1. Introduction
With the increasing emphasis on fires by petrochemical enterprises and the increasing awareness of fire safety and the requirements of national standards and regulations, petrochemical enterprises have gradually installed installations, tanks, control rooms, substations, and instrument cabinets in petrochemical enterprises in recent years. The automatic fire alarm system played a good role in detecting and controlling the initial fire. However, because of the harsh environment characteristics of the large-scale dust, corrosive nature, outdoor waterproof and explosion-proof requirements of the petrochemical enterprises, as well as the design, construction, daily operation test management, and maintenance, the automatic fire alarm system also occurs during actual use. Repeated failure alarms can easily result in the laziness of the on-duty personnel and the lack of attention to the confirmation work after the alarm, thus affecting the use of the initial fire detection and control. Therefore, this article mainly discusses the types of fault alarms, failure alarm reasons and preventive measures that have been used for the Norma R21 type automatic fire alarm system used in the plant area of ​​Zhenhai Refining & Chemical Company for 6 years.
2. Fault alarm type
When a fault occurs, the Nomura R21 fire alarm controller will issue an "abnormality" fault alarm sound, display the type of fault, and print out any fault display of the system. Nominal R21 fire alarm system generally has 13 types of fault alarms: CPU abnormality, fuse abnormality, printer abnormality, connector abnormality, main power supply abnormality, standby power supply abnormality, IC card abnormality, test abnormality, transmission shift abnormality, and display disk abnormality , Abnormal output value, main signal line abnormality, and monitor line abnormality.
Among them, three types of fault alarms, such as abnormal output values, abnormal main signal lines, and abnormal transfer reports, are the most common and the causes are complex. Therefore, the causes of the three types of fault alarms are specifically analyzed below.
3. Analysis of the causes of several common fault alarms
3.1 "Abnormal Output Value" Failure Alarm Analysis
This kind of fault is caused by the failure or fouling of the intelligent detector. The cause of the fault alarm is caused by the following situations.
(1) Accumulated dust after the detector has been used for a long time, or internal electronic component parameters drift, resulting in deterioration of the detector performance and failure alarm.
(2) Improper selection of detector design.
(3) The installation position of the detector is not properly arranged in strict accordance with the specifications.
(4) The special places such as the dining room are easy to produce aroma gathered in the ceiling, easily causing the fly to stay or bite the metal mesh on the ceiling detector, causing the detector to have a serious contamination and a fault alarm.
(5) Rainy fog diffuses into the room or is wet due to the weather, causing indoor smoke detectors to malfunction.
(6) Because of the large dust in the installation place of the smoke detector, it is easy to accumulate ash or dust into the dark room inside the detector after a period of use, and a fault alarm occurs.
(7) The linear beam smoke detector has caused its transmitter, receiver lens contamination due to long-term maintenance, or the deviation of the optical path of the linear beam smoke detector, the above two conditions will make its receiver The amount of light received is reduced and a fault alarm occurs.
(8) The detectors of outdoor flame detectors, manual alarm buttons, etc., due to poor waterproof performance, the internal electronic modules will generate a fault alarm after entering the water.
3.2 "Main Signal Line Abnormal" Fault Cause Analysis
The main reason for this type of failure is that the address coding device is faulty or removed, or the alarm device binary signal bus is disconnected or short-circuited.
(1) The terminal screws were not tightened during construction, causing the wires to loosen or loosen and causing a disconnection.
(2) The construction does not meet the requirements of the “Construction and Acceptance Criteria for Automatic Fire Alarm Systemâ€, and it is prone to disconnection or short circuit.
(3) After the automatic fire alarm system has been running for a long time, it will be disconnected or short-circuited due to aging of the line, loose wiring, and poor contact.
(4) There are many characteristics of reconstruction and expansion construction in the petrochemical enterprise installation site. It is easy to damage the directly buried fire alarm signal cable at the site during construction, resulting in bus disconnection or short circuit.
3.3 "Transmission report abnormality" failure alarm analysis (1) The fire alarm controller networked equipment stops working (power failure or failure), resulting in communication interruption.
(2) Network transmission equipment (fiber transceivers, digital-to-analog converters, communication protocol converters, network cards) or transmission lines (cables, optical cables) malfunction, causing communication interruptions.
