Dust may affect the cooling of a lamp as well as having corrosive effects on the lamps surface. The dust can be flammable, later leading to an explosion. Having dust proof lighting fixtures is in high demand nowadays. Different countries also have their own requirements for the dust environment. Generally speaking in North America we use the Class 2 to distinguish the dust from the gas of Class 1, and Zone 21 & 22 to divide the dust in Europe and some other countries.