Over the past 30 years a handful of fires in medical oxygen high pressure gas storage systems involving aluminum alloy cylinders have been deemed to be associated with mechanical impact-induced ignition of a contaminated system. For example, hydrocarbon contamination and mechanical impact promoted by being dropped during transportation. While the number of these incidents is minuscule compared to the number of systems used in the field, the effect is significant when such an ignition occurs. The kindling chain and initial ignition point of these fires, however, is poorly understood. Although made from more oxygen compatible metallic materials, the cylinder valves attached to these aluminum cylinders contain nonmetallic materials and are in direct contact with the cylinder threads, which are the thinnest cross section of the cylinder. A mechanical impact test was developed to investigate the conditions required to cause ignition of a cylinder and valve assembly by this ignition mechanism, with and without a wide range of controlled contaminants. Specially prepared small cylinders were assembled with commonly used brass cylinder valves and positioned under a drop tower capable of delivering energies up to 434 J (320ft-lb). Cylinder assemblies were tested with various orientation and impact points including the cylinder valves and no ignitions were recorded in a total of 23 tests.