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Andrew Forecast and Peter Barker of Chiltern International Fire respond to frequently asked questions about timber-based fire doorsets with up to 60 minutes integrity performance.
How can I upgrade existing doorsets?
There are numerous methods for upgrading existing doorsets to enhance their inherent fire resistance, although every upgrade is specific to each doorset and consequently may not necessarily be appropriate for another design. The only way to ensure that the most appropriate method is chosen – and to have the enhanced integrity performance underwritten – is by commissioning a site survey by a qualified fire engineer. The relatively large number of components that make up a fire-rated doorset are integral to its performance and a comprehensive knowledge of these components is needed, for example:
– whether the door can be upgraded to the required integrity
– the most appropriate upgrading measures
– whether there are other issues that may negate the performance of the door,
such as sidelights or over panels
– how to address matters such as glazing, panelling, ironmongery and
intumescents.
Is a 10 x 4mm intumescent seal for 30 minutes integrity and a 20 x 4mm intumescent seal for 60 minutes integrity adequate?
While it is generally true that larger intumescent strips are used for higher integrity periods, the intumescent specification for the door must be as tested or assessed for that particular doorset. This is the case for the size of the intumescent seal, the location of the seal and the type of seal.
The type of seal is also particular to the manufacturer, as different manufacturers’ seals do not perform comparably, even if they are of the same generic type, eg graphite. It is for this reason that interchanging between different seal types and/or manufacturers is not permitted, unless there is test evidence available to demonstrate otherwise.
Can a test laboratory provide me with copies of test/assessment reports?
No, not without the written permission of the test sponsor, as all door manufacturers’ test and assessment data is held in confidence by the relevant test laboratory.
Traditionally, an FD20 doorset comprised a 25mm doorstop, no intumescent and a 30-minute blank. Is this still acceptable?
Prior to 1972, the British Standards prescriptively defined how to construct a fire doorset and this included using 25mm doorstops. Since then, the standards have been changed and the method of proving performance is by independent testing. For economic reasons, manufacturers generally test to achieve 30 minutes and sell the same product for 20-minute applications as well. Purchasers should satisfy themselves that acceptable evidence exists, rather than working to out-of-date prescriptive solutions.
Can I use rising butt hinges as a closer for my fire door?
Approved Document B cites rising butt hinges as acceptable for use on fire resisting doorsets, providing there is suitable test evidence available. To the best of our knowledge, there is no supporting fire test data for their use and this, coupled with their known limitations, lead us to recommend that such hinges are not used with fire resisting doorsets.
In order for rising butt hinges to operate effectively, either the leaf head or frame head has to be chamfered, which means there will be the correct leaf to frame gap on one side of the door, but too large a gap on the other. If the gap is too large, the intumescent seal will not react as intended and may negate the performance of the leaf.
In some instances both the leaf and frame head may be simultaneously chamfered, giving rise to a different but potentially serious problem. Here, the reacting intumescent seals in the head force the leaf open due to the direction of flow and pressure from the reacting material.
Another problem with rising butt hinges is that they rely on gravity to close the door over the latch, and it is quite common for pressure differentials to prevent the hinges from doing so. This can lead to the door ‘bouncing’ on its latch and not fully closing within its frame reveal, so failing as an effective fire resisting doorset.
Do any timbers have an inherent spread of flame classification? And how do I treat timbers for class 1/class 0?
Spread of flame and fire resistance are two quite separate performance characteristics. Fire doors must prove their fire resistance rather than spread of flame performance.
A few tropical hardwoods of high density do have an inherent spread of flame characteristic of class 1. In Approved Document B, the typical performance rating for untreated timber or plywood with a density of more than 400kg/m3 is class 3, and so any untreated timber will need test evidence to prove that it has a higher rating.
In general, timber will need treatments to achieve the higher ratings. It is recommended that a timber treatment specialist is consulted to ensure that the most appropriate method is chosen.
Can intumescent strips be over-painted?
Most manufacturers of intumescent seals recommend that ideally, intumescent strips should not be painted over. For further clarification contact the seal manufacturer for supporting evidence and advice.
Can I/how do I put glass into my fire door? Does this have to be done by an approved installer?
