EXPLANATION
LPG is colorless and odorless, and not detectable by normal human senses. To provide an olfactory warning in the event of a leak, LPG intended for domestic or commercial use is intentionally odorized so as to be readily detectable well below flammable or suffocating concentration levels of LPG in air. The most common odorant used is ethyl mercaptan.
This test method covers a rapid and simple procedure using length of stain tubes for field measurement of ethyl mercaptan in the vapor phase of LPG systems. Although length-of-stain tubes are available to detect ethyl mercaptan concentrations in the range of 0.5 to 120 ppm by volume, this test method is specifically applicable to systems containing 5 ppmv or more of ethyl mercaptan in LPG vapors. A chromatographic technique can be used for more precise, quantitative determination of ethyl mercaptan in LPG.
TEST SUMMARY
Using a manually operated vacuum pump, a sample of LPG is drawn through a detector tube made specifically for mercaptan detection. The length of stain (color change) produced in the detector tube when exposed to a measured volume of sample is directly proportional to the amount of ethyl mercaptan present in the sample being tested. The length of stain produced in the detector tube is converted to concentration, in ppmv, by comparison with a calibration scale provided by the stain tube manufacturer.
Detector tubes can be subject to interferences from materials other than the target substances. Methyl mercaptan will likely interfere; however, because different detection chemistry is used by different manufacturers, interferences can vary. Propylene will cause an interfering gray discoloration with some tubes.
TEST PRECISION
Within the precision limits given above, this test method has no bias.