Fire doors
There’s not much to say about a door is there? You open it, usually to get from one room to another, or you close it, usually to stop a draft!
But when it comes to fire safety in a commercial property, a fire door has a far greater significance.
The installation of a correctly specified fire door will help you meet your legal obligations when carrying out a fire risk assessment and it may save a life: including your own!
On a day-to-day basis fire doors must not cause too much hindrance to the movement of people and goods. However, in the event of a fire they serve two important functions:
- To delay the spread of a fire and smoke between two adjacent sections of a building when they are closed, and:
- To provide a means of escape when they are open
Every fire door will act as a barrier to the passage of smoke and/or fire to varying degrees. There are a number of factors to consider including what the fire hazards are in that building and its location.
Intumescent seals
The gap between the door and the frame is the weak point in the performance of any fire door. A technique has been developed for minimising the susceptibility of door edges to early penetration by fire.
A fire door that is designed to provide resistance to the passage of a well developed fire must be fitted with intumescent seals. These are seals that sit in the gap between the door and frame that expand when there is a dramatic increase in temperature from the heat of a fire. This closes the gap between the door and its frame and prevents the fire creeping around the edge of a door.
Intumescent paints have been used but the most successful and reliable technique is the intumescent seal. The seal is about 4mm thick by 10mm wide and it is cut into a groove in the door or the frame edge. Where there is a larger gap this may be surface mounted but these seals must not interfere with the door’s operation.
As soon as the temperature in the vicinity of the strips exceeds 200°C, usually about 10-15 minutes after the start of a fire, the seal swells and seals the gaps.
One fire door seal is adequate for a half-hour (30-minute) fire door and for the increased protection needed with one-hour (60-minute) fire doors two of these seals will be necessary. There are fire doors that are able to resist the passage of fire for more than 30 or 60 minutes but these are more likely to be used for the protection of property than for means of escape from fire.
Cold smoke seals
In the early stages of a fire there may not be the heat to trigger the expansion of the intumescent seal but there will be a significant amount of smoke. This may create as much of a threat as the flames and to prevent the ingress of smoke around the edges of a door, a fire door should be fitted with a ‘Cold Smoke’ seal.
Specification of fire doors
BS 476: Part 22: 1987 or BS EN 1634-1: 2000 specifies the test to measure the performance of timber fire doors.
The tests are made on complete door assemblies or doorset as it is known. A doorset includes the fire door and doorframe with all the requisite hardware (e.g. locks, latches, hinges, etc). This ensures its genuine performance under fire conditions is known as differing doorsets will affect how it will resist the spread of smoke and flame.
Manufacturers can certify fire doorsets, both for identification purposes and to guarantee their performance in a fire situation. The first step for the manufacturer is to construct a fire doorset designed to a specification that, in their opinion, will resist a fire for a specified length of time. This doorset will then be tested by an approved fire testing centre and, if it is passed, any doorsets constructed to that specification can be considered for certification.
The test procedure consists of exposing one face of the door to the heat conditions anticipated in a fire while observing the door for stability and integrity. A combustible pad is placed on the unexposed side of the door to assist in identifying when integrity of the door is deemed to occur.
Integrity failure is deemed to occur when cracks or other openings develop through which flames or hot gases can pass or when the pad ignites on the unexposed face of the door.
The standard requires the tests to be carried out with the upper part of the door under a small positive pressure, to simulate the conditions likely to occur in a fire. Stability failure is deemed to occur when the door collapses.
The test is then repeated with an identical doorset but this time with the other face exposed to the heat and pressure and the combustible pad placed on the other side of the door.
A half-hour fire resisting door must not have ‘integrity’ or ‘stability’ failure within 30 minutes. A one-hour fire resisting door must not have integrity or stability failure within 60 minutes.
It is reasonable to assume that the same results will be experienced for all fire doors and doorframes that are manufactured to the same specification as the two specimen doors and frames. Therefore once the test results are known for those samples, the ability of that type of fire door to resist the effects of heat and smoke will be known for all fire doors and frames that are manufactured to that specification.
Identifying fire doors
Certified fire doors
Manufacturers will identify the doors and doorsets they have manufactured to the certified specification by affixing a label identifying the manufacturer, the date of manufacture and the designated fire rating of the door type.
This identification label is usually affixed to the top edge of the door. For hospitals, fire doors display a disc at the top of each face of the door showing the designated fire performance (see HTM58). A colour-coded plug may be inserted into the door, instead of or in addition to the label.
Identification marks can sometimes be removed or painted over during the installation or adjustment of a fire doorset but, if the work has been professionally carried out under the auspices of the BWF/FIRAS Accredited Fire Door Installers Scheme, the chance of this happening can be avoided.
