The use of prefabricated aircraft fueling skids is very popular in the general aviation fueling industry and is gaining in popularity in the smaller commercial aviation markets. The ability to have a factory fabricated system that can be fully tested and commissioned prior to delivery to the site reduces the construction costs of field fabricated systems, the need for multiple equipment representatives to visit the site during start up, and provides for a package unit that can be relocated in the future.
If you are in the market for a new system, it is imperative that you do your homework up front or hire a professional engineer with aviation fueling experience to design or specify your system as it has been my experience that nearly 99 percent of the general aviation fueling systems either do not meet all required fire and electrical codes, do not take all available steps for fuel quality, or are simply not designed in accordance with appropriate practices, all of which can lead to unsafe conditions. How can this happen in today’s regulatory environment? The answer to this question can be found in the fact that designers, owners, and permitting authorities often have limited or no experience with aviation fueling facilities. The resulting poor design documents are then used to bid the work to contractors and equipment vendors who are forced to make assumptions and take cost cutting measures in order to remain competitive.
Over the years of performing site inspections, designing replacement systems, and as a personal user of self serve Avgas systems, I have come across a number of deficiencies in various systems. The following paragraphs highlight a few of the more prevalent examples.
Fire Codes and Electrical Codes
There are two national fire codes that address fuel storage; either of which may be adopted by the local municipality. These include the National Fire Protection Association (NFPA) and the International Fire Code (IFC). There are subtle differences in the two codes; however, both reference NFPA 407, Aviation Fuel Systems. NFPA 407 defines aviation fuel as a petroleum fuel used in aircraft engines. Therefore, this code applies to both Jet-A and Avgas systems which are the two most common fuels dispensed from general aviation facilities.
NFPA 407 provides a majority of the guidance for general aviation fueling systems, whether bulk loading Jet-A or Avgas into refueler vehicles or a simple self service system that dispenses directly into aircraft. The National Electric Code (NEC) addresses the requirements for all electrical work in the hazardous areas around fueling facilities.
Unfortunately, system designers, fabricators, and permitting authorities frequently overlook or ignore portions of the code that could be critical to life safety. Examples of this situation include:
- Gaskets - NFPA 407 requires the gaskets in flanged connections to be of a material and design to resist fire exposure for a time comparable to the flange and bolts. Often paper gaskets are used in lieu of a spiral wound metal gasket.
- Fusible Valves - NFPA 407 requires that each outlet valve, whether on a dispenser or a refueler load rack, have a fusible device that causes the valve to close automatically in case of a fire.
- Aluminum Components - NFPA 407 does not allow the use of aluminum components unless specifically allowed by the authority having jurisdiction. Aluminum meters are commonly used in lieu of steel due to the lower costs. They will, however, melt in a petroleum fire. If the code requires the gasket materials to have the same temperature rating as the flange and bolt connections, it is not wise to install a component between two flanges with a lower temperature rating.
- Static Relaxation - NFPA 407 states that aviation fuel shall be provided a minimum of 30 seconds from the time fuel is filtered until it is placed in either a tank or refueler vehicle to allow the static charge that builds in the filtering process to dissipate. The 30 seconds of relaxation can be accomplished with either a sufficient length of piping between the filter and tank or with the use of a static relaxation vessel installed immediately downstream of the filter vessel.
- Bulk Loading - Both NFPA 30 and the IFC requires bulk loading connections and unloading connections to be 25 feet for Class I(Avgas) liquids and 15 feet for Class II(Jet-A) liquids from the tank as measured from the nearest fill spout or connection. Most installations with the bulk loading/unloading equipment located on the end of a horizontal tank do not meet this requirement.
- Dispenser Location — Dispensers are often located too close to the tank per the fire code and per the NEC. NFPA does not provide any requirements for the distance between the tank and dispenser (see photo on page 26), the IFC requires 50 feet of separation for above-ground tanks. This can be reduced to 25 feet with the use a UL2085 Protected Tank. Automotive type dispensers and credit card readers are commonly located on the end of a horizontal tank. By code, any area within 10 feet of a fuel storage tank is classified as a Class I Division 2 hazardous area. The components used in the upper housing of automotive dispensers, i.e. the LCD displays and fluorescent back lit panels, are typically not Division 2 rated. Additionally, the credit card readers are not intrinsically safe and should not be placed within 10 feet of a tank.
- Electrical Seal-offs - Finally, one of the most frequent items missed is the improper use of electrical seal offs as required by NEC when a conduit transitions a hazardous boundary. This is more frequently a concern of the actual installing contractor rather than the equipment manufacturer. This issue can be addressed by providing detailed design documents and retaining a licensed electrician, who is familiar with NEC, speciffically the requirements of the hazardous area’s classifications.
In aviation circles, “fuel quality” refers to providing clean fuel that is free of water, particulates, or other contaminants that may impact the operation of the aircraft. There are presently no fuel quality standards for general aviation which are widely used or required. The commercial airlines use ATA 103, Specification for Jet Fuel Quality to provide design guidance and operational parameters. ATA 103 requires the fuel to be filtered three times from the time it first arrives at the fuel farm until it is placed on an aircraft. There is no such standard for Avgas and as such, the fuel is normally only filtered as the aircraft is fueled.
There are four major components of a system design to ensure fuel quality:
- Provide both Inbound and Outbound Filtration;
- Use epoxy lined carbon steel tanks and piping or unlined stainless steel tanks and piping;
- Install the tank with a slope to allow any water or contaminants to migrate to a low point drain where they can be removed by the operator with daily tank and filter separator water draw off connections;
- Use floating suction arms to ensure the fuel that is drawn from the top of the tank where water and particulate matter is least likely to be found.
Poor Design Practices
It is all too common that these critical facilities are designed and/or permitted by entities that do not routinely work with aviation fuel or do not design a system specifically for a location. Poor engineering practices can lead to a higher probability of fire, explosion, spills, or endanger human life. Two simple items that are commonly overlooked but could significantly decrease the likelihood of a fire or spill at your facility are identified below.
Thermal Relief - Thermal relief valves are provided in a system to prevent over-pressurization of the piping or filter vessels in the event a manual valve is closed while ambient temperature is rising and the fuel is expanding. Each section of piping that can be isolated should be provided with a means to protect the piping from over pressurization.
Air Elimination - Positive displacement (PD) pumps are often used for offloading of transport trucks in lieu of a more expensive system that includes a centrifugal pump and control valve. When a PD pump is used to remove the last bit of fuel from the delivery truck, a large amount of air can end up in the filter vessel. The next time the pump is turned on a slug of fuel is introduced into the filter vessel which is full of air. The air eliminator on the filter vessel is not sized to discharge the air quickly enough and the fuel compresses the air in the vessel resulting in a potentially explosive condition. This issue can be easily remedied through the use of a self priming centrifugal pump with an external air release head. Air from the system should then be discharged to the downstream side of the filter vessel or directly into the tank.
How can you protect yourself when buying or specifying a new system for your airport? Use a reputable company, hire a professional engineer with aviation fuel experience to perform a code review and to specify and design a suitable system for your airport, and ask for certification from the manufacturer that their system meets all local codes.
about the author
Dan Frank is a mechanical engineer with 19 years experience in aviation fueling system design and construction oversight. He is the Vice-President of Engineering for Argus Consulting, Inc., an engineering consulting firm specializing in commercial, military, and general aviation fuel system design. He is licensed professional engineer in MO, TX, NY, ID, AK, WA, Alberta, and British Columbia.