The job of a fire door is to hold back fire and smoke. Intumescent strips and smoke seals are fitted around the door to seal the gap between the door leaf and the frame. The door leaf is the part of the door that opens and closes. This guide explains what each one does, what S in FD30S and FD60S means and what to check on your fire doors.
FD30 and FD60 are fire door ratings. They mean the resists fire for 30 or 60 minutes.
What Do Intumescent Strips Do?
Intumescent strips swell when they are heated. They fill the gap between the door leaf and the frame, which stops fire and smoke passing through it. To do this, they expand to several times their original size.
This is how intumescent strips are fitted and replaced:
- They can be fitted in grooves in the two vertical sections and the top edge of the door frame
- Uninterrupted strips should go in the frame or lining where possible
- They must be used as the door leaf manufacture recommendsThe same type should used all the way around the door when seals are installed or replaced
What Do Smoke Seals Do?
Smoke seals stop smoke passing through the gaps around a closed door. This is a separate job from the one conducted by intumescent strips. You can buy combined intumescent strips and smoke seals. Smoke seals are a Building Regulations requirement in some situations. These include between flats and common areas and in protected lobbies and along escape routes.
What Does the S in FD30S and FD60S Mean?
The S shows that the door has had a smoke seal added. An FD30S door is an FD30 door with a smoke seal, the same applies for an FD60 door with an S.
Check your project specification to see whether your doors to be FD30S or FD60S. Where smoke seals are required, a door without them does not meet the requirement and needs to be upgraded to ensure compliance.
How Big Is The Gap Under A Fire Door?
A fire door needs a small gap between the bottom of the door and the floor covering. If the gap is too small, the door may not close reliably. If it’s too large, flames and smoke can get through. (LFS FAQs)
The gap is usually around 10mm. If the door needs smoke seals, the gap is 3mm. The exact figure depends on the door, so check the manufacturer’s instructions for yours.
What Should You Check On Your Fire Doors?
- Intumescent strips run along the top and both sides of the frame, or the door edge and are the same type all the way round
- Smoke seals are fitted if the door requires them
- The seals match what the door manufacturer recommends
- The fire door closes fully. Our FAQs highlight a gap that is too small may stop the door closing reliably or stop the intumescent strips working properly.
- Any seals you add, such as acoustic seals, are covered by the certificate, which shows which seals, hinges, closers and other ironmongery are permitted.
Our guide to acoustic fire doors explains how acoustic seals fit alongside fire seals.
Talk To LFS About Your Project
We manufacture FD30 and FD60 (30 and 60 minute) fire doors in-house at our Kent facility. If you are not sure what seals your doors need, get in touch with us or call 0800 035 6827.
You can also read more about our fire door manufacture.