There are two associations that have certifiable fire door systems: TRADA (Q-Mark) fire door scheme and the British Woodworking Federation Certifire fire door scheme.
For more details visit www.bmtrada.com or www.bwfcertifire.org.uk.
The most commonly specified integrity levels are:
- FD30 – 30 minutes
- FD60 – 60 minutes
- FD90 – 90 minutes
- FD120 – 120 minutes
FDXX fire doors only require intumescent seals, whereas FDXXs fire doors require both cold smoke seals and intumescent seals.
Nominal fire doors
Nominal fire doors are doorsets that are not certified but may hold back a fire for a specified period of time. Identifying nominal fire doors is very difficult but there are a number of clues.
There may be documentation that was supplied with a fire door giving you all the necessary information. Unfortunately, as there is no standard method of identifying fire doors other than the Q-Mark or the CERTIFIRE fire door schemes, insisting on written proof that a door meets all the necessary standards, for example a test certificate, might still be necessary.
All dedicated fire doors providing a half hour or greater performance are usually fitted with intumescent seals. These may be encased in a PVC sheath, of any colour, which may also hold a blade or brush smoke seal for smoke sealing purposes. These seals are fitted in the door leaf edges or the frame to seal the head and long edges of the assembly.
A door may be fitted with a concealed intumescent system whereby the vertical sealing is housed within the construction of the door. Intumescent seals will be visible at the head of the door. Doors 44mm thick fitted with 10-15mm wide intumescent seals are likely to be FD30, while doors 54mm thick using at least 20mm width of intumescent seal, fitted as one or two strips are likely to be FD6O.
Some doors with a rating in excess of FD6O have the appearance of timber, but may be constructed with a mineral core. Expert assistance may be required to identify such doorsets. They are rarely used on escape routes or to protect people but may be found where the preservation of property is important e. g. data storage areas where documents cannot be removed in the event of fire.
Fire door jambs need to be over 25mm wide and, because of the weight of a fire door and to prevent it warping, fire doors are usually fitted with three fire door hinges. They will have automatic closing devices (fire door closers) fitted. Spring-loaded self-closing hinges and concealed Perko door closers with chains might also be in evidence.
Hollow flush doors using egg box or similar construction will not be FD30. This can be detected by the weight of the door, because fire doors are much heavier than a hollow door. To check the weight of a door, instead of removing it, you can detach the self closer and swing the door between your thumb and index finger. This gives a good indication of the weight of the door. Hollow doors are reasonably easy to detect using this method.
Older panel doors, especially if less then 44mm thick, are unlikely to be FD30. They could, however, they could have been upgraded or modified to achieve fire resisting standard. These days you might find certified panelled fire doors with wood surfaces to fit into traditional homes.
Existing doors
In most cases it is more economical to replace the door rather than alter it. However in the case of historic or listed buildings it may be necessary to upgrade the existing door.
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-combustable 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).
Dandwiching panels
For paneled doors, the weakest area is generally the panel itself. In many cases, the timber will be less than 10mm 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
Intumescent paper and card can be used selectively to 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-minute 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.
Suitability of doors for upgrading
| Door type | Suitable? | Comments |
|---|---|---|
| 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 intumescent seal |
| Framed, ledged and braced | Yes (20 mins only) | Extremely dependent on joints and fixings |
| Framed, solid with solid panels | Yes | Depends on thickness, minimum 44mm, and panel construction |
| Framed, solid with glazed panels | Yes | Depends on thickness, minimum 44mm and type/installation of glazing |
Maintenance of fire doors
It is important that Fire Doors are regularly inspected and maintained to permit them to perform at their best on the one and only occasion when they are called upon so to do. They are designed to save lives and property and so should not be taken for granted.
Doorsets fitted with hold open devices should be closed daily, particularly overnight. For busy buildings which are occupied 24 hours a day fire doors should be closed at least weekly. All fire doors should close effectively using only the door closer.
There are a number of reasons why doors may fail to close from the latch not operating correcting and needing lubrication to smoke seals being incorrectly fitted or damaged.
Mechanical items such as hinges, locks, latches, closer, floor springs etc are likely to wear over time. Maintenance provisions should comply with the hardware supplier’s recommendations where these are known. Otherwise, locks and latches may require occasional light lubrication.
Some hinges use self-lubricating bearings that will not need additional lubrication.
Intumescent seals should be checked at least once every 6 months, and damaged or missing ones replaced. The gap between the fire door and the frame should be 2mm to 4mm wide.
Where it is necessary to replace worn hardware on a fire door, the essential items should be replaced with products to the same specification as the original where possible and should have been proven for use in timber fire rated doorsets of the required performance. Hardware that has been successfully tested in metal doorsets may not be suitable for use with timber doorsets.
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