Silent Killer

• Evaluation of CO detectors, including specific makes and models. • Placement of CO detectors in the cabin. • Exhaust system maintenance and inspection. Visit www.SportAviation.org for a PDF of the research paper. Overall, deaths from unintentional CO poi- soning have dropped sharply since the mid-1970s thanks mainly to lower CO emis- sions from automobiles with catalytic converters (most CO deaths are motor vehicle related) and safer heating and cooking appli- ances. But CO-related airplane accidents and incidents haven’t followed this trend. The ADs issued against Independence-built Cessna 172s and 182s and Mooney Ovations demonstrates that even brand new airplanes aren’t immune. CLOSE CALLS In addition to these events in the NTSB accident database where CO poisoning was clearly implicated, there were almost cer- tainly scores of accidents, incidents, and close calls where CO was probably a factor. In January 1999, for example, a Cessna 206 operated by the U.S. Customs Service was on a night training mission when it inexplicably crashed into Biscayne Bay a few miles of the south Florida coast. The experienced pilot survived the crash, but had no recollection of what happened. The NTSB called it simple pilot error and never mentioned CO as a possible contributing factor. However, enough COHb was found in the pilot’s blood that the Customs Service suspected that CO poisoning might have been involved. The agency purchased sensitive industrial electronic CO detectors for every single- engine Cessna in its fleet and discovered that many of the planes had CO-in-the-cockpit problems. On-board CO detectors and CO checks during maintenance inspections have been standard operating procedure for the Customs Service ever since. HOW MUCH CO IS TOO MUCH? It depends on whom you ask. EPA calls for a health hazard alert when the outdoor concentration of CO rises above 9 parts per million (ppm) for eight hours, or above 35 ppm for one hour. The U.S. Department of Labor’s Occupational Safety and Health Administration originally estab- lished a maximum safe limit for exposure to CO in the workplace of 35 ppm, but later raised it to 50 ppm under pressure from industry. The FAA requires that CO in the cabin not exceed 50 ppm during certification test- ing of new GA airplanes certified under FAR Part 23 (e.g., Cessna Corvalis, Cirrus SR22, Diamond DA40). Legacy aircraft certified under older CAR 3 regulations required no CO testing at all during certification. Once certified, the FAA requires no CO testing of individual aircraft by the factory, and no follow-up retesting during annual inspections. A March 2010 FAA SAIB (CE- 10-19 R1) recommends checking CO levels with a handheld electronic CO detector during ground run-ups at each annual and 100-hour inspection, but in my experience very few shops and mechanics do this. UL-approved residential CO detectors are not permitted to alarm until the con- centration rises to 70 ppm and stays there 26 Sport Aviation December 2014 CHOOSING A CO DETECTOR Chemical spot detectors: Stay away from those ubiqui- tous el-cheapo adhesive-backed cardboard chemical spot detectors that are commonly sold by pilot shops and mail-order outfits under trade names like Dead Stop, Heads Up, and Quantum Eye. They have a very short useful life (about 30 days) and are extremely vulnerable to contamination from aromatic cleaners, solvents, and other chemicals routinely used in aircraft maintenance. These things often remain stuck on the instrument panel for years, providing a dangerous false sense of secu- rity. What’s worse, there’s no warning that the detector is outdated or has been contaminated—in some ways, that’s worse than not having a detector at all. Even when fresh, chemical spot detectors are incapable of detecting low levels of CO. They’ll start turning color at 100 ppm, but so slowly and subtly that you’ll never notice it. For all practical purposes, you’ll get no warn- ing until concentrations rise to the 200 to 400 ppm range, by which time you’re likely to be too impaired to notice the color change. Residential electronic detectors: Although battery-pow- ered residential electronic detectors are vastly superior to those worthless chemical spots, most are designed to be compliant with Underwriters Laboratories specification UL-2034 (revised 1998). This spec requires that: • The digital readout must not display any CO concen- tration less than 30 ppm. • The alarm will not sound until CO reaches 70 ppm and remains at or above that level for four hours. Even at a concentration of 400 ppm, it may take as much as 15 minutes before the alarm sounds. For aircraft use, you really want something much more sensitive and fast-acting. I like the non-UL-compliant CO Experts Model 2015 ($199 from www.Aeromedix.com). It displays CO concentrations as low as 7 ppm and provides a loud audible alarm at concentrations above 25 ppm. It updates its display every 10 seconds (compared to once a minute for most residential detectors), which makes it quite useful as a “sniffer” for trying to figure out exactly where CO is entering the cabin. Industrial electronic detectors: Industrial CO detec- tors cost between $400 and $1,000. A good choice for in-cockpit use is the BW Honeywell GasAlert Extreme CO ($410 from www.GasSniffer.com). This unit displays CO concentrations from 0 to 1,000 ppm on its digital display and has a very loud audible alarm with dual trigger levels (35 and 200 ppm). Purpose-built aviation electronic detectors: Tucson- based CO Guardian LLC makes a family of TSO’d panel-mount electronic CO detectors specifically designed for cockpit use. These detectors detect and alarm at 50 ppm (after 10 minutes) or 70 ppm (after five minutes), and will alarm instantly if concentrations rise to 400 ppm. The digital display models ($599 and up) will show concentrations as low as 10 ppm. Available from www.COGuardian.com. Obviously, panel-mount detectors cannot be used as a sniffer to locate the source of a CO leak. Five CO detectors (left to right): chemical spot, UL-compliant residential (Kidde), non-UL-compliant (CO Experts 2015), industrial (BW Honeywell), TSO’d panel-mounted (CO Guardian 551). for four hours. (This was demanded by firefighters and utility companies to reduce the incidence of nuisance calls from homeowners.) Yet most fire departments require that fire- fighters put on their oxygen masks immediately when CO levels reach 25 ppm or higher. It’s important to understand that low concentrations of CO are far more hazardous to pilots than to nonpilots. That’s because the efects of altitude hypoxia and CO poisoning are cumulative. For example, a COHb saturation of 10 percent (which is about what you’d get from chain-smoking cigarettes) would probably not be noticeable to someone on the ground. But at 10,000 feet, it could seriously degrade your night vision, judgment, and possibly cause a splitting headache. After studying this hazard for many years and consulting with world-class aeromedical experts, I have come to the following conclusions: • Every single-engine piston aircraft should carry a sensitive electronic CO detector. • Any in-flight CO concentration above 10 ppm should be brought to the attention of an A&P for troubleshooting and resolution. • Any in-flight CO concentration above 35 ppm should be grounds for going on supplemental oxygen (if available) and making a precautionary landing as soon as practicable. • Smokers are far more vulnerable to both altitude hypoxia and CO poisoning, since they’re already in a partially poi- soned state when they first get into the aircraft. Because of COHb’s long half-life, you’d do well to abstain from smok- ing for eight to 12 hours prior to flight. Mike Busch, EAA 740170, was the 2008 National Aviation Maintenance Technician of the Year, and has been a pilot for 44 years, logging more than 7,000 hours. He’s a CFI and A&P/IA. E-mail him at mike.busch@savvyaviator. com. Mike also hosts free online presentations as part of EAA’s webinar series on the first Wednesday of each month. For a schedule visit www.EAA.org/webinars. www.eaa.org 27