The Sulphur hexafluoride (SF6) is colourless, non-flammable, non-toxic, heavy gas, which is 6 times heavier than air.
The molecular weight and specific weight are 5 times those of air. It was discovered by Henri Moissan during a study of the fluorine features conducted in the nineteenth century.
The quality of sulphur hexafluoride does not change over time. Now, the SF6 gas is mainly used in electrical equipment above 35 kV due to its rapid recombination (reverse ionization process) after decomposition.
Physical-Chemical Properties of SF6
The SF6 gas is a highly inert substance that does not communicate with acids, alkalis, oxidizing agents, and reducing agents.
However, if the temperature exceeds 1,100° С, the compound decomposes releasing poisonous gas, which has a rather pungent and peculiar smell. The SF6 gas is not suitable for inhalation; therefore, when it accumulates in the room, there is a high probability of an oxygen deficiency. According to GOST 12.1.007-76, the SF6 gas is assigned to the 4th level of threat (low hazard). The maximum permissible concentration (MPC) of sulphur hexafluoride in the atmosphere of industrial premises is 5,000 mg/m3. The MPC in the atmosphere is 0.001 mg/m3.
Good dielectric stability of the SF6 gas guarantees a significant degree of insulation at small volumes and spaces, which makes it possible to minimize the weight and dimensions of electrical equipment.
The leakage of the SF6 gas makes problems not only due to failures of electrical equipment. The presence of this compound in the air is a danger to workers and maintenance personnel. SF6 is a toxic substance whose decomposition products can cause severe poisoning and significant harm to the environment. There is also an economic aspect — the SF6 gas is quite expensive, so installing an SF6 leak detector is much easier and more profitable than deal with the consequences.
The rules for the technical operation of power plants and networks in Russia provide for the installation of SF6 gas detectors signalling that the MPC is exceeded in rooms with gas insulated switchgears having an SF6 component. These devices shall trigger the supply and exhaust ventilation, as well.
You can measure the concentration of SF6 in a room using various types of equipment manufactured by the “INKRAM” LLC Research and Production Company”: