Gas mask (10)
I believe the answer is:
respirator
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">gas mask</span>' is the definition.<br/ ><span class="explanation-format__explanation">(I know that gas mask can be written as respirator)</span><br/ ><br/ >This is all the clue.<br/ ></span>
(Other definitions for respirator that I've seen before include "breather" , "Supplier of clean gas" , "Breathing aid" , "Breathing apparatus" , "protective equipment" .)