• What is Intumescent Material and Why is it Used for Fire Doors?

    By SWD Team

    So what is intumescent material?

    An intumescent material is one that expands when heated. It is a poor conductor of heat, therefore it is ideal for many 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 therefore, preventing the fire getting through the edges.

    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. This is 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.

    Intumescent Strip
    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. In many parts of the UK, law dictates a garage must be smoke proof straight away.

    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 off 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 area to area. Some areas are more strict than others. Our advice is if you are in any doubt as to what you need to do, you should consult your building control officer or the person responsible for signing off the building.

    For further information on fire doors and building regulations visit BWF-CERTIFIRE

    �intumescent door diagram
    Diagram showing intumescent strip inside a fire door.

    So what does FD30 mean?

    If a fire breaks out in a room the FD30 door on that room is meant to halt the spread of fire 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 are made from appropriate material and intumescent material. All parts must be 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. Ultimately you will need all these other components in place to make sure it works. Below is a video showing what happens when intumescent material is reaches the temperature in which it is activated (usually around 170 degrees celsius)

    Video http://www.basf.com

    What are fire doors made of?

    Most modern fire doors including ours 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 usually 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 also 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 doors often need four hinges. On the taller doors this is because of the extra weight of these taller doors. In fact many are often over 80KG.

    With standard fire doors that weigh around 60Kg, two fire hinges would carry the load. However, three hinges 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.  The correct intumescent material has been already put into the frames and around the locks and behind the hinges.


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