How does ATEX apply downstream of a flame arrestor?

[freshtrax]

If I am building an ATEX certified boiler assembly, how does ATEX apply to components such as valves and swtiches located within my boiler if they are downstream of a certified flame arrestor but also in close proximity of an ignition source (our burner)?

 

[micalbrch]

You have an explosive atmopshere inside and outside? If so, I think ATEX applies to the switches and valves concerning the outside atmosphere and not concerning anything in contact with the internal gas and/or fluid due to the flame arrestor.