With the development of industrialization, toxic and harmful gases have become a dangerous source that we must not face in production and life. Including petrochemical enterprises, chemical industry, environmental emergency accidents, terrorist attacks, dangerous goods storage and transportation, landfills, urban sewage treatment, various underground pipelines, etc., we may be threatened by dangerous gases without knowing it. .

The people-oriented concept requires us to care about our health and safety whenever and wherever possible. All kinds of leaks and explosions continue to cause social crises and the destruction of public property. However, the detection of various gases is always a complex task, and it is more difficult to choose a suitable gas monitor. Based on ISC (Industrial Scientific)'s decades of experience in gas detection around the world (including China), we have compiled this selection guide to give readers an idea of ​​the various sensing technologies used for gas monitoring. The introduction of different instrument types will help the user to choose the most suitable gas monitor.

At present, the more common types of gas sensors for on-site detection include: electrochemical sensors, infrared sensors, catalytic combustion sensors, photoionization detectors, solid state sensors, semiconductor sensors, and the like.

All gas sensor technologies rely on the physical or chemical properties of the gas itself to convert it into electrical signals that can be processed, amplified, and transmitted by electronic circuits. Therefore, as a relative detection technique, all gas monitoring instruments must be calibrated regularly with a standard concentration of gas. At the same time, although these sensors are more and more sophisticated in manufacturing, they are unable to meet the performance specifications of analytical instruments due to the limitations of their own principles. They are also difficult to use as gas quantitative analyzers. Their best gas concentration readings are used. Do not mention the safety of your location. In any case, the relevant gas concentrations provided by such sensors will play an important role in safety, environmental protection and public health. As an on-site safety instrument, this type of gas monitor detects the concentration value in real time in the presence of harmful gases and, when it exceeds a certain limit, immediately issues an alarm to guide people to act. In order to adapt to different purposes, such instruments generally adopt a portable or fixed type, which has the characteristics of simple operation, convenient maintenance and reasonable price.

To date, there are no gas sensors that are specific to a particular gas. Analytical instruments are still used if higher selectivity is required. There are many analytical instruments currently used for gas monitoring, such as Fourier transform infrared, gas chromatography, and mass spectrometry. These instruments provide the most accurate and highly selective gas concentration data. However, they are generally expensive, and are not suitable for on-site gas monitoring due to high maintenance costs, long response time, large volume, cumbersome operation, and inability to reflect on-site concentration immediately. As laboratory gas monitoring instruments, they often serve as the final judge.

The detection of hazardous gases is a systematic management project. We need to determine the gases to be detected on the basis of understanding the occurrence, development and existence of various harmful gases, and select suitable detectors to ensure the safety of various personnel and industrial and mining enterprises.

Confined spaces (including reaction tanks, oil tanks, poorly ventilated workshops, underground pipelines, underground drains, underground storage tanks, cabins, etc.) are important sites for hazardous gas detection. Anyone who is about to enter and has entered the confined space to work must constantly monitor the concentration of toxic and harmful gases inside the workplace, which may have existed before the workers entered the confined space, or because of them The activities in between are formed. The vast majority of accidents occur in the absence of workers' detection of hazardous gases before and during their work in confined spaces.

Petrochemicals and other chemical enterprises are places where toxic and harmful gases are more common. From the raw materials, production processes, product storage and transportation, etc., the occurrence and leakage of flammable and explosive gases and toxic and harmful gases occur.

With the wide application of industrial products, the handling of environmental emergency accidents is increasingly placed in front of governments at all levels and accident handling teams. How to monitor toxic and harmful gases before the accident, track toxic and harmful gases during the accident, and detect the environment and personnel residues after the accident. This is also the most basic of gas monitoring instruments in environmental emergency accidents. application.

After the 9/11 terrorist attacks in the United States, people’s methods of committing terrorists became ruthless, and biochemical threats also caused great panic around the world. The Japanese subway sarin gas is a practical example of this threat. At that time, due to the lack of necessary gas monitoring equipment, the number of deaths caused by personnel panic was much higher than the number of deaths caused by gas poisoning. Therefore, the necessary appropriate gas detection technology has penetrated into every aspect of our lives.

Detection principle and classification of toxic and harmful gases

For all kinds of different production occasions and testing requirements, the choice of a suitable gas detector is a must for every person engaged in safety and health work. Here we will introduce some specific situations for your reference.

