February 2007 - American Bonanza Society

A QUICK PRIMER ON COWhat is carbon monoxide (CO)? It's aninvisible. odorless. colorless gas. so you haveno way of detecting it without special instrumentation.Where does it come from? CO is a byproduclof Ihe incomplete combuslion of fossilfuels such as gasoline. Complele combuslionproduces harmless carbon dioxide(CO'). which in normal concenlrations isnol as harmful in Ihe cockpil. whereas carbonmonoxide is formed when Ihere's nolenough oxygen present 10 complelelyoxidize all Ihe fuel-in olher words. a richmixture.The highesl concenlralions of CO in Iheexhausllend 10 occur during Ihe phases offtight when Ihe mixture is richesl,roundoperolions. lakeoff. climb. inslruclionalftighls. elc. The mare aggressively Ihe engineis leaned. Ihe less CO il produces.How does it get into the cabin? The moslcommon way for large amounls of CO 10 findils way inlo Ihe cobin of a single-enginepislon aircraft is Ihrough Ihe cobin heatsyslem. When cabin heal is being used. anycracks or holes in Ihe muffler con allowCO-rich exhousl gas 10 conlaminole thecobin. However. smaller concenlrolions ofCO-enough to make you feel ill and impairyour pilol skills-can enler Ihe cabin inmany olher ways. even if your exhouslsyslem is perteclly leak-free.Inadequole sealing of Ihe firewall. lailcone. doors. windows and wheel wells arecommon polhs of enlry for CO. Air condilioningsyslems mounled in Ihe loil cone ofsingle-engine aircraft have proven 10 beespecially vulnerable.What happens when you breathe it? WhenCO is inhaled. il combines with your hemoglobin10 farm "carboxyhemoglobin" (COHb).The COHb band is over 200 limes slrongerIhon oxygen's bond wilh hemoglobin. Thus.Ihe CO effeclively puis your hemoglobin aulof commission and deprives your body of Iheoxygen il needs 10 funclion. Sensilive parts ofyour body like your nervous syslem. brain.heart and lungs suffer the most from Ihis lockof oxygen.What are the symptoms? Symploms of mildCO paisoning include headache. faligue.dizziness. vision problems (particularly doublevision). nausea and increased pulse andrespiralian. (Unfartunolely. Ihese symplomsare often affribuled 10 flu. indigeslion or Ihecommon cold .)AI higher levels of COHb soluralion. youmay suffer difficulty brealhing. loss ofconsciousness, collapse, convulsions, comaand even dealh.How long does it last? The super-slrongnalure of Ihe COHb bond explains why evenvery liny concenlralions of corbon monoxidecan paison you slowly over a period ofseveral hours. and why it may lake a long.long lime far your body 10 eliminale CObuildups from your bloodslream.COHb typically has a "half-life" of moreIhan five hours. So if you crash-land in a hayfieldwilh COHb saluration of 40% (enoughto make you pass oul). your COHb level canbe expecled 10 drop 10 aboul 20% (slillenough 10 make you very sick) after aboulfive hours. 10 10% (still enough 10 make youwoozy 01 oltilude) after 10 hours. and soforth.Brealhing 100% oxygen reduces Ihehalf-life 10 aboul2.5 hours.Once certified, FAA requires no CO testing of individualaircraft by the factory, and no follow-up retesting during annualinspection s.UL-approved residential CO detectors are not penniuedto alarm until the concentration rises to 70 ppm and Slays therefor four hOllrs. (This was demanded by firefighters and utilitycompanies to reduce the incidence of nuisance calls fromhomeowners.) Yet most fire departments require that firefightersput on their oxygen masks immediately when CO levelsreach 25 ppm or higher. Some doctors believe that long-temlexposure to CO levels as low as 10 ppm can lead to cogni tiveand physical problems.Whomever you believe, it's important to understand thatlow concentrations of CO are far more hazardous to pilots thanto nonpilots. That's because the effects of altitude and the effectsof CO poisoning are cumulative. For example, a COHb saturationof 10% (which is about what you'd get from chain-smokingcigarettes) would probably not be noticeable to someone onthe ground. But at 10,000' it could seriously degrade your nightvision, judgment and possibly cause a splitting headache.After studying this hazard for many years and consultingwith world-c lass aeromedical experts, I have come to the followingconclusions:I . Every single-engine piston aircraft should carry a sensitiveelectronic CO detector. Failing thi s, it should at minimumbe retested for inflight CO in the cabin at least annuallyprior to the onset of cold weather.2. Any in-flight CO concentration above 10 ppm shouldbe brought to the attention of an A&P for troubleshooting andresolution.3. Any in-flight CO concentration above 35 ppm shouldbe grounds for going on supplemental oxygen (if available)and making a precautionary landing as soon as practicable.Speaking of cigarettes: If you must smoke, for heaven'ssake don't do it before you fly! Smokers are far more vulnerableto both altitude hypoxia and CO poisoning. since they'realready in a partially poisoned state when they first get into theaircraft. Because of COHb's long half-life, you'd do well toabstain from smoking for 8 to 12 hours prior to flight.