The quenching distance between plane parallel plates has been measured for propane‐air flames at eight pressures ranging from 0.0832 to 2.77 atmos., and air‐propane ratios ranging from 11 to 24. Other tests have been made at atmospheric pressure in which (a) the temperature of the quenching plates has been varied from 80° to 715°F, (b) the temperatures both of the inlet gas and the quenching plates have been varied from 80° to 545°F, and (c) a series of six different solid surfaces was tested. The minimum quenching distance is found to occur at an air‐propane ratio between 13.5 and 14.0, and is proportional to the minus 0.91 power of pressure. Lean mixtures are found to be slightly less pressure‐sensitive. When both the inlet gas and plates are heated, the minimum quenching distance is found to be proportional to the minus 0.5 power of absolute temperature. The quenching effect appears to be independent of the nature of the surface.