ETL 1110-3-481
31 Mar 97
The odds of system activation occurring in the same period as a 5
year - 24 hour rain event is extremely small. If one assumes one
false activation per year, the odds of this activation occurring
within 2 days (48 hours) of a 5 year - 24 hour maximum rain event
is less than 1 in 333,000. Since the containment is designed to
accommodate this unlikely event, designing for greater rainfall
is not required.
No Containment Required
6.6
There are geographical areas in the world where no containment
system is necessary. They would be in dry climate areas, where
there are little or no open water, streams or wetlands and no
high ground water table. In these areas, solar evaporation would
be a method for disposal of the foam solution.
Containment For Closed Systems
6.7
The containment systems listed above are, for the most part, for
containing large discharges that are associated with open
systems. Closed system discharges are limited to testing only.
Containment requirement for testing are less than that for
inadvertent discharges associated with open systems. Testing
produces less solution discharge since the flow duration is only
three minutes, testing can be planned, and testing can be
conducted sequentially on individual systems after the
containment system is emptied. Containment could be an
impermeable pit or an open concrete vault which could contain the
full test flow. It is important that any collection system must
be designed to contain the full force of the flow, which is
usually from several 2-1/2 inch fire hoses, flowing
simultaneously.
AFFF DISPOSAL AND TREATMENT OPTIONS
7.
Discharge To Wastewater Treatment Plants
7.1
The most common method of disposing of foam solution is to treat
it biologically in a wastewater treatment plant. This is
generally accepted as the preferred method of disposal. Where
feasible, solution should go directly to the treatment plant via
sanitary sewer lines serving the facility. Another method of
disposal allowed in some areas is solar evaporation. Disposal of
the AFFF solution is a design consideration that be must
coordinated with the base or installation officials.
Discharge To Flowing Sewers
7.1.1
A-12
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