Safety muscle of larynx:
During forced inspiration, both pas of the rima are triangular, so that the entire rima is lozenge shaped; the vocal cords are fully abducted and we all know that muscles which open the glottis, are posterior cricoarytenoids. So in one way we can consider them as safety muscles which help in respiration (forced inspiration)
Lateral cricoarytenoid
Transverse arytenoid
Posterior cricoarytenoid
Cricothyroids