How To Choose A Gas Detector

Gas detector is widely used in petrochemical, environmental protection, gas, coal and other industries, for different kinds of safety production occasions and testing requirements, the selection of appropriate gas detector for each person engaged in safety and health work must be very important.

Confirm the type and concentration range of the gas to be detected

Each production sector encounters a different type of gas. Consider all possible scenarios when selecting a gas detector. For example, in the mining environment of coal mine, methane and alkanes with less toxicity are in the majority, so the choice of combustible gas detector is undoubtedly the most appropriate. This is not only because the principle of combustible gas detector is simple and widely used, but also because it is convenient for maintenance and calibration. If there are toxic gases such as carbon monoxide and hydrogen sulfide, it is necessary to choose a gas detector that can detect combustible gas, carbon monoxide, hydrogen sulfide and oxygen at the same time to ensure the safety of workers. If more organic toxic and harmful gas, considering that it may cause a lower concentration of poisoning personnel, such as aromatic hydrocarbons, halogenated hydrocarbons, ammonia (amine), ether, alcohol, fat, etc., you should choose the PID photoionization detector, and never use the combustible gas detector to deal with, this may lead to casualties. If the types of gas cover the above types of gas, the choice of a composite gas detector may achieve a multiplier effect.

2 determine the place of use

Different types of gas detectors are selected for different industrial environments.

(1) stationary gas detector

This is used more frequently in industrial installations and production processes. It can be installed at specific test points to detect specific gas leaks. The stationary detector is generally divided into two types. The detection probe composed of sensor and transmitter is installed at the test site, while the secondary instrument composed of circuit, power supply and display alarm device is installed in a safe place for easy monitoring. The stationary gas detector is more suitable for the continuous and long time stability required by the test. They also need to be selected according to the type and concentration of the gas in the field, and be careful to install them in the location where certain gases are most likely to leak, such as the most effective height for sensor installation based on the specific gravity of the gas.

(2) portable gas detector

Because the portable instrument is easy to operate and compact in size, it can be carried to different parts of production. The detector of electrochemical sensor is powered by alkaline battery, which can be continuously used for 1,000 hours. The new type of combustible gas detector, PID photoionization detector and composite detector use rechargeable batteries (some have adopted the non-memory nickel hydrogen or lithium ion batteries, so that they can generally continue to work for nearly 12 hours, so as this kind of instruments in various factories and health sector applications are more and more widely.

If this kind of instrument is used as an alarm in an open place, such as an open workshop, it can be used to wear the diffusion gas detector, because it can continuously, real-time, accurate display of the concentration of toxic and harmful gases in the field. The new instruments also come with vibration alarm accessories -- to avoid audible alarms in noisy environments -- and computer chips to record spikes, STEL (15-minute bursts) and TWA (8-hour weights) -- to provide specific guidance for worker health and safety.

If you are entering a confined space, such as reaction tanks, storage tanks or containers, sewers or other underground pipelines, underground facilities, agricultural closed grain silos, railway tank trucks, ship cargo holds, tunnels, etc., choose a multi-gas detector with a built-in sampling pump. Because the gas distribution and gas types in different parts of the confined space are very different.

For example: generally speaking, the proportion of flammable and explosive gas is relatively light, and most of them are distributed in the upper part of the confined space; Carbon monoxide has the same density as air and is generally distributed in the middle of confined Spaces. Heavier gases, such as hydrogen sulphide, are found in the lower part of the confined space. At the same time, oxygen concentration is one of the types that must be detected. In addition, a detector that can detect organic gases is also needed if the evaporation and leakage of toxic organic gases are taken into account. Therefore, a complete closed space gas detector should be equipped with a built-in pump suction function -- so that it can be non-contact, partial detection; Multi-gas detector -- to detect dangerous gases with different spatial distribution, including inorganic gas and organic gas; Oxygen detector -- prevent hypoxia or rich oxygen. Only in this way can the absolute safety of workers entering the confined space be guaranteed. In addition, after entering the confined space, the gas composition shall be continuously tested to avoid the concentration change of volatile organic compounds or other toxic and harmful gases caused by personnel entering, sudden leakage, temperature and other changes.

If used for emergency accident, leak detection and patrol, the pump type, short response time, sensitivity and high resolution instruments should be used, so that it is easy to determine the location of the leak point.

In the case of industrial hygiene testing and health surveys instruments with data recording and statistical calculations and functions such as linking computers are very convenient to be used.

At present, with the development of manufacturing technology, portable multi-gas detector is also a new option for us. Because the detector can be equipped with the required multiple gas (inorganic/organic) detection sensors on a single host, it has the characteristics of small size, light weight, and multi-gas concentration display. What's more, the price of the pump type compound gas detector is lower than that of multiple single diffused gas detectors, and it is more convenient to use. It is important to note that when choosing this type of detector, it is better to choose an instrument that has the function of turning on and off each sensor separately, so as to prevent the damage of one sensor from affecting the use of other sensors. At the same time, in order to avoid water due to the occurrence of blockage, the choice of intelligent pump design with stop pump alarm instrument is also safer.

