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 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 control unit have been restored to their normal condition, 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 is unattended.

Initiating Devices

Frequently used detectors for gaseous agents are spot-type ionization smoke detectors and ratecompensated 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 otherwise provided. . 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.

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