4. Failure prevention measures
In order to reduce the occurrence of fault alarms and improve the operational reliability of fire alarm systems and the accuracy of fire alarms, it is necessary to take preventive measures in the aspects of design, construction, daily operation test management and maintenance.
4.1 Design
(1) Design selection: Select a new intelligent fire alarm system with advanced performance, mature products, good performance, and high reliability.
(2) The three parties of the owner, design, and supplier sign a technical agreement at the design stage. The technical agreement will specify the conditions of use, degree of protection, major equipment and technical requirements, operational requirements, technical services provided by the supplier (engineering services including documentation, on-site installation guidance, joint commissioning and transportation, and final fire acceptance).
(3) Correctly select the detector according to the actual site to reduce the failure alarm rate after the commissioning.
(4) It is forbidden to correctly arrange the installation position of the detector according to the specification.
(5) The design should be based on the protection level of the site, explosion-proof grade, strong requirements of Zhenhai Refining and Chemical Corrosion, select the fire alarm equipment that meets the field protection level, explosion-proof grade, and anti-corrosion grade.
(6) The industry mainly plans to review plans in advance so as to intervene early and find that the design is unreasonable or does not meet the regulatory issues. It promptly proposes modifications to the designer and reduces the fault alarm from the source.
4.2 Construction
4.2.1 General requirements for construction The construction unit shall carry out the construction according to the design drawings and shall not arbitrarily change it. The installation and commissioning of fire alarm equipment and the dark and concealed parts of the pipeline should be carefully documented.
4.2.2 Requirements for wiring construction (1) The wiring of fire automatic alarm system shall comply with the current national standard "Code for Construction and Acceptance of Electrical Installations", and the wiring shall be correct and standardized; the lines of different systems, different voltage levels, and different current categories Should not be worn in the same tube or slot in the same slot.
(2) Before threading, the water and debris in the pipe or groove should be removed.
(3) The conductor shall not have joints or kinks in the pipe or in the slot. The joints of the wires shall be welded in the terminal box or connected by terminals.
(4) When the tube is put into the box, the outer side of the box should be sleeved to lock the mother, and the inner side should be equipped with a protective mouth. When laying in the ceiling, the inner and outer sides of the box should be sleeved and locked.
(5) When laying all kinds of pipelines and trunkings in ceilings, separate fixtures or supports shall be used for fixation.
(6) After the conductors are laid, the insulation resistance shall be measured with a 500V megger for each return conductor, and the insulation resistance to ground shall not be less than 20 megohms.
(7) If the circuit of the automatic fire alarm system adopts metal pipe, fire protection measures shall be taken. The thickness of the protection during dark laying should not be less than 30mm; when laying in the clear, fireproof paint should be applied on the metal pipe.
4.2.3 Fire detector installation and construction requirements (1)Prevent the detector from being damaged before being put into use: The detector can only be installed when it is about to be commissioned, and it should be properly kept before installation. Dust, moisture, and corrosion prevention measures should be taken.
(2) The threading hole of the detector base should be blocked, and the detector base after installation should be protected.
(3) The detector base should be fixed and reliable, and its wire connection must be reliably crimped or welded. When using soldering, corrosive fluxes must not be used.
(4) The installation position of the point detector should meet the specification requirements.
4.2.4 Good Grounding Ensure that the fire alarm system is well grounded. When a dedicated grounding device is used, the value of the grounding resistance should not be greater than 4 ohms; when a common grounding device is used, the value of the grounding resistance should not be greater than 1 ohm.
4.2.5 Commissioning and acceptance requirements (1) After the completion of construction, the construction unit shall perform the commissioning work for the entire fire automatic alarm system according to the requirements of the "Code for the Construction and Acceptance of Automatic Fire Alarm Systems" and issue a commissioning report after normal. 120 hours of continuous operation.
(2) After the completion and acceptance of the fire automatic alarm system, under the guidance of the * fire supervision agency, the construction supervisor shall preside over the design, construction, commissioning and other units to participate in and jointly carry out inspections according to specifications.
4.3 Daily Operation Test Management
(1) Before the automatic fire alarm system is delivered for use, the construction unit and the manufacturer shall require the construction personnel and the on-duty personnel designated by the use unit to provide technical disclosure and special training.
(2) When the automatic fire alarm system is officially put into operation, it shall have the system as-built drawings and the technical data of the equipment, operating procedures, duties of the watchman, and duty records.
