vifaa vya kuzuia gesi ya sumu

kifaa cha kuzuia gesi ya sumu (lit. object for preventing poisonous gas)
kinyago cha kujikinga gesi (lit. mask for protecting oneself from gas)
chombo cha kuzuia gesi (lit. vessel for preventing gas)
helmeti ya kuzuia gesi (lit. helmet for preventing gas)
kofia ya kuzuia gesi (lit. hat for preventing gas)
kichuja-hewa (lit. air-filterer)
Note: There is no particularly great one-to-one translation for this apparatus. All of the above describe it well enough. 

Kifuniko cha kuzuia gesi ni kifaa kinachozuia vichafuzi vinavyosambazwa kupitia hewa na nyenzo za sumu zisipumuliwe.

A gas mask is an apparatus that prevents airborne pollutants and toxic materials from being breathed in.

kichafuzi (pollutant)
nyenzo (material)
kupumuliwa (to be breathed in)

inayosambazwa kupitia hewa (airborne; lit. spread through air)