An intumescent grille is a ventilation opening that closes itself in a fire. It is used where air has to pass through a fire separating element for ventilation or for equipment cooling, and it works on the same principle as a door seal: an inert material that expands when heated and blocks the opening it was fitted into.
How it works
The grille contains layers of intumescent material forming the airway. Under normal conditions air passes through freely at a stated free area. When the material reaches its activation temperature it expands and the airway closes, restoring the integrity of the element it sits in. The closure is one way and the product is replaced after any event that triggers it.
Where they are used
Transfer air between a room and a corridor where mechanical ventilation requires it. Cooling for plant enclosures, risers and cupboards containing equipment that generates heat. Ventilation of protected spaces where a conventional grille would be an unacceptable hole. In a fire door leaf where the certification permits an aperture, which is a narrower case than people assume.
The conditions that come with them
The grille has to be tested for the fire resistance period of the element and installed in a supporting construction it was tested against. In a door leaf it must be within the doorset's own certification, at or below the tested aperture size and position. Cutting a hole in a certified fire door for a grille the certification does not cover ends the certification, which is a common finding in older commercial fit outs.
What they do not do
They do not stop cold smoke in the early stages, because nothing has got hot. A grille in a wall between a room and an escape route is a smoke path for the period that matters most, and where smoke control is the concern a mechanical or ducted solution with a fire and smoke damper is the answer rather than an intumescent grille.
Questions people ask about intumescent grill
Can an intumescent air vent go in any fire door?
Only where the doorset's certification covers an aperture of that size in that position, with that product. Many certifications do not permit apertures at all.
Do they need maintenance?
They need to be kept clear and undamaged and checked visually. They are replaced after activation and where the intumescent is contaminated or painted.
Are they the same as a fire damper?
No. A fire damper is a mechanical device in ductwork, often with a fusible link or a motorised actuator, and it is inspected and tested on a schedule. An intumescent grille is passive.