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1. Extinguishing Mechanism of Aerosols Aerosols are agglutinating aerosols formed by the agglutination method. The resulting combustion products cool off after leaving the flame and condense into solid particles. Due to its small particle size and good diffusibility, it can diffuse into any corner of the fire extinguishing space, and the sedimentation effect is weak. The particles can be kept in suspension in the fire protection space for a long time and used as an all-submerged fire extinguishing agent.
Absolute majority of aerosols are gases, solid particles are mainly metal oxides and carbonates, gas products are N2, a small amount of CO2 and CO, main * solid particles endothermic decomposition cooling effect, chemical inhibition of gas phase and solid phase Diluted with inert gas to achieve extinguishing.
The formed aerosol solid particles have a diameter of about 1 μm, and the particle size of this particle is much smaller than that of the dry powder fire extinguishing agent. Particles that enter the flame increase their temperature (heat-melting) when they absorb heat from the flame. When the temperature rises to a certain value, the particles melt, gasify or decompose, and further absorb heat. The effect of heat absorption and temperature reduction is very high. obviously. For example, K2O decomposes when the temperature is greater than 350oC, and K2CO3, when the temperature is greater than 891, decomposes the endothermic reaction.
For small particles, the gaseous species generated by the gasification decomposition play a dominant role in the flame homogeneous inhibition process, and due to the longer residence time of the small particles in the flame, the non-homogeneous inhibition effect is also enhanced. In addition, the gasification decomposition of small particles enables the flame to be cooled, so there is a synergistic effect of physical fire extinguishing and chemical extinguishing in the fire extinguishing process of the aerosol, and the fire extinguishing efficiency is high.
Since the formed aerosol particles are very small and have a strong diffusibility, the aerosol can flow around obstacles and can enter into microscopic voids with gas-like properties. Aerosol solid particles have a large surface area and can absorb heat in a flammable flame, causing gasification and decomposition reactions to lower the flame temperature. Their homogeneous and heterogeneous chemical suppression are very strong, and thus have a high Fire extinguishing effectiveness.
Second, the aerosol fire extinguishing system components and function The fire extinguishing system mainly includes three parts: Fire extinguishing device, control device and alarm device.
The fire extinguishing device is mainly composed of a cartridge, a gas generator and a box. The cartridge consists of an electric igniter, a igniter, an extinguishing agent, and a housing. The drug cartridge is contained within the gas generator. The gas generator is generally composed of an extinguishing cooling chamber and a cooling chamber, and the generator is installed in the cabinet. The box only serves as a protective decoration. According to different models, one box can hold several gas generators.
Alarm devices include: smoke detectors, temperature detectors, bleed lights, sound and light alarm boxes, emergency start and stop buttons.
The control device generally has a dual-circuit fire detection alarm function, provides fault alarm output, fire alarm output, can store fire alarms, operation records and so on.
When there is a fire, the control device emits a compound fire alarm sound after the temperature and smoke detectors all detect the fire signal. At this time, if the control device is in the manual state, the on-duty personnel can immediately start the fire extinguishing device through the emergency start-stop button and the emergency start button of the control device to achieve extinguishing.
If the control device is in an automatic state, generally after a delay of 30 seconds, the control device will output a starting current to the fire extinguishing device to cause the electric igniter to ignite the igniter by the electric igniter, so that the ignition energy is expanded, and then the fire extinguishing agent is ignited, Fire extinguishing agents burn chemical reactions to produce aerosols. The produced aerosol is extinguished by flame, cooled and then ejected from the nozzle to reach the protection space for the purpose of extinguishing the fire.
Third, aerosol fire extinguishing agent Aerosol fire extinguishing agent is a pyrotechnic composition composed of oxidants, flammable agents, binders and additives. The oxidant provides the oxygen needed for combustion, the flammable agent generates the required heat and produces the desired gas product when the pyrotechnic composition burns, and the adhesive provides the agent with a certain plastic strength and acts as a flammable agent. In addition, there are additional components used to generate solid particles and inert gas components required for fire extinguishing. Oxidizers and flammables form the basis of the extinguishing agent. Oxidants such as nitrates, chlorates, etc.; flammable agents are inorganic flammable agents, organic flammable agents; binders are also organic and inorganic.
The formulation of fire extinguishing agent is generally designed and adjusted by oxygen balance. The oxygen balance refers to the relationship between the oxygen content of the agent and the amount of oxygen required for the complete oxidation of the flammable agent when the fire extinguishing agent reacts. When the difference is positive, it is called positive oxygen balance, when it is negative, it is called negative oxygen balance, and when it is zero, it is called zero oxygen balance.
Reasonable selection of pharmaceutical ingredients is an indispensable condition for reducing the sensitivity of pharmaceuticals and is also the basis for the safety of pharmaceutical formulations. Therefore, the fire extinguishing agent should be used with good safety and low sensitivity oxidants, and easy to release oxygen, stable within a certain temperature range, not decomposed by the water effect, good moisture resistance, harmless to the human body, to ensure that its pharmaceutical agents have the required Burning speed and low mechanical sensitivity are not explosive. The flammable agent must have enough thermal effect to ensure that the pyrotechnic agent can achieve the best special effect. The combustion reaction requires less oxygen, is easily oxidized, has sufficient chemical and physical stability, and has low hygroscopicity and is harmless to the human body. .
