I am an anesthesiologist with 30 years of experience, and a frequent commercial passenger. As someone who works with inhaled gas mixtures every day, I started wondering about the passenger oxygen systems available when depressurization occurs at altitude. I knew that the oxygen generators were chemically-based canisters that provide a low flow of oxygen for 6-10 minutes, usually enough time to reach a lower altitude. I spoke with a number of flight attendants, but none of them had ever been in a real oxygen mask deployment. I also spoke with a few captains, two of which had been in such a situation. These two pilots stated that even with the low-flow oxygen, as many as 30 % of the passengers will lose consciousness until lower altitudes are reached. The actual number undoubtedly depends on the altitude at which pressurization is lost, the age and health of the passengers and the time before a lower altitude is reached. I was wondering if anyone else could confirm this scenario. Mark S Donnell, MD Silver City, NM