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Utilitiesman (Advanced) - Manual for electric, plumbing, water and other utilities | Next
Inspection, Testing, and Maintenance of Gaseous Systems |
. Flammable liquids or flammable gases
are present.
l Surface-burning combustible solids are
to be protected.
. For high value objects or processes.
. The area to be protected is occupied by
people.
. Availability of water or space for other
types of systems is limited.
Generally, Halon 1211 and Halon 1301 are
used in total flooding applications.
For effective fire-fighting purposes, a
minimum concentration of 5 percent is
recommended for total flooding systems for
surface fires of ordinary combustibles.
Deep-seated fires, as in cable insulation,
require much larger concentrations and
extended holding times.
Halon 1211 is toxic to people when
concentrations exceed 4 percent. This prevents
its use as a total flooding agent for areas
occupied by personnel. Halon 1211 is normally
used in portable extinguishers because it is not
in enough concentration to be a hazard for
people. Equipment for halon fire extinguishing
systems
is
similar
to
that
used
for
high-pressure carbon dioxide systems. Halon
1301 is stored in a cylinder super pressurized
with nitrogen to 600 psi (at 70°F) to provide
an expellant pressure for the agent in excess of
the agent’s normal vapor pressure.
Because of the high ozone depletion factor
of halons, installation of new Halon 1301
systems are prohibited except by special
approval from NAVFACENGCOM.
Halon 1301 is the least toxic of the
halongenated gases and does not harm
personnel when concentrations are below 10
percent. Systems that remain in use are located
in computer rooms.
PHASE OUT OF HALONS
Because of the high ozone depletion
potential of CFCs, HCFCs, and halon gases, the
EPA enacted the provisions of the Montreal
Protocol into regulations for the United States.
This will eliminate the production of halons by
the year 2000. If you are maintaining a system
that contains halon gas, consult engineering for
information pertaining to system conversion.
GASEOUS EXTINGUISHING SYSTEM
ALARMS
There are special considerations for gaseous
system alarms because of possible toxic effects
on personnel, the need for a reasonably fast
response, and reliable operation. Response
time for gaseous extinguishing agents is not
usually as urgent as foam agents, considering
the types of hazards protected. Personnel
safety precautions also effect the speed
requirement. Heat and /or smoke detectors are
frequently used as initiating devices.
Cross-zoning is also frequently used for
gaseous extinguishing systems. The first
detector (zone) actuation is arranged to cause
a local audible and/or visual signal. The second
detector (zone) actuation causes a distinctive
local signal to warn personnel that the
extinguishing agent is about to be released.
Some gaseous extinguishing systems,
usually those protecting populated spaces, have
an abort feature to avoid unnecessary discharge
of an expensive, possibly toxic gaseous agent.
Extinguishing systems with the abort feature
have a time delay between actuation of the
second (or only) detector and release of the
agent. The delay may be factory-set or
adjustable. It is usually set in the range of 15 to
60 seconds, so personnel can leave the area
before release of the
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