Flammable liquids or flammable gases are present.
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 70F) 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.
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.
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 theContinue Reading