...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.