Ex cargo clown,
Why the difficulty of detecting poison air in a confined space?
Carbon Monoxide could be monitored in front line RAF Hawker Typhoon fighter aircraft in the middle of WW2. Most light aircraft have CO detectors nowadays.
Surely a basic CCTV system would allow the pilots to see VISIBLE oil fumes in passenger cabins and to turn off bleed air systems pumping unfiltered toxic air into the cockpit and cabin?
At the moment, crew depend entirely upon their sense of smell and vision - all those in favour of Toxic Air Detectors in 'modern' jet aircraft - say: "Aye".
All against say: "Arrrgghhhh"