Intumescent Fire Blocks

These are air transfer fire blocks. They are not mechanical fire dampers and they work differently: there are no blades, no fusible link and no actuator, so there is nothing to seize, nothing to reset and nothing to test annually. That makes them the practical answer for door transfer grilles, wall openings and duct terminations where fitting and maintaining a mechanical damper is not realistic. They are single use, so a block that has activated is replaced rather than reset.

Frequently asked questions

What is an intumescent fire block?

It is a passive fire protection component that allows air to pass through an opening in normal conditions and seals that opening when it gets hot. The core is an intumescent material, meaning it swells when heated. The expansion closes off the free area and blocks the path that flame and hot gas would otherwise take through a door, wall or duct penetration.

Is an intumescent fire block the same as a fire damper?

No, and the distinction matters when you are specifying. A mechanical fire damper has moving blades held open by a fusible link or an actuator, is classified and CE marked under the relevant product standard, is resettable, and has to be inspected and tested at least annually. An intumescent block is passive, has no moving parts and no maintenance regime, and is replaced rather than reset once it has activated. They solve different problems. If your fire strategy or specification calls for a classified fire damper at a duct penetration, a block is not a substitute for it.

What fire performance do these blocks offer?

The manufacturer states up to 60 minutes in timber doors and up to 120 minutes in walls and ducts. Those are application figures rather than an EI classification under a harmonised product standard, so if your specification calls for a specific classified rating, check the requirement before ordering and we will tell you honestly whether these meet it or whether you need a mechanical damper. We would rather lose the sale than have the wrong product go into a fire compartment.

Where are they normally used?

The common applications are door transfer grilles where air has to move between rooms without compromising a fire door, wall openings and air transfer paths between compartments, and the individual room supply and extract terminals of MVHR and MEV systems in blocks of flats. They are also used where a duct penetration is too small or too awkward for a mechanical damper to be installed and accessed.

What size do I need?

Size on the opening rather than the duct. Square blocks run 150mm, 200mm, 250mm, 300mm, 350mm, 400mm, 450mm, 500mm and 600mm. Circular blocks run 100mm, 125mm, 150mm and 200mm and are sized to spiral duct. All are 38mm deep. Bear in mind that free area is approximately 60%, so the block restricts airflow compared with an open grille of the same size and you may need to go up a size to maintain the design flow rate.

Do they need testing or maintenance?

No. That is the main reason people choose them. There is no mechanism to seize, no link to corrode and no actuator to fail, so there is no annual drop test and no access panel requirement. A visual check that the block is still in place, undamaged and not painted over or obstructed is all that is normally required. Compare that with a mechanical fire damper, which must be inspected and tested at least annually by a competent person.

Can they be painted or finished to match?

They come in black or grey as standard and other colours are available on request. Do not paint over the intumescent material itself, because a heavy paint film can affect how it expands. If you need a specific finish, ask us before ordering rather than painting on site.

Do you supply intumescent fire blocks for trade and project work?

Yes. We supply contractors, housing associations, facilities managers and M&E consultants, and blocks of flats are the single most common application we quote for. If you have a schedule covering multiple plots, send it over and we will price the lot. Call 0161 399 3825 or email hello@efans.co.uk.

For mechanical dampers, see our fire damper guide.