We get often asked if gaps are allowed underneath fire doors and if so, how big they can be. We researched on your behalf and compiled this blog to explain the current recommendations. What happens in case of a fire? There is positive pressure in a room on fire (until the fire is vented) but at the base of the fire the pressure must be negative to draw in the air for the fire to receive oxygen. The smoke and the fire will try to push through the side and top gaps around a fire door while (usually) drawing air from underneath the door. The Development of Fire Door Testing The old test of fire doors to BS 476 Part 8 (for fire resistance) was carried out simply in a furnace increasing the temperature to that found in rooms on fire and the door was checked to ascertain when the fire would breach the door, usually at the gaps at the head and sides of the door. This was changed in the eighties to BS 476 part 22 which was similar, however, the furnace was now pressurised. Old BS 476 Part 8 fire doors failed this new test (usually after around 20 mins for a 30 minute FD30 fire door), so intumescent strips, also called fire door seals, were introduced to ensure fire doors passed the test.

However, cold smoke can still seep through the gaps around the door and cause death from smoke inhalation. In some applications  therefore fire doors with cold smoke protection around the sides and top are required (recognisable by the ending ‘s‘, e.g. FD30s). This is usually achieved by installing fire door seals with integrated cold smoke brushes. Fire doors tested in accordance with the cold smoke test requirement BS 476 part 31 ensure that in the early stages of a fire, the cold smoke does not percolate into escape routes and makes them impassable. At first the standard was only concerned with the gaps at the head and the sides of the door, as the air passing though the threshold gap to feed the fire keeps the smoke in the affected room. However, now the standards have changed and for fire doors requiring cold smoke control, the threshold gap does now have to be considered as well. This is quite confusing, as fire fighters were always taught that at floor level there is a layer of an inch thickness of fresh air no matter how severe the fire is and if you get caught, get your nose on the floor to breathe.

Consequently, the threshold gap was never considered important and BS 8214:1990 reflected this by stating a threshold gap of 6/8mm was acceptable. Nevertheless, in BS 8214:2008 this changed and it states that under-door (threshold) gaps should be in accordance with the manufacturer’s installation instructions for the particular doorset design. When fitted, smoke seals should give an even contact with the floor but should not exhibit significant increased frictional forces that could interfere with the closing action of the door (see BS 5588-11). BS 5588-11 is now withdrawn and BS 9999 is the current standard. BS9999:2008 recommends for fire doors with cold smoke control that the threshold gap should be either less than 3mm in height or should be fitted with a threshold seal. When speaking with manufacturers, however, a common statement is that a fire doors gap of up to 8 mm underneath the door is permissible. This is probably just referring to normal FD30 applications, as the fire door manufacturer is not involved in upgrading fire doors to cold seal protected standard (FD30s).

Ask your fire door manufacturer for their recommended threshold gap. If this information is not available it seems reasonable to permit a gap of up to 8mm for general fire doors (eg FD30). If you have a requirement for cold smoke control (eg FD30s) your threshold gap should be less than 3mm or you should fit a threshold smoke seal.front door knockers brass This advice applies for most applications, however, special requirements must be considered in a your fire risk assessment.old doors for sale knoxville tnHomeProductsCatalog & CAD LibrarySpec HelpSales AgenciesNewsContact Usbi fold door threshold details Catalog and CAD Libraryold door knob spindles

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Accessories13Adjustable8, 9, 10Bulkhead11Butt & Transition12Carpet Divider4Expansion Joint & Covers10, 11Floor Closer Threshold3Handicap1, 2, 3, 5, 7, 12Interlocking13Rabbeted5, 6Ramp7, 12Rubber4, 10, 12Thermal Break2, 3, 4, 6Traction Tread™9Utility1, 2, 3Water Return13Wheelchair Shower 14 Automatic Door Bottoms1, 2, 3, 4, 5Automatic Door Bottom, Electrical5Automatic Door Bottom, Lead-lined3Door Sweeps6, 7, 8, 9Door Sweep with Intumescent8End Caps, Locking Key5FLO Option4, 7, 8 Anti-Bacterial Gasketing - BioWall™(BIO)16Glass Door Weatherstripping17, 18Head & Jamb, Adjustable Seals2, 3Head & Jamb, Contact Seals4, 5, 6, 7, 8, 9Head & Jamb, Interlocking Seals10Head & Jamb, Magnetic Sealing4Head & Jamb, Spring-Loaded3Head & Jamb Protection, Intumescent5Kerf Mount Weatherstripping8Ligature-Resistant Gasketing (ZAG)21Meeting Stiles 11, 12, 13, 14, 15Mullion Application20Self-Adhesive Weatherstripping9Sliding Overhead & Hangar Doors22Strike Plate/ Door Closer Mounting Brackets3, 10Water Shed/ Rain Drip10Wood Doors/ Wood Frames19

Cam Lift Hinge1Continuous Unigear Hinges2, 3, 4Continuous Hinge Options4Mortise Hinge1Door Holder, Heavy-Duty Spring Recoil6Barrel-Type Unipin Continuous Hinges5 Weatherstripping - Double-Hung, Casement1, 2Weathercheck, Sash Pulley, Chain1 Anchors2Double Coated Foam Tapes1Magnetic Strip1Screws, Thru Bolt3, 4, 5, 6 Acoustical Louvers4Pairs of Doors - Sound Trap3Single Doors - Sound Trap2Sound Barrier Sheet8Sound Control Systems - Single & Double Doors9Sound Control Technology - Sound Trap1Structural Acoustics, Floors and Walls6Vision Lites4, 5Wall Insulator System - Sound Trap7Windows and Curtain Wall Partition5 Door Solutions1, 2, 3Firestopping Applications6Glazing Tape5Intumescent Lock Packs/ Hinge Pads5Intumescent Technology7Louver Solutions4Smoke & Draft Control System3Specialties - Auto Door Bottom5Specialties - Fire Block, Fire Bolt5 Directional Signs, Door Kits2Door Hardware Marking4Exit Door Kits2, 4Floor Demarcation Lines4Head & Jamb, Sill Marking4Stair Marking3Stairway Marking System1"Traction Tread" Glow3