How Do Intumescent Strips In Fire Doors Help Prevent The Spread Of Fire?

26 August 2021

Fire Doors are a legal requirement in the majority of buildings in the UK, from offices to shopping centres and from multi-occupancy apartment blocks to public service spaces like hospitals and schools.

The Building Regulations also demand that fire doors have intumescent strips.

So, what are intumescent strips? And how do they help prevent the spread of fire?

Fire Door Intumescent Strip

What Are Intumescent Strips?

An intumescent strip – also known as a seal or fire door strip – is one of the key components in a fire door.

Running around the edge where the fire door meets the doorframe, an intumescent strip is a length of plastic extrusion that is chemically designed to swell up when heated, thus protecting the material underneath or sealing a gap in the event of a fire.

Why Are Intumescent Strips So Important?

If a fire were to break out in a room, the heat would cause the strip to expand and seal the gap around the frame.

This chemical process will help contain the fire and give you – or your building’s inhabitants – a vital window of time in which to escape to safety and call the fire brigade.

The most important role an intumescent strip plays is in saving lives but they prevent the spread of fire and minimise building damage.

How Do They Differ From Smoke Seals?

Smoke inhalation is the most common cause of fire-related deaths and injury. Smoke seals are an effective means of preventing tragedy.

Fire Door Strips

They are placed between the doorframe and surround the door on all sides. These seals stop smoke passing through the gaps, thereby preventing deadly smoke progressing to other parts of the building.

The key difference is that intumescent strips block flames, while smoke seals prevent the spread of lethal smoke.

Can You Use Smoke Seals And Intumescent Strips Together?

You can indeed.

Smoke seals are positioned in the same places as intumescent strips, although they are more visible than the latter.

In most cases, a regular fire and smoke seal will be fitted to a fire door together to prevent fire and smoke seeping through the sides or bottom of the door. Handily, you can get these visible seals in a variety of colours to match your door and interior design.

Specialist hygienic fire and smoke seals, meanwhile, are a popular choice with hospitals, schools and businesses alike because of their easy-to-clean nature. A quick wipe with a damp cloth is all it takes to remove grime and keep the seals looking like new.

You can also get fire, smoke and draught seals, which are single or double blades that give you the added benefit of keeping out unwanted draughts, thereby helping prevent chills and keep those heating prices down.

Is The Size Of The Gap Important?

The gap between the door and the frame is an extremely important factor when fitting intumescent and smoke seals.

Intumescent Strips

Really, the gap between the two vertical longer edges and the shorter top should not exceed 3-4mm.

The gap at the bottom of the door is usually 10mm when not taking smoke seals into consideration; but if you are (and you should!), again, the gap should be no greater than 3-4mm.

What Should You Know Before Buying Smoke Seals And Intumescent Strips?

You should try to buy all your fire door components as one; from the door to the frame (thereby completing the doorset) to the seals and closer.

And, if you’re buying a door with a glass panel, be sure that the glass has been properly tested and is certified fire-resistant.

Only buy from fire door suppliers whose doors have been certified safe by the BWF (British Woodworking Federation) Fire Door Alliance.

The BWF is a membership organisation made up of timber fire door manufacturers, licensed door processors and manufacturers and/or suppliers of fire door assembly components.

BWF Fire Door Alliance

The BWF Fire Door Alliance’s mission is to ensure that every fire door or fire doorset sold in the UK meets required standards through its service life.

Read this blog to find out more about why it’s important that fire doors have proper BWF certification

Why It’s So Vital To Contain Fire and Smoke

In short, containing a fire to one room significantly reduces risk to life and damage to property.

Containment of fire and smoke gives people the chance to escape and raise the alarm, and fire doors – and their components, like the intumescent strips which seal the gap between the door and frame – are one of the most effective ways to create this life-saving compartmentalisation.

Play It Safe When It Comes To Preventing Tragedy

There’s no such thing as being too careful when it comes to fire safety and measures to prevent the spread of deadly smoke. 

Fire safety awareness has come on leaps-and-bounds in the past decade, but there are still scores of fire-related deaths every year in the UK that could be prevented by fire doors and components like high-quality intumescent and smoke seals.

That’s why it’s so important to purchase your fire doors from a supplier like Vigor Doors that is committed to ‘Doors For Life’ and so passionate about fire safety.

If you want Fire Doors and fire-related products that could one day save the lives of the people occupying your property or the property you’re responsible for, please speak to a member of the Vigor Doors team on 01642 265 034 or drop us a line at

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