Fuel Test

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a fuel test?

If your company is using or distributing fuel, you’re at risk of contamination from microbiological growth (also called microbial contamination).

Recent changes to fuels designed to help the environment mean that it’s now easier for dangerous microbes to grow in tanks and engines.

Serious contamination can be devastating — even simple fuel treatments cost thousands, and taking your assets out of operation for treatment could cost much more.

Circular dish showing dark spores of microbial contamination as used by Conidia Bioscience and the Fuelstat team

What is microbial contamination?

Microbial contamination comes from microbes that develop in fuel, feeding off the hydrocarbons in the fuel as well as even the smallest droplet of water.

These microbes and their by-products produce bacterial matting known as biomass, biofilms or slime, along with acids capable of inducing metal corrosion.

The microbial contamination is commonly called Diesel Bug, AKA Jet Fungus or algae, though it is not actually related to algae. It is a mixture of bacteria, filamentous fungi and yeasts.

These bugs thrive in any water bottom, particularly at the boundary between fuel and water, where they form biofilm and/or biomass. Biomass adheres to structures and clings onto tank walls, becoming a slimy material known as biofilm.

Read More >> Fuel Contamination // Diesel Fuel Contamination // Diesel Fuel Contamination Test Kit

Where does microbial contamination come from?

Fungal spores and bacteria are ever-present in air and water, and it’s practically impossible for them to be kept out of fuel.

Once fuel leaves a refinery, it’s almost guaranteed to be exposed.

The amount of microbial contamination, and whether it reaches dangerous levels, will depend on the conditions the fuel is stored in. The bugs grow fast in places with higher temperatures and more humidity, where condensation is commonplace.

While it’s not possible to stop microbial contamination, it’s important to control it. Minimising the level of water in fuel and practising diligent husbandry of fuel is crucial to managing the issue.

Glass jar holding some contaminated liquid with fungal spores and bacteria which has been tested using a Fuelstat test kit

FUELSTAT® 15-minute fuel test kit

Test for all known microbes that are dangerous to fuel in minutes.

Why microbial contamination risks are increasing for fuel users


Fuel industry bodies like the Joint Inspection Group (JIG) have long recommended minimising the amount of water in fuel tanks. This helps to control contamination, so the advice continues to be helpful. However, in the case of biofuel, it has become more challenging to completely remove water from fuel tanks at all times.

FAME (Fatty Acids Methyl Ester)

FAME (Fatty Acids Methyl Ester) added to diesel is hygroscopic, meaning that it absorbs and retains water more than ordinary diesel. In diesel with FAME, free water is typically found at the bottom of a tank, but there’s sometimes a hazy layer of suspended water above it. Although this hazy fuel can still be drained away, it’s much more difficult to expel the water droplets left behind in the fuel.

What happens if microbial contamination is left to grow?

blockage & corrosive effects

Prolonged, heavy microbe infections are very costly because of their ability to block filters and injectors and cause corrosive effects. Businesses need to take assets out of operation, repair mechanical parts, replace or treat the fuel itself, and de-contaminate fuel systems.

Polishing & biocide application

The fuel itself may need both fuel polishing and biocide application if it is to be saved for reuse. Even low/moderate contamination levels can lead to filter clogging, pump and injector wear, plus metering and gauging problems that affect fuel quantity indication systems. This can lead to expensive operational and commercial issues.

Proactive maintenance is the key to preventing costly contamination issues

proactive strategy

Many users have concluded that taking action with microbial contamination early on is the cheapest and best solution. Investing a small amount in a proactive strategy can mean huge savings in the long run.

fuel maintenance

As an operator, you need a fuel maintenance plan that incorporates a fuel test. You can test fuel with various tests on the market that gauge the levels of contamination in the tank, fuel system, or supply chain.

Testing methods

Each testing method has pros and cons regarding the time involved to obtain results, the cost, the equipment and expertise. When developing your fuel maintenance plan, consider these different methods along with the contamination risks that apply to your situation.

What fuel test options are available?

When you want to test fuels, the options available today are:

CFU growth tests such as IP385 Growth Tests, Thixotropic Gel Tests or ‘Dipslide’ Test

ATP (Adenosine Triphosphate) testing

Immunoassay-based tests

ATP and CFU testing methods are long-established tests that yield broad results, while immunoassay tests are more modern technology and more focused on fuel contaminants. Let’s take a look at all three.


CFU Growth Test: a ‘catch-all’ fuel test conducted in an off-site laboratory

This laboratory test very commonly used to test fuel, often referred to as IP385, requires a scientifically trained lab worker who places fuel samples into an incubating oven on a growth medium. After a waiting period (typically 3-7 days) the colonies that grow are analysed to produce test results.