Not all fire rated doorsets can tolerate glazing and it is therefore essential to check the test evidence/assessment data for that door. If the door can accept glazing, it is of paramount importance that the exact guidelines are followed, as apertures may need to be internally framed/lined with timber.
The following is an excerpt from ‘A Guide to Best Practice in the Specification and Use of Fire-Resistant Glazed Systems’ written by the Glass and Glazing Federation (GGF):
“Fire resistant glass must only be used as part of a fire resistant glazed system – which includes the glass, the glazing seal, beads, fixings and frame. All the essential components of such a system must be compatible under fire conditions, and the performance must be referenced to appropriate and relevant test evidence”
There is currently no legal requirement to be certified to glaze fire-resisting doors. But it is recommended that anyone undertaking this type of work attends an appropriate training course specifically on glazing, or at the very least a general course that outlines the construction of these performance products. Attendance will also help provide evidence that the installer is competent. (Suitable third-party certification can be obtained from a UKAS-accredited certification body).
What qualifications do I need to install a fire door?
The British Standard that provides recommendations on the installation of fire doors is BS 8214: 1990 Code of practice for fire door assemblies with non-metallic leaves. While there is no requirement to be third-party certified, becoming an approved installer is a good way of demonstrating competence and, more importantly, should guarantee that the installed doorset will perform for the intended period of fire resistance.
If the door does not fit, can it be resized?
Resizing a doorset is not something that should be done without first contacting the manufacturer. Most door designs rely on components being of a minimum size in order to perform in a fire. Lippings are particularly important on typical flush door leaves – removing 3mm or 4mm can in some instances halve the depth of a lipping, which could have a detrimental effect on the fire performance.
What is the recommended gap between leaf edge and frame for a fire rated door?
The recommended leaf edge to frame gap specified in BS 8214: 1990 is 4mm on all edges. Intumescent seals are engineered to react within this size of gap, to give optimum sealing and clamping performance.
It is through extensive testing of fire rated doorsets, together with knowledge of the pressure regime within a fire test, that a larger gap is permitted at the threshold of the door. There is negative pressure at the threshold during test conditions and so cool air is drawn in underneath the door. It is for this reason that there is unlikely to be a failure at the threshold, and also why there is no need to fit a perimeter intumescent strip at this location (doorsets below FD60 performance). A larger gap at the threshold is also useful for accommodating floor coverings. We recommend a gap of 10mm from the bottom of the leaf to the structural surround.
Can an FD60 doorset be hung in a softwood frame?
In practice, it is very difficult to pass a 60 minute fire test using a softwood frame, simply because it chars more quickly than most hardwoods. For this reason, dense hardwoods are usually used, but softwood is permissible if supported by appropriate test evidence.
Can I fit a letter plate or eye viewer to my fire-rated door?
Fitting a letter plate or eye viewer will breach a fire rated doorset, and has the potential to allow a direct passage for hot gases and flames. It is therefore important that:
– There is test/assessment data for the fire rated doorset to tolerate the
ironmongery.
– The ironmongery being fitted has been previously tested in a doorset of
comparable construction.
Can kick/push plates be fitted to the face of the fire door?
It is usually permitted to face-fix kick plates and push plates to a fire-resisting door. We permit facing the door with metal to a maximum of 30% of the timber area of the leaf, provided that the metal face is surface fixed and does not wrap around any leaf edge or interfere with any essential intumescent seal. Above the 30% limit of timber surface area, or for any other condition, further test evidence must be generated. The reason for limiting the area of metal on a door is because when heated in the fire, the metal will expand while the wood will shrink, causing distortion. It can also act as a heat sink, accelerating char and erosion at localised areas.
What are the benefits of third-party certification?
To achieve third-party certification, manufacturers and installers will undergo stringent performance and production audits on an ongoing basis, to ensure that every product will provide the same levels of performance as that originally tested. Third party certification is undertaken by independent expert bodies, and they will typically list accredited manufacturers and installers on their website. For example, a list of fire door manufacturers who are full members of the BM TRADA Certification Q-Mark scheme can be located at www.bmtrada.com along with a list of registered installers.
Chiltern Fire and sister company BM TRADA will be hosting a series of
Timber Fire Doors Explained seminars during 2007. For further information contact the training department on 01494 569620, email training@chilternfire.co.uk or visit www.chilternfire.co.uk