Diesel fuel can become contaminated during long-term storage


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Potential issues:

  • Exposure to water.
  • Exposure to the oxygen in the air
  • Extreme heat or cold temperature swings.
  • Biological contamination (Bacteria, fungi, and mold)
  • Low quality and contaminated fuel mixed with clean fuel to solve the problem.
  • Ultra-low sulfur diesel (ULSD) has a greater tendency to oxidize than higher sulfur diesel since sulfur is a natural antioxidant.

Temperature/ Exposure to Oxygen

  • Wax crystals form when fuel is not prepared for use in cold temperatures, and those crystals will clog fuel filters.
  • Oxidized fuel is more acidic and forms larger molecules (gums, varnishes) that will fall out of solution and plug filters. Oxidation is caused by exposure to air in time. This process gets worse with more extreme temperature exposure (hot days/direct sun on tanks, and colder nights).
  • Biodiesel – Diesel blends tend to oxidize faster than Diesel alone.
  • Acidified fuel can corrode the tank which can lead to clogged filters, unnecessary generator component wear and downtime for the company.


  • Free water pooled at the bottom of diesel tanks can be drained off, but dissolved water will need to be run through water-absorbing filters.
  • Water in the fuel can lead to biological growth.

Biological growth

  • Bacteria, fungi, and mold can grow in diesel fuel and will clog filters with growth. Existing growth will need to be filtered out and treated with chemicals.

Other contaminations

  • Other tests like distillation can show if there is an appreciable amount of another fuel like gasoline or a chemical solvent.


Taking a representative sample is critical in understanding the nature of your fuel.

Different factors can determine where you sample:

  • Sampling dead bottom can give an idea of what water, sediment, and biological growth you have in the tank.
  • If you have water in the tank, sampling just above this water layer will give you an understanding of if your fuel is starting to oxidize and, also if it has biological growth.
  • However, if you suspect that your diesel has been contaminated with gasoline, for example, it would be better to sample at the top of the tank (since gasoline is less dense).
  • Taking an Upper, Middle and Lower sample might be appropriate for some tanks while taking an “All Level” sample might work for others.

The following is our recommended monitoring program:


Make Fuel Testing Part of your Maintenance Program

  • Diesel fuel testing can benefit any fuel quality assurance program by identifying problems so the fuel can be salvaged.
  • The best approach is to monitor the fuel yearly (larger group of tests) with a check-up on critical ones every three months.

Yearly Monitoring

Main sample (Sample taken above water layer (if one is present)
Cetane Index (ASTM D976) – Distillation (ASTM D86 or D7345) – Sulfur (ASTM D5453 or D7039) – Bacteria and Mold/ Fungi (D6469) – API/ Density (ASTM D4052) – Cloud Point (ASTM D5773) – Pour Point (ASTM D5949)
Sediment and Water (ASTM D2709) – Oxidation Stability (ASTM D7545) Flashpoint (ASTM D93).

Bottom sample(Sample taken at “dead bottom”)
Visual analysis (ASTM D4176)
Bacteria and Mold/ Fungi (D6469)
Sediment and Water (ASTM D2709)

Quarterly Monitoring

(Sample taken at “dead bottom”). Visual analysis (ASTM D4176) –
Sulfur (ASTM D5453 or D7039) – Sediment and Water (ASTM D2709) – Oxidation Stability (ASTM D7545) – Bacteria and Mold/ Fungi (D6469)

Other tests like Particle Count (ASTM D7619) and Karl Fischer Water Content (ASTM D6304) are available upon request.

Fuel, like the generator itself, needs maintaining, testing and continual monitoring. We can ensure that your fuel is viable and keeps your tank clean and generator running smoothly.

Be proactive with your fuel.

How to Get the Best Jet Fuel Testing 

Denver Jet Fuel

When it comes to jet fuel, what you cant see can hurt you.

Contaminated jet fuel causes engine flameouts, fuel gauge malfunctions, and other fuel system difficulties. In May 2019, a Cessna C550 on an air medical flight experienced a total loss of power in both engines because diesel exhaust fluid had been confused with de-icing fluid, which looks the same.

