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Bell Fuel and Tank Services

ATP-by-Filtration Testing for Aviation


Testing of aviation fuel needs to be done “in-field” in order to maximize its value. The options for doing this have really blossomed over the last ten or fifteen years. It’s no longer necessary to go through the hassle and expense of packaging and shipping fuel samples to a laboratory, only to wait days or weeks for microbial test results. That’s no longer good enough. The aviation industry needs in-field testing options to make the calibre of decisions that are essential to it.


A quick review of the marketplace finds at least three major kinds of microbial test “kits”. They all work differently, but they’re all trying to do the same kind of thing - measure microbial contamination in a fuel sample that was pulled from a bigger system.  Depending on if the results are interpreted as low, medium, or high (or whatever corresponds to that), you can know what actions are recommended to come out of that. Moderate contamination may require some kind of biocide application while heavy contamination might require more intensive steps like emptying and cleaning of the tank or system. The required action depends on what the aviation user has determined is the best action for them. 


Any time you’re talking about manual cleaning of fuel tanks for aviation customers, you’ve got extremely expensive propositions being thrown around. Yet, if the microbial contamination is there, and is severe enough, there’s no way around having to do that. Without reliable microbial testing to confirm this, how would aviation fuel users know if/when such severe action was needed? Microbial testing eliminates the guesswork inherent in this - and you want as little guesswork as possible when thousands and millions of dollars are on the line (not to mention the proposition of pulling a plane or an essential system offline for days or weeks at a time).

Microbial testing for aviation fuel is essential to any best practice fuel management protocol that aims to detect and flag microbial contamination at the earliest stage where it is easiest and least expensive to fix.

In-field microbial tests for aviation all try to do the same kind of thing, but they don’t all work in the same way, nor do they do it equally well. If you’re looking at these different kinds, you’re likely to end up comparing three kinds - culture tests, immunoassay, and ATP measurement. 


Culture tests try to regrow the microbes from a sample on (or in) a growth medium, with results read after an incubation period of 4-7 days. Their biggest pro is they are simple to do. But their downsides are significant. They may not display all of the microbes present in a sample equally well, for a number of reasons. In short, this means what a culture test displays after incubation may be significantly different from the level of microbial contamination in the starting sample. The incubation waiting period is also a significant downside, as the user must wait days for results - culture tests cannot give you instant results.


Immunoassay antibody tests are a step above culture tests. They generate semi-quantitative results (“low”, “medium”, “high”) by detecting the levels of antibody present in a prepared sample. The antibody levels are supposed to correlate with the levels of microbial contamination in the sample.  These kinds of tests are slightly more “involved” than simple culture tests but are still simple enough that almost anyone can do them. They also have the significant advantage over culture tests in that they deliver results within 10-15 minutes instead of multiple days.  This makes them suitable for use as “in-field” tests.


The third group of tests are known as ATP tests and look to assess the levels of microbial presence by measuring the amount of ATP (adenosine triphosphate) present in the sample. All living cells use ATP as an essential molecule for energy transport, which means that higher numbers of microbes will have higher amounts of ATP present. ATP tests generate their results by using a luminometer to detect the amount of light given off by the reaction of cellular ATP in the sample with an enzyme added during the test method. This type of testing has several advantages over culture and immunoassay tests.

  1. Results are generated in 5-10 minutes, making them suitable for in-field testing situations that require information in order to make real-time business decisions (such as servicing a quick-turnaround plane).
  2. The test results cover all living microbes in the sample. Immunoassay tests only apply to part of the microbial population, and culture tests only show the small portion of microbes that were able to grow (and be detected visibly) on the growth medium after a period of time.
  3. ATP test results tend to be more quantitative and more specific in nature, with lower limits of detection. In other words, ATP tests are better at reliably detecting lower levels of microbes, and they give their results in more specific numbers that are more useful for trending and analysis. 

This final point is especially important and useful for the aviation industry. Microbial testing (like ATP-By-Filtration) have been used in upstream oil and gas sectors for years. Microbial levels in their equipment and fluids can approach many millions of microbes per mL.  Moreover, the control limits for upstream oil and gas are extremely high, and that means a test that doesn’t detect low microbial levels very reliably will still be useful for them. Aviation is a different animal - control limits for the aviation industry are much, much lower. As such, the ability for a microbial test to reliably detect and measure microbial levels approaching 1,000 or 2,000 or 3,000 microbes (or their equivalent) per mL matters a lot more. 


ATP-By-Filtration testing is also optimized for the aviation industry through the availability of self-contained testing boxes that provide all of the test reagents and supplies necessary for 5 or 10 ATP tests. These 5-pack or 10-pack kits are very useful for aviation users needing to test fuel or water samples drained from multiple ports on a plane. The kits are designed for convenience and portability, both important functional needs in in-field testing situations for the aviation industry.