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Will Jarvis, technical design and development director of FyreSpan, offers some cool insights into a hot subject…
When it comes to fire doors and creating fire zones the glass required is very special. Conventional float glass melts at about 1,000°C (soda lime) and during a fire test the temperatures achieved are at least 800°C at 30 minutes and 940°C at 60minutes, so how does it work?
The quality that makes fire glasses special is their ability to cope with thermal shock. A normal glass will crack at less than 100°C and gets pliable at around 30 minutes. Fire glass is designed to maintain its integrity.
There are various different types of fire glasses and some have an ability to withstand a lot higher temperatures than others before they crumble.
Clear Integrity only glass is the modern equivalent of Georgian wired plate. Wired glass was designed to hold together even if it is cracked, very useful in the case of attempted burglary and fire.
It is possible to achieve a 30 minute fire rating with a wide range of glasses but when it comes to 60 minute fire rating, a highly sophisticated chemical composition is required. There are two quite well known products which achieve 60 minutes fire rating.
Laminated glass, literally a sandwich of different inter-layers and gels of various thicknesses and characteristics, can be designed to insulate as well as preserving the sort of integrity you can get with old fashioned wired glass.
There is an initial sacrificial layer, designed to more or less self destruct as it comes into contact with a blaze. The idea behind this is that the burnt layer provides protection for the rest of the sandwich of glass in much the same way as the charred surface of a block of wood will prevent the combustion of the rest of the timber.
The remainder of the glass sandwich is designed to minimise heat transmission so that on the fire free side it is quite safe for people to get close to the door, at least for the duration of the fire rating.
Of course, fire doors are not just a question of glass. It is also vital to ensure that the perimeter isn’t breached by any potential blaze. There has to be a careful balance between the glass and the strength of the frame. Slim doors need higher performance glass to support itself under fire conditions.
FyreSpan’s FL doors and screens, tested to beyond 60 minutes integrity (BS476 part 22) at Warrington Fire, have probably the world’s slimmest metal section on a performance door. This system can have door leafs over a metre wide and an opening height of more than three metres. The customer can also choose from a large range of options, including handles, locking arrangements and access control systems.
Increasing numbers of building control officers seem to be requiring the installation of fire safety doors, with fire officers demanding more and more escape routes and safety zones as buildings get taller or house more people
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The market is also changing with architects and specifiers demanding increasing amounts of glass to create buildings that are more open and airy, especially in major cities. The general trend seems to be towards frameless glass.
A reputable fire door supplier ought to be able to offer various different product combinations to suit the building’s fire strategy.
If the idea is to have fire integrity, the design of partition screens can be relatively simple. The key task will be to avoid the possibility of fire bursting through within the specified fire rating time.
One example would be the need to ensure lift lobby doors maintain integrity, making it harder for a fire to spread rapidly through multi storeys.
Where narrow corridors are designated escape routes there may be a need to protect the area from heat as well as the spread of fire. This is where insulated fire doors come into their own.
Although there does not appear to be a trend towards longer fire ratings, the demand for insulated fire doors seems to be growing faster than the demand for integrity only systems.
Integrity only is a screen that will stand there and stop any fire going across but it doesn't necessarily hold back temperature, so the surface of the side where there is no fire may be almost as hot as the side facing the blaze.
Current regulations require insulation doors to have a temperature of no more than 130° above ambient during the rated fire proof time.
This means people can get very close but feel only a minimal effect from the fire. The system could be used in areas where there are escape routes because it holds back the temperature enough to allow people to egress safely.
Fire doors are always going to be more expensive than a stud wall but there is a balance between elegance and cost. General partitions glazed or unglazed can be specified but they will rarely make a building look up market.
The glazed fire door business is worth many millions a year and it is concentrated in urban areas like London, Manchester, Glasgow, Edinburgh, Cardiff, Belfast and Birmingham. Higher spec buildings tend to be in city areas. But fire doors are also specified in suburbs, for example in software centres.
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