Problems and Discussions in Automatic Fire Alarm Linkage Control

    The linkage control of the automatic fire alarm system is the soul of the building's automatic fire-fighting facilities. The objects of its control mainly include: ventilation and smoke exhaust facilities, fireproof roller shutters, normally open fire doors, elevators, non-fire power supply control, fire emergency broadcasts, fire alarm devices, emergency lighting and evacuation instructions, etc. The quality of the linkage control system directly affects the fire prevention and extinguishing efficiency of the building's automatic fire-fighting facilities. This article analyzes and discusses the problems existing in the linkage control of the automatic fire alarm system.

   1. The linkage equipment does not operate in a standardized manner

    During project acceptance, we may often see the following scenes: when a certain smoke sensor is activated, the simulated fire floor immediately activates the alarm, fire broadcast, cuts off the non-fire power supply of the floor, all elevators are forced to land on the first floor, all fire curtains are lowered to the bottom, and smoke exhaust fans are started. At this time, the construction unit believes that the linkage test has been successfully passed. In fact, there are major problems with the linkage logic relationship of this project, which is mainly manifested in that the linkage equipment is activated after the first alarm or the second alarm is confirmed. There is a very clear statement on the linkage logic relationship in GB50116-98 and JGJ16-2008. After an alarm, the linkage equipment should only act as follows: closing the normally open fire door, actuating the fire curtain, and starting the smoke exhaust facility (including stopping the air supply of the air conditioner). After confirming the fire (i.e. the second alarm), the following actions should be taken: cutting off the non-fire power supply of the relevant parts, turning on the alarm device and emergency lighting and evacuation sign lights, forcing the elevator to land on the first floor, automatically opening the door controlled by the access control system, automatically opening the electric revolving door in the lobby and the electric gate in the courtyard, automatically opening the electric fence in the paid parking garage, and turning on the camera of the safety technology prevention system on the relevant floor to monitor the fire. It is worth pointing out that the linkage control of the elevator in JGJ16-2008 is different from that in GB50116-98. It requires that after the fire occurs, the elevator is forced to land on the first floor or the elevator transfer floor, and the power supply of the passenger elevator is cut off. From the above analysis, it can be seen that the specification has made clear provisions on the actions of the linkage equipment, and its starting point is mainly to meet the requirements of early fire fighting and avoid the unrest of the crowd caused by false fire alarms. It should be noted that the specifications do not clearly state that automatic control must be used to cut off non-fire power supplies, turn on alarms and fire emergency lighting and evacuation sign lights, make elevators make emergency landings on the first floor, and turn on the cameras of the safety technology prevention system to monitor the fire scene. Designers may consider using manual control as appropriate.

    2. Installation of detectors on both sides of fire shutters and normally open fire doors

    During project acceptance or commissioning, it is often seen that after any smoke detector in a fire partition sounds an alarm, the fire shutter will immediately move. There is a certain controversy about this phenomenon. The reason is that different specifications have different descriptions of the settings of detectors on both sides of fire shutters and normally open fire doors. When different design standards are adopted, the settings of detectors and the logic programming of linkage controllers should be different. GB50116-98 stipulates that the fire shutters on the evacuation passage are as follows: 6.3.8.1 Fire detector groups and their alarm devices should be installed on both sides of the fire shutters on the evacuation passage, and manual control buttons should be installed on both sides; the fire shutters for fire separations are stipulated as follows: 6.3.8.3 For fire shutters used as fire separations, the shutters should be lowered to the bottom after the fire detector is activated; the control requirements for normally open fire doors are as follows: 6.3.7.1 After the fire detector on either side of the door sounds an alarm, the fire door should be automatically closed. The JGJ16-2008 requirements for the detectors on the fire shutter side are: 13.4.5, paragraph 1: On both sides of the electric fire shutter of the evacuation passage or fire partition, it is advisable to set up a dedicated smoke and temperature detector group, alarm device and manual control button, and there should be measures to prevent misoperation; the requirements for the detectors on the normally open fire door are: 13.4.5, paragraph 2: (Electric fire door) Both sides of the door should be equipped with dedicated smoke detectors to form a control device. When the detectors on either side of the door alarm, the fire door should automatically close. The only difference between the two specifications in the description of the detector setting is: dedicated detectors. Whether to use dedicated detectors has a clear difference in the linkage control of the system. When only general detectors are used, any point in the fire partition can trigger the action of the fire shutter and the normally open fire door; when dedicated detectors are used, only when smoke drifts to the side of the fire shutter (fire door) can the dedicated detector alarm be triggered to link the equipment. Obviously, whether or not to install dedicated detectors plays a crucial role in when the fire shutter (normally open fire door) will operate. The author believes that whether to use dedicated detectors should be decided comprehensively based on the nature of the building, fire load, population density, and reference to the review opinions of the fire department.

    3. The form of linkage control command

    The signal output of the fire linkage control module of the automatic fire alarm system is divided into two types: pulse signal and self-holding contact signal. In engineering design, the two output forms must be correctly selected. For some DC24V or self-dedicated control devices, the output module can maintain the level output to keep the equipment working normally. However, for equipment with dedicated control devices and control voltage of AC220V or AC380V, such as fire pumps, smoke exhaust fans, etc., if self-holding output contact signals are used to maintain the operation of the equipment, the continuous working time required by the specification cannot be achieved. For such controlled objects, only pulse signal output can be used, and the control command is maintained by the controlled object's own control device. In the case of fire, the specification JGJ16-2008 stipulates the minimum continuous power supply time of various fire-fighting electrical equipment during the fire, such as ≥10min for automatic fire alarm devices, >180min for fire hydrants and fire pumps, >60min for automatic sprinkler systems, and >180min for fire and smoke exhaust equipment. However, the high-level specification GB50045-95 stipulates that the fire duration of the automatic sprinkler fire extinguishing system is 1.00h, the fire hydrant is 2.00h, and the smoke exhaust fan should be in working condition until the air flow temperature at the total outlet of the smoke exhaust pipe reaches 280℃. Obviously, the specification stipulates that the continuous working time of the automatic fire alarm device in a fire is much shorter than that of the fire pump, smoke exhaust facilities, etc., so the control command of this type of controlled object can only be maintained by the secondary circuit of the control cabinet itself. So far, we can conclude that it is very dangerous to use the output signal of the fire automatic alarm system linkage module to maintain the control state of the fire pump and smoke exhaust fan, and it should be avoided in construction.

    The linkage control of the automatic fire alarm system is the central nervous system of the entire fire protection system. Its control logic relationship and construction cannot be sloppy. Some linkage details should be carefully selected: the linkage equipment should select the action time node according to the requirements of the specification. The detectors on both sides of the fire shutter and the normally open fire door should fully consider the differences between the two, and then select appropriate trigger devices in combination with the nature of the building. The selection of linkage control commands should enable the controlled equipment to meet the fire duration required by the specification.