Lately, we have logged several calls on the same topic from facilities confused about the quantity of diesel fuel required by authorities for on-site diesel-powered EPS (emergency power supply) engines. We have responded to all inquiries with the same answer; it all depends on your local Authority Having Jurisdiction (AHJ). While this may seem like “passing the buck,” it is the only answer that is always correct.

For the most part, AHJ’s refer to NFPA standards for guidance; however, you would be wise not make a buying decision based on any “standard” until you have a specific written agreement with the local AHJ. NFPA 99, Health Care Facilities Code, defers to NFPA 110, Standard for Emergency and Standby Power Systems, for design requirements of Type I, II and III essential electrical system (EES) power sources. Each of these designated “Types” are further designated as “Type 10, Class X,” as defined by NFPA 110.

According to NFPA 110 (2010 and 2016 Edition):

  • “Type” refers to the maximum time, in seconds, that the EPSS will permit the load terminals of the transfer switch to be without adequate electrical power.
  • “Class” refers to the minimum time, in hours, for which the EPSS is designed to operate at its rated load without being refueled.

“Class X” is defined as the time, in hours, as required by the application, code, or user. In other words, NFPA 110, through its classification structure, creates broad guidelines concerning how to utilize the EPSS, and the AHJ’s then make the specific calls.

Why do variances exist? Each local AHJ makes a judgment about fuel stored on each site based on local factors, including the estimated time a facility would have to wait for fuel delivery, seismic classification, storm history, and general history of power outages.

The need to store substantial quantities of fuel on site for potential long-lasting emergency creates a problem, the one of dealing with aging fuel. During extended run times, most EPS fuel system failures are caused by “old” diesel fuel.  We have addressed this serious issue more than once and described several possible solutions. You can have too much fuel on hand if it is not being treated and used within an acceptable time frame.

Although you must check with the local AHJ for their recommendation, we favor having the equipment, such as boilers, use fuel from the same tank as the EPSS. The fuel in “dedicated” tanks, especially EPS skid mounted tanks, are normally not used or “turned over” at the same rate as non-dedicated tanks. In these types of setups, the pickup tubes for the other equipment are inserted into the tank in such a manner that the EPSS “dedicated” fuel is not disturbed.

“Fuel polishing” has become the standard way of ensuring fuel meets the manufacturer’s standards.  It can be accomplished using either a portable or permanently installed apparatus.  Economics is a concern as well as having a plan to ensure clean fuel whenever an event will occur.  See “Fuel polishing aids facility in emergency power readiness” (Health Facilities Management)