Shadowfax
Established Member
This is not a good title really because I don't want this to be about performance testing of doors again.
JFC asked me to find some information about how doors behave in a fire situation and why three hinges are normally specified etc.
So I trawled through a great deal of stuff on the databases available to me at work. Much of it was repetitive and a lot was not relevant to the basic subject. It is also difficult to extract exactly what you want sometimes but I decided that it might be quicker to copy type some of the bits that seemed relevant.
The thing that has radically changed the performance of fire-resisting doors over the last twenty odd years is the use of smoke seals and intumescent materials in strip form and as gap fillers behind hinges and locks.
This is taken directly from parts of BS 8214:
"Leaves of single swing doors are generally hung on hinges and thus one side of the leaf is firmly restrained at one vertical edge. Even when fitted with a latch, which helps to restrain the other vertical edge of the door leaf, there is little to prevent door leaf distortion, under fire exposure, in the form of bowing on plan.
Single swing doors have doorstops, and it is widely recognised that door assemblies are often able to offer greater fire resistance when opening away from the direction of fire exposure. This has led to the erroneous belief that doorstops make an important contribution to fire resistance performance. Timber door leaves generally exhibit distortion due to shrinkage of the face towards the fire and the result is often seen as the edges and corners of the leaf tending to move towards the fire. Thus, if a door leaf opens in towards the fire the doorstop becomes irrelevant as the leaf distorts away from it. With a door leaf opening away from a fire the doorstop is on the exposed face and movement of the leaf edges or corners towards the fire is checked. This checking effect can only be temporary as eventually doorstops of any dimension will be charred away.
When heat activated sealing systems are used, the doorstop makes no significant contribution to fire resistance. The size, type and fixing of the stop is, therefore, unimportant.
One area of contention regarding door frame dimensions has often been the depth of the rebate. With current design of fire doors incorporating heat activated intumescent door leaf/frame edge seals the doorstop dimension is irrelevant. The availability of double swing door assemblies able to offer periods of fire resistance up to 120 minutes can be seen to support this.
As with basic frame cross section, the doorstop dimensions are influenced by cold state requirements. Provided doorstop sections can be securely fixed to resist normal usage there is no need for the stop to be worked from solid, i.e. be integral with the basic door frame section.
Doorstops can only ever offer any significant contribution to fire resistance if there are no intumescent or heat activated fire seals present and then only if the door leaf remains free of distortion during fire exposure enabling the face of the door leaf to remain in continuous intimate contact with the doorstop. Fire resisting door leaves will invariably exhibit some degree of distortion or movement under fire exposure thus breaking contact with any doorstop, potentially allowing the passage of flames or hot gases, in such cases a 12mm deep doorstop would be just as effective as a 25mm deep doorstop but in all cases gaps should be kept to a minimum.
Letterplates can allow the through-flow of air or gases. Under fire conditions, the upper part of a doorset will be subject to positive pressure while the lower part will be subject to negative pressure. A letterplate above the neutral pressure axis, more than 900mm up from the foot of a doorset will generally be unable to prevent flames and gases egressing from the fire without the aid of a second (internal) flap. A letterplate installed towards the lower part of the doorset will be exposed to negative pressure and air will be drawn into the fire through the letterplate aperture. While this is less likely to lead to a conventional integrity failure, the ingress of oxygen rich air is likely to cause a more rapid erosion of the adjacent door core and a large aperture may develop which could cause ignition of the unexposed face.
Therefore, a letterplate should be installed in the neutral pressure zone, i.e. between 800mm and 100mm above the threshold. Letterplates with a maximum aperture size of 250mm x 38mm complying with BS2911 having well-fitting spring or gravity internal and external flaps manufactured from materials such as steel, stainless steel and some brasses have proven successful for periods of up to 30 minutes fire resistance when tested and only these should be fitted. Letterplates with larger apertures should not be used.
There is no evidence to suggest that overpainting of the intumescent seals by conventional paints or varnishes, in normal thicknesses, has any harmful effect. Indeed, such painting can provide added protection to the seals.
It is recommended that at least three hinges should be used on fire and escape route doors. BS 4787 details the position of door hinges as follows: one hinge shall be positioned on the centre line of the door height, the other two hinges being a 770mm either side of the centre hinge. With fire-resisting doors tending to become heavier there is a practice to fit two hinges at the top of the door with the third at the bottom. With this configuration the hinges are positioned as follows: centre line of the top and bottom hinge 250mm from the top and bottom edge of the door. Centre line of the third hinge 200mm below the centre line of the top hinge".
Rising butts should never be fitted to fire-resisting doors. The essential door furniture should have a melting point of at least 800 degrees C and any screws should be 30mm to 38mm in length.
I can probably add some more if people are interested.
