the FAA rules governing the use of oxygen in flight (12.5, 14, 15,000' rule). Hypoxia affects individuals differently depending on their physiology and physical condition. Smokers, for example experience hypoxic symptoms at altitudes 5,000' lower than non-smokers. Another variable is whether the flight is day or night; night vision starts becoming impaired at altitudes below 12,500'

With these variables in mind along with your intent to remain as alert as possible during all phases of flight, what are your personal minimums regarding the use of oxygen? Why?