Oxygen is neither explosive nor combustible, but because it does support combustion its potential fire hazards must be recognized. The principal fire hazards of long-term oxygen therapy are (1) the ignition potential of plastic delivery devices and (2) oxygen leaks (a) from high-pressure cylinders and cryogenic reservoirs into nearby combustible materials; (b) from oxygen concentrators, which are electrical devices; and (c) within piping systems. We found that with 100% oxygen a nasal cannula ignited and burned in about 2 minutes. With 60% oxygen the burning rate was slower, and with 40% the cannula did not ignite. We also studied various sizes of oxygen delivery tubing and found that tubing 3/16" or smaller with 40% oxygen flowing self-extinguished a flame. The safe use of oxygen in the home requires that patients and their families be knowledgeable about the hazards.