MIL-HDBK-1022A
8.5
ABOVEGROUND SECONDARY CONTAINMENT (VAULTED) TANKS
8.5.1
General Design Considerations. When small
aboveground storage tanks are required (250 to 12,000 gallon
(900 to 45 000 L) capacity) and there are clearance or fire
exposure problems and the additional cost can be justified,
consider the use of concrete-encased storage tanks. The main
advantages of vaulted tanks over the single wall steel tanks
are that a separate dike (containment) may not be required and
the vault system provides an added measure of fire protection.
NFPA 30 and 30A have specific criteria for omitting dikes when
using this type of tank. All of the criteria in the NFPA
regulations for the appropriate application must be met before
this type of tank is used without a dike. Additional benefits
include added protection from ballistic and vehicular impact
and reduced evaporation of volatile fuels in warm climates.
Require tanks to be factory-constructed with a UL 142 welded
steel primary tank, generally low profile and rectangular in
design. Tanks may be used in applications where, in addition
to the above considerations, construction of a separate dike
for secondary containment purposes would have a negative
impact on operations and/or aesthetics. Tanks located close
to buildings or with integral fuel dispensers must be UL-
listed secondary containment tanks, utilizing steel inner and
outer tanks that can provide interstitial containment which is
both pressure testable and verifiable. Such tanks usually
have a fill of regular or insulating concrete. Ensure the
two-hour fire rating meets or exceeds all requirements of NFPA
30A for "fire resistance" tanks, meets the requirements of
ICBO UFC Articles 52 and 79, and provides a minimum 2-hour
fire rating in accordance with ICBO UFC, Appendix Standard A-
II-F and UL 2085.
8.5.2
Installation
a) For flammable liquid installations, require
additional curbing containment based on tank filling rates if
there is a chance of a fuel spill entering a critical area.
b) For applications not requiring secondary
containment, such as residential heating oil tanks where
aesthetics may be the prime concern, consider concrete
encased, exposed aggregate, vault tanks with a UL 2085
secondary containment protected rating without the outer steel
jacket.
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