1. Laboratory safety
With the development of the economy, my country has increased investment in scientific research in various fields, and the corresponding laboratories have developed rapidly. However, in recent years, laboratory safety accidents have also occurred frequently; there are many reasons for laboratory safety accidents. Laboratory gas Improper storage and use is one of them. A wide variety of gases need to be used in the analysis of laboratory instruments. These gases are an indispensable part of the operation of the laboratory. We need to fully understand some common or the gases we will use. , And then use it according to its characteristics to reduce the occurrence of safety accidents.
2. Laboratory gas
General laboratories may use hydrogen, acetylene, oxygen, methane, nitrogen, carbon dioxide, argon, compressed air, helium, carbon monoxide, nitrous oxide, hydrogen sulfide, sulfur dioxide and other gases. The following is a brief summary of the safety of each high-pressure gas characteristic:
2.1. Hydrogen: Hydrogen is much lighter than air. When used and stored indoors, it will rise and stay on the roof if it leaks. It will not be easily discharged. It can form explosive mixtures when mixed with air or oxygen. It will explode when exposed to heat or open flames.
2.2. Acetylene: colorless and odorless, lighter than air, mixed with air or oxygen can form an explosive mixture, and it is easy to burn and explode when exposed to open flames, high-temperature objects, static electricity, radioactivity and other ignition sources. It can produce explosive substances with copper, silver, mercury and other compounds. Under certain temperature and pressure conditions, pure acetylene will also directly decompose and explode by itself.
2.3. Oxygen: colorless and odorless, slightly heavier than air, and form explosive mixtures with combustibles (such as hydrogen, acetylene, methane, etc.)
2.4. Methane: colorless, odorless, lighter than air, flammable, and suffocating. It can form explosive mixtures when mixed with air or oxygen, and will explode when exposed to heat or open flames.
2.5. Nitrogen: colorless, odorless, non-flammable, suffocating with high concentration.
2.6. Carbon dioxide: colorless, odorless, non-flammable, suffocating with high concentration.
2.7. Argon: colorless, odorless, non-flammable, suffocating with high concentration.
2.8. Compressed air: colorless and odorless, with combustion-supporting properties.
2.9. Helium: colorless, odorless, non-flammable, suffocating with high concentration.
2.10. Carbon monoxide: colorless, odorless, flammable and explosive gas, toxic, combined with hemoglobin in the blood, causing tissue hypoxia.
2.11 Nitrous oxide: a colorless and sweet gas, supporting combustion.
2.12 Hydrogen sulfide: a colorless and foul-smelling gas, heavier than air, flammable, and highly irritating. It is a strong nerve poison and has a strong stimulating effect on the mucous membrane.
2.13. Sulfur dioxide: a colorless and odorous gas, heavier than air, non-flammable, toxic, and highly irritating.
3. Laboratory gas source form
3.1. The supply method of laboratory gas is as follows:
Laboratory gas sources usually come from high-pressure gas cylinders, gas storage tanks, gas generators, gas compressors, and air distribution network gas.
3.2. Commonly used bottled gases are classified as follows according to the gas source:
Compressed gas: air, oxygen, nitrogen, argon, helium, hydrogen, methane, carbon monoxide, etc.;
Dissolved gas: acetylene;
Liquefied gas: carbon dioxide, nitrous oxide, hydrogen sulfide, ammonia, sulfur dioxide, etc.
3.3. Gas storage tank
Commonly used gas storage tanks are liquid nitrogen and liquid argon.
3.4, generator
Commonly used generators are air generators, nitrogen generators, and hydrogen generators.
3.5, gas compressor
This method is mainly used for air, the general laboratory air consumption is large, and the gas requirement is low, so you can consider setting the corresponding air compressor according to the gas consumption. The air compressor needs to consider the heat dissipation of the equipment and the gas generated Treatment of oil, water and impurities.
