1.1 This test method describes a rapid and simple procedure using length-of-stain tubes for field measurement of ethyl mercaptan in the vapor phase of LP-gas systems. Although length-of-stain tubes are available to detect ethyl mercaptan concentrations in the range of 0.5 to 120 parts per million by volume, this test method is specifically applicable to systems containing 5 ppm by volume or more of ethyl mercaptan in LP-gas vapors.