FIRE RESISTANCE OF TIMBER DOORS

Upgrading the fire resistance of timber doors

Doorways are potential routes of fire spread. There is little advantage in having a fire-resisting door set (door and its frame) if the door is left open during a fire. This can be prevented by having electrically released door hold-open devices actuated by fire detection. Panels above doors should be checked for fire resistance, and the presence of a glazed panel should be carefully considered.

Radiation through the glazed area may be acceptable if transmitted radiation cannot ignite materials on the other side, and this can be calculated. If the level of incident radiation on combustible objects or finishes near the unexposed face is unacceptable then an glass laminate may be used, if the greater thickness and weight can be tolerated.

Timber shrinks when it is heated and loses moisture. This can mean that tall doors may bow towards a fire and, especially at the top, allow the passage of hot gases and flames, Figure15. Extent of bow depends on design, thickness and direction of grain.

Points of door restraint, i.e. hinges and latches, require careful consideration.

To prevent failure of integrity and insulation at door edges, intumescent seals may be used, Figure 16. The data in Figure 16 assumes that there is a good fit between the door face and the door frame and that the gap between the edge of the door and frame is not greater than approximately 3mm. The strips can be preformed and simply placed in a groove in the door and frame. The positions of strips in the door or frame is important and should allow for bowing of the door toward the fire, Such seals on their own will not prevent the spread of cold smoke, and where this is important intumescent seals should be used with smoke seals, the latter being flexible and robust for the design life.

A special design of fire and smoke seal for use with double swing doors.An extruded aluminium section incorporating intumescent material and a neoprene smoke seal is fixed into a groove in each door edge along the top and the sides using metal nails. The aluminium soaks up the heat from the fire gases and conducts the heat to the intumescent causing it to swell as early as possible so preventing charring of the timber.

Conclusion:

• Rags and cloths which have been used to mop up or apply flammable liquids should be disposed of in metal containers with well fitting lids and removed from the workplace at the end of each shift or working day.
• There should be no potential ignition sources in areas where flammable liquids are used or stored and flammable concentrations of vapour may be present at any time. Any electrical equipment used in these areas, including fire alarm and emergency lighting systems, needs to be suitable for use in flammable atmospheres.
• Flammable or combustible should not be stored, even as a temporary measure, in escape routes such as corridors, stairways or lobbies, or where it can come into contact with potential sources of heat. Accumulations of combustible rubbish and waste in the workplace should be avoided, removed at least daily and suitably stored away from the building.
• Do not allow combustible waste, unused materials, and redundant packaging, such as cardboard, wooden or plastic containers and wooden pallets, to build up at the workplace; these must be safely stored until they are removed from your premises. Where a skip is provided for the collection of debris or rubbish, it should be positioned so that a fire in it will not put the workplace, or any other structure, at risk.
• Parts of the workplace which are not normally occupied, such as basements, store rooms and any area where a fire could grow unnoticed, should be regularly inspected and cleared of non-essential flammable materials and substances. You should also protect such areas against entry by unauthorised people.

If the workplace has waste or derelict land nearby, you should keep any undergrowth under control so that a fire cannot spread through