Carbon Monoxide (CO) exposure is an important public health issue that poses as serious risk in aviation. Exposure is most common in single engine piston-driven aircraft where air is passed over the exhaust manifold to serve as cabin heat. Effective primary prevention of this exposure is the regular inspection and maintenance of aircraft exhaust systems, as required by law.
For high-risk situations, should exposure occur, installation of active warning devices for Con intrusion into cockpits may improve secondary prevention. Modern studies should be performed of occupation-specific abilities to support 50 ppm FAA CO exposure standard and 50-70ppm FAA Technical Standard Order (TSO) for CO monitors alerting pilots to the possibility of exhaust gas intrusion into their cockpits.
The Risks in Piston-Powered Aircraft
- Piston-powered aircraft create high levels of CO, and provide the highest risk that CO can enter the cabin during flight. Oftentimes, these aircraft are flown solo, making the impact from CO ingress even more severe. Most piston-powered aircraft are heated by directing fresh air over the engine muffler. Any cracks, holes, or poor fitting components in the exhaust system, can cause CO-rich exhaust gases to enter the cabin. Engine exhaust may also enter the cabin through inadequately sealed firewalls and wheel wells.
- Previous Toxicology reports from fatal U.S. aircraft accidents between 1967-1993 showed that at least 360 victims had been exposed to a sufficient amount of CO before or after the incident. This would have greatly impaired their abilities and decreased their chance of survival. It is also important to note that some CO poisoning occurred post-crash and that CO poisoning in these incidents couldn’t be attributed to the incident. It is also possible that passengers and flight crew were exposed to low concentrations of CO, and deduced that their symptoms were due to airsickness or fatigue. Because the symptoms were brief and not life-threatening, such instances were never reported.
The Risks in Turbine-Powered Aircraft
- When taxiing behind another aircraft, CO can enter the cabin from external sources. If this happens, it will immediately be noticed, due to the smell of the other exhaust gases mixed in.
- It is possible for situations to arise, where the cabin air becomes contaminated with lubricating oil, hydraulic fluids, and de-icing and anti-icing fluids. These include engine and auxiliary power unit oil seal failures and inappropriate application of de-icing and anti-icing fluids into engine and APU air intakes. The only possible source of CO is when leaking aircraft engine lubrication and hydraulic oils are subjected to high temperatures. When presented with these circumstances, oils can degrade into several different compounds (including CO) through a process known as pyrolysis.
Protective Measurers in PPA
The best method of defense against CO poisoning is simply to avoid exposure. In order to best avoid exposure, it is important that effective maintenance measures are taken to ensure the health and longevity of the aircraft. Particular attention should be given to the heating and ventilation system in order to ensure that the exhaust system components and manifolds are not leaking; especially when working with older aircraft. Due to the risks and severity associated with CO, it is a good idea to have a means of CO detection and warning in the aircraft.
Below is a list of some methods that are practiced, and if no detection and warning system is available, then it is important that pilots are familiar with associated symptoms and react immediately.
- Turn the cabin heat fully off
- Select maximum rate of fresh air ventilation to the cabin
- Open windows if the environment, flight profile and operating manual permit
- Land as soon as possible/practicable
- Before continuing the flight, have the aircraft inspected by a certified mechanic
Protective Measures in TPA
When on the ground, the most effective way of preventing CO from entering the cabin and flight deck, is to close the doors and hatches. The air-conditioning system can either be used to ventilate the cabin or shut-off to prevent further pollution, depending upon the location of the source. Overall, the effective application of mandatory maintenance programs, quality assurance, safety systems, routine inspections, and cleaning programs, greatly reduce the chances of any contaminant entering the aircraft from the engines and APU via the bleed air system. Operational and emergency procedures are in place to protect against hypoxia, fire, smoke, and fumes.