Fire doors save lives, so it's vital to specify the right one and ensure it's properly installed. What's more, it's costly to replace the wrong one …
Fire doors play a vital role in making buildings safe. They compartmentalise the building to prevent the spread of fire and they provide escape routes. To do this, they need to provide an effective barrier to fire, smoke, heat and pressure, yet be open when needed to allow escape. This is why the fire performance of doors is expressed in terms of thermal resistance and the means of closing.
Timber is by far the most common material for doors. Timber fire doors usually have a minimum thickness of 44 mm, rising to 55 mm for higher performance doors. They can also be heavy. Many contain manmade cores providing the strength and the incombustibility needed.
Any vision panels within the door have to provide the same level of fire performance as the rest of the door and this will depend on the size of the panel, the fixing and the type of glass. For relatively small areas where budgets are tight, specifiers can use Georgian wired polished plate glass with fire-performance beads. Many will regard this as aesthetically crude and instead use fire-resisting glass and high-performance beads, usually containing an intumescent bead, within the glazing channel.
Metal fire doors have the ability to resist high temperatures and pressures, but they need special thermal resistance measures to prevent buckling. Metal fire doors combined with fire-resistant glazing can offer several hours' resistance - but at a price.
For many years, BS 476 fire tests on building materials and structures was the prime standard. Part 22 1987, "Fire tests for non-load-bearing elements", is the key reference for doors. This rates the performance of a fire door in terms of how many minutes of resistance it offers for each of the criteria and gives them a classification - FD30, for example.
Doors and frames are tested and rated together and this is how they should be specified and installed. Usually, the required fire resistance of the door will be half that of the surrounding wall with the most common performance level being FD30S (the S being for smoke-stopping provisions). Additionally there are now European standards, which are gradually replacing British standards in the drive towards harmonisation. Although these standards cover similar ground, there are differences, so specifiers should use one standard throughout a project to avoid confusion.
The above standards are referenced in Part B of the Building Regulations, section 6. Fire performance requirements are set out in Table B1 Appendix B, and Appendix A table A4 for performance of any glazed elements. This also covers the ironmongery, locks, hinges and closers, which all need to perform to the stated requirements to ensure safe and dependable operation.
Be careful to specify the appropriate closers where both fire performance and access for disabled people is required. There is a conflict between the resistance of the closer to keep the door closed for fire performance and the degree of force a disabled person can be expected to exert to open it. This was initially a problem for specifiers, but now a compromise standard is available.
Doors will usually have to open freely in the direction of escape unless the number of people involved is likely to be less than 60. All doors must open more than 90° and no door should restrict the effective fire escape width of a corridor or stair when open.
Ensure the complete doorset is installed correctly otherwise the specified performance will not be achieved. Take care to ensure fire performance is maintained between the door frame and wall junction. Using a system to achieve this is preferable to an ad hoc assembly as the specified materials can be guaranteed to work together.
BS 8214:1990 is the code of practice for fire door assemblies with non-metallic leaves. This requires a maximum 3 mm gap around the door leaf for optimum performance. Some floor finishes make this difficult; drop-down thresholds are available to get around this problem.
BM TRADA offers a quality checking service to ensure that the installation is satisfactory.
Most fire doors use intumescent seals to achieve a high level of fire resistance. Activated at temperatures in excess of 180°C, the seal expands to close off any gaps long after the occupants have hopefully escaped.
Smoke performance has improved over the years and fire doors can now cope with most type of smoke.
Additionally brush, gasket and blade seals ensure minimal smoke passes through the doorway at any temperature. Smoke seals are specified to BS476 Part 31:1983. Bear in mind these seals can be so effective it can make lobby doors difficult to open, so a pressure relief vent may be needed with its own fire resistance built in.
6: Important points
Fire doors are expensive so ensure you specify the correct level of performance.
- All fire doors must be able to open freely, but remain closed in a fire. Check security and disabled access requirements to ensure there is not a conflict.
- Most fire doors will have a self-closer delayed action device. Fusible links can also be used - the link breaks when it reaches a specific temperature.
- Ensure appropriate fire signage is specified on the door and adjacent to it.
- Ensure the doorset is from a certified source and is identified as such.
- Check other performance requirements such as acoustics to avoid conflicts.
- Match glass performance to that of the door assembly.