A UL2085-listed tank located at the The Hyde County Airport in North Carolina.
The new U-Fuel 'Double Fire Resistant' Box station at Atlantic Aviation's FBO at the Charleston Executive Airport.
At most airports fuel for aircraft and ground vehicles is stored in aboveground storage tanks (ASTs). Each State will have their own regulations defining size and number of tanks, locations, setbacks, safety equipment, and specifications for loading and dispensing fuel.
While each state has the right to determine its own regulations, states generally adopt national fire codes and modify them to fit local requirements. The most popular code adopted is the National Fire Protection Association (NFPA) code.
Adhering To Code
The Sections of NFPA regulating aboveground storage tanks are NFPA 30, titled Flammable and Combustible Liquids Code, and NFPA 30A, Automotive and Marine Service Station Code. NFPA 30 primarily deals with fuel tank design and safety, and NFPA 30A deals with fuel handing and safety issues at service stations and marinas.
While NFPA 407 regulates airport fuel systems, many states use NFPA 30A to regulate fueling small aircraft by pilots.
Typically, NFPA 30 and 30A regulate aboveground storage tanks according to three factors:
1.) Type of inflammable or combustible liquid stored;
2.) Location of the tank in relation to property lines, public ways, and buildings on the same property; and
3.) Type of intended use.
The NFPA allows unattended service stations with aboveground tanks provided the tanks are ‘Fire Resistant’. A Fire Resistant Tank is designed and tested by a Nationally Recognized Testing Laboratory (NRTL) to maintain its structural integrity for a period of not less than two hours when exposed to a temperature of 2,000oF, as described in UL 2085, Standard for Insulated Aboveground Tanks for Flammable and Combustible Liquids.
Three UL codes and two SwRI codes relate to ASTs:
UL142 AST: a construction standard for steel tanks; does not require a fire test.
SwRI 97-04 Fire Tested Tank: requires a two hour, 2000oF fire test; primary tank must pass 5 psi air pressure test for one hour. No temperature limits. Optional: Vehicle impact resistance, ballistics resistance.
UL2080 Fire Resistant tank: requires a two hour, 2000oF fire test, temperature limit: 800o F avg., 1000o max. at any one thermocouple. Optional: Vehicle impact resistance, ballistics resistance.
SwRI 93-01 Protected Tank: requires a two hour, 2000oF fire test, temperature limit: 260o F avg., 400o max. at any one thermocouple. Optional: vehicle impact resistance, ballistics resistance.
UL2085 Protected tank: requires a two hour, 2000oF fire test, temperature limit: 260o F avg., 400o F max. at any one thermocouple. Optional: vehicle impact resistance, ballistics resistance.
In most instances, ASTs that comply with the UL142 construction standard and SwRI 97-04/UL2080 fire tests are acceptable for use at airports, in particular for the turnkey, self-service fuel stations that my company specializes in.
The Steel Tank Institute (STI), a trade association representing fabricators of steel construction products and their suppliers, licenses many tank manufacturers to sell their products under the Flameshield ® (UL142, Fire Resistant) and Fireguard ® (UL2085, Protected) trademarks.
While concrete has been a traditional insulator, the significant weight increase this brings has led some tank manufacturers to now offer lightweight thermal insulation that can be 75 percent lighter than concrete, reducing the costs for shipping, installation, and relocation.
But are UL2085-listed tanks worth the additional cost and weight? First, let’s consider the need for the lower temperature limits dictated for UL2085 tanks.
The principal difference between UL2085 and UL2080 fire test criteria is that the former limits the average temperature rise to 260o F average above ambient, with a maximum for any one thermocouple limited to 400o F above ambient.
The SwRI 97-04 Fire Resistant criteria is based on the NFPA definition of a Fire Resistant tank which does not require these temperature limits. As noted by Bob Benedetti, Senior Flammable Liquids Engineer of NFPA, in the Flammable and Combustible Liquids Code Handbook:
...the autoignition temperature of typical motor and aviation gasolines is well above 800o F. More importantly, their boiling points are in the 100o F to 400o F range. During an actual fire incident, by the time internal conditions reach the autoignition temperature, the gasoline should have boiled away and been expelled through the emergency vent, leaving precious little vapor behind to be ignited (pg. 384).
In a nutshell: the higher temperature limits of SwRI 97-04/UL2080 are perfectly adequate for aviation fuels, ie a Fire Resistant tank suffices and a UL2085-listed tank is not necessary, from the standpoint of explosion potential.
Next, let’s consider the need for vehicle impact and ballistics resistance. (As an aside - fuel trucks used to deliver fuel to ASTs or dispense it to aircraft are required only to have single wall aluminum tanks as opposed to the double wall steel tanks required for stationary ASTs that will never be driven down an Interstate highway at 70 mph!)
In nearly all AST installations, some form of relatively inexpensive collision protection around the fuel tanks is required, for instance steel posts (aka bollards) set in the concrete pad and themselves filled with concrete. This is generally more than adequate to protect the tank from vehicle collision.
But what about the need for ballistics protection? This is primarily a matter of the probability that the AST will be shot at or be exposed to flying debris in a tornado or hurricane. (As an aside again — although a fuel transporter operating on public roads is exposed to a far greater risk of being shot at, ballistics protection is not required for these.)
UL2085 generally requires bullet resistance whereas SwRI 97-04 does not. Additionally, it is important to note, as stated by Bob Benedetti in the NFPA’s Flammable and Combustible Liquids Code Handbook:
“Bullet impact resistance is not warranted, based on past use of traditional steel tanks that were designed to UL142, Standard for Steel Aboveground Tanks for Flammable and Combustible Liquids, or other acceptable specifications and the miniscule number of worldwide reports of actual incidents of exposed steel tanks being damaged by gunfire.”
In summary, the requirement for UL2085-listed tanks appears to be without much merit when considering the actual autoignition temperatures of aviation fuels, the common use of collision protection around ASTs, the very low probability of damage due to gunfire, and the real danger of explosion if a tank was actually penetrated by ballistics.
Given the increased costs for UL2085-listed tanks and their higher weight — leading to increased shipping, site prep, installation, and relocation costs — airports and their authorizing agencies (typically the state or local fire marshal’s office) would be well advised to consider accepting UL142 Fire Resistant tanks in most applications.