ETL 1110-3-484
26 Sep 97
10.2.1 AFFF Concentrate. Use only 3% aqueous film-forming foam concentrate (AFFF)
conforming to the current military specification (MIL-F-21385).
10.2.2 AFFF Concentrate Tank. Provide a single foam concentrate storage tank. Do not provide
a reserve tank unless specifically required by applicable Department of Defense (DoD) design
criteria. Tank capacity should be based upon the maximum calculated foam solution demand for a
duration of 10 minutes unless a longer duration is otherwise required by applicable design criteria.
For design purposes, an additional amount of approximately 20% should be added to the
calculated capacity requirement.
10.2.2.1 Atmospheric Tanks. Tanks constructed of fiberglass or polyethylene are generally used
for pumped AFFF concentrate systems because they are impervious to the corrosive effects of the
AFFF concentrate. Vertical tanks are recommended because they require less floor space than
horizontal.
10.2.2.2 Diaphragm Tanks. Provide bladder tanks of the horizontal type in lieu of vertical type
to facilitate filling, maintenance and bladder removal. Lessons learned indicate these tanks are
often located in equipment rooms where insufficient space is allocated for proper maintenance and
filling. To assure sufficient space for bladder removal, the bladder tank can be positioned in the
room opposite double doors or a single overhead door.
10.2.3 Concentrate Piping System. Specify all piping systems, piping, valves and fittings, that
comprise the AFFF concentrate system to be stainless steel. Specify welded fittings to avoid leaks
associated with threaded joints. Do not use galvanized steel or plastic piping. Route foam
concentrate piping aboveground inside buildings. Do not install concentrate piping underground
or under concrete floors.
10.2.4 Concentrate Control Valves. Provide an automatically-actuated control valve in the foam
concentrate line upstream of each proportioner. This valve is a critical component in the system,
since foam cannot be produced if this valve fails to open. Automatically-actuated valves operated
by system water pressure are specified because of their simplicity of operation and inherent
reliability as compared to electrically powered motorized valves. Arrange to operate from the
alarm line trim of its respective automatic water control or alarm check valve. Provide an
electrically supervised manual ball valve upstream of the automated valve to facilitate maintenance
without impairing other systems or the entire AFFF concentrate system.
10.2.5 Proportioning Systems.
10.2.5.1 Concentrate Pumping. Provide AFFF concentrate pumps of the positive displacement
rotary gear or vane type. Provide one pump to meet the system demand and a back-up or reserve
pump of the same capacity. Establish pressure rating at approximately 207 kPa (30 psi) greater
B-9
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