Sulfur hexafluoride (SF6) is a good gas insulator and is widely used for gas insulation of electronic and electrical equipment; its typical application is as gas insulation in high-voltage switchgear of power transmission and transformation stations, power plants, etc. of power supply departments. To protect sulfur hexafluoride, we must first understand the physical and chemical properties of sulfur hexafluoride. Pure sulfur hexafluoride has low toxicity and stable properties. However, after a few minutes of inhaling a mixed gas of 80% sulfur hexafluoride + 20% oxygen, the human body will experience numbness of the limbs and mild excitement symptoms. There is a certain pressure when sulfur hexafluoride gas is filled into the high-voltage switchgear, so the probability of gas leakage is high, and the oxygen content in the air is sufficient, so that the conditions for sulfur hexafluoride to combine with oxygen to produce toxicity after leakage are sufficient. This is one of the situations that need protection.
Once sulfur hexafluoride gas encounters high heat and high temperature (such as: electric arc), byproducts—sulfur oxide and hydrogen fluoride gas—will be produced, which coexist with undecomposed sulfur hexafluoride gas. At this time, there are three kinds of toxic gases. Sulfur oxide is a sulfuric anhydride, which is easily absorbed by the moist mucous membrane surface of the human body to form sulfuric acid and sulfurous acid, which has a strong irritating effect on the eye and respiratory mucosa. The specific manifestations are tears, coughing, burning throat, conjunctival and respiratory tract stinging. When it encounters human sweat, it will cause redness and swelling of the skin. Hydrogen fluoride is easily soluble in water. It is also easily absorbed by the moist mucous membrane surface of the human body to form hydrofluoric acid. Its harm to the human body is the same as sulfur oxide – the eyes and respiratory tract, but it is more harmful. Hydrofluoric acid is often used to etch glass, which shows that it is extremely corrosive. If it encounters human sweat, hydrofluoric acid is formed on the surface of human skin. It can penetrate the skin surface to penetrate deep into the skin, forming ulcers and necrosis, and it is not easy to cure. If bone damage causes fluorosis, it will not be able to recover. The toxicity of hydrogen fluoride is even worse than that of sulfur oxide and sulfur hexafluoride.
The “Handbook of Chemical Hazards Safety” of the Ministry of Chemical Industry stipulates the values of the above three chemicals as follows:
1. Sulfur hexafluoride TWA (8-hour weighted average): 1000PPM (5790mg/m3) STEL (short-term exposure limit concentration): Undetermined
2. Sulfur oxide TWA: 5PPM (13 mg/m3) STEL: 5PPM (13 mg/m3)
3. Hydrogen fluoride TWA: 3PPM (2.6 mg/m3) STEL: 3PPM Undetermined
TWA value: The cumulative concentration of toxic gas inhaled by the human body in a working day (8 hours) will not cause harm to the human body if the time-weighted average is not greater than this value.
STEL value: The human body will not be harmed if it is exposed to the toxic gas at this concentration for no more than 15 minutes. If this value is undetermined, it means that the human body is not allowed to enter the toxic gas environment without taking protection. From the above values and the degree of harm to the human body, it can be seen that there are two aspects of protection against sulfur hexafluoride: one is the sulfur hexafluoride gas itself; the other is the byproducts of sulfur hexafluoride when it encounters high temperature, and the protection of byproducts is more important. As far as the human body is concerned, the focus of protection is the eyes and respiratory tract; the second is the human skin. At this point, we can choose the corresponding protective supplies and equipment in a targeted manner. The respiratory system is the first of the three major elements of life survival and must be considered first.
Because there may be a variety of toxic gases in the leaked contaminated area. If a filter-type gas mask is used, because it is a negative pressure type, the protection safety factor is low, and the possibility of people bringing in toxic gases when inhaling is greater. For places where there are multiple toxic gases, the toxicity is relatively high and the concentration is uncertain, it is not appropriate to use a filter-type mask. The use of a positive pressure air respirator can completely isolate the toxic gas, regardless of the number of toxic gas types and the concentration, so the positive pressure air respirator is the preferred protection product. However, when choosing a positive pressure air respirator, the factor of whether the toxic gas directly causes death should be considered in order to make the correct choice. When a toxic gas leak occurs, on-site personnel should use protective equipment nearby, such as an escape device, and quickly evacuate the source of the leak. The poisoned personnel should leave the scene to a place with fresh air, and use oxygen resuscitation equipment or artificial respiration to rescue on the spot when necessary; emergency response personnel must wear air respirators, appropriate protective clothing and gloves before entering the accident area, ventilate the scene, and dilute and diffuse. When entering a high-concentration area, someone must be on guard.
Post time: Jul-14-2025