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Marine Fuel Test

Marine fuel testing for microbial contamination: a practical guide

Every year, numerous sea vessels experience technical and mechanical problems caused by fuel contamination.

In many of these cases, the fuel was on-specification and didn’t have dangerous levels of contamination when it was uploaded. Microbial contamination can grow quickly in short time periods – so testing your marine fuel is very important.

Luxury yacht on the water after successfully testing their marine fuel using the Conidia Bioscience testing kit

Why marine fuel management is becoming more important

The upcoming IMO 2020 regulations are important for fuel users, as they require fuel manufacturers to use less sulphur.

With less sulphur in fuels, it may become easier for microbial contaminants to grow and flourish, although this is not as yet an established fact. These contaminants, often called diesel bug or diesel fungus, can seriously affect fuel quality and cause costly damage to engines.

If you’re an MGO user, these changes mean it’s vital to conduct a regular fuel management programme that includes testing for microbial contamination.

Read More >> Diesel Fuel Contamination Test Kit

After IMO 2020, it seems likely that fuel costs will increase as demand outstrips supply. With that in mind, it makes solid financial sense to minimise any potential risks to your expensive refined MGO. The keys to doing this are improving fuel management and conducting regular marine fuel tests.

Further consideration should be given to vessels with dual-fuel capability which requires the switch over from Heavy Fuel Oil (HFO) to Marine Gas Oil (MGO) upon entering Emission Control Areas (ECA). In this situation, microbial contamination can occur within the MGO during a vessel’s passage through open waters and the management of this precious cargo is essential to minimising the potential risk of fuel supply issues upon fuel switch over. The use of FUELSTAT® provides a vessel with the ability to test for the presence of microbial contamination during transit and make informed decisions on any remedial requirements that may be needed.

FUELSTAT® off-shore marine fuel test – FUELSTAT Diesel Plus (FMD8)

Test for all known microbes that are dangerous to fuel in just 15 minutes

What is diesel bug - microbial contamination, and how does it affect marine fuel?

Diesel bug, also called diesel fuel fungus, is often the filamentous fungi Hormoconis resinae that damages marine fuel along with bacteria and yeasts that can thrive and do damage in fuel.

Microorganisms are found virtually everywhere where fuel is found, entering through air and water. They can feed on components of the additives or on fuel hydrocarbons and are capable of multiplying at an incredible rate.

Diesel bug microbial contamination creates a slime called a biofilm or biomass that can cause several issues. If left for long periods without treatment, it can:

  • Block filters
  • Wear injectors
  • Stop engines from working
  • Induce corrosion, potentially resulting in tank leakage

Read More >> Diesel Fuel Contamination

To prevent this, many fuel manufacturers recommend complete fuel tank drains and cleaning on a periodic basis.

In addition, there are several tests that can detect microbial contamination levels to determine if fuel treatment is necessary. The fuel systems in ships are a perfect habitat for microorganisms to live and grow in, so it’s sensible business practice to use these tests.

How can diesel bug be controlled?

Microbiological contamination in ships and vessels is usually promoted by the presence of water in diesel fuel. Water is the breeding ground for microorganisms, so industry operators describe minimising water as the ‘holy grail’ of fuel maintenance. However, it is very difficult to effectively remove all water from a fuel system.

With this in mind, the diesel bug microorganisms will always be present in fuel to some degree. It’s possible to control the problem with a combination of marine fuel testing, filtering, filter inspection, and fuel treatments. These treatments available include biocides, fuel polishing and mechanical cleaning.

This kind of proactive approach requires an investment of time and money. However, it is considerably more straightforward and cheaper than dealing with tank and engine damage resulting from contamination. We highly recommend conducting marine fuel testing before bunkering to avoid taking contaminated fuel on-board.

A birds eye view of a large red fuel tanker which has recently tested it's marine fuel using the Fuelstat testing kit

Does removing water prevent diesel bug?

For many years, fuel industry specialists have recommended minimising water in order to tackle the diesel bug problem.

This advice is still totally valid today. However, it’s now much more difficult to effectively remove water from diesel and MGO that contains biofuel.

Biofuels often contain FAME (Fatty Acid Methyl Esters). This material is extremely hygroscopic—in other words, it absorbs and holds on to water more than traditional mineral diesel. In fuel containing FAME, free water can usually be found at the bottom of a tank. But above this free water layer, there is often a hazy layer of suspended water.

While the free water is fairly easy to drain away, droplets of water often remain in the fuel. It is very difficult to remove these droplets. And wherever there is an interface between fuel and water, the dangerous microorganisms can live and multiply.

What are the options for testing marine fuel?

