It is widely used in electrical switchgear, but due to various reasons, SF6 gas and its toxic decomposition products generated under high-temperature arcs are emitted into the atmosphere, which not only pollutes the environment but also adversely affects the normal operation of electrical equipment and people's health.
Pure SF6 gas is a colorless, odorless, essentially non-toxic, non-flammable halogen compound. The chemical properties of SF6 gas are very stable; it does not burn or support combustion in air, and does not react with water, strong bases, ammonia, hydrochloric acid, sulfuric acid, etc. At temperatures below 150°C, SF6 gas is chemically inert, sparingly soluble in water, and slightly soluble in alcohols. It does not chemically react with common metals and other organic materials used in electrical equipment. However, SF6 gas can decompose and release various products at high temperatures, mainly SF4 and SF2, as well as small amounts of S2, F2, S, F, etc. Typically, SF6 is used under conditions where the temperature is -40°C ≤ t ≤ 80°C and pressure P < 0.8MPa. Within this range, SF6 mainly exists in gaseous form.
Sources of toxicity in SF6 gas use
The toxicity of SF6 gas mainly comes from five aspects:
(1) SF6 gas is impure, containing highly toxic low-fluoride sulfur, hydrogen fluoride, and other toxic gases at the time of shipment;
(2) SF6 gas in electrical equipment produces certain toxic products when reacting with high-temperature arcs;
(3) SF6 gas decomposition products in electrical equipment react chemically with moisture inside to generate certain toxic products;
(4) SF6 gas and its decomposition products in electrical equipment react with electrodes (Cu-W alloy) and metal materials (Al, Cu) to generate certain toxic products;
(5) SF6 gas and its decomposition products in electrical equipment react with insulating materials to generate certain toxic products.
Hazards caused by SF6 gas and preventive measures
For a long time, due to improper use and management of SF6 gas, many toxic and corrosive gases and solid decomposition products have been emitted into the atmosphere, causing environmental pollution and even endangering people's health.
From a medical perspective, the degree of impact of various decomposition gases and products on the human body depends not only on their toxicity but also on the amount inhaled and each individual's physical condition.
In an epidemiological survey of workers from two enterprises that produce and use SF6 gas, workers with similar age, gender, labor intensity, professional seniority, and smoking habits were grouped and compared; no obvious damage to the health of the workers was found. However, from the statistical incidence of symptoms, a larger number of people showed fatigue, poor memory, sore throat, and chest tightness.
Preventive measures to take
(1) Strengthen supervision and management, strictly control the allowable content of SF6 gas and its toxic decomposition products in the air;
(2) Reduce and control the moisture content in SF6 gas;
(3) Strengthen the recovery and treatment of SF6 gas and its decomposition products;
(4) Improve product design level to reduce SF6 gas leakage rate;
(5) Use other alternative gases or mixed gases.
