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 includes 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 interlocks 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 area.

INSPECTION, TESTING, AND MAINTENANCE OF GASEOUS SYSTEMS

Inspection, testing, and maintenance of gaseous fire extinguishing systems are required to be sure they are in proper operating order. Inspection 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 percent. To weigh cylinders, do the following: . Loosen each cylinder support and disconnect each discharge head. Discharge heads are designed to be removed and replaced without tools.

Table 8-4.-Summary of Inspection and Test Frequencies for Gaseous Systems

. Weigh cylinders with a beam scale or with a platform scale. To weigh with a platform scale, remove the cylinders completely from the rack and lift them on to the scale.

Test cylinders and hoses hydrostatically as follows:

Hydrostatically test cylinders to a minimum pressure of 3,000 psi. The frequency for testing is as follows:

. If discharged after 5 years from date of last test, perform hydrostatic test.

. If not discharged after 12 years from date of last test, discharge cylinder and perform hydrostatic test.

Hydrostatically test hoses to a minimum pressure of 1,250 psi. The frequency of testing is the same as for cylinders.

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