3.6. Air separation network gas
Chemical laboratories are usually built in chemical plants, and their plant areas usually have air separation devices. The gas produced by the air separation devices can be used and transported to the laboratory; the main ones include pipe network nitrogen and pipe network air.
3.7. Relatively speaking, high-pressure gas cylinders are more dangerous for the above-mentioned gas supply methods.
4. Decentralized gas supply in the laboratory
4.1. In traditional laboratories, it is often found in the laboratory that there is a high-pressure gas cylinder placed near the instrument for nearby gas supply; the use of nearby gas supply has the following hidden dangers:
(1) Laboratory gases are diverse and complex. According to the characteristics of commonly used gases, these gases basically have potential safety hazards, and are flammable, explosive, toxic, and suffocating. At the same time, high-pressure gas cylinders have high internal gas pressure, Due to the large stock, once the high-pressure part leaks, it may cause a major safety accident in a short period of time.
(2) Some gases will react with each other. If a strong reaction gas such as combustion or explosion leaks at the same time or a series of explosions, it may also cause personal injury, loss of analysis data and economic loss.
(3) The pressure of a general 40L high-pressure gas cylinder is mostly 15Mpa. If the parts in the high-pressure section of the gas cylinder are damaged, it may damage nearby analysts and instruments.
4.2. Analytical instruments commonly used in laboratories, such as chromatography and mass spectrometry, require continuous use of gas during work, and the gas supply is required to be uninterrupted, so as not to affect data analysis and scientific research results; if dispersed gas supply is used, the gas cylinder needs to be used for a long time. At the same time, the number of instruments that cannot be shut off in general laboratories will be relatively large, which will increase the number of scattered gas cylinders, which will cause analysts to frequently replace gas cylinders, increase transportation costs, reduce work efficiency, and occupy limited experiments. Room space.
4.3. Many gases in the laboratory belong to Class A and Class B items strictly controlled by fire protection (such as hydrogen, acetylene, methane, oxygen, etc.). There are strict restrictions on the amount of Class A and Class B items stored in the laboratory. Exceeding the regulations will cause the building to fail to be accepted.
4.4. Comprehensive consideration, the laboratory recommends the use of centralized gas supply, and the gas source station is set as an independent building.
5. Centralized gas supply in the laboratory
5.1. Various gases in the laboratory are centrally placed in independent gas source stations. Combining relevant standard specifications and laboratory gas characteristics, it can be known that the following contents should be considered when constructing gas source stations and centralized gas supply systems:
(1) Independent gas source stations need to be constructed in accordance with national regulations. According to the types of gases in the gas source station, select the corresponding building type, the fire resistance level of the building components, and the corresponding building ground. The flammable and explosive gases need to be constructed accordingly. For building explosion venting calculations, the electrical facilities in the gas source station shall be selected and designed according to the corresponding level.
(2) Under certain conditions, some gases will react with each other and may explode, cause poisoning, etc. Therefore, these gases need to be stored separately when storing gas sources, such as hydrogen, acetylene, methane and other flammable and explosive The gas needs to be stored separately from oxygen, compressed air and other combustion-supporting gases; in addition, flammable and explosive gases should be placed in separate rooms as far as possible to avoid mutual influence and serial explosions.
(3) The gas characteristics of the laboratory determine that the gas cylinders need to be stored in a cool gas source station away from direct sunlight, and at the same time away from fire and heat sources. The temperature of the gas source station should not exceed 30 degrees Celsius, and the gas cylinders should be kept well sealed to avoid leakage and safety accidents.
(4) There are differences in the gas consumption of various gases in the laboratory. The design needs to estimate the gas consumption of various gases within a certain service cycle, so as to determine the storage volume of various gas cylinders, avoid frequent replacement of gas cylinders, and pass Reduce unnecessary storage of gas cylinders, reduce hidden dangers, and reduce gas cylinder rental costs.
