agent and to allow for manual interruption of the
agent release sequence. If the situation is not
dangerous, the sequence can be interrupted by a
manual abort switch. When the detectors and con-
trol unit have been restored to their normal con-
dition, the abort switch can be restored. The abort
switch is usually designed to be held in (until the
control panel is reset) so that the agent discharge
cannot be accidentally impaired when the switch
Frequently used detectors for gaseous agents
are spot-type ionization smoke detectors and rate-
compensated heat detectors. Factors affecting
detector effectiveness, such as electrical power and
air pressure, if pertinent, are supervised.
One or two manual methods for release of the
gaseous agent are usually provided.
. Manual fire alarm devices are frequently
connected to the alarm system control unit to
cause immediate discharge of the gaseous agent,
regardless of cross-zoning and time delays other-
. Manual devices may also be connected
electrically to cause direct release of the agent,
independent of the alarm system.
. Direct mechanical release of agent maybe
by manual actuation of a control valve.
Whether the agent release is caused by an
alarm control unit auxiliary output or by an
independent manual method, there should be an
alarm at the alarm system control unit. Manual
release of the gaseous agent usually causes an
alarm by actuating a pressure switch that senses
the increase in pressure in the gas line or manifold
between the release valve(s) and the nozzles.
Sequence of Alarms
The normal circuit arrangement for a building
alarm system to release a gaseous extinguishing
agent is the same as for a building system with
added features such as cross-zoning, the abort
feature, manual release of agent, and other
specific auxiliary functions of the alarm system.
Alarm systems that release a gaseous extinguishing
agent use auxiliary alarm outputs to segregate the
protected area and reduce dispersion and dilution
of the agent. Typical auxiliary functions are fan
shutdown, door (and window) closure, and
closure of air-handling system dampers. Gaseous
agent-releasing alarm systems applied to computer
room installations also shut down computer
power at the time the agent is released to eliminate
the heat source for possible electrical fires.
A typical sequence of alarm system-initiated
events in a computer room installation that in-
cludes all the usual features is as follows:
. Detection of fire by first detector in an area
causes local and remote alarm indication, fan
shutdown, door and damper closure, and other
miscellaneous auxiliary functions through inter-
locks with building systems.
. Detection of fire by second detector in the
area (cross-zoned with first detector) causes a
distinctive local audible signal and initiates a time
delay during which agent release and computer
power shutdown may be aborted.
. At the end of an adjustable delay
(normally 20 seconds), assuming the release is not
aborted, computer power is shut down and the
extinguishing agent is released into the protected
INSPECTION, TESTING, AND
MAINTENANCE OF GASEOUS
Inspection, testing, and maintenance of
gaseous fire extinguishing systems are required to
be sure they are in proper operating order. Inspec-
tion and test frequencies for these systems are
summarized in table 8-4.
Carbon Dioxide High-Pressure Systems
Check hoses and nozzles, cylinders, and
cylinder pressure as follows:
Weekly, check that all nozzles and hand hose
lines are clear and in the proper position and that
all operating controls are properly set.
Semiannually, weigh cylinders and replace any
that show a weight loss of greater than 10 per-
cent. To weigh cylinders, do the following:
. Loosen each cylinder support and dis-
connect each discharge head. Discharge heads are
designed to be removed and replaced without