Fire doors are a major element of a building’s passive fire protection system, and a key component of a fire door is the intumescent strip. 

 What is an Intumescent Strip and what is it made of? 

An intumescent strip is a seal generally found around the edges of a fire door and a door frame. 

Intumescent strips are made of synthetic chemicals and binders. This mix of materials do not burn immediately when exposed to extreme heat. Instead they expand in volume, which results in blocking the gaps between the fire door and door frame. With these gaps blocked, the spread of fire and smoke into unaffected parts of a building is delayed. 

As a result of this sealing action, fire doors are able to contain the spread of smoke and fire from 30 to 60 minutes depending on the type of intumescent strip installed. These few minutes of fire resistance translate to an increase in the number of lives saved from a fire and decrease in damage to property. 

Intumescent Strips for Fire Doors 

Intumescent fire door seals are fitted into a door set’s stiles and head, and in the doorframe’s grooves or mounted on its surface in some rare instances. As mentioned earlier, intumescent strips will help hold fire and smoke back from 30 to 60 minutes. This time variation depends on the thickness of the seal used. An intumescent seal measuring 10mm to 15mm thick can be expected to resist a fire for 30 minutes, while one that is least 20mm thick will be able to hold out for 60 minutes.  

To prevent the passage of cold smoke, fins or brushes can be found on the intumescent strips. These fins or brushes are designed to form an airtight or complete seal to prevent the passage of smoke around a door if the intumescent strip has not been activated by the heat of a fire.  

The fins and brushes should also be inspected and checked to ensure that they are not damaged or have been painted over. This would prevent the seal from working and allow smoke to pass around the door leaf. If you see this, report it to the relevant person or request a fire door survey so any other issues can be highlighted, a fire door inspection should be completed annually and remember, it is there to contain the fire and protect life. 

Things to take note as a property owner or manager: 

• Adding intumescent strips into a regular door does not make it a fire door as it will not provide the same level of protection and will not meet regulatory requirements as well. 
• While it is not illegal to paint over intumescent strips, it is best to err on the side of caution from a compliance perspective. Painting over an intumescent strip may affect its integrity as it may be damaged by the paint itself or the painter’s preparations. 
• Having fire doors complete with intumescent strips is one thing, while properly using them is another. A common occurrence in buildings is wedging fire doors open – just one of the ways that fire doors are misused. Misuse will render your fire door ineffective in the event of a fire. 

Fire doors and their components such as intumescent strips are susceptible to regular wear and tear and damage. Fire door intumescent seals can warp, crack, or detach over time or from heavy usage, emergency events, or building repairs. To ensure that the quality of fire protection provided by your fire doors are up to par, it is important to have regular inspections and fire door surveys done on your fire doors and seals.