Select Suitable Toxic and Harmful Gas Detectors and Solutions Based on These Two Aspects
1, Confirm the type and concentration range of the gas to be detected
The types of gases encountered by each production department are different. When choosing a gas detector, all possible scenarios should be considered. If methane and other less toxic hydrocarbons are predominant, choosing an LEL detector is undoubtedly more suitable. This is not only because the principle of LEL detector is simple and widely used, but also because it has the characteristics of easy maintenance and calibration. If there are toxic gases such as carbon monoxide and hydrogen sulfide, it is necessary to prioritize the use of a specific gas detector to ensure the safety of workers. If there are more organic toxic and harmful gases, considering their low concentration that may cause poisoning to personnel, such as aromatic hydrocarbons, halogenated hydrocarbons, ammonia (amines), ethers, alcohols, lipids, etc., the photoionization detector introduced in the previous chapter should be chosen instead of using LEL detectors, as this may lead to 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 usage scenario
The selection of gas detectors varies depending on the industrial environment.
1. Fixed gas detector
This is a commonly used detector in industrial equipment and production processes. It can be installed at specific detection points to detect specific gas leaks. Fixed detectors are generally two-piece, with a detection head composed of sensors and transmitters installed as a whole on the detection site, and a secondary instrument composed of circuits, power supplies, and display alarm devices installed as a whole in a safe place for easy monitoring. Its detection principle is as described in the previous section, but it is more suitable for the continuous and long-term stability required for fixed detection in terms of process and technology. They also need to be selected based on the type and concentration of the gas on site, and attention should be paid to installing them in the most likely leak location of specific gases, such as selecting the most effective height for sensor installation based on the specific gravity of the gas, and so on.
2. Portable gas detector
Due to its convenient operation and compact size, the portable instrument can be carried to different production sites. The electrochemical detector is powered by alkaline batteries and can be used continuously for 1000 hours; The new LEL detectors, PID and composite instruments use rechargeable batteries (some have already adopted memory free nickel hydrogen or lithium-ion batteries), which allow them to work continuously for nearly 12 hours. Therefore, as such instruments are increasingly being used in various factories and health departments.
If this type of instrument is used as a safety alarm in an open environment, such as an open workshop, a 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 attachments to avoid audible alarms in noisy environments, and computer chips are installed to record peak values, STEL (15 minute short-term exposure level), and TWA (8-hour statistical weighted average) - providing specific guidance for worker health and safety.
If entering a confined space, such as reaction tanks, storage tanks or containers, sewers or other underground pipelines, underground facilities, agricultural enclosed grain warehouses, railway tankers, shipping cargo holds, tunnels, etc., personnel must undergo testing before entering, and testing must be conducted outside the confined space. At this point, it is necessary to choose a multi gas detector with a built-in sampling pump. Because there are significant differences in gas distribution and types in different parts (upper, middle, and lower) of a confined space. For example, generally speaking, combustible gases have a lighter density and are mostly distributed in the upper part of enclosed spaces; Carbon monoxide has a similar specific gravity to air and is generally distributed in the middle of enclosed spaces; Heavier gases such as hydrogen sulfide exist in the lower part of the enclosed space (as shown in the figure). Meanwhile, oxygen concentration is also one of the types that must be detected.
