ASTM D6021-06

Excessive levels of hydrogen sulfide in the vapor phase above residual fuel oils in storage tanks may result in health hazard, OSHA limits violation, and public complaint. An additional concern is corrosion that can be caused by the presence of H₂S during refining and other production activities. Control measures to maintain safe levels of H₂S require a consistent method for the assessment of potentially hazardous levels of H₂S in fuel oils. (Warning—H₂S is a highly toxic substance. Extreme care must be used in the sampling and handling of samples that are suspected of containing high levels of H₂S.)

A concentration of 0.1 μg/g (ppmw) of H₂S in the liquid phase of a No. 4, 5, or 6 residual fuel oil can generate an actual gas concentration of 10 to 100 μL/L (ppmv) of H₂S in the vapor phase; therefore an accurate analytical method is required to determine the total H₂S concentration of these residual fuel oils. This test method was developed so refiners, fuel terminal operators, and independent testing laboratory personnel can analytically measure the amount of H₂S in residual fuel oils.

Test Method D 5705 provides a simple and consistent field test method for the rapid determination of H₂S in the residual fuel oils storage tank vapor phase. However, it does not necessarily simulate the vapor phase H₂S concentration of a fuel storage tank nor does it provide any indication of the liquid phase H₂S concentration. This test method provides a quantitative measure of a residual fuel oils liquid phase H₂S concentration. It requires a laboratory and a skilled operator to perform the test but gives a more quantitative indication of potential H₂S exposure than Test Method D 5705.

Note 1—Because of the reactivity, absorptivity, and volatility of H₂S any measurement method only provides an H₂S concentration at a given moment in time.

1.1 This test method covers a method suitable for measuring the total amount of hydrogen sulfide (H₂S) in heavy distillates, heavy distillate/residual fuel blends, or residual fuels as defined in Specification D 396 Grade 4, 5 (Light), 5 (Heavy), and 6, when the H₂S concentration in the fuel is in the 0.01 to 100 g/g (ppmw) range.

1.2 The values stated in SI units are to be regarded as the standard. The values given in parentheses are for information only.

This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety and health practices and determine the applicability of regulatory limitations prior to use. For specific warning statements, see 5.1, 7.5, 8.2, 9.2, 10.1.4, and 11.1.