Commercial and public building are compartmented to delay the spread of fire from one room to another. Usually all rooms are linked together by doorways allowing the passage of foot traffic throughout the building. Therefore internal fire doors play a very important part during the outbreak of a fire. Firstly, they delay the spread of fire from room to room and secondly, they are used by people to escape out of building during a fire. Internal domestic fire doors are also required in domestic houses under certain circumstances for example houses of more than two floors.
Fire doors are very important and it is imperative that the doors are installed correctly. Your local building inspection officer and the fire service are generally only too happy to advise you on the fire safety requirements so give them a call.
In addition to the delaying the spread of flames, a fire door also is used to stop the spread of smoke from room to room, as many fatalities during a fire are quite often caused by smoke inhalation.
Fire Door Specification
When designing a fire door the following should be carefully considered:
- The physical door and frame
- Door ironmongery such as hinges, door closing devices and the locks
- Fire and smoke transfer mechanisms
When fire doors are tested for their performance they take into account all of the above items during the complete test. Apart from the door acting as a barrier, there is no point designating a doorway as a fire door if that door is often left in the open position, therefore there is a need for a door closing device. In addition the hinges should have melting point not less than 800ºC and be capable of keeping the door in place while acting as an effective barrier. The hinges should not incorporate nylon bushes. Locks play an important part especially if the door is designated as an escape door. This door should be fitted with easy opening devices so that the escapee can easily unlock the door and escape without having to look for a key.
Intumescent Fire and Smoke Seals
Intemescent strips should be fitted in fire doors. These strips (about 4 x 10 mm) are fitted into a recess in the long leading edges and top edge of the door or in the frame. If there is a temperature rise in the vicinity of the door, on the exposed side, to about 200ºC, the material in these strips will swell and close the gap between the door and the frame, forming an effective fire barrier.
One strip is generally adequate for a door to achieve ½ hour resistance. Wider (4 x 20 mm) or additional strips are fitted to doors requiring 1 hour resistance.
Retention of smoke during a fire is also very important. To prevent the movement of smoke between compartments during a fire the doors, where designated, should be fitted with ‘cold smoke seals’. These types of seals will prevent the smoke leakage between the door and the frame.
Intumescent strips are available with cold smoke seals in the form of a brush or blade. Intumescent strips are fitted to fire doors with or without smoke seals depending on the functionality of the fire door.
Detail of intumescent strip fitted to the edge of a fire door
Stability and Integrity Of Fire Doors
The stability failure of the internal fire check doors is deemed to have occurred when collapse of the door structure takes place during the fire. Integrity failure of the door has occurred when cracks or openings appear in the door allowing the passage of smoke, flames and hot gases. Failure also deemed to have occurred if flames are present on the unexposed face of the door.
Glazing in Fire Doors
Glazed internal fire doors are permitted. The vision panel in glazed internal doors may be for a person to see in or out of a room or for the transfer of light. Standard glass cannot withstand heat from a raging fire for very long and will fail quickly, therefore special fire rated glass is required for internal glass fire doors. This glass is capable of withstanding heat for up to 60 minutes prior to failure. Frameless Internal glass doors are not possible as a fire doors.
In order to ensure that a fire door with a vision panel works careful attention is required on how the glass is held in position in the door. There is no point having fire resistant glass fitted and the door fails because the beads holding glass in place have burnt away quickly. The overall dimension of the glass panel, and how it is held in place, is important and will determine the integrity of the door. A larger pane will tend to fail quicker than a smaller one. Unprotected beads will burn out in about 20 minutes. To prolong this, it will be necessary to protect timber beads with fire resistant surface coating or install beads made from a non combustible material or install intumescent glazing channels. In the event of a fire the channel swells and secures the glass in place and also protects the opening.
Detail of vision panel in a fire door