All intumescent strips are the same, right? Wrong! You might be surprised to know, that there’s a variety of different types that behave slightly differently and that it’s important to choose the right one for every application.

Intumescent strips should be fitted to fire doors so that, when they are exposed to the high temperatures of a fire they will intumesce (swell), expanding to close any gaps or edges and stopping the spread of smoke and flames giving people time to escape while the emergency services work.

British Standards require most fire doors to be smoke sealed. This means they need to limit the leakage of ambient smoke to three cubic metres of smoke through one metre of door edge per hour. Simply adding intumescent strip to any old door won’t make it a fire door though: a door is only a fire door where it has been tested and certified as such by the manufacturer.

So why does a fire door have gaps round it anyway? Well that’s to allow the door to close and open in normal operation but the gap should be limited to 3-4mm around the edges and top of the door while the gap at the bottom of the door must be around 10mm for non-smoke conditions, 3-4mm when smoke seals are fitted. If you want to check the gaps around a fire door, why not request one of our handy gap testers?

So here’s the science bit. There are four main types of intumescent strip, all of them act differently in a fire so are suitable for particular applications.

Mono Ammonium Phosphate activates at about 180C generating virtually no pressure during expansion. It is an excellent gap filler and can accommodate significant movement of components in fire conditions. This is the perfect choice for glazed apertures in fire resisting doors and screens.

Hydrated Sodium Silicate activating at around 110C – 120C, this strip expands predominately in one direction forming a rigid foam whilst creating substantial pressure. The pressure created in the gap helps restrain movement and hold adjacent components together so it’s the ideal choice for the edges of timber fire doors and their frames.

Intercalated Graphite: This strip combines multi-directional gap filling properties with high pressure forming, activating at around 200C. Graphite is non-hygroscopic, meaning it will not absorb moisture, so it does not require protection from the atmosphere making it a good choice the edges and frame of external timber doors.

If you want to make sure you are getting the right intumescent for your project, why not give us a call and run through your options on 01661 830088.