ETL 1110-3-481
31 Mar 97
In hangar protected with open fire suppression systems,
activation of the foam system would result in large quantities of
foam solution entering the floor drainage system. If not
diverted, such copious amounts of foam solution would become
influent to the oil-water separator. Such a large volume of foam
solution would overwhelm the capability of the separator designed
for much smaller amount of spilled fuel. The likely result would
be the accumulation of excessive amounts of foam solution within
the facility. To preclude this, automatically-actuated valves
are needed in the drainage piping upstream of the oil-water
separator to prevent foam solution from entering the separator
and to divert flow to a containment system.
CONTAINMENT SYSTEMS
6.
A system engineered to collect and contain AFFF solution is
needed where fixed AFFF fire suppression systems are installed.
Numerous types of systems can be used, depending upon the fire
protection system, anticipated maximum discharges, size of
facility, site conditions, climatic conditions, disposal method,
and other factors. Several types of systems are addressed below.
However, designers are encouraged to consider other innovative
methods and systems as may be deemed appropriate for each
specific application.
Underground Tanks
6.1
The storage of foam-water solution in underground tanks prior to
controlled release or other disposal means is an option which may
sometimes be utilized. The tank may, in most cases, be located
so gravity flow to the tank can be utilized. The underground
tank also does not have to be sized to accommodate rainfall
during the retention period. Generally underground tanks for
this application are not required to be double-walled or have
leak detection. Underground tank can be costly, particularly if
the retention system must accommodate a large amount of foam
solution. For example, a tank needed for retention of 20,000
gallons of solution would have an approximate diameter of 10 feet
and a length of 35 feet. Emptying of the tank could be
accomplished by metered pumping to the wastewater treatment plant
or by other methods covered in this document.
Aboveground Tank With Sump
6.2
6.2.1 For open AFFF systems, this method utilizes a sump pit
with a vertical shaft pump or submergible pump which diverts
solution to a vertical storage tank. This method is suitable if
A-10
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