Summary
• Glass undergoes third-party testing.
• It is essential that doorset systems are tested as a whole.
• Laminated glass can now improve sound attenuation and security.
• Privacy interlayers allow glass to be switched from clear to opaque.

The integrity of any fire door is judged by the time for which it provides critical resistance to smoke, heat and flames in the event of fire. As the link between compartmented areas of buildings, a timber fire door must fulfil a number of requirements. Firstly, in the early stages of a fire, it’s required to prevent smoke, and other by-products of combustion, passing through to other parts of a building. Should a fire develop and become firmly established, it’s also required to contain flames and smoke, preventing the spread of the fire to other locations within the property.

Many fire doors are, of necessity, glazed to ensure sufficient light and visibility between one section of a building and another. Specifying a high quality glazed fire door has much to do with the correct combination of frame, door and glass. A good indication of a high quality product is third-party certification, which relies on a rigorous testing programme and, critically, glass also undergoes this third-party testing. This is vital, especially now, because using advanced lamination techniques, a range of other properties can be added to fire-resistant glass to allow glazed fire doors to provide other functions, such as sound insulation and high security. It is essential, therefore, that the full doorset system, containing all its constituent parts, is tested as a whole, in order to ensure that the fire resistance of the glass isn’t compromised for the sake of versatility.

The initial advance that lamination brought about was one of safety, the plastic interlayer holding any glass fragments together in place in the event of damage. Whereas a glass panel was once the potential weak part in a building, a panel produced by laminating will stay in place and can, depending on its specification, continue to be load bearing. This means that in a fire door, or indeed in any timber frame, it is possible to include an extremely strong panel that does not require wiring to preserve its integrity.

Using leading-edge lamination techniques, glass processors can now also provide an acoustic fire resistant safety glass that still preserves the integrity of thetimber fire door. Architects now routinely specify a set level of sound attenuation, particularly in line with Part E of the Building Regulations, which govern the passage of sound in buildings. Recent advances have meant that modern acoustic fire-resistant glass, while meeting these sound attenuation requirements, is thinner and lighter than previous products, making a glass panel more feasible in this setting.

Glass panel advantages

The first advantage is in allowing a see-through material to be used in preference to a solid door, and secondly in reducing the corresponding weight of the door. In a fire, being able to see through the door can help to identify a safe escape route and to allow a more accurate assessment of the state of the fire.

Some buildings require privacy as well as safety, as it isn’t universally desirable to be able to see through the door at all times. Modern technology makes allowances for this too. The introduction of privacy interlayers has allowed new ground to be broken in recent years, making it possible to produce a glass panel that can be switched between opaque or optically clear according to the user’s requirements. The privacy interlayer, which is sandwiched between two or more fire-resistant glass sheets, relies on a small electric current to change its appearance. When switched off, randomly oriented fibres in the interlayer render the glass opaque; but, at the flick of a switch, the current passes through, causing the strands to line up, allowing light to pass through the glass, making it optically clear in appearance.

Crime is an increasing concern and in the past year a new generation of highly secure glass has been developed. This can also be combined with fire resistance so that well-constructed timber and glazed fire doors can be used to deter intruders. This glass can also be applied in timber window frames, providing higher protection, especially for ground floor windows. For high net worth individuals this is a highly attractive combination, with the aesthetics of both wood and glass being combined with safety and security. Recently developed glass products have even been endorsed by the Association of Chief Police Officers’ (ACPO) Secured by Design initiative.

Twinned with the worry of increasing crime is an understandable concern to prevent, or at least to minimise, the possible effects of terrorism, especially in commercial settings. Glass processors have been working on this too, producing a new variety of bullet-resistant glass, which is both thinner and lighter than before, and which, again, can be combined with fire-resistant properties. Buildings that require high security can be served by a high specification timber fire door fitted with a bullet- and fire-resistant glass panel. A new type of blast resistant-glass is also in development.

Testing

Specialised glass panels are already manufactured under exacting conditions and tested against a range of standards. However, there is no real substitute for testing them for use with the fire door to be specified, and it isn’t only the timber doors themselves that undergo testing, but the glass in them too. Testing the combination of glass, frame, beading, sealant and fire door allows the industry to build up knowledge about how they will perform together in situ. The aim of the British Woodworking Federation’s CERTIFIRE approval scheme for timber fire doors is validation and accountability. Each door manufactured by scheme members carries a label which relates directly to the results of the testing of its model by independent UKAS-accredited testing laboratories such as Exova, Chiltern International Fire, and BRE. Therefore, when selecting timber fire doors and glazing, the specifier can be sure that its performance in the event of a fire is predictable and reliable in a real time scenario.

Testing fire doors and glass panels together ensures that the performance of the finished door has not been compromised by the use of the two together, or by any system of fixing the panel within the door. As an industry, we already have a comprehensive testing programme, largely due to a legal requirement, but also due to a high level of professionalism. As leading glass processors submit their products to the same testing procedures after adding in further functions and properties to their increasingly hi-tech glass, we can be confident of achieving consistency of performance under real life testing conditions and, quite literally, saving lives through progress.