a) Zone 0 – explosive gas is always or for long periods; continuous existence of risk is greater than 1000 hours / year in the region
b) Zone 1 -flammable gas in the instrument’s proper course of their work may occur or exist;
intermittently dangerous of 10 to 1,000 hours / year in the region
c) Zone 2 -general case, there is no flammable gases and even if the occasional presence of time base very short; the accident risk of state, there is 0.1 to 10 hours / year in the region