What’s the difference between intumescent strips and smoke seals?

Fire internal doors

A fire door is specially designed to keep fire at bay for a minimum of 30 minutes. In residential buildings, this is usually ample time for the household to evacuate the building via the designated fire escape. The robust build quality and thickness of the door play a significant role in the door’s fire-stopping capability. But intumescent strips and smoke seals are also integral in maintaining the safety barrier between the fire and the rest of your property.

Look at the edge of your fire door and you may find intumescent strips, or smoke seals, or a combination of both. Here, we’ll look at the part these features play in ensuring that your fire doors keep smoke, heat and flames at bay.

What are intumescent strips and how do they work?

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.

What are smoke seals and how do they work?

Like intumescent strips, smoke seals can also be found around the edge of the door leaf and the fire door’s frame. However, they work in a slightly different way.

Smoke seals, also known as cold smoke seals, are designed to prevent smoke from escaping through the tiny gaps between the door leaf and frame. These are made from materials like nylon or neoprene and have a soft and fuzzy texture that traps smoke particulates.

Smoke seals are very important, as smoke inhalation is actually the leading cause of fire-related deaths, accounting for an estimated 50%-80% of fire deaths. Smoke inhalation can prevent oxygen from getting to the brain, potentially causing a loss of consciousness and even death. Approximately 40% of fire deaths are from smoke inhalation alone with no burns or other damage.

As well as preventing the spread of smoke throughout the home, smoke seals also do a great job of containing draughts and preventing warm air from seeping out of living spaces through gaps between the door leaf and frame.

What’s the difference between intumescent strips and smoke seals?

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.

Can intumescent strips and smoke seals work together?

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.

Are intumescent strips and smoke seals requirements for UK fire doors?

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.

Take a look at our range of FD30-rated fire doors

The right fire-rated door can make all the difference to your home’s fire safety. Fortunately, you don’t have to compromise on style to keep your household safe. Take a look at our FD30-rated internal fire door range and you’ll find a range of styles and finishes to suit all tastes and aesthetics.