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Is your backup generator at risk of failure?

Article from Data Centre Dynamics

If diesel bugs grow sufficiently, they can pose a serious risk to the fuel system and the generator itself.

Our modern, data-centric society is heavily reliant on data centers being available 24/7. If there is a power failure, backup power needs to be instantly available to keep systems running. Most data centers therefore employ an emergency backup power system in the form of generators, many of which use a diesel-fueled combustion engine. However, data center operators may not be aware that the reliability of diesel generators may be compromised by a phenomenon called microbial contamination.

Commonly known as the ‘diesel bug’, microbes, such as bacteria and fungi, grow in microscopic water droplets entrapped within the fuel in the storage tanks. As the diesel generators are only used as backup they are not ‘fired-up’ on a frequent basis and the microbes have time to grow. If these microbes grow sufficiently, they can pose a serious risk to the fuel system and the generator itself meaning, the data center may not have the emergency power it is expecting.

data centre

Biodiesel helps the environment but brings additional risk

Water gets into diesel fuel because of condensation, rainwater penetration or adsorption from the air. Since the introduction of BioFuel with the addition of Fatty Acid Methyl Esters (FAME) and reduced sulphur the quality and life expectancy of fuels has been adversely affected. FAME is hydroscopic so any water in the fuel goes into suspension increasing the risk of contamination. Microorganisms extract oxygen from the water in biodiesel and feed from the hydrocarbon in the fuel, creating an ecosystem where they can thrive. As the microbes grow, they can block filters, foul equipment, promote corrosion, and lead to engine failure.

Data center emergency gensets are at particular risk of microbial contamination because they are not operational on a regular basis. Microbial contamination is not as common where fuel supplies are regularly replenished, such as in cars, which have relatively small fuel tanks that are being frequently refilled. The issue arises where fuel is stored, and the organisms have time to multiply. Water is heavier than fuel and so you may expect it to settle at the bottom of a tank. The hygroscopic nature of modern biodiesel, however, means water molecules, and therefore microbes, are suspended in the fuel for longer, which can further enhance injector damage and blocking of conventional filters.

The term ‘diesel bug’ refers to multiple types of organisms, the presence of which will vary according to individual site conditions based on factors including temperature and humidity. The ‘bugs’ include bacteria, mold, and yeast, all of which can combine to form thicker biofilms. The lead organism is most often Hormoconis resinae (H.res), which has a filamentous (long stranded) fungi structure. This acts as a binding material for other micro-organisms to cling to which results in the formation of a biomass in the fuel.

Stopping the Diesel Bug

So, if microbial contamination in biodiesel supplies is a real risk, what measures are being taken? Unfortunately, the risks associated with the ‘diesel bug’ are only just working their way into service guidance from generator equipment manufacturers. The risk posed to equipment is well recognized in industries such as aviation and marine, but awareness is not as high amongst data centre operators, who instead often rely on fuel polishing services provide by fuel maintenance contractors. These contractors should perform testing and provide reports to the operators as verification of fuel quality.

The British Standards Institute replaced BS5410-3:1976 with an updated release in 2016 to cover concerns about failure of critical standby generators and states that: “Fuels for emergency generators should be tested every six months for quality and suitability if fitted with a fuel polishing system, if there is no polishing system the fuel should be tested every three months.” These are, however, only guidelines and not a regulatory requirement. In many countries there is no guidance and testing for microbial contamination may not be happening at all. Even if a data center has a fuel management program, this usually involves starting the generator for a few minutes every six weeks. The long interval and the fact that the fuel is not “mixed” sufficiently during the short-run period, means that facilities managers should review testing based on the guidelines above.

If samples are being taken offsite for testing, this ideally needs to happen quickly as the microbial community may change while samples are preserved in transit, meaning the test results may not be representative of the microbial growth in the tank/generator. The Standard Guide for Microbial Contamination in Fuels and Fuel Systems, ASTM D6469 – 14, states in Section 8.5 that: “Samples for Microbiological testing should be kept on ice for transport to the laboratory. Tests should be performed within 4 h and no later than 24 h after sampling. Samples stored at higher temperatures, or for longer times, can show the presence of microbial contamination that does not represent actual fuel system conditions.” Overall, it makes more sense to carry out testing onsite to avoid these issues altogether. This can be achieved using an immunoassay antibody test kit.

FUELSTAT solo working (1 Test Kit)

Immunoassays have long been used in the medical industry to accurately detect specific molecules. They use antibodies that bind to a specific antigen to detect its presence and produce a measurable signal in response to this binding that can be used to assess fuel contamination levels. Microbial contamination levels correlate to the activity of microbial growth in the sample and the amount of antigen produced when microorganisms grow in the fuel is measured for a known sample size. This shows the presence of microorganisms actively growing in the fuel and provides a fast indication of contamination levels.

Immunoassay antibody testing can easily be carried out onsite by a member of the center’s maintenance team and especially during solo working conditions as a result of the ongoing pandemic. The kits give quick results and require no capital investment for sophisticated test readers or other high-tech equipment. Indeed, when factoring in labor and other costs, these kits are one of the lowest cost options. They require no special handling or storage and have no onerous disposal requirements beyond the usual procedures for the disposal of fuel. The very nature of how the test works means that there is minimal risk of cross-contamination, results are accurate and completely reliable – and facility managers can take control in ensuring they will not be caught out by undetected contamination.


The move from petrochemical diesel to biodiesel was a good one, but it requires additional care if fuel is stored for longer periods. Emergency generators that often lie dormant are clearly at risk from microbial contamination. Unfortunately, current testing or maintenance activities may not ensure equipment reliability at the critical time it is needed.

Furthermore, transporting fuel samples to a laboratory adds uncertainty to the veracity of test results. Onsite testing can be fast, reliable, straightforward and a low-cost way to provide the peace of mind needed to keep data centers operational.