Confirm the type and concentration range of the gas to be tested:

The type of gas encountered in each production department is different. All possible situations should be considered when selecting a gas detector. If methane and other less toxic alkanes are the most common, the LEL detector is the most suitable. This is not only because the LEL detector has a simple principle and a wide application, but it also has the characteristics of convenient maintenance and calibration. If there are toxic gases such as carbon monoxide and hydrogen sulfide, it is necessary to select a specific gas detector to ensure the safety of workers. If there are more organic toxic and harmful gases, considering the lower concentration of people who may cause poisoning, such as aromatic hydrocarbons, halogenated hydrocarbons, ammonia (amines), ethers, alcohols, fats, etc., you should choose the light introduced in the previous chapter. Ionize the detector and never use the LEL detector, as this can result in personal injury or death.

Determine the use of the occasion:

The type of gas detector is different depending on the industrial environment.

A) Fixed gas detection protocol:

This is the use of more detectors on industrial plants and in production processes. It can be installed at a specific inspection point to detect specific gas leaks. The fixed detector is generally two-piece type. The detection head consisting of sensor and transmission is installed in the inspection site. The secondary instrument consisting of circuit, power supply and display alarm device is installed in a safe place for easy monitoring. Its detection principle is the same as that described in the previous section, but it is more suitable in the process and technology for the continuous and long-term stability required for fixed detection. They are also selected according to the type and concentration of the gas on site, and care should be taken to install them where the specific gas is most likely to leak, such as selecting the most effective height for sensor installation based on the specific gravity of the gas.

B) Portable gas detector:

Because portable instruments are easy to operate and compact, they can be carried to different production sites. The electrochemical detectors are 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 The use of non-memory hydrogen or helium-ion batteries makes them generally work for nearly 12 hours in a row, so the use of such instruments in various factories and health departments is becoming more widespread.

If it is open, such as an open work shop using such instruments as a safety alarm, you can use a diffused gas detector that you wear, because it can display the concentration of toxic and harmful gases in the field continuously, in real time and accurately. Some of these new instruments are also equipped with vibration alarm accessories to avoid audible alarms in noisy environments, and computer chips are installed to record peaks, STEL (15-minute short-term exposure levels) and TWA (8-hour statistical weight average) ) Provide specific guidance for worker health and safety.

If it is entering a confined space, such as a reaction tank, storage tank or container, sewer or other underground pipeline, underground facilities, agricultural closed granary, railway tanker, shipping cargo bay, tunnel, etc., it must be tested before personnel enters. And to test outside the confined space. In this case, you must select a multi-gas detector with a built-in sampling pump. Because the gas distribution and gas type of different parts (upper, middle and lower) in the confined space are very different. For example, in general, the proportion of flammable gases is relatively light. Most of them are distributed in a confined space. The carbon monoxide and air have a similar proportion. They are generally distributed in a confined space. The heavier gases such as hydrogen sulfide are trapped in the air. The lower part of the space (as shown). At the same time, the oxygen concentration is also one of the types that must be detected. In addition, a detector that can detect organic gases is also needed if one considers the volatilization and leakage of possible organic matter in the tank. Therefore, a complete closed space gas detector should be a built-in pumping function to enable non-contact, sub-site detection with multiple gas detection functions to detect different spatial distribution of hazardous gases, including inorganic gases and organic gases with oxygen detection. A portable instrument that prevents hypoxia or rich volume and does not affect workers' work. Only in this way can the absolute safety of the personnel entering the confined space be guaranteed.

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

If used for emergency, leak detection and inspection, pumping, short response time, high sensitivity and high resolution instruments should be used to make it easy to determine the location of the leak. In the case of industrial hygiene testing and health surveys, it is very convenient to use instruments with data logging and statistical calculations and functions that can be connected to a computer.

At present, with the development of manufacturing technology, portable multi-gas (composite) detectors are also a new choice for us. Since the detector can be equipped with a plurality of gas (inorganic/organic) detection sensors required on a single host, it has the characteristics of small size, light weight, correspondingly fast, and simultaneous multi-gas concentration display. More importantly, the pump-type hybrid gas detector is cheaper than multiple single-diffusion gas detectors and is more convenient to use. It should be noted that when selecting such detectors, it is best to select instruments with individual sensor functions to individually switch to prevent other sensor usage from being affected by one sensor. At the same time, in order to avoid the occurrence of blockage of the getter pump due to water ingress, it is safer to select an intelligent pump design with a pump stop alarm.

1. Introduction of toxic and harmful gases commonly found in the production process

In the production process, the factors that cause damage to property and human health and life can be roughly divided into three aspects: physical, chemical and biological. Among them, the influence of chemical factors is the most harmful. Toxic and harmful gases are the most common and common part of chemical factors. Therefore, this section focuses on knowledge of toxic and harmful gases.