Hope this is a bit helpful.
SF
JFC asked me to find some information about how doors behave in a fire situation and why three hinges are normally specified etc.
So I trawled through a great deal of stuff on the databases available to me at work. Much of it was repetitive and a lot was not relevant to the basic subject. It is also difficult to extract exactly what you want sometimes but I decided that it might be quicker to copy type some of the bits that seemed relevant.
The thing that has radically changed the performance of fire-resisting doors over the last twenty odd years is the use of smoke seals and intumescent materials in strip form and as gap fillers behind hinges and locks.
This is taken directly from parts of BS 8214:
"Leaves of single swing doors are generally hung on hinges and thus one side of the leaf is firmly restrained at one vertical edge. Even when fitted with a latch, which helps to restrain the other vertical edge of the door leaf, there is little to prevent door leaf distortion, under fire exposure, in the form of bowing on plan.
Single swing doors have doorstops, and it is widely recognised that door assemblies are often able to offer greater fire resistance when opening away from the direction of fire exposure. This has led to the erroneous belief that doorstops make an important contribution to fire resistance performance. Timber door leaves generally exhibit distortion due to shrinkage of the face towards the fire and the result is often seen as the edges and corners of the leaf tending to move towards the fire. Thus, if a door leaf opens in towards the fire the doorstop becomes irrelevant as the leaf distorts away from it. With a door leaf opening away from a fire the doorstop is on the exposed face and movement of the leaf edges or corners towards the fire is checked. This checking effect can only be temporary as eventually doorstops of any dimension will be charred away.
When heat activated sealing systems are used, the doorstop makes no significant contribution to fire resistance. The size, type and fixing of the stop is, therefore, unimportant.
One area of contention regarding door frame dimensions has often been the depth of the rebate. With current design of fire doors incorporating heat activated intumescent door leaf/frame edge seals the doorstop dimension is irrelevant. The availability of double swing door assemblies able to offer periods of fire resistance up to 120 minutes can be seen to support this.
As with basic frame cross section, the doorstop dimensions are influenced by cold state requirements. Provided doorstop sections can be securely fixed to resist normal usage there is no need for the stop to be worked from solid, i.e. be integral with the basic door frame section.
Doorstops can only ever offer any significant contribution to fire resistance if there are no intumescent or heat activated fire seals present and then only if the door leaf remains free of distortion during fire exposure enabling the face of the door leaf to remain in continuous intimate contact with the doorstop. Fire resisting door leaves will invariably exhibit some degree of distortion or movement under fire exposure thus breaking contact with any doorstop, potentially allowing the passage of flames or hot gases, in such cases a 12mm deep doorstop would be just as effective as a 25mm deep doorstop but in all cases gaps should be kept to a minimum.
Letterplates can allow the through-flow of air or gases. Under fire conditions, the upper part of a doorset will be subject to positive pressure while the lower part will be subject to negative pressure. A letterplate above the neutral pressure axis, more than 900mm up from the foot of a doorset will generally be unable to prevent flames and gases egressing from the fire without the aid of a second (internal) flap. A letterplate installed towards the lower part of the doorset will be exposed to negative pressure and air will be drawn into the fire through the letterplate aperture. While this is less likely to lead to a conventional integrity failure, the ingress of oxygen rich air is likely to cause a more rapid erosion of the adjacent door core and a large aperture may develop which could cause ignition of the unexposed face.
Therefore, a letterplate should be installed in the neutral pressure zone, i.e. between 800mm and 100mm above the threshold. Letterplates with a maximum aperture size of 250mm x 38mm complying with BS2911 having well-fitting spring or gravity internal and external flaps manufactured from materials such as steel, stainless steel and some brasses have proven successful for periods of up to 30 minutes fire resistance when tested and only these should be fitted. Letterplates with larger apertures should not be used.
There is no evidence to suggest that overpainting of the intumescent seals by conventional paints or varnishes, in normal thicknesses, has any harmful effect. Indeed, such painting can provide added protection to the seals.
It is recommended that at least three hinges should be used on fire and escape route doors. BS 4787 details the position of door hinges as follows: one hinge shall be positioned on the centre line of the door height, the other two hinges being a 770mm either side of the centre hinge. With fire-resisting doors tending to become heavier there is a practice to fit two hinges at the top of the door with the third at the bottom. With this configuration the hinges are positioned as follows: centre line of the top and bottom hinge 250mm from the top and bottom edge of the door. Centre line of the third hinge 200mm below the centre line of the top hinge".
Rising butts should never be fitted to fire-resisting doors. The essential door furniture should have a melting point of at least 800 degrees C and any screws should be 30mm to 38mm in length.
I can probably add some more if people are interested.
Hope this is a bit helpful.
SF
