Your Guide To Understanding Class B Fires

What are Class B fires?

A Class B fire is a specific type of fire, whereby flammable or combustible liquids are the fuel. Examples of substances that create a Class B fire include oils, petrol, diesel, propane and butane.

It is so important to understand the type of fire you’re dealing with, especially in the industrial and automotive sectors due to the quantity of these substances present. The more you and your team understand the principles of Class B fires, the better prepared you can be. However, it is also useful to understand Class B fires in household settings too, in order to prevent a serious incident at home.

One of the best options you have for combatting a Class B fire safely is extinguishers, with certain extinguisher types designed specifically with a certain fire class in mind. We’ll cover extinguishing methods in more detail later.

What causes Class B fires?

We’ve covered a few of the materials that fuel a Class B fire, like liquid chemicals, but for a fire to start there also has to be oxygen and a source of ignition.

Potential ignition sources are never far away when operating in a commercial or industrial setting. This can include sparks, static electricity and open flames. These are all common in many industrial settings, whether it’s because of hot works stations or general machinery in the area.

Smoking is also a common source of ignition, with embers and ashes igniting liquids that have been spilt or have leaked. This is why any smoking areas should be well away from your building and from where any flammable substances are kept.

Oxygen is, of course, a core component of the fire triangle, and is naturally present in the air. Flammable liquids will react with oxygen when there is an ignition and heat source, creating a potentially disastrous combination. Only by removing one of these elements will you be able to extinguish a Class B fire.

There is an additional risk of flames spreading much further when a flammable liquid has ignited, since they are able to quickly travel across a spillage and create fires where they come into contact with organic materials — or even other chemicals in the vicinity.

Identify Class B fires

Knowing how to identify a Class B fire can make all the difference when it comes to safely extinguishing the flames. Here are a few signs that can indicate you’re facing a Class B fire:

• Nearby fuel sources – If you can visually see a flammable liquid, or a mixture of them as the source or nearby, you can be fairly certain of the fire class and act accordingly to mitigate any risks.
• Behaviour of the flames – Class B fires are known to ignite quickly and burn intensely due to the liquids involved. The flames will also spread across the surface of any liquid. A Class B fire can be quite volatile due to the low flash point of most chemical liquids.
• Colour of the smoke – Often, a burning chemical will give off a thicker black or grey smoke. This smoke, due to the substances burning, can also be toxic, presenting an additional risk.

A Class B fire is distinct from other fire classes, such as Class C fires that involve gases and can show blue flame, or electrical fires that can start as a result of overloading or overheating an electrical item. 

Extinguishing Class B fires: best methods and tools

Now you know how to identify a Class B fire, it’s time to look at ways in which you can safely put out the flames. We would like to point out that you should only attempt to extinguish a fire if it is small enough and only if you feel totally confident to do so.

There are three extinguishers recommended for dealing with flammable liquid fires, all of which can be used since they don’t further the spread of the liquid or the flames.

Foam extinguishers

• Steps for using a foam extinguisher on a Class B fire:
  • Pull the pin to break the seal
  • Aim the extinguisher nozzle over the fire from a safe distance and squeeze the handle
  • Sweep the nozzle and cover the flammable liquid in a blanket of foam
  • Keep your distance until you’re sure the flames are fully extinguishers

CO2 extinguishers:

• Steps for using a CO2 extinguisher on a Class B fire:
  • Position the discharge horn if it is not a frost-free horn, and pull the safety pin
  • Point the CO2 at the base of the flames, but be careful not to splash the liquids
  • Only use a CO2 extinguisher in open spaces as it displaces oxygen and can lead to asphyxiation

Dry powder extinguishers:

• #Steps for using a dry powder extinguisher on a Class B fire:
  • Pull the pin to break the seal
  • Aim the nozzle at the edge of the fire from a safe distance and squeeze the handle
  • Sweep the nozzle to drive the flames back and cover the liquid with the powder
  • Move forward to cover the area if safe to do so

Knowing the above, you might now be asking yourself “which extinguishers should you not use to put out a flammable liquid fire?” Well, you shouldn’t use either water fire extinguishers or wet chemical extinguishers. This is because they’re likely to be ineffective and can actually make matters worse if the force spreads the flammable liquid or chemical around.

Fire suppression systems for Class B fires

Aside from the three fire extinguishers mentioned previously, you can also look at fire suppression systems for Class B fires if the risk is great enough to warrant it. This is common in large industrial settings where a quick response is needed.

An automatic fire suppression system typically uses foam to cover the entire area when a chemical fire is detected, ensuring any fire doesn’t have a chance to spread and devastate the whole business. In some cases, a carbon dioxide system might be in place for areas of a building not attended but which still require protection. This uses gases to displace oxygen and stop a fire in its tracks.

Surrey Tech Services Ltd’s expertise with Class B fires

With a full range of fire extinguishers available for your business, we can advise you on the right type of unit and quantity to keep your premises safe. If you store flammable liquids such as paints, oils, diesel or petrol, simply contact us to get your premises kitted out with the right fire safety equipment wherever you are in London and the Home Counties.

We have the experience and the high-quality equipment to help you uphold your legal obligation and keep people safe.