ASTM D5705 Test Method for Measurement of Hydrogen Sulfide in the Vapor Phase Above Residual Fuel Oils
4. Summary of Test Method
4.1 A 1 L H2S-inert test container (glass test bottle) is filled to 50 % by volume with fuel oil from a filled H2S-inert container (glass sample bottle) just prior to testing. In the test container, the vapor space above the fuel oil sample is purged with nitrogen to displace air. The test container with sample is heated in an oven to 60 °C, and agitated on an orbital shaker at 3.67 s(-1) +/- 0.08 s(-1) (220 r/min +/- 5 r/min (revolutions per minute)) for 3 min.
4.2 A length-of-stain detector tube and hand-operated pump are used to measure the H2S concentration in the vapor phase of the test container. The length-of-stain detector tube should be close to but not in contact with the liquid surface.
5. Significance and Use
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.
6. Interferences
6.1 Typically, sulfur dioxide and mercaptans may cause positive interferences. In some cases, nitrogen dioxide can cause a negative interference. Most detector tubes will have a precleanse layer designed to remove certain interferences up to some maximum interferant level. Consult the manufacturer's instructions for specific interference information.
