unrespirable
/(ˌ)ʌnˈrɛsp(ɪ)rəbl/ /(ˌ)ʌnrɪˈspʌɪrəbl/adjective
Not able or fit to be breathed; not able to sustain respiration; (in later use also, of particles, fibres, etc.) not capable of being inhaled into the lungs.
Origin
Early 18th century; earliest use found in John Quincy (d. 1722), apothecary and physician. From un- + respirable.