Wednesday, 25 January 2017

What is Intumescent Material and Why is it used for Fire Doors?

So what is intumescent material?

An intumescent is a material that expands when heated. It is a poor conductor of heat, so it is ideal for fire-proofing applications, including doors. 

In doors these are special strips that are inserted into rebated grooves in the frame. When the fire causes the strip to expand, it essentially glues the door in position around the edges of the frame to stop it distorting and the fire getting through the edges. So this is the key. Fire doors don’t work by the fire literally burning through the door, they will basically fail if the door distorts and bends, letting the fire get through by going around the edges.

The intumescent is nearly always in the frame. The only time you will see it on a door is in a set of double-doors, where the intumescent strips are rebated into the meeting stiles.  If the strips are not put into the frames then you may have no choice but to put them all around the door.

An intumescent strip.

Smoke Seals

Intumescent strips may also come with small brushes sticking out of them. The brushes act as fire door smoke seals. This is for the prevention of smoke passing through the door until the intumescent strip has reached the temperature to be activated. Again these are commonly found in the middle of double-doors, or a garage (because in many parts of the UK, law dictates a garage must be smoke proof straight away. It would help keep out car fumes too)

UK Law regarding Fire Doors

We supply a high percentage of fire doors often up to a bespoke size of 2.4 metres and even 2.7 metres tall, click here to view the doors. Fire doors in a residential scenario are often required for buildings with a adjoining garage door. When the dwelling exceeds two floors either on a new build or even a refurbishment (a loft or basement would count as a floor), then fire doors are required to protect the means of escape. Basically this is to prevent the spread of fire from a room to the stairway. So you would expect most of the bedrooms of the landings and the room around the hallway on the ground floor to be fire doors, normally FD30.

Many years ago most fire doors needed to be self closing, this however was changed in 2007.  This still exists in the regulations in commercial premises and in most apartment entrance doors and communal areas but has been more or less eliminated in the residential market. The only door that may need to be self closing is possible the door to the garage if it adjoins the main house

Lastly comes the burning question excuse the pun: Should fire doors be left open? Obviously not as an open fire door would not be very efficient of containing the fire.

Fire regulations in UK can vary from other areas. Some areas are more strict than others. Our advice is if you are in any double as to what you need to do, you should consult your building control officer or the person responsible for signing off the building

Diagram showing intumescent strip inside a fire door. 

So what does FD30 mean?

Well simply this is that if a fire breaks out in a room the FD30 door on that room is meant to halt the spread of fire from that room for 30 minutes.  Our fire doors have been tested in laboratories to make sure that under a controlled fire test that they withstand the fire breaking through for a least 30 minutes. 

This requires the fire door in conjunction with the correct fire tested hinges, locks, frames and stops made from appropriate material and intumescent material are all arranged in the correct way so the door will hold up to the fire. 

In other words just having a fire door itself is not enough, you will need all these other components to make sure it works. Below is a video showing what happens when intumescent material is reaches the temperate in which it is activated (usually around 170 degrees celsius)

Video from

What are fire doors made of?

Most modern fire doors including outs are made from fire tested solid core material with solid wood lippings. They are made this way as the construction is very stable and wont easily distort in a fire. So can fire doors be made of solid wood? Well I guess no is the answer, as solid wood when put under very high heat situation will distort too much even for the intumescent material to do its job. Most external doors we make are made from a high percentage of solid wood but front doors are never required to be fire rated. Solid wood used in this instance can handle the moisture and external conditions better then a solid-core fire door.

Hinges and hardware

It is also important when hanging the fire door leafs that you are using fire tested hinges and locks - if these fail then the fire will break through. Fire door regulations are set so that  they should have at least three hinges. Taller than standard doors often need four hinges. On the taller doors this has something to do with holding the weight of the doors that are often over 80KG. With standard fire doors that weigh around 60Kg, two fire hinges would carry the load but three are required mainly to prevent the door from distorting or bowing in the middle. In most fire tests usually the hinges have intumescent pads behind them and so do the locks and latches.

With our pre-hung door sets you don’t have to worry about this as all the correct intumescent material has been put into the frames and around the locks and behind the hinges already.

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