How to select a suitable combustible gas detector

2022-08-06
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How to select a suitable combustible gas detector

every person engaged in safety and health work must pay great attention to selecting a suitable gas detector for various production occasions and detection requirements. Here we will introduce some specific situations for your reference

1) confirm the type and concentration range of gas to be detected: the types of gas encountered by each production department are different. All possible situations should be taken into account when selecting the gas detector. If methane and other less toxic alkanes are in the majority, LEL detector is undoubtedly the most suitable. This is not only because LEL detector has simple principle and wide application, but also has the characteristics of convenient maintenance and calibration. If there are toxic gases such as carbon monoxide and hydrogen sulfide, a specific gas detector must be selected first to ensure the safety of workers. Install the corresponding jaw into the upper and lower jaw seats. The concentration measured by the poison gas detector based on the electrochemical principle is usually ppm. If there are more organic toxic and harmful gases, considering the low concentration that may cause poisoning, such as aromatic hydrocarbons, halogenated hydrocarbons, ammonia (amines), ethers, alcohols, lipids, etc., with the gradual introduction of electric vehicles and plug-in hybrid vehicles in the market, the photoionization detector should be selected instead of LEL detector, Because it may cause casualties. If the gas types cover the above gases, selecting a composite gas detector may achieve twice the result with half the effort

2) determine the application occasion: the type of gas detector selected varies with the industrial environment

a) fixed gas detector: this detector is widely used in industrial devices and production processes. It can be installed at specific detection points to detect specific gas leakage. The fixed detector is generally a two-part type. The detection head composed of sensor and transmission is installed on the detection site as a whole, and the secondary instrument composed of circuit, power supply and display alarm device is installed in a safe place as a whole, which is convenient for monitoring. Its detection principle is the same as that described in the previous section, but it is more suitable for the continuous and long-term stability required by fixed detection in terms of process and technology. They should also be selected according to the type and concentration of on-site gas. At the same time, they should also be installed at the position where specific gas is most likely to leak. For example, the most effective height of sensor installation should be selected according to the specific gravity of the gas

b) portable gas detector: because the portable instrument is easy to operate and small in size, it can be carried to different production sites. The electrochemical detector is powered by alkaline battery and can be used continuously for 1000 hours; New LEL detectors, PID and composite instruments use rechargeable batteries (some have adopted non memory nickel hydrogen or lithium ion batteries), which makes them generally work continuously for nearly 12 hours. Therefore, as such instruments, they are more and more widely used in various factories and health departments. If such instruments are used as safety alarms in open places, such as open workshops, the portable diffusion gas detector can be used because it can continuously, real-time and accurately display the concentration of toxic and harmful gases on site. Some of these new instruments are also equipped with vibration alarm accessories - to avoid not hearing audible alarms in noisy environments, especially when the production capacity is released. Computer chips are installed to record the peak value, STEL (15 minute short-term exposure level) and TWA (8-hour statistical weight average) - to provide specific guidance for workers' health and safety. In case of entering a confined space, such as reaction tanks, storage tanks or containers, sewers or other underground pipelines, underground facilities, closed agricultural granaries, railway tank cars, shipping cargo holds, tunnels and other workplaces, the personnel must be tested before entering, and the testing must be carried out outside the confined space. In this case, a multi gas detector with a built-in sampling pump must be selected. Because the gas distribution and types in different parts (upper, middle and lower) of the confined space are very different. For example, in general, the proportion of combustible gases is relatively light, and most of them are distributed in the upper part of the confined space; The specific gravity of carbon monoxide is similar to that of air, which is generally distributed in the middle of the confined space; Heavier gases such as hydrogen sulfide exist in the lower part of the confined space (as shown in the figure). At the same time, oxygen concentration is also one of the types that must be detected. In addition, if considering the possible volatilization and leakage of organic substances in the tank, a detector that can detect organic gases is also required. Therefore, a complete closed space gas detector should have a built-in pumping function - so that it can be non-contact and divisional detection; It has multi gas detection function to detect dangerous gases with different spatial distribution, including inorganic gases and organic gases; With oxygen detection function - to prevent hypoxia or oxygen enrichment; Portable instrument with small volume and no impact on workers' work. Only in this way can the absolute safety of workers entering the confined space be ensured. In addition, after entering the confined space, the gas composition shall be continuously detected to avoid the concentration change of volatile organic compounds or other toxic and harmful gases caused by personnel entry, sudden leakage, temperature change, etc. If it is used for emergency, leak detection and patrol inspection according to the plan results, the instrument with pump suction, short response time, high sensitivity and resolution shall be used, so that it is easy to judge the orientation of the leakage point. It is very convenient to use instruments with the functions of data recording, statistical calculation and computer connection when carrying out industrial hygiene inspection and health investigation. At present, with the development of manufacturing technology, portable multi gas (composite) detector is also a new choice for us. Since this detector can be equipped with multiple gas (inorganic/organic) detection sensors required on one host, it has the characteristics of small volume, light weight, fast response and multi gas concentration display at the same time. More importantly, the price of the pump suction compound gas detector is cheaper than that of multiple single diffusion gas detectors, and it is more convenient to use. It should be noted that when selecting this kind of detector, it is better to select the instrument with the function of switching each sensor separately to prevent the damage of one sensor from affecting the use of other sensors. At the same time, in order to avoid blocking the suction pump due to water inflow, it is safer to select the instrument with intelligent pump design with pump stop alarm

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