When we think about explosive environments we can not just say this environment is explosive this is not. Instead of this kind of classification we have levels of explosive environments which are called “zones”.
Zone 0: Continuously there is a mixture of explosive gas air mixture in the environment. You may think like the tank inside in a petroleum station is a zone 0 explosive environment.
Zone 1: This is an environment where there is an explosive gas air mixture in the environment for a short period of time especially while system is working.
Zone 2: Explosive gas is not in the environment generally but it may be seen in an extraordinary situations in a short time.
While it is called like this for gases the same classification is done for dust and it is called as Zone 20, Zone 21 and Zone 22 where their meanings are similar to the gas ones.