I. Types of gases used in laboratories

Common laboratory gases are high purity gas used in precision instruments, experimental gas used in chemical reaction experiments (chlorine gas) and auxiliary experimental gas, compressed air, etc. High PURITY GASES USED IN PRECISION instruments such as GAS CHROMATOGRAPHY, mass spectrometry, ATOMIC ABSORPTION and ICP mainly include NON-pure gases (nitrogen and carbon dioxide), inert gases (helium and argon), flammable gases (hydrogen and acetylene), combustion-supporting gases (OXYGEN) and so on.

The gas used in the laboratory is mainly provided by gas cylinders, and some gases can be provided by gas generators. Common external color distinction and logo of cylinders: oxygen cylinder (sky blue and black characters), HYDROGEN cylinder (dark green and red characters), nitrogen cylinder (black and yellow characters), compressed air bottle (black and white characters), acetylene bottle (white and red characters), carbon dioxide bottle (green and white and black characters), argon bottle (gray and green characters), helium bottle (brown).

Two, laboratory gas supply mode

Laboratory gas supply system can be divided into decentralized gas supply and centralized gas supply according to its supply mode.

(1) Decentralized gas supply is to place the gas cylinder or gas generator in each instrument analysis room, close to the gas point of the instrument, easy to use, gas consumption saving, less investment; However, because the gas cylinder is close to the experimentals, the safety is not good, so the explosion-proof gas cylinder cabinet is generally required, and the alarm function and exhaust function are required. The alarm is divided into combustible gas alarm and non-combustible gas alarm. Gas cylinder cabinets shall be equipped with gas cylinder safety warning signs and gas cylinder safety fixing devices.

(2) Centralized gas supply means that all kinds of gas cylinders needed by various experimental analysis instruments are placed in independent gas cylinders outside the laboratory for centralized management. All kinds of gases are transported from gas cylinders to different experimental instruments in each laboratory in the form of pipelines according to the gas consumption requirements of different experimental instruments. The whole system includes the gas source collection pressure control part (busbar), the gas transmission line part (EP grade stainless steel pipe), the secondary pressure regulating split part (function column) and the terminal part (joint and stop valve) connected with the instrument. The system has excellent air tightness, high cleanliness, durability and safety and reliability, can satisfy the experimental apparatus for all kinds of gas uninterrupted continuous use requirements, and in the process of using instruments working conditions according to the experiment on the whole or partial pressure, flow rate of gas full range adjustment to meet the requirements of different experimental conditions.

Centralized gas supply can realize centralized gas source management, far away from the laboratory, to ensure the safety of laboratory personnel; But the gas supply pipeline is long, leading to waste of gas, open or close the gas source to the gas cylinder, not easy to use.

Iii. Safety specifications for gas cylinders and gas cylinders

(1) The gas cylinder should be dedicated to the special bottle, and other kinds of gas can not be modified at will.

(2) The gas cylinder room is strictly forbidden to be near the fire source, heat source and corrosive environment.

(3) Explosion-proof switches and lamps are not allowed to be used in the gas cylinder room, and open flames are not allowed to be used around it.

(4) The cylinder chamber should have ventilation equipment to keep cool, and the vent hole should be left on the top of the cylinder chamber to prevent the accumulation of hydrogen.

(5) The empty bottle and the solid bottle shall be placed in partitions. Cylinder chamber Flammable and explosive cylinders should be isolated from combustion-supporting cylinders.

(6) cylinder valve, pipe screw and pressure reducing valve and other accessories are complete, no leakage, sliding wire, loose hands and other dangerous situations, all kinds of barometer generally not mixed.

(7) The gas cylinder must be placed upright during storage and use. When the working place is not fixed and moves frequently, it should be fixed on the special trolley to prevent dumping. It is forbidden to lie down and use it.

(8) The gas cylinder is strictly forbidden to be near the fire source, heat source and electrical equipment, and the distance from the open fire is not less than 10m. When the oxygen cylinder and acetylene cylinder are used at the same time, they cannot be put together.

(9) After use, empty bottles should be moved to the storage area of empty bottles, and the label of empty bottles should be added. It is forbidden to store empty bottles with solid bottles.

(10) The gas in the cylinder must not be exhausted, and a certain residual pressure must be maintained.

(11) Gas cylinders shall be inspected regularly, not exceeding the use of oxygen cylinders and acetylene cylinders. The inspection cycle of liquefied petroleum gas cylinders is 3 years, and that of argon and nitrogen cylinders is 5 years.

(12) The cylinders shall be placed in the cylinder storage room outside the subject building. For the gas with daily gas volume less than one bottle, a gas cylinder of this gas can be prevented in the laboratory, but the gas cylinder should have safety protection facilities.

(13) The hydrogen and nitrogen gas cylinder storage rooms should be ventilated with no less than three air changes per hour.

Iv. Code for gas pipeline design

(1) Hydrogen, oxygen and gas pipelines and branches of gas pipelines introduced into the laboratory should be clearly applied. When there are hydrogen, oxygen and gas pipelines laid in the pipeline well and the technical layer of the pipeline, ventilation measures should be taken to change air 1-3 times /h.

(2) For the universal laboratory designed according to the standard unit combination, all kinds of gas pipelines should also be designed according to the standard unit combination.

(3) The gas pipeline passing through the wall or floor of the laboratory should be laid in the embedded sleeve, and the pipe segment in the sleeve should not be welded. Non - combustible material should be used to close the pipe and casing.

(4) The end and the highest point of the hydrogen and oxygen pipelines should be equipped with empty pipes. The empty discharge pipe should be 2m above the top of the layer and located in the lightning protection area. A sampling point and a purging port shall also be provided on the hydrogen pipeline. The position of the empty pipe, sampling port and purging port shall meet the requirements of gas purging and replacement in the pipeline.

(5) Hydrogen and oxygen pipelines should have grounding devices to guide and remove static electricity. The grounding and bonding measures of gas pipelines with grounding requirements shall be carried out according to the current relevant national regulations.

(6) Pipeline laying requirements

1) The pipe conveying dry gas should be installed horizontally, and the pipe conveying wet gas should have a slope of not less than 0.3%, and the slope direction condensing liquid collector.

2) The oxygen pipeline and other gas pipelines can be laid on the same shelf, and the distance between them should not be less than 0.25m. The oxygen pipeline should be above other gas pipelines except the oxygen pipeline.

3) When the hydrogen pipeline is laid parallel to the combustible gas pipeline, the spacing should not be less than 0.50m; When laying across, the spacing should not be less than 0.25m. When layering, the hydrogen pipe should be located above. Indoor hydrogen pipe should not be laid in the trench or directly buried. Do not cross a room that is not suitable for hydrogen gas.

4) The gas pipeline shall not be laid on the same shelf with the cable and the line to the store.

(7) Seamless steel pipe should be used for gas pipelines. Stainless steel pipe, copper pipe or seamless steel pipe should be used for gas pipeline with gas purity greater than or equal to 99.99%.

(8) Metal pipes should be used for the connecting section of pipes and equipment. If non-metallic hoses are used, PTFE or PVC pipes should be used instead of latex pipes.

(9) Material of valve and accessories: for hydrogen and gas pipelines shall not use copper material, other gas pipelines can use copper, carbon steel and malleable cast iron and other materials.