Along with starting batteries, fuel is the most common reason an emergency power supply (EPS or “generator”) fails to start. Problems with the fuel system stem mainly from foreign matter such as fine abrasives, water, and “coagulated” aging fuel. These contaminants cause reduced performance and expensive repairs, not to mention preventing the generator from starting in an emergency.
The need to store substantial quantities of fuel on-site for a potential long-lasting emergency creates a problem, the one of dealing with this “aging” fuel. The technical committee responsible for NFPA 110, Standard for Emergency and Standby Power Systems, recently held its annual meeting to discuss proposed changes. One topic of discussion included stored diesel fuel.
Problems with Storing Diesel Fuel
When tanks are not full, excess air space allows for warm, humid air to enter the tank and condense moisture during the cooler evenings. The presence of this water leads to microbiological contamination and growth, causing tank and tank component corrosion. A regularly scheduled maintenance program is needed to ensure the build-up of any contaminants are not present, preventing the EPSS from operating efficiently and reliably.
Fuel tanks should be kept cool and dry, and the tank as full as possible to help with the reduction of water build-up. But over time there is no stopping the degrading of fuel quality — especially tanks exposed to extreme temperature variations, such as storage tanks located outside and above ground.
Diesel fuel maintained in a condition as close to “refined” as possible will outperform fuel that is poorly maintained. To achieve optimal fuel quality, the contaminants in fuel must be filtered out, water must be separated and removed, and the fuel must be conditioned. This process of filtration, separation, and conditioning (known as the fuel polishing process) is the foundation for achieving and maintaining, the quality of fuel necessary for ultimate reliability.
- Filtration – Contamination removed to prevent clogging and abrasive wear
- Separation – Remove water to avoid increased engine compression and growth
- Conditioning – Reduce particulate sizes to prevent filter clogging
Fuel Quality Tests
NFPA 110, 8.3.7 (2019 edition) states: “A fuel quality test shall be performed at least annually using appropriate ASTM standards or the manufacturer’s recommendations.”
During the recent technical committee meeting, proposed changes were introduced to expand fuel testing requirements, including references to specific ASTM standards. The ASTM standards included in the NFPA 110 proposed changes include:
- D4507 Standard Practice for Manual Sampling of Petroleum and Petroleum Products
- D7464 Standard Practice for Manual Sampling of Liquid Fuels, Associated Materials and Fuel System Components for Microbiological Testing
- D6469 Standard Guide for Microbial Contamination in Fuels and Fuel Systems
- D2709 Standard Test Method for Water and Sediment in Middle Distillate Fuels by Centrifuge
- D7371 Standard Test Method for Determination of Biodiesel (Fatty Acid Methyl Esters) Content in Diesel Fuel Oil Using Mid Infrared Spectroscopy (FTIR-ATR-PLS Method)
- D975 Standard Specification for Diesel Fuel
- D7545 Standard Test Method for Oxidation Stability of Middle Distillate Fuels—Rapid Small Scale Oxidation Test (RSSOT)