Originally Posted by afterburn81

I have always wondered about CO2 in the cabin. Unless something is burning I'm not sure where it would come from in a jet aircraft. Bleed air from the engines is extracted from the compressor. Simple physics shows that a gas will go from a higher pressure to a low pressure so I'm not sure how the combustion could flow back into the compressor on a high bypass turbofan. In no way am I doubting this situation. Clearly they had some type of contamination. Does anyone have an idea as to where this sort of thing could come from if nothing was actually burning?