What’s an intumescent strip and how does it prevent fire spreading?

When a fire starts, the biggest danger to human life, apart from the flames, is smoke inhalation, which can damage the lungs, cause unconsciousness, and even kill if inhaled in large enough quantities.

While fire doors are excellent at keeping back flames, they wouldn’t be half as effective without their intumescent seals to assist with stopping the fire breaking through and preventing smoke from circulating around the building, giving people precious time to escape.

What is it about the intumescent strip that makes it so effective? The material the strips are made from is a very poor conductor of heat, which makes it unlikely to burn and allow the fire to spread through the gaps in the door. Not only that, but intumescent material swells on contact with heat, thereby sealing your fire door in place and preventing it from warping and allowing the fire to come through. With fire doors, it’s not so much that a fire will eventually burn through the door material as it is that the heat can make the door warp, allowing flames to get through the gaps that are left, but with intumescent strips in place, the door remains a solid, straight barrier for its rated time, whether that’s FD30 which will keep a fire back for 30 minutes, FD240 (240 minutes) or anything in between.

Intumescent strips can come with a double blade or single blade smoke seal, or a brush smoke seal, to help prevent smoke from getting through before the heat reaches the door and the seals swell up. Most modern intumescent seals usually do have cold smoke elements in one seal.

For an incredibly vivid demonstration of how much difference a good fire door seal can make, watch this demonstration from the British Woodworking Federation, where you can see one door holding back the flames because it is properly installed, and one door completely failing because the installation was poor. This is also a frightening demonstration of why fire doors make such a difference in saving lives and what would happen if fire doors weren’t fitted.

Watching that video, it doesn’t take a lot of imagination to see how quickly fire and smoke would spread, and how many lives would be lost without fire doors to give people time to escape.

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