scope:

This method covers the determination of ethyl mercaptan in LP-gas. Limited data (Appendix A) show a precision of ±10% of the measured amount. The suggested range of tubes to be used is 0.5 to 25 ppmv. A chromatographic method should be used for more precise, quantitative determination of ethyl mercaptan in propane.

CAUTION: This test procedure requires the release of combustible LP-Gas vapors. The user is warned to take proper safety precautions to prevent the accumulation of a combustible mixture and prevent ignition. This procedure should never be performed in an enclosed building unless a properly designed vapor recovery exhaust hood is provided. Liquid propane evaporates rapidly and can freeze flesh quickly. If any liquid propane is encountered, avoid any skin contact.

Purpose

This standard covers the determination of the concentration of Ethyl-Mercaptan in LP Gas using a length of stain tube. While other mercaptans and sulfur species may be indicated in this stain tube it is important to remember that the tubes are calibrated for and intended to be used to determine the concentrations of Ethyl Mercaptan in LP Gas.

This standard has seen only reprinting and no revisions since 1989, when it was adopted as a tentative method. It was revised in 1989 and reprinted in 1990 and 1998.

In 1989 major studies were performed by Sung I. Johnson and W.J. Hines. At that time the team evaluated four brands of tubes and developed accuracy statements which would hold true today and were actually better than, in most cases, the manufacturer's stated accuracies.

The current revision updates some materials used in the procedures which by today's best practices would be found obsolete in terms of what we would use to collect or transport a sample to the stain tube, i.e. gum rubber tubing, etc.

The most significant addition to the standard is a "Cautionary Statement". The intention of the statement is to inform the user that it is critical that manufacturer's instructions be followed implicitly. Each lot of stain tubes is tested by the manufacturer for compliance to stated accuracy and each lot or box of stain tubes quite possibly is slightly different in terms of how they are to be used, i.e. exposure times, indicating colors or contaminants, etc. Further the manufacturer's instructions will state the exponent to be used for multiple or partial testing "pulls" of the pump or if these are allowed at all. This information may vary from lot to lot and from one brand of tube to another.

Also of significance is the concept that if high accuracy and repeatability is required and chromatography is not indicated or feasible, then there is many portable handheld electronic devices which offer these things, as well as low power usage and intrinsic safety. So the user should consider if a length of stain tube is really the best commercially available option based on their situation and requirements.