-Not necessarily - there's a bunch of ATEX Ex relays in my desk drawer. Conventional, not solid state ones - they are just put in some potting compound, hermetically sealing them.

Was it a flammable atmosphere? Liquid oxygen would have been venting, but there shouldn’t have been any significant fuel in the air.

-Given sufficient oxygen levels, anything is fuel - including engineers...

Well sure, but a tiny spark in a relay isn’t going to ignite the engineer.

It might ignite the metal in the relay, before igniting the engineer.