire area completely.
The Classification of Fires and How to Extinguish Them
Class A Fire – Solid Combustibles
Class A fires involve solid materials such as plastic, rubber, textiles, paper, wood, green waste (like leaves and grass) and most types of household rubbish. These items are all commonly found in the average household, contributing to the frequency of domestic fires.
How to Extinguish a Class A Fire:
The recommended types of extinguishers include Water, Foam, Dry Powder and Wet Chemical. These agents are effective in both cooling and smothering the fire to extinguish solid combustibles.
Extinguishers that should NOT be used for Class A fires include CO2 extinguishers, as they are not effective in cooling the fire and may not adequately smother the burning material.
Class B Fire – Flammable liquids
Class B Fires involve liquid such as petrol, diesel, oil, alcohol, solvents, kerosene and grease (often leftover from industrial processes).
How to Extinguish a Class B Fire:
Effective extinguishers for Class B fires include Foam, Dry Powder and CO2, as they are formulated to smother and suppress fires fuelled by flammable liquids.
Extinguishers that should NOT be used for Class B fires include Water or Wet Chemical extinguishers, as they can spread the fire or cause dangerous reactions with the flammable liquids.
Class C Fire – Flammable Gases
Class C fires involve flammable gases, such as propane, butane, methane and ammonia. Flammable gases are commonly used for heating or cooking substances, but they can present significant risks if mishandled or stored incorrectly.
How to Extinguish a Class C Fire:
The recommended extinguisher for a Class C fire, which involves flammable gases is Dry Powder. Dry Powder extinguishers are effective because they do not conduct electricity and can smother the fire by separating the fuel from the oxygen.
Extinguishers that should NOT be used for Class C fires include Water, Foam, CO2 or Wet Chemical extinguishers. Using these types of extinguishers on a Class C fire can be dangerous as they may not adequately suppress the fire or could even spread the flammable gases.
Class D Fire – Burning Metals
Class D fires involve metals such as aluminium, potassium, magnesium, titanium or lithium. These metals are often found in the manufacture of components, batteries and various industrial processes.
How to Extinguish a Class D Fire:
The recommended extinguisher for a Class D fire is Dry Powder, as they are specifically designed to smother and extinguish fires involving reactive metals by excluding oxygen and cooling the material.
Extinguishers that should NOT be used for Class D fires include Water, Foam, CO2 or Wet Chemical extinguishers. Using these types of extinguishers on a Class D fire can be ineffective or even hazardous, as they may react with the burning metal or fail to extinguish the fire properly.
Class E Fire – Electrical Fires
Class E fires involve energised electrical equipment, such as wiring, circuits, panels and outlets or appliances including computers, microwaves and washing machines.
Safety Markings
Safety markings on electrical equipment indicate compliance with relevant regulatory requirements. There are two main types:
- CE marking: Used for products produced before Brexit or in the EU, indicating compliance with EU regulations.
Source: The European Commission: https://single-market-economy.ec.europa.eu/single-market/ce-marking_en - UKCA marking: Used for products produced post-Brexit in the UK, showing compliance with UK regulatory standards.
Source: Gov.UK: https://www.gov.uk/government/news/design-for-new-product-safety-marking
These markings ensure that electrical equipment meets safety and performance standards mandated by their respective regulatory frameworks.
How to Extinguish a Class E Fire:
For a Class E fire, the recommended extinguishers are Dry Powder or CO2. Dry Powder extinguishers are effective because they do not conduct electricity and can smother the fire by separating the fuel from the oxygen.
CO2 extinguishers work by displacing oxygen, effectively suffocating the fire.
Extinguishers that should NOT be used for Class E fires include Water, Foam or Wet Chemical extinguishers. Using these types of extinguishers on an electrical fire can be dangerous as they can conduct electricity or cause damage to the equipment.
Class F Fire – Cooking Oils and Fats
Class F Fires involve cooking oils, fats and leftover grease from cooking processes.
How to Extinguish a Class F Fire:
For a Class F fire, the recommended extinguisher is Wet Chemical. Wet Chemical extinguishers are specifically designed to tackle fires fuelled by oils through cooling the fire and creating a barrier between the fuel and oxygen.
Extinguishers that should NOT be used for Class F fires include Water, Foam, Powder or CO2 extinguishers. Using these types of extinguishers on a Class F fire can be ineffective or even dangerous, as they may not adequately cool the oils and fats or could cause the fire to spread.
It is crucial to ensure you choose the correct type of fire extinguisher, designed to safely and effectively extinguish the fire at hand. Failure to do so could compromise your own safety, as well as compromise the surrounding contents and structure of the building.
Be Fire Ready
It’s crucial to equip yourself with the necessary information to stay protected from fire risks. Fortunately, Rainbow Restoration offers a wealth of resources to educate you on all aspects of fire safety.
We’ve curated a set of commonly asked questions and provided comprehensive answers in a convenient FAQ section on our essential resource, the Property Hub. Our campaign ‘Be Fire Ready‘ provides essential support and resources for domestic fire safety and preparedness.
We cover a variety of fire-related topics in our Blog, including titles such as ‘How many smoke alarms do I need‘, ‘Surviving a house fire – Emergency Guide‘ and ‘How to reduce the risk of fire and flood whilst you are away‘, alongside many more.
If you are unfortunate enough to have suffered from the devastation of a fire, we can help. We have over 50 branches across the UK, meaning no-matter where you are situated we can reach you.
We provide first class smoke and fire restoration services, which will restore your property and help your house feel like a home again. You can Contact Us or call our 24-hour helpline 365 days a year on 01624 422 488.