Current mistakes in choosing the detector of toxic and harmful gas:

In China, due to historical and cognitive reasons, there are still many problems in the selection of various detectors, which are embodied in the following aspects:

A. the detection of combustible gas is more important than that of toxic gas.

B. the detection of gases that may cause acute poisoning is more important than that of gases that may cause chronic poisoning.

As a result of many combustible gas leakage caused by the blood of the explosion accident lessons, so that people on the combustible gas detection is very important, can say, any refinery, chemical plant, the vast majority of dangerous occasions to choose the gas detector is combustible gas detector. But gas detectors alone are not enough to truly protect workers' safety and health. What is undeniable is that most volatile hazardous gas is flammable and explosive gas, however, the catalytic combustion type easily combustible gas detector (LEL) is not for all the combustible gas detection is the best choice, because they can detect the lower limit of combustible gas other than the methane concentration is far higher than the allowable concentration.

For example: for benzene, ammonia and other dangerous toxic gas, the simple use of flammable and explosive gas detector is a very dangerous practice. For example, benzene has a lower explosive limit of 1.2 percent, and its calibration coefficient on the combustible gas detector is 2.51, which means that the concentration of benzene on a combustible gas detector calibrated with methane is only 40 percent of its actual concentration! ! Thus, the minimum alarming concentration of benzene that can be detected with a combustible gas detector is 10% LEL, which is nearly 600 times higher than the allowable concentration of benzene! ! . Similarly, the alarm level for ammonia with a combustible gas detector is about 1,000 times higher than the allowable level. Therefore, it is safer and more reliable to choose specific toxic gas detector than combustible gas detector.

In addition, we for gas can cause acute poisoning, such as hydrogen sulfide, hydrogen cyanide acid detection more attention, but for gas can cause chronic poisoning, such as aromatic hydrocarbons, alcohols and other test not enough, in fact, the latter for worker health and safety hazards have no worse than can cause acute poisoning gas! In addition to cognitive reasons, the lack of gas detectors capable of detecting lower concentrations in the previous market is also an important reason.

With the development of science and technology and the improvement of people's health awareness, people are no longer satisfied with "coming to work happily and going home safely", but pursue higher quality of life and living conditions. People are not only concerned about today's work, more concerned about tomorrow -- after retirement life. Therefore, in the work of industrial hygiene and industrial safety, new concepts and new ideas should be introduced constantly in order to avoid future tragedies. And to avoid the occurrence of future tragedies, all these need to be constantly improved and improved through the enactment of laws and the improvement of people's quality.

The following problems should be paid attention to when using the gas detector:

Pay attention to regular calibration and testing

Poisonous and harmful gas detector with other analysis of the testing instrument, are evaluated using the method of relatively measured: with a zero and a standard concentration of gas to calibration of instruments, standard curve of stored in the instrument, measurement, the instrument will generate the electrical signals to gas concentration measurement signals compared with standard concentration, to calculate accurately the gas density. Therefore, it is necessary to zero the instrument at any time and to calibrate the instrument regularly to ensure the accuracy of instrument measurement. It should be noted that many gas detectors can be replaced with detection sensors, but this does not mean that a detector can be equipped with different detector probes at any time. Whenever the probe is replaced, the instrument must be recalibrated in addition to a certain sensor activation time. In addition, it is recommended to test the response of standard gas before the use of various instruments to ensure the accuracy and effectiveness of the instruments.

Pay attention to the detection interference between different sensors

In general, each sensor corresponds to a specific detection gas, but none of the sensors is specific. Therefore, when choosing a gas sensor, it is necessary to know the detection interference of other gases to the sensor as far as possible, so as to ensure its accurate detection of specific gases.

Pay attention to the life of all kinds of sensors

All kinds of gas sensors have a certain service life, that is, life. Generally speaking, in portable instruments, the gas sensor has a long life, which can be used for about three years. The lifetime of the photoionization detector is four years or more; The lifetime of electrochemical specific gas sensors is relatively short, generally one to two years; The oxygen sensor has the shortest life of about a year (the life of the electrochemical sensor depends on the drying of the electrolyte in it, so if you don't use it for a long time, sealing it in a lower temperature can extend its service life). Because of the relatively large size of the stationary instrument, the sensor has a longer life. Therefore, as far as possible in the effective period of the sensor, once the failure, timely replacement.

(4) pay attention to the concentration of the test instrument measurement range

Each kind of poisonous and harmful gas detector has its fixed detection range. Only when the measurement is completed within the measuring range can the instrument be accurately measured. And measuring beyond the range for too long can cause permanent damage to the sensor.

Combustible gas detectors, for example, can completely burn down their sensors if accidentally used in an environment that exceeds 100 percent LEL. Toxic gas detectors, working for a long time in a high concentration of use will also cause damage. Therefore, if the fixed instrument sends out the over-limit signal, the measuring circuit should be closed immediately to ensure the safety of the sensor. In a word, poisonous and harmful gas detector is a powerful tool to ensure industrial safety and workers' health. We should choose the appropriate gas detector according to the specific environment and the required functions. At present, we can choose from a variety of instruments including stationary/portable, diffused/pumped, single gas/multiple gas, inorganic gas/organic gas and so on. Only by choosing the right gas detection instrument can we achieve twice the result with half the effort and prevent it from happening.