On May 12, 1999, Southwest Research Institute
(SwRI) successfully conducted a fire performance
evaluation of a double-walled aboveground
storage tank (AST), manufactured for the Steel
Tank Institute. The AST was identified as an
F921® cylindrical tank 360° wrap,
UL#786046. The purpose of the test was to
determine if the AST would maintain its
structural integrity following the high
intensity fire exposure and hose stream test.
Evaluation of the tank was conducted for fire
exposure, leakage, and hose stream tests which
were performed in accordance with SwRI Test
Procedure 97-04, Testing Requirements for
Fire Resistant Aboveground Flammable Liquid/Fuel
Storage Tanks in Accordance with Section 2-4.5
of NFPA 30A (1996).
The fire test required the tank to be placed
in a 2000°F oven for two hours. This test
exposed the aboveground storage tank to heat
flux and temperature conditions representative
of total engulfment in the luminous flame regime
of a large, free-burning, liquid-hydrocarbon
fueled, pool fire. At
the end of the test, the tank was immediately
removed from the oven and subjected to the
cooling, erosive and impact forces of the hose
stream test (as outlined in UBC Standard 7-1,
Section 7-108). After a cooling period, the
primary tank was air pressure tested at five psi. This pressure was maintained for one hour.
The primary and secondary containment tanks
remained airtight for the entire test period.
SwRI reported, "The structural integrity
of the primary tank and its supports were
maintained during and after all testing. Also,
the emergency venting remained operational
during and after all testing."
STI also opted to equip the tank with 12-inch
high saddles. After the test, the saddles were
thoroughly examined and were found to be in
excellent condition. The assembly was not
deformed, did not sag, did not collapse or
suffer other significant damage as a result of
the fire exposure.
History
NFPA created the definition of "fire
resistant tank" in the 1993 Edition of NFPA
30A. Section 2-4.5(a) states (in part):
"The construction that provides the
required fire-resistance protection shall
prevent release of liquid, failure of the
primary tank, failure of the supporting
structure, and impairment of venting for a
period of not less than 2 hours when tested
using a fire exposure that simulates a high
intensity pool fire..."
Around the same time, Underwriters
Laboratories issued UL 2085
which at that time covered both Protected and
Fire Resistant type tanks. The 2nd edition of UL
2085, published December 1997, removed fire
resistant type tanks, leaving only fire
protected tanks. UL has since proposed a new
standard, UL 2080, which consists of the prior
UL 2085 requirements for fire resistant tanks.
SwRI 93-01 was issued in 1993 to provide a
listing program for tanks tested according to
UFC79-7. SwRI 97-04 was in 1997 for tanks tested
according to NFPA30A, 2-4.5.