According to the hazards, we classify toxic and harmful gases into flammable gases and toxic gases. Toxic gases are classified into three categories: irritating gases, asphyxiating gases and acutely poisoned organic gases according to their different mechanisms of action on the human body.

The irritating gases include chlorine gas, phosgene, diphosgene, sulfur dioxide, nitrogen oxides, formaldehyde, ammonia, ozone and the like. The action of irritating gases on the body is characterized by strong irritating effects on the skin and mucous membranes, some of which have strong corrosive effects at the same time. The degree of damage of the irritating gas to the body is related to its solubility in the water and the site of action. In general, water-soluble chemicals, such as chlorine, ammonia, sulfur dioxide, etc., rapidly cause irritation to the eyes and upper respiratory tract, and soon the eye and upper respiratory tract irritation; small water-soluble chemicals such as light Gas, nitrogen dioxide, etc., have a significant effect on the lower respiratory tract and alveoli. The severity of the lesions caused by irritating gases, in addition to the nature of the chemicals themselves, is most closely related to the concentration and timing of the exposure chemicals. Short-term exposure to high concentrations of irritating gases can cause severe acute poisoning, while long-term exposure to low concentrations can cause chronic damage. Acute irritant gas poisoning usually precedes eye and upper respiratory tract irritation, such as conjunctival hyperemia, tearing, salivation, dry throat, cough, chest tightness, etc., and then these symptoms can be alleviated or disappeared, after several hours to three days. After the incubation period, the symptoms suddenly reappear and quickly become worse. In severe cases, chemical bronchopneumonia and pulmonary edema may occur, which may be severe cough, white or pink foam, dyspnea, cyanosis, etc., due to pulmonary edema or complicated acute Respiratory distress and the like lead to disability.

Asphyxiating gases include gases such as carbon monoxide, hydrogen sulfide, hydrogen cyanide, and carbon dioxide. The hypoxia of tissue cells caused by these compounds entering the body varies. After entering the body, carbon monoxide mainly combines with the hemoglobin of red blood cells to form carboxyhemoglobin, so that the red blood cells lose oxygen carrying capacity, so that the tissue cells do not get enough oxygen. After hydrogen cyanide enters the body, cyanide ions directly act on cytochrome oxidase, causing it to lose the ability to transfer electrons. As a result, cells cannot ingest and utilize oxygen, causing intracellular asphyxia. Methane itself has no obvious toxicity to the body, and the hypoxia caused by tissue cells is actually due to the hypoxic asphyxia caused by the decrease of oxygen concentration in the inhaled gas. The role of hydrogen sulfide after entering the body is multifaceted. Hydrogen sulfide binds to ferric iron in oxidized cytochrome oxidase, inhibits the activity of cellular respiratory enzymes, and causes hypoxia hydrogen sulfide in tissue cells to bind to the thiol group of glutathione, inactivating glutathione and aggravating Hypoxia of tissue cells In addition, high concentrations of hydrogen sulfide cause intense parasitic sputum and even sudden death through chemical stimulation of the olfactory nerve, respiratory mucosal nerve, and carotid sinus and aortic body chemoreceptors.

The organic solvent for acute poisoning is n-hexane, dichloromethane, and the like. The above organic volatile compounds, like the above inorganic toxic gases, may also cause harm to the respiratory system and nervous system of the human body, and some may cause cancer, such as benzene. Since organic compounds are mostly flammable substances, most of them have been tested for explosiveness before the detection of organic compounds, but the minimum explosive limit of organic compounds is far greater than the value of its MAC (maximum allowable concentration of space). That is to say, it is necessary and necessary to test the toxicity of organic compounds.

The hazard of flammable gases is mainly caused by the explosion of gas, which causes damage to property and human life. However, flammable gases must have certain conditions for explosion. A certain amount of combustible gas, sufficient oxygen and a source of ignition. The above three conditions are indispensable. The concentration of gas that normally explodes a combustible gas is called the minimum explosion limit and is generally expressed in LEL. Different combustible gases have different LELs. Therefore, the detection of combustible gas generally detects its LEL.

Carbon Cleaning Towel

The woven-in carbon fibers increase the coefficient of friction of our microfiber cloth and leave even stubborn dirt on your car windows no chance.

Carbon Cleaning Towel

Changshu Juhao Clean Textile Co., Ltd. , https://www.juhaoclean.com