gas helmet vs respirator

gas helmet and respirator both are nouns.

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

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

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

Other synonyms of gas helmet include gasmask.

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