Fire Door Seals

Originally published in November 2013. Updated in August 2019.

We’ve mentioned the use of both intumescent strips and fire seals earlier – but many people are unaware of the differences in function and where each should be used. Here is a more detailed explanation of these two important safety features.

What is a fire door seal?

Fire door seals are fitted between a door and its frame to fill any gaps that would otherwise allow smoke and fire to escape, in the event of an emergency. They are a vital part of any fire door and they must be correctly designed and fitted to guarantee that the protection they offer is effective.

In any door fitting there has to be a gap between the door leaf and the frame so that the door can open and close easily. However, this same gap can cause problems in the event of a fire, because it would allow toxic smoke and heat to escape, which would limit the fire door’s ability to contain the damage to property and risk of danger to people. This is why the seal within a fire door installation is so important: it allows for everyday opening and closing of the door without obstruction, but if a fire breaks out it expands in order to seal the gap.

Seals within fire door mechanisms are designed in such a way that when they expand considerably when they heat up, so if there is a fire, the high temperatures will activate this enlargement automatically. This allows the seal to fill the space between a door and its frame, preventing any smoke from leaking out of the gaps, and stopping fire from spreading. Seals are an essential part of a fire door’s capability to limit the spread of an outbreak of fire for anything from 30 minutes to two hours, containing it to a single part of a building to minimise smoke and flame damage to people, property and external and internal structures.

Types of fire door seal

Intumescent strips

An intumescent strip is a chemically designed product that helps to prevent the spread of fire from travelling from one space to another. The strip is fitted around the door frame and, when subjected to extreme levels of heat (as would be generated in a fire outbreak), expands through a chemical reaction and fills any gaps between the door itself and the frame, thus preventing heat from transferring through to another area.

The main function of an intumescent strip is prevent the spread of fire and heat – whilst it will also prevent a certain amount of smoke transfer, that is not its’ primary purpose. It will lock heat away and buy precious time for escape as well as protecting areas of the building not already ablaze.

Smoke seals

A smoke seal is similar to an intumescent strip, but more effective at preventing smoke from travelling from one area to another. It works in much the same way, naturally expanding when subjected to excessive heat, providing valuable time for evacuation of an area, or building, and halting the spread of potentially fatal smoke fumes.

A smoke seal’s primary function is to contain potentially toxic smoke fumes – like an intumescent strip, it is fitted between the fire door frame and the door itself, but is more ‘prominent’ than an intumescent strip. Smoke seals are clearly visible regardless of the position of the door, whereas the strips are more discreet.

It is widely accepted that, in the event of fire, smoke inhalation kills more people than the fire itself. The fitting of smoke seals will prevent this smoke inhalation and will lessen the possibility of people evacuating a building being adversely affected by lung damage and potentially passing out, thus endangering life.

Can they be used together?

The simple answer – and the recommendation – is “Yes”! It is sensible to fit your fire doors with both smoke seals AND intumescent strips to provide as much protection as possible. Combining the two will give people the best possible chance of escaping without injury in the event of a fire outbreak.

If people are exposed to smoke and fumes they can quickly pass out and leave themselves unable to get out of harm’s way if you fail to seal the doors effectively, and smoke moves from one area to another.

Whilst it is essential that all official fire doors are protected in this manner, it is a good idea to consider fitting seals and strips to other internal doors as well.

Where are door seals located?

Fire door seals are usually present in the frame or lining of the door, but they can be fitted on the edge of a door if necessary.

When properly designed, built and installed by specialist fire door manufacturers, the seals can remain effective for many years after installation. Once the system is in place, you can feel reassured and confident that, should the worst happen, your fire door leaf, seal and frame will work together to contain the fire and smoke to a single part of a building.

Fire is incredibly destructive to property, and the spread of smoke is the biggest danger to human life when a fire breaks out, as well as being the cause of significant damage to belongings. By segmenting buildings into specific areas, fire doors guarantee that, when used and maintained properly, they will contain the damage to one area, letting people safely escape, and allowing the fire service to arrive and tackle the blaze before it spreads. The seal between a fire door and its frame is a key part of the mechanism, as it plays a very important role in limiting the potential losses.

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