Specifying Notes - Fire Door Seals

Current provisions for safety in case of fire, in the majority of buildings, rely upon separating the whole building up into smaller areas by using fire resisting barriers, in the form of walls and ceilings. This separation is required to protect different occupancies, or to provide safe 'means of escape' for either occupants or the public.

Under current Building Regulations, as well as all other relevant regulations, the ability of the walls, ceilings etc. to act as effective barriers is referred to as their 'fire resistance'. This is quantified in 'minutes', i.e. the time that barrier would last if tested to the British Standard fire resistance test method (currently BS476: Part 22: 1987).

For most buildings the fire resistance requirements for the doorsets will be stated in the appropriate national building regulations (for instance, in England and Wales, the Building Regulations Approved Document B) although in certain cases other regulations or requirements may apply. Examples of additional requirements would be the BS5588 series of 'Codes of Practice'. Health Authority guidlines, etc.

All fire doors are tested as 'doorsets', a term used to include the door leaf, door frame and all the essential ironmongery - usually hinges, door closer and possibly a latch.

It is important to realise that a fire door leaf on its own - no matter how well made - cannot be expected to provide its full fire resistance performance unless it is properly installed. This will usually require it being hung on hinges sufficient to provide full support, that will not melt or transmit too much heat through the leaf; for it to be installed in a frame of appropriate quality timber, and finally the leaf should have adequate protection in the form of intumescent strips. These strips must themselves be appropriate to the type and configuration of door leaf that they are being fitted to. Sealmaster recommends that anyone regularly involved in the design, specification or obtain a copy of BS8214: 1990, the 'Code of Practice for the fire door assemblies with non-metalic leaves'. The fire resistance performance of fire doors is a complex subject, where each part of the doorset must work in harmony to contribute to the whole. Details matter, and this code of practice gives much useful information on what to consider when combining different products to make effective fire resisting doorsets.

In addition to resistance to fire, many doors are also required to restrict the speed of cold smoke. This is designated by the suffix 'S' after the fire door rating of 30 or 60 minutes. Such doorsets must not allow an air leakage of more than 3m³/hr/m run of leaf perimeter (excluding the bottom edge) through the door assembly, if tested to BS476: Part 31.1. If all other gaps are well sealed (e.g. glazing, letter plates and other openings), then it is generally accepted that the fitting of a tested smoke seal is adequate.

To the specifier, presented with the myriad of intumescent strips available from numerous manufacturers, it is often difficult to recognise essential differences from a purely visual appraisal. Sealmaster's intumescent strips are unique, for they alone use a high volume, low pressure intumescent material (known as mono-ammonium phosphate) in a robust aluminium carrier. This particular intumescent material has the virtues of producing very large quantities of resilient foam, which has expansion and gap-filling properties that are superior to all others.

Traditionally, this material has been very difficult to use in a suitably robust and reliable seal, however the use of an aluminium carrier has changed this. The carrier not only retains the intumescent, it also conducts heat to the intumescent very efficiently and quickly. This accelerates activation, so leading to a further reduction in smoke leakage. Many Sealmaster seals also have the facility to allow smoke-sealing blades to be mounted on the carrier, so reducing the purchase and installation costs of additional 'cold smoke' seals for 'S' rated doorsets. The strips are easily cut to length, and are simply pinned into place using the fixings provided. Once in place, they are robust and vandal resistant. Sealmaster has its own fire test and laboratory facility that is used to run both research and quality control tests on their wide range of products. This helps to ensure that their performance in a real-fire situation can be relied upon with total confidence.

Certain intumescent materials produce high pressure on activation. Whilst these materials do have some desirable characteristics, great care must be taken when specifying them, for in certain applications a pressure-forming intumescent can be quite dangerous, forcing doors open or creating additional stress on door components at a time when they are most vulnerable. Given this disadvantage, the recognised benefit of such high-pressure intumescents is their high 'gripping' property, which in some circumstances is necessary. Where this characteristic is required, Sealmaster recommend their Ultima seals which combine both high and low pressure intumescents in carefully specified proportions, producing a strong yet flexible seal.

BS8214: 1990 "Code of Practice for fire door assemblies with non-metallic leaves". Available from BSI, Chiswick, London, (020 8996 9001).

FRGGSA/IFSA - "Role of intumescent in timber and metal based fire resisting glazing systems". Available from FRGGSA/IFSA, 20 Park Street, Princes Risborough (01844 275500).

The Building Regulations Approved Document B (Fire Safety) 2000 (as amended 2002). Published by ODPM. Available from TSO (0870 600 5522).

The Guild of Architectural Ironmongers "Code of Practice for architectural ironmongery suitable for use of fire resisting self-closing timber and emergency exit doors". All available from the GAI (020 7790 3431).