Glazing may range from a small vision panel in a door to a glazed screen for maximum light transmission and safety. Ordinary glass cracks when exposed to heat and is liable to fall out fairly early in a fire. Fire resisting glass can withstand exposure to the heating condition in a fire test for at least 60 minutes before it reaches a temperature high enough to soften it. The main reason for this is that in clear FR glazing nearly 50 per cent of the incident heat is transmitted through the glass by radiation.
The size of the glass and the method of its retention are important factors which influence its integrity. As the temperature approaches the softening point a large sheet will tend to collapse earlier than a smaller one. On the unexposed face, beading retaining the glass is subjected to radiant and conducted heat through the glass and to convection currents at the top of the pane.
This can raise the temperature sufficiently to ignite timber beading after about 20 minutes. To delay the ignition of beading to 30 minutes it is necessary to provide protection by impregnation of a surface coating or a surface covering of non-combustible material or fit a fire resistant glass secured using a fire resistant glazing systems which hold the glass firmly in place during normal use, but in the event of fire the intumescent material expands securing and insulating the glass and protecting the surrounding timber.
For longer periods of fire protection, an improved retention system for the glazing is needed, The glass panel should be small and the method of fixing it should ensure that no direct path can be created for the transference of hot gases.
Fore more detailed information go to Glass and Glazing Federation and download Fire Resistant Guide.
Years ago it was accepted practice to improve the performance of an existing door to a half-hour fire-check or fire-resisting standard, although in some cases it was more economical to replace the door rather than alter it. The doors were usually panel type or a light core flush type about 44mm thick: they require a facing on the risk side with a non combustible board.
It is now the accepted practice to fit new fire doors and fire doorsets preferably to upgrading them.
These days you can configure and order entire fire doors with 30 minutes protection (FD30) online. These fire doors can be configured with or without frame.
Suitability of doors for upgrading.
|Unframed, hollow core, flush||No||Too light and insubstantial|
|Framed, hollow core, flush|
|Framed, solid core, flush||Yes||If core of flaxboard, timber or solid chipboard|
|Ledged and braced||No||Insufficient thickness at the edges to accommodate an intumescentseal|
|Framed, ledged and braced||Yes(20 min only)||Extremely dependent on joints and fixings|
|Framed, solid with solid panels||Yes||Depends on thickness, minimum 44 mm, and panel construction|
|Framed, solid with glazed panels||Yes||Depends on thickness, minimum 44 mm and type/installation ofglazing|
Methods of upgrading
There is no ‘one size fits all’ method of upgrading existing doors and the solution chosen will depend on the door construction, condition, situation and customer requirements. Techniques that have been successfully used in the past include:
Facing the door leaf with a non-combustible board
This is one of the easiest methods of upgrading, although it does create a visually unattractive result. It is, however, favoured by some heritage authorities as it a reversible process; removing the facing returns the leaf to its original condition. If used, facings should be applied symmetrically to each face (note that the increased thickness and weight may affect the door frame and ironmongery specification).
For paneled doors, the weakest area is generally the panel itself. In many cases the timber will be less than 10 mm thick at the thinnest point. One method of upgrading is to remove the panels, split them through their thickness and insert a sandwich material, either an appropriate intumescent sheet or a non-combustible board. This is more difficult than other approaches but does enable the original finish to be maintained, which can be important for heritage projects.
Intumescent paper and card can be used to selectively protect vulnerable areas such as the fielded area of paneled doors. The application thickness is controlled by the thickness of the paper but can be veneered to restore a timber finish.
Intumescent paints and varnishes
Intumescent paints and varnishes are available for use on timber-based fire resisting doorsets where a maximum performance of 30 minutes integrity is required. These products require extremely specific application techniques and are reliant on the underlying condition of the doorset construction. Great care should be taken to ensure that full-scale test data for the product is both available and appropriate for the application in question.
It is likely that other upgrading measures will be required in conjunction with any of these measures.
For more information download the following documents.
Fire Door Furniture and Ironmongery
An important aspect of ensuring fire doors meet the required standard, is the fitting of certified door furniture, which is overlooked on many occasions. If you go to Fire Door Fittings and Ironmongery there is a detailed description of all the door furniture suitable for fire doors and the appropriate standards.