Andrew Forecast, senior consultant with Chiltern Fire International Fire, discussess the technology of fire resisting doorsets, highlighting aspects of design and installation that will ensure performance in fire.
Fire doorsets – the door leaf or leaves, the frame in which the door is hung, essential ironmongery, intumescent and smoke sealing devices – are complex products requiring specialist knowledge. For the specifier, however, the single most important consideration is that, if the worst should happen and fire breaks out, the doorset will perform as it has been designed to do.
It has been Chiltern Fire’s contention for many years that fire resisting doorsets should be manufactured, and ideally installed by, companies which can demonstrate – through testing or third-party certification – that they are experts in this field. Furthermore, we strongly recommend that specifiers choose, wherever possible, a complete manufactured doorset, rather than individual components which may not be correctly assembled on site. If it is not feasible to specify a complete doorset, it is important to ensure that there is precise and definite test/assessment data supporting use of the selected components, in addition to detailed instructions for their assembly.
Specifiers can and should ask suppliers for test evidence for their fire doors. In order to determine the fire resistance time, a doorset is exposed to an ‘average’ fully developed fire in a test furnace until failure occurs according to certain criteria. It is worth stressing that the times specified in all legislation relate to the time of exposure to the fully developed fire after flashover (the ignition of all exposed combustible materials) has occurred. It specifically does not include the time taken for the fire to develop to this stage.
A fire resisting doorset is required to perform one of three main functions:
1. To protect escape routes from the effects of fire, to enable the occupants to reach final exits;
2. To protect the contents and/or structure of the building by limiting the fire spread;
3. Permit fire fighting.
Thus the doorset, together with its surrounding wall, will be required to contain the fire in ts compartment of origin for a specified time. Subsequent protected compartments will further inhibit fire spread. The measure of a doorset’s ability in this respect is known as its integrity rating.
Where an escape route is required to be kept free of smoke, the fire resisting doorset might be required to perform the added function of controlling ambient temperature smoke, as well as being fire resistant. In such cases, either a combined intumescent and smoke seal may be used, or a separate smoke seal may be fitted in addition to the correct intumescent specification. Smoke seals must have been tested to BS 476: Part 31.1 and have demonstrated to maintain the ‘leakage’ rate below 3m3/m/h when tested at 25Pa. In addition:
4. It may be necessary to limit the amount of radiation from a door if highly flammable materials are likely to be stored within a short distance of the doorway, or if it is adjacent to a protected means of escape.
5. Under certain circumstances, it may be a requirement for the door to have an insulation rating, i.e. not to get excessively hot on the unexposed face.
The Building Regulations and most fire protection/ prevention Codes call for a minimum performance with respect to 1, 2 and 3. Requirements 4 and 5 are relaxed in regulations and codes, although individual specifiers or insurers may call for doors with specified levels of performance with regard to radiation and unexposed face temperature.
The fire resistance of a doorset is measured by subjecting a complete operational doorset to a test in accordance with either BS 476: Part 22: 1987 ‘Methods for the determination of the fire resistance of non loadbearing elements of construction’; or BS EN 1634-1:2000 ‘Fire resistance tests for door and shutter assemblies’.
Assessments are also an accepted form of proof of fire resistance, if prepared by experienced consultants such as those at Chiltern Fire. Assessments will be based on actual test data, which may have been sponsored by door, glass or intumescent manufacturers and referenced with their express permission. This type of report may negate the need for actual testing by the client or significantly reduce the number of physical tests required.
Quality assurance
It is becoming increasingly difficult to identify fire resisting doors by weight and thickness. New materials and methods of construction have led to the production of thinner and lighter fire resisting doors and it is now possible to purchase 38mm thick 30-minute doors and 44mm thick doors with fire resistance in excess of 60 minutes.
Concern has been expressed that manufacturers could submit a `hand built’ specimen for fire resistance testing, and that then doors of the same design from the production run might not give the same result. Manufacturer members of the BM TRADA Certification Ltd Q-Mark Scheme for fire doorsets, however, must produce fire resisting doors under quality controlled conditions. They will submit to initial type testing and audit testing to ensure consistency in quality and performance. They must also operate a quality management system to comply with ISO 9001:2000 or equivalent.
The Q-Mark scheme encompasses door blank suppliers, fire door manufactures, fire door fabricators and installers. A list of member companies is available at www.bmtrada.com.
BS 476: Part 22 and BS EN 1634-1 are performance standards and do not contain details of how doorsets should be made. Over the years, the materials used and methods of construction have become very diverse. Most fire resistance tests are carried out for individual manufacturers and as such, the detailed designs are their confidential property.
Installation
The fire resistance of a doorset can be severely reduced at the installation stage. Should there be any doubt regarding the full specification of the doorset, information should be obtained from the door manufacturer who can provide details of the original test specimen, eg types of intumescent seal, frame section and ironmongery.
There can often be up to 25mm between the rear of the frame and the structural wall into which the doorset is installed. This gap may be covered with architraves, but will have to be infilled with some form of seal. This can be plaster, well-fitted mineral wool, or an intumescent mastic – the precise method chosen depends upon the size of gap to be filled. If architraves are not to be fitted, then intumescent mastic, plaster or proprietary gap sealant should be used, but the suitability of product will again be dependent on the gap size. Guidance on the sealing of the structural opening against the door frames is given in BS 8214: 1990 Fire door assemblies with non-metallic leaves.
Gaps around door leaves strictly should be those exhibited by the original test specimen, but this may not be achievable in practice. Evidence suggests that gaps of up to 4mm between leaf and frame, or between leaves in the case of a double doorset, may be tolerated without loss of fire resistance performance, provided that all the relevant intumescent seals are used.
Evidence has shown time and time again that many of the faults relating to fire doors occur on site. In an ideal world, the manufacturer would always install the finished doorsets, but where this is not possible, the door supplier should provide clear, concise and unambiguous instructions to be followed to the letter by the installer.
If this is not done, installers should not attempt to ‘have a go’ but should contact the manufacturer. If no instructions are forthcoming or if the information supplied is inadequate, the doorset should be installed in accordance with BS 8214: 1990, Code of practice for fire door assemblies with non-metallic leaves. The contractor should be made aware that it has not been possible to install the doorset to the manufacturer’s instructions and inform the building owner accordingly.
In an ideal world, any variation from the tested doorset should be evaluated by test but this is not practical, either from an economic viewpoint or because testing facilities might not be available. Manufactures should consult an independent laboratory, such as Chiltern Fire, to approve or assess changes (where considered to be appropriate) to a tested design, since modifications or changes can seriously reduce the fire performance of a doorset. Likely modifications include:
– The doorset may be larger or smaller than that tested
– The architect may wish to use different ‘essential’ door furniture from that tested
– There may be a need for additional door furniture, eg letter plates, panic bolts.
– Non-standard door facings may be needed for decorative or hygiene purposes
– The doorset may require glazing or modifications to glazing
– The door frame design or material may need to be changed.
Assessments may provide a definite and full scope of approval for specific designs, thus eliminating any ambiguity in terms of what may or may not be accepted.
Maintenance
Some form of maintenance will be necessary, especially in public buildings, as was shown very clearly by an examination of 292 single and double doorsets in 25 buildings – selected by seven local authorities – with a range of public and private uses. Of the doorsets examined, 92% would have failed their period of resistance if tested to Part 22 in the condition in which they were found.
Intumescent seals will need periodic inspections, as will door closers. The door leaves should never be fitted with cabin hooks, while the use of wedges or fire extinguishers to keep the doors open is also to be avoided.