There are three types of marine fuel test that are available today:

Generally, an on-shore test takes several days and is conducted in a sterile laboratory by highly-trained specialists.

Alternatively, there is a method called thixotropic gel that can be done on-site but also requires the same incubation as with all CFU growth tests.

A fast test that can be carried out off-shore using specialised equipment. Extensive training is required.

A rapid modern type of on the spot test, often used when operational at sea, which can be carried out without any special equipment and without needing extensive training.

We’ll take a closer look at all three marine fuel tests after a quick note regarding on-shore testing.

Is sending samples onshore for marine fuel tests worthwhile or economical?

Traditionally, marine fuel testing methods have depended on fuel samples being sent on-shore for analysis. The next step is a waiting period of up to 10 days to get the results.

Sending the fuel samples isn’t simple. They must be transported as a dangerous good to a sterile laboratory and tested within 24 hours, as per ASTM D6469 Section 8.5. They are then run through a growth test known as IP385.

However, after the journey to the laboratory, the sample may not remotely reflect what was originally removed from the tank. Microorganisms in a sample can multiply in heat, go dormant in colder conditions, and even die off. By the time the sample arrives, the ship may literally have sailed and taking action based on the results may be very difficult, and risky to assets.

Marine fuel tests


CFU Growth Tests: a catch-all on-shore marine fuel test to detect microbial contamination

The commonly used IP385 test is based on growing culturable microorganisms that are present in the fuel—even ones not dangerous to fuel.

The technician who did the test then manually interprets the results by referencing agreed industry limits for contamination. If unsafe contamination levels are detected, treating the fuel will usually be the next recommendation.

However, the broad testing scope makes it impossible to understand exactly what the microorganisms are, and whether they’re threatening to marine fuel systems. When contamination is detected, the result might actually be a misleading result. Without further laboratory analysis, there’s no way of knowing.

A misleading result means that costly fuel treatment may be recommended where none was actually required. In addition to the cost, using biocide treatments too often is problematic. Biocide requires strict handling and application, and if used too often, can lead to the microorganisms becoming resistant to the treatment.


ATP: a highly technical off-shore marine fuel test

A newer faster technique called ATP (Adenosine Triphosphate) often requires fuel samples to be sent on-shore, but gives an almost instant result once the fuel gets there, an advantage over CFU Growth Tests.

However, it does require purchasing an expensive hardware unit if this was to be considered by ship owners. So, ATP may not be an option for many ship owners, fleet managers or fuel bunkering companies who do not test large enough volumes to justify the expenditure.

ATP testing must also be carried out by trained technicians with laboratory experience. Results are given as a number (concentration of total ATP present in the sample), and the technician who conducted the test has to interpret it against set industry limits for contamination. Like IP385, ATP is a ‘catch-all’ marine fuel test that doesn’t specify what microbes are found, meaning misleading results are possible.


Immunoassay: rapid antibody testing at sea to detect microbial contamination

The newest option is immunoassay antibody testing, which is fast as ATP, but doesn’t require expensive equipment.

It can be carried out on a boat, on the spot, and requires very little training to use.

Immunoassay is unique because the technology only searches for specific microorganisms that can thrive and do damage in marine fuel systems. The outcome is that cross-contamination from other microorganisms is no longer an issue, and the likelihood of misleading results is greatly reduced.

The method gives clear and simple results, requiring very little interpretation from the tester. You get a clear readout explaining what groups of microbes are present and what is the contamination level, without the need for calculation or cross checking.

FUELSTAT® is the immunoassay antibody Marine Fuel Test that takes just 15 Minutes

FUELSTAT® Diesel Plus the Marine Fuel test, based on immunoassay antibody techniques, is the ideal solution for the maritime environment.

It can be used wherever fuel is manufactured, stored, distributed or consumed, in as little as 15 minutes.

This is the only test available that detects all known organisms affecting fuel systems while ignoring harmless ones. Unlike with CFU or ATP tests, there is almost no chance of false-positive results. It provides simple alert levels that can be used to inform remedial actions—all without any special skills or equipment.

FUELSTAT® is sold in over 130 countries and trusted by 400 airlines (and counting). It is fully compliant with International Standard ASTM D8070.

A Fuelstat® immunoassay test kit being held up in preparation for use with marine fuel to test for microbial contamination

Learn more about FUELSTAT®

See how FUELSTAT® can save you time and money by testing for marine fuel contamination early.

Easy three-step process for on-site FUELSTAT® testing:

It really is as simple as 1,2,3:
Fuelstat test process 6

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

FUELSTAT Result (computer screen)

Step 3

Get a Full Analysis Report from the app on the FUELSTAT® Result Portal, with all results stored for later retrieval and analysis