(5) The gas supply system is equipped with main gas cylinders and backup gas cylinders. The main and backup gas cylinders can be automatically switched. In addition, a low-pressure alarm is used to monitor the pressure of the gas cylinder. When the pressure of the gas cylinder is lower than a certain value, a low-pressure alarm is issued The alarm signal reminds analysts to replace gas cylinders in time to ensure continuous gas supply.
(6) Laboratory gases are flammable, explosive, toxic, and suffocating. The hidden dangers need to be eliminated according to the type of gas. The following measures can be adopted:
①Suffocating gas needs to monitor the oxygen content of the storage area. The oxygen content gas detector is close to the leak point, and its installation height is 0.3 ~ 0.6m from the ground (or floor).
②The concentration of combustible gas needs to be monitored in the storage area (proportion of the explosion limit). The installation height of the combustible gas detector needs to be determined according to the proportion of gas to air. The installation height of the combustible gas detector that is heavier than air should be determined. 0.3～0.6m away from the ground (or floor). The combustible gas detector, which is lighter than air, is installed at a height of 0.5～2m higher than the release source.
③The concentration of the toxic gas needs to be monitored in the storage area (the percentage of the highest allowable concentration value). The installation height of the toxic gas detector needs to be determined according to the specific gravity of the gas and the air. The detector that detects the toxic gas heavier than the air should be close to The installation height of the leakage point is 0.3～0.6m from the floor (or floor). A detector for detecting toxic gases lighter than air is installed at a height of 0.5～2m higher than the release source.
④Under normal circumstances, the gas storage area of the laboratory needs to maintain natural ventilation to avoid hazards caused by gas accumulation; under abnormal circumstances, when a large amount of gas leaks suddenly and the gas concentration in the gas storage area reaches a certain value, the gas detector will alarm , At the same time, output an alarm signal to the forced exhaust system, and automatically start the forced exhaust fan to discharge the leaked gas to a safe area, so that the gas concentration is reduced to a safe range, thereby eliminating the hazard.
⑤The combustible and combustion-supporting gas cylinders and pipelines need to be electrostatically grounded to prevent static electricity from accumulating, and to avoid electrostatic detonation of combustible gas explosive mixtures. The combustible gas pipeline needs to be installed in the lightning protection area. All lightning protection and anti-static grounding devices are tested regularly, the grounding resistance is tested at least once a year, and the lightning protection devices in explosive hazardous environments are tested every six months.
⑥The flammable gas and toxic gas are equipped with an emergency shut-off valve to link with the gas detector. When the gas detector alarms, the shut-off valve is automatically controlled to cut off the gas source and eliminate the source of release.
⑦An exhaust system is set up for combustible and toxic gases. The exhaust system empties the residual and replaced gas in the gas source area pipeline to the outdoors, and the exhaust pipeline is more than 2m above the roof.
⑧The combustible gas is equipped with a flame arrestor to avoid backfire of the gas.
(7) Set up special gas cylinder management rules and regulations, and conduct management, supervision, processing, and regular inspections by dedicated personnel.
5.2. Air supply
(1) There is usually a certain distance between the centralized gas source station and the building where the gas is used. It is necessary to set up an overhead pipe gallery. When determining the layout and laying method of the pipeline, it is necessary to combine the actual conditions of the gas type, gas source and gas use area. Comprehensive consideration; Among them, flammable and explosive gases should be transported overhead, and the pipeline supports should be non-combustible. Overhead pipelines are not laid on the same support with cables, conductive lines, and high-temperature pipelines.
(2) Copper must not be used in the production of acetylene pipes, because copper acetylene will be formed, and copper acetylene is a detonating agent.
(3) Use automatic welding or other connection methods that effectively prevent gas leakage between the pipelines, and avoid the use of ferrules, flanges, etc.
(4) The gas pipeline does not enter the room where the gas is not used.
(5) The oxygen valve and pipeline are oil-free.