Cassutts (and other Formula 1 aircraft) also have a reputation for turning CO indicators black, particularly during ground operation. I used an AIM 935 monitor to determine what my actual cockpit environment and breathing air (remember, I wear an oxygen mask supplied with presumably fresh air from the fitting on the right side of the canopy) CO levels were. The following experiments were conducted to gain confidence in the CO monitor as well as determine the quality of the breathing air:
1. Expose monitor to known fresh "country" air. The monitor correctly indicated "Lo" signifying less than 5 ppm of CO.
2. Expose monitor to low levels of CO. I carried the monitor in my car during commutes to work from the clean country air where I live onto the crowded highways of St. Louis. With the windows open and in the vicinity of older (and smelly) cars/trucks, the unit registered increasing CO levels until reaching 10 ppm whereupon the alarm sounded. Highway CO levels peaked around 15 ppm and returned quickly to "Lo" once away from the source. The unit demonstrated excellent sensitivity and response.
Now that I had confidence that the unit is sensitive and responsive, it was time to move into the aircraft environment.
3. Measure cockpit CO during ground operation at idle. This is an important test because we normally start engines and sit stationary on the runway for 6-10 minutes prior to a race. You might think that the prop wash would blow all the CO away but that's not what I found. Immediately after starting the engine the CO levels jumped to 30-100 ppm (and the alarm was sounding). To put this into perspective, the EPA calls for a health hazard alert when the outdoor CO level rises above 9 ppm for an extended period of time and the maximum workplace CO level (OSHA) has ranged from 35-50 ppm. You might be able to sweep a floor safely in a 50 ppm CO environment, but I prefer a lot lower level (like 0) when racing (or just flying) an airplane. CO sensitivity varies among individuals. I'm fairly healthy, don't smoke, and recall getting sick frequently (with CO poisoning symptoms) while working at a truck loading dock where propane powered forklifts were used. Once I changed my work environment to the office (same company), no more headaches/nausea.
4. Measure cockpit CO during flight. Once airborne and with the cabin vent open, the CO levels decreased quickly to 9-15 ppm. Each time the CO level rose to 10 ppm, the alarm would sound and was always quite audible. I wear custom molded ear inserts which do an excellent job of attenuating sound, plus a helmet which also cuts noise, and the alarm was still very evident above the engine noise even with the monitor strapped to my leg. That's a good testimony for the alarm but not such a great breathing environment.
5. Compare vent open to closed. The CO monitor did not register a change with the vent open or closed (monitor strapped to my leg). If I held the monitor directly in the airstream from the vent, the reading fell to "Lo".
6. Test "fresh" air supply quality. For this test, I placed the CO monitor in a modified, hard-sided, clear plastic sandwich container, with my mask supply hose entering the box and another hose leading from the box to the outside air coupling (R/H side of canopy frame). The entire assembly was then sealed inside a zip-lock bag as well as possible to prevent cockpit air from entering the monitor. Only breathing air was intended to pass over the monitor. This test indicated that the "fresh" air system was indeed free of CO, with the unit displaying "Lo" at various altitudes, airspeeds, and power settings.
Following these tests, I had the opportunity to fly another race plane and carried the same CO monitor to assess the cockpit breathing air. During ground operation, the monitor was pegged at "Hi" (greater than 150 ppm). In flight, the monitor stayed pegged on "Hi". The owner is now installing a fresh air breathing system and is happy to have discovered this problem before embarking on a cross country trip.
I'm a firm believer in the AIM 935 CO monitor and the need to breathe uncontaminated air. I'll be loaning monitors to race pilots at Reno so that they can determine what their CO levels are in the interest of safety.
There's a lot of excellent information at AVweb Tests and Aeromedix CO Detectors . Check it out and consider getting a detector for your plane- it could save your life.
Most recent revision: April 11, 2001