Is Sulfur Hexafluoride Toxic?

Sulfur hexafluoride is an inorganic compound with the chemical formula SF6. It is a colorless, odorless, non-toxic, non-flammable stable gas at room temperature and pressure. Its molecular weight is 146.055. Its density is 6.0886 kg/m3 at 20°C and 0.1 MPa, which is about 5 times the density of air. The molecular structure of sulfur hexafluoride is octahedral, with a small bonding distance and high bonding energy. Therefore, it has high stability. When the temperature does not exceed 180°C, its compatibility with electrical structural materials is similar to that of nitrogen.

Is sulfur hexafluoride toxic? Pure sulfur hexafluoride is an inert gas that decomposes under the action of an electric arc. When the temperature is above 4000K, most of the decomposition products are single atoms of sulfur and fluorine. After the arc is extinguished, most of the decomposition products recombine into stable sulfur hexafluoride molecules. During the recombination process, a very small amount of the decomposition products react with free metal atoms, water and oxygen to form metal fluorides and fluorides of oxygen and sulfur. When sulfur hexafluoride is used in electrical equipment, it can decompose from oxygen and sulfur under fault conditions or normal breaking arcs and produce fluoride and metal fluoride powders.

Experience has shown that even in environments containing very small amounts of decomposition products, workers may experience a pungent or unpleasant odor and significant irritation to the nose, mouth and eyes. This reaction occurs within a few seconds before obvious toxic reactions occur.

When sulfur hexafluoride poisoning occurs, it is usually due to its decomposition by high-voltage arcs in electrical equipment. Therefore, pure sulfur hexafluoride is non-toxic, but we should pay attention to the toxic substances decomposed by sulfur hexafluoride. So, what are the toxic substances decomposed by sulfur hexafluoride gas in electrical appliances?

1. Some toxic substances produced by sulfur hexafluoride gas in electrical appliances when high-temperature arc occurs.
2. Sulfur hexafluoride gas and decomposition products in electrical appliances react with electrodes (copper-tungsten alloy) and metal materials (aluminum, copper) to produce some toxic substances.
3. The decomposition products of sulfur hexafluoride gas in electrical appliances react with water in them to produce some toxic substances.
4. Sulfur hexafluoride products are impure and contain highly toxic low-sulfur fluorides, hydrogen fluoride and other toxic gases when leaving the factory.
5. Sulfur hexafluoride gas and decomposition products in electrical equipment react with insulating materials to produce some toxic substances, such as epoxy phenolic fiberglass cloth boards (rods, tubes) containing silicon for insulating parts; or epoxy resin castings, molded parts, porcelain bottles, silicone rubber, silicone grease, etc. With quartz sand and glass as fillers, chemical reactions occur to generate products such as SiF4 and Si (CH3) 2F2.