Fire doors are required under Fire Safety Regulations in many types of buildings. Where fire doors are installed, appropriate intumescent strips must also be fitted.
If intumescent strips are missing, damaged, or incorrectly sized, the door may fail in a much shorter time during a fire. This can allow flames and smoke to spread more rapidly, increasing the risk of injury, fatalities, and extensive property damage.
What Are Intumescent Strips?
Intumescent strips are heat-activated seals fitted around fire doors or within the door frame. They are designed to expand when exposed to high temperatures.
In normal conditions, these strips sit discreetly within the door edge or frame. During a fire, the material reacts to heat and expands many times its original size. This expansion seals the gap between the door and the frame, helping to contain fire and smoke within a specific compartment.
Understanding Fire Door Ratings
Fire doors are classified by the length of time they can resist fire:
- FD30 – 30 minutes
- FD60 – 60 minutes
- FD90 – 90 minutes
- FD120 – 120 minutes
Where smoke control is also required, the door is identified with an “S” suffix, such as FD30S or FD60S. These doors are designed to restrict the movement of cold smoke as well as flames.
The intumescent strip size and specification must always match the door’s fire rating and test evidence.
Choosing the right Intumescent Strip
Typically, the below sizes are most common for intumescent strips:
The correct size depends entirely on the fire door’s tested specification. Using the wrong dimensions may affect compliance and reduce the door’s ability to perform in a fire.
How big should the gaps be around a door and its frame?
The gap between the door and the frame is extremely important and must be suitable for the intumescent seal fitted.
As a general rule, the gap should be between 2-4mm, this is expected to be adhered to along the 2 long edges and also across the top of the door leaf. The threshold gap at the bottom of the door should be a maximum of 8-10mm* for fire only doors, and 3mm for a fire and smoke door.
* Check the door manufacturer’s instructions
The Building Regulations also indicate situations where a fire door may also have to prevent smoke leakage, and in these situations, a smoke seal must also be fitted. It is estimated that smoke inhalation is the cause of 50 - 80% of all fire deaths. You can buy intumescent seals that combine a smoke seal or you can fit two separate seals - a fire seal and a separate smoke seal.
How We Can Help
At FireSealsDirect, we stock the most trusted intumescent sealant brands on the market, including Lorient and Pyroplex, all of which meet the most stringent British and EU regulatory standards.
Need help selecting the right products? Get in touch with our technical team at [email protected] or call 02920 857 959.
You can also explore our Advice Centre, which offers a wide range of guides and useful information on fire safety, fire legislation and more.