Aerosol solid particles have a small diameter (about 50% below 1μm). The main components are metal oxides and carbonates. They are suspended in air for a long time. They extinguish the fire by both heat absorption and chemical inhibition, and they have a good flame-retardant effect. . By adjusting the formulation of the fire extinguishing agent, not only the temperature of aerosol release can be effectively reduced, but also the generated metal oxides and carbonates themselves are not hygroscopic, and even if the hydroxide is generated, it is weakly alkaline and does not absorb moisture, so the corrosivity is Will not exist or be very weak. Effectively reducing the flame temperature, improving the extinguishing efficiency, and the absence of corrosive particles are the directions for the research and development of aerosol fire extinguishing technology.
Fourth, aerosol generator ignition, ignition, fire extinguishing work process to increase the burning rate of fire extinguishing agent, and the use of igniting agents. Normally the extinguishing agent is ignited by a igniting agent, which is a chemical with a high burning rate, a relatively large calorific value and a high ignition sensitivity, to provide sufficient ignition energy and ignition pressure, and is easily ignited by the ignition element. Pharmacy. The igniter is an ignition element. The ignition element is formed by a bridge wire ignition head. When it receives a start-up current that can initiate it, its bridge wire heats up, and ignition reaction occurs around the bridge wire. , The deflagration form ignites the igniting agent, the igniting agent energy is expanded and the extinguishing agent is ignited, so that the extinguishing agent can be fired longitudinally and laterally to generate an extinguishing aerosol. It can be said that the ignition element will not work when the ignition element energy is not given, so the igniter and the extinguishing agent will not work either. Therefore, most cases of false discharge are caused by a malfunction of the control device or a special malfunction of the external power supply.
V. Fire extinguishing controller working principle and fault reason analysis The control device is assembled from many electronic components. It is determined through complex circuit logic to achieve its control purpose. Therefore, the quality of components is a key factor. Practice has proved that poor quality electronic components can easily cause the control device to fail to work or make mistakes. The main power source is also a major cause of misoperation of the control device. Sudden high voltages can cause it to run out of control due to burnout of the circuit.
Therefore, the key is to improve the quality of the control device to ensure the safety and reliability of the work. At the same time, the installation process must be strictly in accordance with the installation and commissioning acceptance standards to prevent stray currents from interfering with the control device and the fire extinguishing device. These can be Prevention.
Through the above analysis, the author believes that the main causes of misfiring are as follows: one is due to the unstable control device quality, the short circuit leads to abnormal output, and the other is due to failure to cut off the system during maintenance, installation and debugging. The start-up line will cause mis-injection due to maintenance and debugging. There is also the possibility of current-induced extinguishing of fire extinguishing devices during lightning storms.
Sixth, the solution to prevent accidental spraying mainly has the following points:
1. Research and design of chemical extinguishing agents, pilot burners and ignition components. Although most of the accidents are caused by the control device, the fire extinguishing device is also jointly and severally liable. If the electronic component is corroded or the secondary fire is caused by accidental spraying, the main responsibility lies in the extinguishing device equipped with extinguishing agent. On the other hand, corrosive aerosol fire extinguishing devices are not suitable for the protection of precision instruments and equipment.
2. Choose a control device that is resistant to high voltage and lightning strike and check it strictly.
3, installation and commissioning should be carried out in strict accordance with the relevant standards and process regulations, under the analog load conditions related to debugging.
4. In the installation process, the control device shall pass the fire extinguishing device after passing the test run assessment.
5, to avoid artificial start wrong injection, when the controller is activated due to misoperation, it should be within 30s operation of the controller on the emergency stop button or stop button on the start button to terminate the start operation.
6. Regularly check whether the components and control devices of the fire extinguishing system are in normal operation. If any abnormal conditions are found, feedback shall be given to them for repair.
In short, accidental spray accidents caused by aerosol fire extinguishing systems are mostly caused by misoperation of control devices. Therefore, it is necessary to have a better understanding of the instructions for the use of the control device. The equipment must be regularly repaired as required, training must be carried out for the relevant personnel, and should not be initiated by humans. The input power must be checked regularly to ensure that it is within the allowable voltage range. If there are measures to prevent lightning strikes, accidental accidents can be avoided.
Aerosol fire extinguishing system and its accidental spray accidents
The accidental accidents of aerosol fire extinguishing systems often occur during operation. The so-called false spray, that is, the fire extinguishing device is activated normally without fire, and the fire extinguishing agent is sprayed. After the accidental spraying, the suppliers of the components belonging to the entire system are implicated, which often causes mutual disputes among the relevant manufacturers, users, and management departments, which seriously affects the healthy development of aerosol fire extinguishing technology. For this reason, it is necessary to discuss the function of pyrotechnics theory and the functions of various parts of the system, in order to seek a unified understanding, to identify the key problems and solutions, and to eliminate the occurrence of accidental accidents.