5.1 Residual fuel oils can contain H₂S in the liquid phase and this can result in hazardous vapor phase levels of H₂S in storage tank headspaces. The vapor phase levels can vary significantly according to the headspace volume, fuel temperature and agitation. Measurement of H₂S levels in the liquid phase provides a useful indication of the residual fuel oil’s propensity to form high vapor phase levels, and lower levels in the residual fuel oil will directly reduce risk of H₂S exposure. It is critical, however, that anyone involved in handling fuel oil, such as vessel owners and operators, continue to maintain appropriate safety practices designed to protect the crew, tank farm operators and others who can be exposed to H₂S.

5.1.1 The measurement of H₂S in the liquid phase is appropriate for product quality control, while the measurement of H₂S in the vapor phase is appropriate for health and safety purposes.

5.2 This test method was developed to provide refineries, fuel terminals and independent testing laboratories, which do not have access to analytical instruments such as a gas chromatograph, with a simple and consistent field test method for the rapid determination of H₂S in the vapor phase above residual fuel oils.

Note 1: D5705 is one of three test methods for quantitatively measuring H₂S in residual fuels:
1) Test Method D6021 is an analytical test method to determine H₂S levels in the liquid phase.
2) Test Method D7621 is a rapid test method to determine H₂S levels in the liquid phase.

Note 2: Because of the reactivity, absorptivity and volatility of H₂S, any measurement method only provides an H₂S concentration at a given moment in time.

5.3 This test method does not necessarily simulate the vapor phase H₂S concentration in a fuel storage tank. It does, however, provide a level of consistency so that the test result is only a function of the residual fuel oil sample and not the test method, operator, or location. No general correlation can be established between this field test and actual vapor phase concentrations of H₂S in residual fuel oil storage or transports. However, a facility that produces fuel oil from the same crude source under essentially constant conditions might be able to develop a correlation for its individual case.

1.1 This test method covers the field determination of hydrogen sulfide (H₂S) in the vapor phase (equilibrium headspace) of a residual fuel oil sample.

1.2 The test method is applicable to liquids with a viscosity range of 5.5 mm²/s at 40 °C to 50 mm²/s at 100 °C. The test method is applicable to fuels conforming to Specification D396 Grade Nos. 4, 5 (Heavy), and 6.

1.3 The applicable range is from 5 μmol/mol to 4000 μmol/mol (micromoles per mole) (5 ppm v/v to 4000 ppm v/v (parts per million by volume)).

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

1.5 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, health, and environmental practices and determine the applicability of regulatory limitations prior to use.

1.6 This international standard was developed in accordance with internationally recognized principles on standardization established in the Decision on Principles for the Development of International Standards, Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee.