PM2.5 detection: teach you how to select a gas detector

　　1) Confirm the type and concentration range of the gas to be detected:

　　The types of gases encountered in each production department are different. When choosing a gas detector, you must take all possible situations into consideration.

　　a. If methane and other less toxic alkanes are the majority, it is undoubtedly the most appropriate to choose an LEL detector. This is not only because the LEL detector has a simple principle and is widely used, but it is also easy to maintain and calibrate.

　　b. If there are toxic gases such as carbon monoxide and hydrogen sulfide, it is necessary to give priority to choosing a specific gas detector to ensure the safety of workers.

　　c. If the gases are mostly organic toxic and harmful gases, considering that the concentrations that may cause poisoning are relatively low, such as aromatic hydrocarbons, halogenated hydrocarbons, ammonia (amines), ethers, alcohols, fats, etc., you should choose the photoionization detector introduced in the previous chapter, and never use the LEL detector to deal with it, because this may cause casualties.

　　If the gas types cover the above categories, choosing a composite gas detector may achieve twice the result with half the effort.

　　2) Determine the use occasion:

　　Different industrial environments require different types of gas detectors.

　　A) Fixed gas detector:

　　This is a detector that is used more frequently in industrial devices and production processes. It can be installed at a specific detection point to detect specific gas leaks. Fixed detectors are generally two-body, with a detection head consisting of a sensor and a transmitter installed as a whole at the detection site, and a secondary instrument consisting of a circuit, a power supply, and a display alarm device installed as a whole in a safe place for easy monitoring. Its detection principle is that 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 the gas on site, and at the same time, they should be installed at the location where the specific gas is most likely to leak, such as choosing the most effective height for sensor installation according to the specific gravity of the gas, etc.

　　B) Portable gas detector:

　　Portable instruments are easy to operate and compact, so they can be carried to different production sites. Electrochemical detectors are powered by alkaline batteries and can be used continuously for 1,000 hours. New LEL detectors, PID and composite instruments use rechargeable batteries (some have adopted memory-free nickel-metal hydride or lithium-ion batteries), which generally allow them to work continuously for nearly 12 hours. Therefore, such instruments are increasingly used in various factories and health departments.

　　If such instruments are used as safety alarms in open places, such as open workshops, wearable diffusion gas detectors can be used because they can continuously, in 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 the sound alarm in a noisy environment, and are equipped with computer chips to record peak values, STEL (15-minute short-term exposure level) and TWA (8-hour statistical weighted average) - to provide specific guidance for worker health and safety.

　　If you are entering a confined space, such as a reaction tank, storage tank or container, sewer or other underground pipeline, underground facilities, agricultural confined granary, railway tank car, ship cargo hold, tunnel and other workplaces, you must conduct a test before entering, and the test must be conducted outside the confined space. At this time, you must choose a multi-gas detector with a built-in sampling pump. Because the gas distribution and gas types in different parts (upper, middle, and lower) of the confined space are very different. For example: the specific gravity of combustible gases in the general sense is lighter, and most of them are distributed in the upper part of the confined space; carbon monoxide and air have similar specific gravity and are generally distributed in the middle of the confined space; and 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 the possible volatilization and leakage of organic matter in the tank are taken into account, a detector that can detect organic gases is also needed. Therefore, a complete confined space gas detector should be a portable instrument with built-in pumping function, so that it can detect non-contact and divided parts; multi-gas detection function, so as to detect dangerous gases distributed in different spaces, including inorganic and organic gases; oxygen detection function, so as to prevent hypoxia or oxygen enrichment; and small size, so as not to affect the work of workers. Only in this way can the absolute safety of workers entering confined spaces be guaranteed.

　　In addition, after entering a confined space, the gas composition therein must be continuously tested to avoid changes in the concentration of volatile organic compounds or other toxic and harmful gases caused by personnel entry, sudden leakage, temperature changes, etc.

　　If used for emergency accidents, leak detection and inspection, a pump-suction instrument with a short response time, high sensitivity and resolution should be used, so that the location of the leak can be easily determined.

　　When conducting industrial hygiene testing and health surveys, instruments with functions such as data recording and statistical calculations and the ability to connect to computers are very convenient to use.