(3) Establish a technical file of the automatic fire alarm system and record its troubleshooting, maintenance and testing.
(4) The automatic fire alarm system shall maintain continuous normal operation and shall not be interrupted arbitrarily. A 24-hour supervision system was implemented to observe and record the operation of the automatic fire alarm system at any time and the fire alarm signal was processed in a timely manner.
(5) Detectors that have failed alarms should be replaced immediately, and they should not be turned off or reused.
(6) The automatic fire alarm system should be checked and tested regularly. The function of the fire alarm controller shall be checked daily; a quarterly special inspection instrument shall be used to test the operation of the detector in batches and confirm the display of the lamp, the sound and light display of the fire alarm device, the control display function of the fire control equipment, and the forced cutoff. Non-fire power supply functional tests and other inspections; a comprehensive inspection test and a sensitive response test for the detectors are performed every year. Do a good job of inspection records for each inspection and file for future reference.
(7) Do a good job in the management of windows and doors installed in smoke detectors, and close them in time before the rainy weather to prevent rain and fog from permeating into the room.
(8) Do a good job in permit management of ground-working permits. When handling the permit for ground-breaking operations, the management unit shall make an on-site submission with the construction unit to explain the direction and protective measures of the underground direct fire alarm signal cable so as to avoid damage during construction operations.
4.4 Maintenance
(1) Regular inspection and cleaning: According to the requirements of national regulations, after the detector is put into operation for 2 years, it should be cleaned every 3 years, and the response threshold and other necessary functional tests should be done. Only qualified persons can continue to use it. Qualified persons are prohibited from re-installing and using.
(2) Regularly clean the fire alarm controller: During the long-term use of the fire alarm controller, a large amount of dust will be adsorbed on the circuit board, which will affect the heat dissipation, and will also short-circuit in wet conditions. Therefore, it is necessary to refer to the three-definition management mode of electrical equipment and arrange a plan to regularly clean the fire alarm controller.
(3) Periodic inspection and replacement of batteries: After the main power supply of the fire alarm controller loses power, the backup battery can ensure that the controller continues to work for a certain period of time. The backup battery is generally a maintenance-free battery with a lifespan of 3 to 5 years. It should be tested regularly with a dedicated battery tester, and the failed battery replaced in time to ensure the safe power supply of the fire alarm controller.
(4) Attach importance to fire alarms and maintenance of control lines. In particular, the terminal box should be inspected with emphasis to eliminate hidden dangers of line aging and poor contact after long-term operation of the system.
(5) Smoke detectors in special places such as dining rooms where aromas tend to collect on the ceiling should be shortened in terms of their replacement cycles, and they should be replaced in advance according to the metal mesh contamination.
(6) Regularly check the waterproof seal and explosion-proof integrity of outdoor fire alarm equipment.
(7) The faults that have occurred in the fault alarm should be promptly maintained. Preventing frequent fault alarms causes watch attendants to lose sensitivity and generate slack.
(8) Do a good job of maintenance on behalf of the contractor's management and controlled work: should be targeted on behalf of the maintenance contractor's work and record inspections, the existence of breach of contract assessment, so that the automatic fire alarm system maintenance work to achieve controlled.
5 Conclusion
According to the analysis of the fault alarm cause of the No. R21 automatic fire alarm system, it is necessary to make joint efforts in the four stages of design, construction, daily operation test management and maintenance in order to effectively reduce the number of fault alarms in the fire automatic alarm system. Good preventive measures and control work at all stages can improve the operational reliability of the fire alarm system, and truly play the role of the automatic fire alarm system in detecting and controlling the initial fire.
references:
[1] Liu Yuyi, Du Shiling. Practical handbook for fire protection design in power plants and substations [M]. Beijing: China Planning Press, August 1999 [2] Liu Guochen. Petrochemical fire protection and fire extinguishing [M]. Beijing: China Petrochemical Press,
September 1998 [3] JB-R21-SG fire alarm controller (linkage type) instruction manual [S]. Shanghai Nomike Cochem Fire Equipment Co., Ltd. [4] Design Specification for Automatic Fire Alarm System [S], GB50116 -98
[5] Specification for Construction and Acceptance of Automatic Fire Alarm System [S], GB50166-92
[6] Building Design Fire Protection [S], GB50016-2006
[7] Design of fire protection specifications for petrochemical enterprises [S], GB50160-92.1999 edition
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