Rupert, you may want to do a bit of research into 'turbine' engines as opposed to 'reciprocating' engines. The air that is 'bled' off the compressors (hence the name 'bleed air') is taken out before the combustion stage. Any fumes being mentioned here are due to leaks from the bearing seals of the oil used to lubricate them. We are not talking about carbon monoxide associated with combusted fuel.