The Regs: Geoff Wilkinson looks at specification of fire doors
Specifying fire doors can be confusing. They can be rated from as little as 20 minutes (of fire protection) up to two hours or more. Depending on their situation, some need to be specified with combined fire and smoke seals, while others only need intumescent seals (seals which swell when heated). Furthermore, some doors require self-closers and others need to be kept locked shut.
The place to start is Table B1 of Appendix B in Approved Document B. This is where you will find the requirements for each type of fire door according to its location. Having checked this information, the process of selecting the actual door can begin.
It was once accepted practice to improve the performance of an existing door to provide fire-resistance. Nowadays, outside of small domestic projects or listed buildings, this is no longer likely to be approved by building control or a fire risk assessor. Architects should therefore only specify ‘certified’ fire doorsets, both for identification purposes and to guarantee their performance in a fire situation. Such doorsets have been tested by an approved fire testing centre by subjecting them to the standard test procedure specified in BS 476 or BS EN 1634. This procedure consists of exposing one face of the door to heat with the upper part of the door under a small positive pressure, to simulate the conditions likely to occur in a real fire.
It should be noted that tests are made on complete door assemblies - door and frame fitted with all the requisite hardware (locks, latches, hinges and so on). It is important that the frame to be used is tested as well because, should a door be tested in one type of frame and then used in another, it will invalidate any guarantee of its performance under fire conditions.
Once the certification is approved, each similarly constructed doorset can be identified by a label identifying the manufacturer, the date of manufacture and the designated fire rating of the door type. There are two main certification schemes. BM TRADA uses a system known as Q-Mark, which uses plugs to identify the doors. The British Woodworking Federation’s Certifire scheme uses physical labels. If neither of these schemes is used Building Control is likely to insist on written proof that a door meets all the necessary standards - a test certificate, for example, or an inspection by a third party under the Fire Door Inspection Scheme might be necessary.
The correct specification of ironmongery is also vital. In the tests, fire doors will typically be fitted with three hinges to prevent warping. You should only be specifying sets of the same type, number and material. In most cases the tested hinges will have been steel and it may have been necessary to use hinges with extended flaps (broad butts) to ensure the door stays in place even when severe charring has taken place to the frame. If the door has only been tested with hinges, it may not be suitable if its paired up with an alternate form of ironmongery, such as floor pivots or sliding gear. Even if that ironmongery has been tested and certified on a different door type, it could still result in the actual door warping in a real fire. If you are determined to use an untested combination for aesthetic reasons, the original test laboratory may be able to provide an opinion on the alternative combination, or may recommend a retest.
Needless to say, the cutting of a fire door to accommodate a sloping ceiling or the planting of an additional piece to make up a non-standard size is likely to invalidate its certificate. The fixing of a lock, letter plate or vision panel to a fire-resisting door could also invalidate the certificate. Vision panels should never be cut in on site but be factory-fitted and delivered ready glazed with the correct type of glass. Lastly the type of smoke or fire seal should be chosen carefully as not all intumescent materials act in the same way. Changing the specification from the tested assembly can have unexpected results. There are two types of seal - low-pressure seals (which expand in all directions but do little to prevent distortion) and high-pressure seals (which exert pressure in one direction and help prevent distortion of the door leaf) - swapping them can again affect performance.
Geoff Wilkinson is managing director of approved inspectors Wilkinson Construction Consultants