5.1 Representative samples of fuel products and associated substances are required for the determination of microbial contamination in fuels and fuel systems in order to accurately assess the biodeterioration risk posed to the fuel, fuel-system components or both. Uncontrolled microbial contamination can affect fuel specification properties adversely.⁶ As discussed in Guide D6469, microbes can cause a variety of operational problems, including filter plugging and microbially influenced corrosion (MIC), the latter of which causes valve failure, tank and pipeline failure.

5.2 These practices for microbiological sampling decrease the risk of contaminating samples with extraneous microbes, thereby increasing the probability that the original microbial population in the sample does not change significantly between the time of sampling and the time of testing.

5.3 The objective of sampling for microbiological testing is to obtain a representative sample that is likely to reflect the degree and nature of microbial contamination in the system from which the sample is collected. Manual 47⁷ addresses the rational for and design of microbial contamination programs.

5.4 The physical, chemical and microbiological property tests to be performed on a sample will dictate the sampling procedures, the sample quantity required, and many of the sample handling requirements.

5.5 Fuel systems are not normally designed to facilitate optimal microbiological sampling. Consequently, the selection of sampling device and sample source reflect compromises between accessibility and suitability for meeting the sample collection objective.

5.6 The guidance provided in Practice D4057 generally applies to this practice as well. Consequently, this practice will address only those procedures that apply uniquely to microbiological sampling.