And to be sure maybe another chemical introduced into the cabins ventilation, pilots and anyone else uses portable oxygen.
“And to be sure maybe another chemical introduced into the cabins ventilation, pilots and anyone else uses portable oxygen.”
No.
In a pressurized aircraft, the source of pressurization is bleed air from the engines. This air is cooled and pumped into the cabin to create the pressure. Outflow valves in the back of the aircraft open and close to maintain the desired level of pressurization. So any substance introduced into the cabin ventilation is going to go out the back of the aircraft within a short time after being introduced.