Because much of what contaminates fuel isnt visible with the naked eye, jet fuel testing ensures what goes into an airplane tank is only what should be there. Its a critical step, so you want to make sure you have it done right and done well.

When looking for a jet fuel testing company, the highest quality control standards are critical. Here are a few things to keep in mind as you consider your choices.

Follow The Correct Standards

Testing jet fuel works like any other kind of technical testing in that there are various standards to meet. These standards are set by several different groups for conventional jet fuel. you need standardized, world wide accepted testing that is very specific and acceptable to the jet fuel handling industry.

The most commonly used specifications and practices for Jet A or Jet A-1 include:

  • ASTM D1655 — US and international
  • UK Defence Standard 91-91 — UK and international
  • Joint Inspection Group Aviation Fuel Quality Requirements for Jointly Operated Systems — international
  • GOSST 10227 TS-1 — Russia and CIS
  • Number 3 Jet Fuel — China

For the most part, these standards are fairly similar because they deal with the same product. Minor variations in test limits can be dealt with by using the AFQRJOS checklist as it incorporates the strictest elements of ASTM D1655 and DEFSTAN 91-91.

Other specific standards deal with the more than 30 tests that might be done on your fuel, including checking sulfur levels, acidity, and freezing point, among others. You will also want to find out what standards the lab and its equipment are held to. 

ISO/IEC 17025 Accreditation 

States the lab operates competently and delivers valid results. That level of certification ensures your test results will have international approval.

Test The Right Stuff

Not only do you need a service that knows how to test jet fuel, but they also need to be testing that fuel for the right things. In some cases, the what and how of testing is handled by following standards, but its good to have a basic understanding of what you should expect a service to provide.

When you talk to a testing company, ask about how they stay on top of new issues that arise and require testing, such as discovering the DEF in the Ohio incident.

Contamination Sources 

The most common fuel contamination sources are water, particulates, surfactants & residues, and microbial growth.

While your fuel might have a low water content upon delivery, sitting around in storage provides ample opportunity for for water condensation to get in fuel. This could be rainwater leaks or damp outside air flowing in. Even a temperature change in the fuel itself can increase the chances of water condensing and changing the fuel makeup.

Particulates include dust and dirt, an inevitability despite new protective coatings on the interior surfaces of pipes and tanks. Airborne solids like dust and pollen or rubber from damaged hoses can also contribute to contamination.

Accidental contamination with DEF continues to be a possibility as changes to the standards for diesel vehicles at airports means it is on hand more. Another new contaminant being encountered is Fatty Acid Methyl Ester, which tends to show up when biodiesel fuel passes through a common fuel distribution system.

Microorganisms from air and water can get into the fuel and form solid debris that plugs fuel filters. The most common ones found are bacteria, yeasts, and fungi.

Fuel Types

Most commercial aircraft run on conventional turbine fuel called Jet A or Jet A-1. It comes directly from crude oil. Any testing company will be able to handle standard testing on this type of fuel.

Alternative fuels that are semi or fully synthetic have been added to the ASTM and DEFSTAN standards. More are on the horizon based on non-petroleum materials such as coal, biomass, and even algal growth. If youre considering a move to one of these fuels, you need a company that ensures its tests and procedures keep up with fuel innovation.

Experienced Jet Fuel Testing

Most of the time, there is no need for extreme speed on the part of your jet fuel testing service. But when you need it now, you need it now.

Cheap jet fuel testing can become problematic. You need a service that is open when you need them (including holidays!) and can perform tests now rather than later. A good service is going to be able to come on-site to pull samples for you and get them off for testing quickly.

The Final Word on Testing

An airplane engine is sensitive to any contamination in the jet fuel. Ensure your fuel product remains up to standards and safe for flying with proper jet fuel testing conducted at appropriate points along the supply path. The best testing services will be able to work with you and provide tests to the standards you require and to suit your timeframe.

If you are looking to add testing to your safety protocols, contact us to get a quote on our ISO accredited service.