Portable combustible gas alarm detector
Note: Due to the large number of configurations, the price does not represent the real price, and the product description is only used for display and description, which may be different from the real object. Please contact the manufacturer directly for the accurate price and product parameters.
1、 Definition of limited space
Limited space refers to the space that is closed or partially closed, with narrow inlet and outlet, is not designed as a fixed workplace, has poor natural ventilation, and is easy to cause the accumulation of toxic, harmful, flammable and explosive substances or insufficient oxygen content. Confined space operation refers to the operation activities carried out by operators when they enter the confined space.
The limited space is divided into three categories:
Class I: closed equipment such as cabin, storage tank, vehicle tank, reactor, pressure vessel, pipeline, flue, boiler, etc.
Class II: underground confined space, such as underground pipelines, basements, underground warehouses, underground projects, waste wells, cellars, sewage pools, biogas tanks, septic tanks, sewers, etc.
Class III: limited space on the ground, such as storage room, fermentation tank, garbage station, cold storage, granary, etc.
2、 Common gas in confined space
The main hazard factors of the confined space are shown in the figure below. It can be seen that most hazards in the confined space are concentrated in gas. Before entering the operation, gas concentration detection is required to ensure safety.
1. Toxic and harmful gases
The common toxic and harmful gases in the confined space include hydrogen sulfide, carbon monoxide, ammonia, phosphine, organic volatile gas, etc. For example, due to the fermentation and decomposition of microorganisms, hydrogen sulfide will be produced and accumulated in limited spaces such as sewers, septic tanks and sewage tanks.
Ammonia is used as refrigerant in cold storage, phosphine is used as fumigation gas in granary, and acetone, toluene and other organic gases are often found in the reaction kettle of pharmaceutical and chemical industry.
2. Anoxic asphyxia (oxygen)
Oxygen deficiency in confined space is mainly caused by two reasons:
First, oxygen consumption is caused by biological respiration or material oxidation;
Second, simple asphyxiant gases such as carbon dioxide, nitrogen and methane occupy oxygen in the confined space, leading to hypoxia.
The normal oxygen concentration is between 19.5% VOL and 23.5% VOL, and below 19.5% VOL will be harmful to people.
3. Flammable and explosive gas
Common flammable and explosive gases in confined space include methane, hydrogen, etc. Once the explosion limit is reached, explosion may occur in case of ignition source.
The lower explosive limit LEL is used as the unit for the detection of combustible gas, which is generally dangerous if it is higher than 25% LEL.
3、 Key points of purchasing gas detector in confined space
1. Gas and sensor selection
Due to different physical and chemical properties of different gases, sensors with different principles are generally used for selection. In general, the common gas choices are as follows:
Characteristics of gas detection principle
Oxygen electrochemistry
Single detection
Normally 19.5% vol and 23% vol are alarm values
hydrogen sulfide
carbon monoxide
ammonia
For single electrochemical detection, several sensors are required for several gases
Through measurement of catalytic combustion of combustible gas, one sensor can detect the content of most combustible gases
Toluene and other PID photoions are used to detect the total content of various volatile organic gases
2. Internal pump and external pump
As the confined space is a closed environment, it is necessary to configure a gas extraction pump for sampling and detection. At present, there are two kinds of common pump suction gas detectors on the market: built-in pump and external pump.
Internal pump External pump
Distinguish that the pump is integrated in the gas detector and cannot be taken out. The gas detector is a diffusion type detector, which is used in combination with the air extraction pump
Advantages Small size, easy to carry
The external pump is powered separately, so the suction is greater and the response time is shorter
Used in combination and can be worn as a diffusion instrument for patrol inspection
Disadvantages
Volume limits power, suction and response time are inferior to external pump
It can not be used for diffusion type use and needs to be used in combination. Its volume and convenience are inferior to those of built-in pump products
Before entering the confined space for operation, sampling inspection is required. The operator can enter the operation only after the detection is correct. In order to prevent the leakage of toxic and harmful gas caused by various factors such as misoperation during operation, it is recommended that the operator carry a gas detector for real-time monitoring. Therefore, the external pump products that can be used as diffusion type are more suitable.
3. Explosion proof and protection grade
Explosion proof equipment refers to electrical equipment that will not cause ignition of the surrounding explosive environment under specified conditions. Different explosion-proof levels can be applied to different places.
When detecting the confined space with the risk of flammable and explosive gas leakage, the gas detector shall be explosion-proof equipment, and the explosion-proof grade shall not be lower than EXib Ⅱ CT3.
IP protection grade is to grade electrical appliances according to their characteristics of dust and moisture prevention. IP protection grade is composed of two numbers. The first number represents the grade of electrical appliances for dust prevention and prevention of foreign intrusion, and the second number represents the degree of airtightness of electrical appliances against moisture and water immersion. The larger the number, the higher the protection grade.
For the gas detector in confined space, considering that the user is not fixed and there are often risks such as falling, in order to ensure the durability and long-term stability of the instrument, it is recommended to select a gas detector with IP level no less than IP55.
Portable combustible gas alarm detector, portable gas detector, gas detector, gas alarm, gas detector
performance parameter
Industry classification: test equipment
Delivery form: complete machine
Performance parameters: detection gas: combustible gas
Application scenario: petrochemical industry