Fire Door Components
A fire door is more than just a door; it is a carefully selected configuration of components, which have been rigorously tested and assembled in order to prevent the spread of fire and smoke.
The LPCB state that “the term fire door comprises any doorset … including any frame or guide, door leaf or leaves… etc., which is designed to give a fire-resisting capability when used for closing off permanent openings in separating elements of construction. This includes any side panels, vision panels, or transom panels together with the door hardware and any seals which form the assembly.”
Fire Door Keep Shut Signs
Fire door keep shut signs are known as a 'mandatory' notice and are therefore required to be installed on all fire doors. This often means that fire doors are easily distinguished from standard doors. However, don't be fooled! Some buildings will put one of these signs on anything with three hinges and a handle. To truly distinguish a fire door, you will have to look at all the components on the door.
Fire Resistant Glass
If we were asked to design the perfect fire door, glass would most definitely be excluded from the finished products. However, a number of building regulations stipulate that glass is required on certain doors depending on their locations. For example, doors in hallways must have glass to allow individuals to see if anyone is standing on the opposite side of the door before opening, thus preventing injury.
Fire rated glass can be distinguished by a marking or its design. The cheaper version of fire rated glass is known as 'Georgian Wired Glass' and will contain a grid-like pattern of metal wire within the glass. The more expensive clear glass, however, is distinguished by the use of an etching in the corner of the pane, usually containing the manufacturers information and the fire resistance properties of the glass.
The door leaf is probably the most important component of the door set, and as such it is often the most tested. Contrary to many people’s beliefs, fire doors are rarely made out of solid wood. Instead they tend to consist of a low, medium or high density chipboard core depending on the requirements, with a hardwood lipping around all four edges to protect the door and a decorative facing allowing for elaborate designs or a simple paint grade finish.
Door leafs are available in a number of thicknesses, however the most popular would be 44mm doors providing 30 minutes of fire resistance, and 54mm doors providing 60 minutes of fire resistance.
Hinges are often overlooked as a component of fire door sets. Doors are required to close with a maximum gap of 4mm on the top three edges. Hinges hold doors in the frame and ensure that the door set consistently maintains these gaps, in spite of ongoing use and charring wood in a fire scenario. The hinges should be made from a metal with a melting point of no these that 800 degrees centigrade, usually stainless steel. In general fire doors will have 3 sets of hinges, however this is dependent on the weight of the door leaf and the configuration in which the door was tested.
All fire doors, other than locked riser doors and cupboards, should be fitted with a self-closing device. As we know, fire doors should be kept closed at all times, and a door closer will ensure that the fire door closes itself automatically after use, sealing the fire compartment.
According to BSEN1154, closing devices should be provided with a 'power rating' between 1 and 7, which corresponds the weight of the door leaf it will be installed on. Heavier door leafs such as 6o minute 54mm leafs will require a more powerful door closer. However, other guidelines exist to support the accessibility of buildings for people with disabilities. For example, BS8300 notes that the maximum closing force of a door should be 35 newtons between 0 and 30 degrees and 22.5 newtons from 30 degrees onwards.
Intumescent Strips and Smoke Seals
Intumescent strips are installed around the perimeter of the door or the frame, in addition to the glazing and door hardware. In the event of a fire, these strips react with the heat and begin to swell, filling all gaps around the door and preventing the spread of fire. For intumescent strips to be effective, gaps around the door should ideally be 3mm to allow an effective seal to form. Despite being effective at prevent the spread of fire, intumescent strips are ineffective at preventing the spread of 'cold smoke'. To prevent this, smoke seals are required.
Smoke seals are composed of either a rubber strip or a brush (often integrated into the intumescent strip) and create a constant seal around the door at all times, essentially creating an air lock. Therefore, in the event of a fire the travel of smoke through a building will be blocked, providing valuable time for escape.
Handle and Lock
In order for the door to maintain an effective fire barrier, it must remain within its frame. For single action door sets, this is usually the job of the latch and the lock, which must secure the door form opening. Alternatively, panic release devices such as push pads can be used in place of locks and handles depending on reasons such as security requirements. These push pads are often preferred on escape routes as the provide easy egress for building occupants.
During installation, locks will have intumescent pads attached to them to fill and voids in the door during a fire, supporting the overall fire barrier.
Hold Open Device
Fire doors are expected to be closed at all times and this is supported through the use of self closing devices. However, these doors can present and obstacle to the young, elderly and disabled or are an inconvenience to the general occupants of a building. Therefore, many people undermine the fire door by propping it open with a wedge or fire extinguisher, which is both dangerous and illegal.
Hold open devices are designed to safely hold doors open in these scenarios and they will automatically release the door in the event of a fire, allowing it to close. In the case of power failure there is often a built in manual release mechanism to allow the door to close.