Whats The Difference Between Intumescent Strips And Smoke Seals

An intumescent strip is a rubbery strip that can be seen running around the edge of a fire door leaf. They may also be attached to the door frame itself. These are made from a combination of synthetic polymers and resin binders like silicone or epoxy, making them extremely tough and impervious to fire damage. When the surrounding temperature reaches around 200°C (usually around 10-15 minutes after the fire has started), they are designed to expand, sealing the tiny spaces between the door leaf and the frame so that heat is not allowed to escape.

This helps to contain the fire and prevents it from spreading throughout the home.

Smoke seals and intumescent strips are often seen on the same area within a fire door, and help to supplement the fire-stopping properties of the leaf itself. As such, there is often some misunderstanding of how the two differ.

While they may be similar in placement, they have different appearances and different properties. While a smoke seal is fluffy and brush-like in texture, an intumescent strip is rubbery. Likewise, a smoke seal will not expand in the presence of heat in the same way that an intumescent strip will.

A smoke seal is designed solely to prevent smoke from seeping into the living space, and is not designed to prevent the spread of fire in the same way that an intumescent strip will. Likewise, smoke may be generated before temperatures have risen to a sufficient degree for intumescent strips to expand.

As we can see, intumescent strips help to contain heat, while smoke seals prevent the spread of smoke around the home. As such, they can be (and often are) used together to enhance the efficacy of an internal fire door. An intumescent strip can seal in heat and prevent the spread of flames from impinging on fire exits, while smoke seals ensure that the air is sufficiently breathable by filtering out smoke particulates.

Fire doors are thicker than most internal doors (44mm in thickness as opposed to an average of 35-40mm). This is amble to accommodate both intumescent strips and smoke seals if you would like to use them together.

According to the British Standard 476 fire safety guidelines, there is no specific requirement for either smoke seals nor intumescent strips to be fitted to a fire door. Fire doors are graded depending on their ability to keep fire at bay for a set time. As such, FD30-rated fire doors will keep fire away for at least 30 minutes, FD60 for 60 minutes and FD120 for 120 minutes. That said, both smoke seals and intumescent strips may be factored into a door’s ability to meet or exceed these required standards.

A fire door also needs to be able to keep smoke leakage to a maximum of 3 cubic metres of smoke per 1 metre of door edge per hour. Internal fire doors may use intumescent strips, smoke seals, or a combination of both to achieve this.