IP 613: Determination of the viable aerobic microbial content of fuels and associated water - Thixotropic Gel Culture Method

This standard describes a procedure for use in the field or in a laboratory to quantify viable aerobic microorganisms present as contaminants in middle distillate fuels, gasolines, biofuel blends and residual fuels and associated water. The procedure quantitatively assesses the viable aerobic microbial content as microbial colony forming units cfu and determines whether the microbial contamination in samples drawn from fuel tanks and systems is absent or present at light, moderate and heavy levels.

NOTE 1 -- The categorisation of light, moderate and heavy levels of contamination will depend on the fuel type, the sampling location, the facility sampled and its specific operating circumstances. The method is intended to provide a tool for assessing whether fuel storage and distribution facilities or end user fuel tanks are subject to microbial growth and alert fuel suppliers or users to the potential for fuel quality or operational problems and the requirement for preventative or remedial measures. Microbiological tests are not intended to be used to determine compliance with absolute fuel specifications or limits. The implementation of specification limits for microbiological contamination in fuels is generally not appropriate and microbial contamination levels cannot be used alone or directly to make inferences about fuel quality or fitness for use. Further guidance can be found in the normative reference and other industry guidance documents.

NOTE 2 --  The test method may also be used to analyse other hydrocarbon, aqueous and non aqueous liquids and products but these applications fall outside the scope of this method.

NOTE 3 -- The test method detects numbers of microbial colony forming units cfu using the same detection parameter used in the laboratory standard procedure IP 385. However, whereas IP 385 provides separate assessment of numbers of viable aerobic bacteria cfu and numbers of viable fungal cfu, this procedure provides a combined total count of viable aerobic bacteria and fungal cfu.

NOTE 4  -- A laboratory study has been conducted to obtain data for the estimation of precision of this test method and further information is provided in the research report RR IP 612-2013 available from the Energy Institute.