How to choose a smoke detector? What is the difference between ionization and photoelectric types?
- Select detectors according to the characteristics of the fire
① There is a smoldering stage at the beginning of the fire, which produces a lot of smoke and a small amount of heat, with little or no flame radiation. Smoke detectors should be used.
② The fire develops rapidly, producing a lot of heat, smoke and flame radiation. Smoke detectors, temperature detectors, flame detectors or their combination can be used.
③ The fire develops rapidly, with strong flame radiation and a small amount of smoke and heat. Flame detectors should be used.
④ The characteristics of fire formation are unpredictable. Pattern recognition tests can be carried out and detectors can be selected based on the test results.
- Select detectors according to the environmental characteristics of the installation site
① The relative humidity is greater than 95% for a long time, the air flow speed is greater than 5m/s, there is a lot of dust and water mist stagnation, corrosive gases may be generated, smoke is stagnant under normal circumstances, and organic substances such as alcohols, ethers, and ketones are generated. Ion smoke detectors should not be used.
② It is not advisable to use temperature detectors in places where smoldering may occur or where failure to report a fire in time will cause major losses; it is not advisable to use fixed temperature detectors in places where the temperature is below 0 °C; it is not advisable to use differential temperature detectors in places where the temperature changes greatly under normal circumstances.
③ It is not advisable to use flame detectors in places with the following circumstances:
A. Flameless fire may occur;
B. Thick smoke spreads before the flame appears:
C. The lens of the detector is easily contaminated;
D. The “line of sight” of the detector is easily blocked;
E. The detector is easily exposed to direct or indirect sunlight or other light sources:
F. Under normal circumstances, there are open flame operations and the influence of x-rays and arc lamps.
- Select detectors according to the height of the room
The sensitivity of the detector should be selected based on the performance and use of the detector. Under normal circumstances (when there is no fire alarm), the system should not have false alarms. At present, most of the high-rise buildings in China use photoelectric temperature detectors. Only in some places, such as kitchens, generator rooms, garages and places with gas fire extinguishing devices, temperature detectors are used. When only “type detectors” are used, In the linkage system, it is easy to produce false actions, which will inevitably cause unnecessary losses, especially in the linkage system. Therefore, two or more types of detectors should be selected. They are in a logical relationship of “and”. When two or two detectors alarm at the same time, the linkage device will act, so as to ensure unnecessary losses.
In short, the detector selection should be based on the actual environmental conditions to select the appropriate detector to achieve the purpose of timely and accurate alarm.
What is the difference between ionization and photoelectricity?
Photoelectric smoke detector
First of all, let’s understand what is a photoelectric smoke detector and the working principle of a photoelectric smoke detector. Photoelectric smoke detector-we also call it a point detector. Photoelectric smoke detector uses the basic property that smoke generated during a fire can change the propagation characteristics of light. A kind of alarm device developed. There is an optical maze inside the photoelectric smoke detector and an infrared emitting tube is installed. When there is no smoke, the infrared receiving tube cannot receive the infrared light emitted by the infrared transmitting tube, but if there is smoke entering the optical maze, the smoke is refracted and reflected, and the receiving tube receives the infrared light, and the intelligent alarm The alarm circuit determines whether the threshold is exceeded, and if the threshold is exceeded, an alarm will be sounded.
The ionization smoke detector has an ionization chamber. The radioactive element used in the ionization chamber is americium 241 (Am241), with an intensity of about 0.8 microcuries. Under normal conditions, it is in a state of equilibrium, but if smoke enters the ionization chamber, this equilibrium relationship will be destroyed. When the smoke concentration reaches a certain threshold, an alarm will be sounded.
The ionization smoke detector is more sensitive to those tiny smoke particles, while the photoelectric smoke detector is just the opposite. The photoelectric smoke detector is more sensitive to those slightly larger smoke particles. If the smoke and dust produced by the fire are all relatively large particles, then it is better to use a photoelectric smoke detector. If the smoke and dust produced by the fire are all relatively small particles, then it is better to use an ionization smoke detector. So whether it is an ionization smoke detector or a photoelectric smoke detector is better, this needs to be determined according to your needs, and it cannot be generalized as which is better or not. We need to analyze specific problems and choose the corresponding products according to the use environment and needs.
