When it comes to hazardous locations, especially chosing led explosion proof light we always hear gas and dust, so what do they mean in linghting fileds?
The tank is filled with flammable liquid. The inside of the tank is defined as Zone 0, because the explosive gas/oxygen mixture is continuously present. Vapor may escape on occasion through the vent on the top of the tank, therefore the area around the vent is categorized as Zone 1. The vapor may also run down the outside of the tank, developing another explosive environment, so the area around the tank is categorized as Zone 2.
At a mill with a feed hopper and filter: A product, which causes dust particles mixed with air to cause a flammable mixture, is loaded into a hopper. Inside the feed hopper and filter, it is categorized as Zone 20. While the product is being loaded, the mixture of dust and air causes a potentially explosive compound in the area where the product is loaded into the hopper, so the area outside the hopper is categorized as Zone 21. Around the hopper where a potential flammable atmosphere exists temporarily is categorized as Zone 22.