Unlike other fuel contaminants, microbes can continue to grow (or die-off) between the time a sample is collected and the time testing begins.  Moreover, microbial contaminants from the skin of the person collecting the sample (healthy skin has more than a billion bacteria per cm²!), the collection vessel, sample bottle or any combination of these can lead to erroneous test results. 

ASTM D 4057 Practice for Manual Sampling of Petroleum and Petroleum Products is a great reference document on how to collect fuel samples for routine product testing.  However, it does not address the special considerations that apply to samples on which microbiological tests will be run, nor does it address sample collection from system surfaces. 

In 2008, ASTM D.01.14 Fuel Stability and Cleanliness developed a new Standard Practice that provides detailed instructions for collecting and handling samples destined for microbiological testing.  The new Standard is D 7464 Practice for Manual Sampling of Liquid Fuels, Associated Materials and System Components for Microbiological Testing.

D 7464 is divided into seventeen sections.  The first section “Scope” identifies what the rest of the Practice is about:

“1. Scope

1.1 This practice covers aspects of sample device preparation and sample handling that prevent samples from becoming contaminated with microorganisms not originally contained within the sample.

1.2 This practice also covers sample handling considerations that reflect the perishability of samples collected for

microbiological testing.

1.3 This practice supplements Practice D 4057 by providing guidance specific to the manual sampling of fuels when

samples are to be tested for microbial contamination.

1.4 The values stated in SI units are to be regarded as standard. No other units of measurement are included in this

standard.

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 and health practices and determine the applicability of regulatory limitations prior to use.”

The next two sections provide a list of references and a glossary of terms that might be unfamiliar to non-technical readers.  Except for the last section, a list of keywords, the balance of the Practice steps through the various protocols for collecting different types of fuel and fuel system samples.

 D 7464 also includes a section that discusses sample handling and chain of custody considerations that ensure samples are delivered to testing facilities without losing their integrity.

Taking much of the mystery out of biocide selection and use, ASTM D 7464 is available on-line at www.astm.org and can be purchased from the web site directly.