Thankfully, CO related GA accidents are rare. Of the nearly 72,000 accidents between 1962 and 2007 in the NTSB accident/incident database studied by the FAA, just 62 (0.008%) was deemed to be C) related. However, the FAA also noted that the age of the exhaust system, particularly the age of the muffler was a major contributing factor---noting that the majority of the CO-related accidents caused by cracks or leaks in the muffler was with muffler usage greater than 1,000 hours. So, if we are flying around in older aircraft (and let's face it, with the average age of the nation's single engine fleet at over 30 years, most of us are), it makes sense to take some precautions.
So, what's a dangerous level of exposure?
- OSHA lists the max time-weighted-average exposure for an 8 hour work day at 50 ppm.
- 200 ppm over a couple of hours will cause mild headaches and nausea
- 400 ppm over 1-2 hours will cause serious headaches, and become life threatening after 3 hours.
- 800 ppm will cause dizziness, nausea in less than an hour and unconsciousness within 2 hours
- And from there on out, the figures become ever more grim until an exposure of 12,800 ppm will cause death in a matter of minutes.
There are a variety of CO detectors on the market from the down right cheap chemical dot types (the cards with a reactive dot that turns black when exposed to CO) to highly sensitive portable electro-chemical detectors. The good news here is that concentrations where things start to get dangerous (>50ppm) are high enough that even the cheapest chemical dot detectors should be able to detect them reliably.
The FAA SAIB is limited to testing electro-chemical type detectors, but offers some tips about preventive maintenance of aircraft, and usage and placement of CO detectors. All around a very interesting read.