Sulphur hexafluoride (SF6) is used as an insulating and arc quenching gas in many types of electrical equipment, including circuit breakers, circuit switchers, current transformers, switchgear and buses. In its pure state, SF6 is an odourless, tasteless, colourless, non-toxic gas. Under normal operating conditions, the gas is totally enclosed within the equipment.
The following potential hazards are associated with SF6 filled equipment.
• SF6 gas used in electrical equipment is usually pressurized.
• SF6 gas is much heavier than air and at high concentrations (>20 %) it may collect in low points of containers or the buildings housing indoor SF6-filled equipment, thereby displacing the air and creating a potential asphyxiation (oxygen starvation) hazard in the affected area.
• When exposed to high temperatures SF6 will decompose producing a complex mixture of gaseous and solid byproducts.
A few of these SF6 decomposition products are highly toxic and most are highly corrosive and irritating when they come into contact with moisture (e.g. in the mouth, eyes or respiratory tract). The composition of the by-product mixture depends on a number of variables, including temperature, moisture, electrode/casing materials and type of arc.
• Some SF6 breaker enclosures are confined spaces and, if they are entered, the requirements of OSH Standard (Confined Spaces) must be met
General Requirements 1 SF6 Cylinders must have WHMIS/GHS-compliant labeling (OSH Standard) and the normal safe handling procedures for pressurized gas containers must be followed. Note: SF6 is normally supplied in cylinders with 52 kg (115 lbs.) of liquefied SF6.
Cylinder pressure is typically 21 MPa (300 psig) at 20 degrees Centigrade (68 F).
Eliminate all sources of heat and open flame (e.g. welding, propane torch and smoking) in indoor work areas when there is an increased risk of SF6 release (e.g. during filling or evacuation of SF6 equipment). Note: SF6 gas may decompose when exposed to temperatures as low as 200°C.
When working around SF6 equipment, care must be taken to avoid sudden impact contact (e.g. dropped tools) with pressurized porcelain and epoxy bushings as this could cause a major gas discharge.