The Hazardous Gas Detection and Alarm System is a dedicated safety and health detector that is used to detect the presence of flammable or toxic gases and vapors in the air at the chemical operation site or within the equipment and to limit the alarm.

In addition, the air-oxygen detector also belongs to this type of instrument.

The detection of harmful gases in hazardous chemical sites mainly includes the following situations:

Leakage detection: Detection leaks on the site of hazardous gases or liquids (vapours) from the equipment pipeline, and leak detection of equipment pipelines.

Inspection and inspection: It is more important to detect residual harmful gases or liquids (vapors) after replacement and maintenance of the equipment, especially before the detection of hot work.

Emergency detection: When an abnormal situation occurs on the production site or an accident is handled, harmful gases or liquids (vapors) shall be tested for safety and hygiene.

Entry detection: When a worker enters a hazardous substance isolation operation room and enters a ditch, cable trench, or equipment operating in a hazardous area, harmful gas or liquid vapors must be detected.

Circuit inspection: When testing for safety and health, it is necessary to detect harmful gases or liquid vapors.

Dangerous chemicals should strengthen safety management, improve safety measures, and control hidden dangers of accidents. However, it is impossible to achieve absolute security and there will still be a situation of loss. Therefore, it is very necessary to detect and alert for hidden accidents and detect and alarm harmful gases or liquids (vapors) in hazardous chemical sites. It is of great importance to avoiding and controlling accidents.

First, the classification of harmful gas detection alarm 1, according to the use of classification:

1 portable hazardous gas detection alarm instrument The sensor, measuring circuit, display, alarm, rechargeable battery, air pump, etc. assembled in a shell, become one-piece instrument, compact and lightweight, easy to carry, pump suction sampling, anytime, anywhere Conduct the test. Pocket instruments are a type of portable instrument. Generally, there is no suction pump diffusion sampling, dry battery power supply, and small volume.

2 Fixed harmful gas detection and alarm instrument This type of instrument is fixed on the site, continuously detects the corresponding harmful gas (vapor), automatic alarm of harmful gas overrun, and some can automatically control the exhaust fan.

Fixed instruments are divided into two kinds of integrated and split.

One-piece fixed hazardous gas detection and alarm instrument: same as portable instruments, the difference is installed on the site, 220V AC power supply, continuous automatic detection of alarms, mostly diffuse sampling.

Split type fixed hazardous gas detection alarm device: sensor and signal transmission circuit are assembled in an explosion-proof housing, commonly known as the probe, installed on the site (dangerous place); the second part includes data processing, secondary display, alarm control and power supply, assembly Into the controller, commonly known as the secondary instrument, is installed in the control room (safety place). Probe diffusion sampling detection, secondary instrument display alarm.

2, according to the measured object and the principle of the sensor classification 1 combustible gas detection alarm (referred to as explosion tester, an instrument to detect a variety of combustible gases) catalytic combustion combustible gas detection alarm device, testing a variety of combustible gases or vapors. Electrochemical toxic gas detection alarm system detects CO, H2S, NO, NO2, CL2, HCN, NH3, PH3 and various toxic organic compounds. Infrared flammable gas detection alarm, detecting various combustible gases (according to filter technology). Semiconductor flammable gas detection alarm device detects a variety of combustible gases. Thermal conductivity type flammable gas detection alarm instrument, which detects hydrogen with a large difference between thermal conductivity and air. Toxic gas detection alarm (referred to as a poison meter, an instrument to detect a toxic gas) Photoionization toxic gas detection alarm, detection of ionization potential of less than 11.7eV of organic and inorganic compounds. Infrared toxic gas detection alarm, detection of CO, CO2 and so on. Semiconductor-type toxic gas detection alarm, detection CO and so on.

Second, harmful gas detection alarm selection principle 1, a clear purpose of detection, choose the type of instrument In short, the detection of harmful gases has two purposes, the first is to measure the explosion, and the second is to measure the virus. The so-called explosion test is to detect the gas content of dangerous places and exceed the standard alarm so as to avoid the occurrence of explosion accidents; the detection of poison is to detect the contents of all poisonous gases in the dangerous place and exceed the standard alarm so as to avoid the poisoning of workers. The range of explosion detection is 0-100% LEL, and the range of poison detection is 0-several (or several hundred) ppm. There is a big difference between the two. There are three kinds of hazardous gases in hazardous areas: first, non-toxic (or low-toxicity) flammable, second, non-flammable, toxic, and third, flammable and toxic. The first two conditions are easy to determine, the first test explosion, the second test poison, the third case if there is a person exposed to test poison, if no personnel exposure can be measured. Select the combustible gas detection alarm device for the explosion test, and select the toxic gas detection alarm device for the poison detection.

2. Defining the purpose of detection Select the type of instrument (portable or fixed) The long-term operation of the production or storage job is to use the stationary detection alarm device; other options such as maintenance inspection, emergency detection, entry detection, and touring inspection are portable (or portable). )instrument. The model number of the instrument includes the three main contents of the manufacturer, function index and detection principle.

3, clear test objects, the best choice for the selection of instrument model instrument type to consider the following principles:

1 The manufacturer speaks of good faith, good reputation, and the quality of production is guaranteed. It has passed the ISO9002 quality system certification, and has a CMC production license issued by the technical supervision department, and has a fire-fighting and explosion-proof certificate.

2 The selected model product function index must meet the requirements of the national standard GB12358-90, GB15322-94, GB16808-1997 and other standards.

3 The detection principle of the instrument must be adapted to the requirements of the test object and the test environment.

III. Harmful Gas Sensors and Their Features Overview of Harmful Gas Sensing: Harmful gas sensors are devices that convert the content of harmful gases in the air into electrical signals. The electrical signals generated by the sensors are processed by electronic circuits, amplified and used by the sensors in the field and subjected to a variety of harsh environments and atmospheres. In particular, the sensors of the stationary instruments have long-term continuous operation, and are also limited in explosion-proof and power supply capacity. The requirements for hazardous gas sensors are very strict. After conversion, display and alarm of harmful gas content are achieved. It can be seen that the sensor is the basic and core component of the harmful gas detection and alarm instrument, and its quality determines the quality and function index of the harmful gas detection and alarm instrument.

Generally, the sensor has the following items: (1) detection range and resolution; (2) detection accuracy and repeatability; (3) stability and zero drift; (4) response speed; (5) selectivity and anti-interference ability; (6) anti-poisoning ability and life span; (7) Anti-environmental (temperature and humidity) influence ability; (8) Safety, explosion-proof performance; (9) Interchangeability and easy maintenance; (10) Small size, light weight; (11) Small current, good electricity saving.