10-minute foam supply, and once that supply is
exhausted plain water will discharge from the foam
system, essentially breaking down the foam blanket.
However, some systems may have more or less foam
than will last for 10 minutes; this should also be
preplanned in advance. Firefighters will have to
watch the system discharge, and once the foam supply is exhausted it may be best to shut off the foam
sprinkler system as only water will be discharged
and that could disrupt/dilute the foam blanket. Of
course, if it is an activation with no fire or flammable liquid spill, firefighters should work to shut the
foam system discharge off right away to minimize
Be prepared to maintain the foam blanket. As
already discussed, the first thing to do to maintain
the blanket is to avoid disrupting/diluting the foam
blanket, whether from water discharge from the
sprinkler system or application of hose streams.
Foam blankets can be disrupted by air flows inside
of buildings and windy or rainy weather outside of
buildings. They can also “drain down” over time,
losing their effectiveness. Foam handlines should
be stretched to the fire/spill area and be set up to
maintain the foam blanket as long as a flammable
liquid spill remains with the potential to ignite.
Understand that although some foam concentrates
are incompatible, and concentrates should NEVER
be mixed, finished foams (once water and air have
been added) are generally compatible, and one
understand compatibilities with fixed foam systems
before an incident occurs.
Avoid the temptation to enter the foam blanket!
As has already been noted, there has been at least
one fatality and several injuries associated with
entering a high-expansion foam blanket. There
have also been a number of fatalities and serious injuries when firefighters were operating in
flammable liquid spills and fires where the blanket
was disturbed and the fire ignited around the
firefighters, including in Philadelphia and Hawaii.
Unfortunately, some foam systems have control
valves located inside of the hazard area, requiring
firefighters to go through the hazard area to shut
the foam system down. This should be closely
reviewed during preplanning.
Control the runoff from both the spill and
the foam discharge. Standard hazmat runoff
control techniques can be used. Cleanup operations should be carefully planned. Be aware
that vacuum trucks may not always be the best
way to pick up foam; they might act as a big
aerator, expanding the foam even more. Consult
with seasoned cleanup experts to help plan any
Be aware of the health risks associated with coming in contact with both the foam concentrate and
the finished foam. The foam concentrate itself is
generally an irritant; consult the Safety Data Sheet
to confirm hazards. Recent concerns have arisen
over the potential for certain ingredients in some
foams to cause cancer. Remember that the foam in
Engineering and air department sailors observe tests of the aqueous film forming foam fire suppression system in hangar bay 1 on the
USS Kitty Hawk. (Photo by Mass Communication Specialist Seaman Kyle D. Gahlau, U.S. Navy.)