respirator vs gas helmet

respirator and gas helmet both are nouns.

Word	Noun	Adjective	Verb	Adverb
respirator	Yes	No	No	No
gas helmet	Yes	No	No	No

As nouns, respirator and gas helmet are synonyms defined as:

respirator and gas helmet: a protective mask with a filter; protects the face and lungs against poisonous gases

Other synonyms of respirator include gasmask.

respirator (noun)	gas helmet (noun)
a breathing device for administering long-term artificial respiration	a protective mask with a filter; protects the face and lungs against poisonous gases
a protective mask with a filter; protects the face and lungs against poisonous gases