Last edited 21 Feb 2021

Intumescent strip

1 Introduction
2 Types of intumescent strip
3 Related articles on Designing Buildings Wiki

[edit] Introduction

Intumescence is a chemical process which involves the swelling of crystals on heating and is often accompanied by a violent escape of moisture.

In a building, the heat of a fire can make intumescent material expand and bubble, sealing gaps, such as those between a door and its frame or around glazing. This is of great importance for fire safety as it can help reduce the spread of smoke and flame, allowing occupants additional time to escape before the fire spreads or there is a dangerous level of smoke.

Placed around a door opening, a strip of intumescent material can stop the spread of fire and smoke for up to an hour. However, these strips should be inspected regularly for any tears or damage. If damage is evident, the strips should be replaced as soon as possible as their performance in a fire may have been compromised.

Intumescent strips are particularly useful in apartment buildings and offices that have shared stairwells and fire escapes. They are usually fitted into the door frame but are sometimes recessed into groves cut into the door. It is possible to fit normal doors with an intumescent strip but this will not make them fire doors.

[edit] Types of intumescent strip

[edit] Fire only

Fire-only intumescent strips are activated on contact with fire, expanding and bubbling as the temperature rises.

[edit] Fire and smoke

This type of intumescent strip expands and seals in the same way. However, it incorporates a brush strip which stops the spread of smoke even before expansion has occurred through heat activation. This is important as, for example, doors at a distance from the fire may not be subject to the heat at the fire’s origin therefore their intumescent strips will not have yet been activated by heat. However, if fitted with a fire and smoke intumescent seal, cold smoke can be prevented from spreading before the heat and flames have reached the door.

[edit] Selecting the right seal

The correct seal type and size for any particular door can be determined by reference to door-test data. Once cut to the right length, most intumescent seals have a self-adhesive backing to allow a secure fit into the groove.