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Diesel Fuel Testing for Cleanliness or Contamination

Posted February 25, 2022 by Caleb Courville

You may already know that over time diesel fuel will degrade and harbor harmful contaminants such as water, microbes, particulate, and sludge. Now, you are looking for a reliable testing method to ensure you do not face the consequences of equipment failure due to subpar fuel quality.

According to the NFPA 110 standard, people who own and operate buildings with emergency generators are required to conduct fuel quality testing annually to ensure their backup power does not fail during a power outage. These tests must be performed to meet the ASTM D975 testing standards.

While annual testing may be sufficient to meet minimum regulatory requirements, it is not necessarily optimal for ensuring that your diesel fuel stays within specification throughout the year. For many facilities that are vested in mitigating downtime, fuel quality testing will likely occur more frequently to either confirm the effectiveness of existing fuel maintenance programs or prescribe remediation services like fuel polishing.

When searching for diesel fuel testing options, it may not be abundantly clear what choices you may have. That is why we went ahead and developed a quick guide to cover all the available options for testing your diesel fuel for cleanliness or contamination.

Lab Testing Options for Diesel Fuel Contamination:

For regulatory reporting, most of these tests are performed offsite in a specialized lab. Facilities will capture several fuel samples from their tank(s) and ship them to these laboratories for analysis.

Depending on the prescribed package of ASTM tests, these labs will look for and measure one or several types of contaminants, giving the facilities crucial feedback on the overall quality of their fuel.

Microbial Lab Test (ex: ASTM D7978)

Microbial contamination can be one of the most alarming signals of poor fuel quality. While microbes will always reside in diesel, they will not over proliferate to damaging levels unless there is a sufficient source of water.

Microbial fuel testing usually looks for specific bacteria and/or fungi known to damage the fuel and produce sludge and sediment. If these microbial levels are beyond a certain measurement, one can infer there is likely water and sediment contamination in their fuel tanks as well.

A remediation service like fuel polishing will be necessary to restore the fuel’s quality in place of just using a chemical additive like a biocide.

Water/Sediment Lab Test (ex: ASTM D2709)

As previously discussed, water contamination is the main prerequisite to rampant microbial contamination and should therefore be monitored and mitigated.

Over time, water can make its way into the fuel through condensation and accumulate at the bottom of the tank, creating perfect conditions for microbial growth which can lead to sediment formation. Water/Sediment testing will measure the amount of water and sediment that is suspended in the fuel.

Particulate Lab Test (ex: ASTM D6217)

Larger particulates in the fuel are known to be especially harmful to engine injector tips. Therefore, a particulate lab test may be necessary to determine the overall cleanliness and quality of the diesel fuel.

This test will measure and report on the size and mass of the particulate present in the provided fuel samples. These measurements will give a good indication of whether the fuel needs additional filtration before it can be safely and reliably used.

Onsite Testing Options for Diesel Fuel Contamination:

While lab testing may be necessary for annual reporting, onsite testing options are a reliable alternative for giving facilities quicker feedback on their fuel quality throughout the year.

Growth-based Microbial Testing

Growth-based microbial tests like Liqui-Cult can be performed onsite or in the lab. These tests take 72-hours to complete as users wait for signs of visible growth to appear within the collected fuel samples.

Users can then determine the severity of bacterial and fungal contamination in their fuel by comparing the color density of the sample bottle(s) with the provided color chart.

Instant Microbial Testing

FUELSTAT® is an instant ASTM D6469 compliant fuel test that checks for specific microorganisms known to damage diesel fuel. These tests take as little as 15 minutes to complete, making them a much faster alternative to traditional growth-based tests.

Users simply prepare the fuel sample and place it in the wells found on the provided test plate. Once complete, the test results can be scanned and verified using the FUELSTAT® Results App.

Water Finding Paste

Kolor Kut® Water Finding Paste offers a simple and instant way to check for the presence of water in diesel fuel. The paste works by simply changing color (golden brown to red) once it contacts any water.

Users can apply the Kolor Kut® paste to a measuring stick or rod and insert it into the tank. By observing the rod or measuring stick, one can gain an idea of the water’s depth in addition to whether it is present in the tank.

Lab vs Onsite Testing Options

Lab testing for diesel fuel cleanliness or contamination is generally a good option and arguably the only option for complying with the NFPA 110 annual testing requirement. The only downfall to this type of testing is the higher cost and decreased accuracy of microbial lab tests.

Many facilities will want to test their fuel on a more frequent basis to ensure its reliability is maintained throughout the year.  

Onsite fuel quality tests like FUELSTAT® are generally less expensive than employing a third-party lab to examine your fuel samples. When conducting any microbial test there is also the concern of its accuracy when a greater amount of time occurs between the sample collection and the actual lab test.

Microbes will continue to proliferate after the sample has been drawn. The longer it takes the sample to reach the lab and for the lab to test the sample, the less representative that sample is of the fuel’s quality.

To further mitigate any threat of facility downtime caused by poor fuel quality, onsite periodic testing is a much better option that will yield more accurate results in a much shorter time frame. This will provide facilities with more time to employ remediation services as deemed necessary by less than desirable test results.

Capturing “Good” Samples for Diesel Fuel Testing

Regardless of what testing method you employ, you will need a means of capturing diesel samples from the areas in the tank that are known to be most problematic. For cylindrical tanks, this would be the very bottom. For base/belly tanks, this would be almost any corner, especially between baffles.

Collecting samples from these areas will help you avoid any illusion of cleanliness, ensuring your fuel gets the maintenance it needs before it can cause any damage to the tank itself or connected equipment.

Two popular products for capturing diesel fuel samples are the fluid sampling pump and fuel tank sampler (a.k.a. the bacon-bomb). The fluid sampling pump is straightforward, featuring a hand pump that pulls fuel through its flexible tubing into a spin-on fuel sampling container.

The fuel tank sampler is a little less obvious in its design. This device is meant to be lower into a tank with two attached chains. One chain is there to guide the device down into the tank while the other is meant to be pulled once the device has reached the desired depth, allowing fuel to flow into and fill the device.

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