CFU tests happen in a sterile laboratory off-site, so your company has to ship the fuel samples as a hazardous good. They must be delivered within 24 hours and kept at six degrees or below, as per ASTM D6469 Section 8.5, an international fuel standard.

However, after transport, the fuel sample may not fully reflect the actual fuel in the tank. Microbes in a sample can multiply in heat, go dormant in colder conditions, or even die off. The test results can therefore potentially exaggerate or understate any issues.

Results from IP385 CFU growth tests are generally interpreted through manual counting of colonies. They are checked against agreed industry limits for levels of fuel contamination.

From the day samples are dispatched, there can be a wait of up to 10 days before receiving results.

IP385 CFU is a ‘catch-all’ fuel test, measuring microbes present that will grow on the agar medium of the test. Because of this, it’s difficult to know what specific colonies have grown, and in what quantities. Most importantly, it’s not clear if the microbes are threatening to fuel systems.

Therefore, CFU tests can potentially result in misleading results—diagnoses of contamination based on microbes that aren’t necessarily dangerous to fuel. Without more scientific investigation, such as DNA sequencing, there is little way of knowing what has been found.

Additionally, if the microbes in the fuel samples die or go dormant during transport, or if they fail to grow in laboratory conditions, the test could fail to identify dangerous contamination.


ATP: a faster ‘catch-all’ fuel test conducted on-site

An ATP (Adenosine Triphosphate) fuel test is carried out on-site using a machine called a luminometer, yielding results in minutes. However, buying a luminometer requires a significant cash investment. The cost means it may not be an option for companies with minor testing needs, or insufficient in-house capabilities.

ATP fuel testing needs trained users with laboratory training to ensure that results are produced in a repeatable manner.

Results of the ATP fuel test are given as a number (concentration of ATP in the sample, captured as relative light units (RLU), which is an indirect indication of the number of living cells). This number is assessed against set industry limits for contamination by the technician who did the test.

Like IP385, ATP is a ‘catch-all’ fuel contamination test that doesn’t tell you what microbes are found. As a result, non-dangerous microbes and other living cells can contribute to the obtained signal, meaning misleading results may occur.


Immunoassay: fast in-house tests that only look for fuel microbial contamination

Immunoassay is a modern test on the marketplace. It’s a fast method that’s carried out on-site by placing a few drops of fuel sample into a test kit. It can be carried safely out on the spot without in-depth training or scientific knowledge.

Immunoassay is different because it only looks for microorganisms that cause problems in fuel systems. The tests assess the level of microbial contamination and provide a simple result.

Because immunoassay only looks at microorganisms that are dangerous to fuel, the chances of false positives are greatly reduced (and almost non-existent).

The test results indicate what groups of microorganisms were found, and whether there is a negligible, moderate, or heavy amount. No further analysis or cross-referencing is needed.

What happens when there are false positive results from ATP or CFU tests?

After a positive contamination result, testing personnel usually recommend fuel cleaning, biocide, or polishing treatments. If the result is misleading, there is no dangerous contamination, meaning the treatments would be totally unnecessary—an unfortunate waste of money.

Besides the cost, unnecessary use of biocide has additional drawbacks. Biocide should be used carefully, and overuse can encourage the bugs to build resistance. This problem is akin to humans developing a resistance to antibiotics.

FUELSTAT® fuel test kit: from sample to digital report in 15 minutes

FUELSTAT® is an immunoassay fuel test kit for microbe detection. It can be used wherever fuel is manufactured, stored, sold or used.

Unlike traditional tests, FUELSTAT® only finds microorganisms that do damage to fuel.

With FUELSTAT®, tests take as little as 10 minutes, unlike current growth-based tests that need at least 72 hours.

The process is self-contained, requiring no additional equipment—just a single FUELSTAT® fuel testing kit for each test. It’s so easy to use, that a single individual can carry out the tests with only minimal training.

The FUELSTAT® Plus test is sold in over 130 countries globally and is compliant with International Standard ASTM D8070. It is used worldwide by over 400 airlines.

Step 1
Test with FUELSTAT® Plus, placing 4 fuel sample drops into each of the 6 test wells
Step 2
Scan the kit with the FUELSTAT® Result app on your smartphone
Step 3
Get a Full Analysis Report from the app on the FUELSTAT® Result Portal, with all results stored for later retrieval and analysis.

Where to buy test kits

You can FUELSTAT® test kits on our website, or through registered stockists in your area (visit our site for more details on stockists).