The title of the article has nothing to do with the Survivor television show. It concerns designing alarm circuits with the ability to survive a fire for a specific time period--the survivability mission required of the fire alarm system when being used for partial evacuation and/or relocation of occupants in buildings such as a high rise or hospital.
NFPA 72 requires that certain circuits have a Level 1, 2 or 3 survivability rating. NFPA 72 doesn’t state (yet) which of the three levels of survivability apply to an occupancy type or minimum occupant load. Instead, the survivability level is chosen by the building owner with input from their engineer, insurance company and other AHJs, through a threat assessment and hazard analysis.
Circuit survivability most commonly applies to ensuring the operation of notification appliances. When certain communication conductors are installed in such a manner that “attack by fire within an evacuation signaling zone doesn’t impair control and operation of the notification appliances outside the evacuation signaling zone,” survivability methods are used. For example, a hospital with a third floor fire cannot allow the fire to impair the notification signals for other floors located above the fire area.
In last month’s column, I mentioned the effort made to remove the term “fire” from NFPA 72 where possible. Since survivability is required for systems used for partial evacuation or relocation of occupants, remember that the purpose of the announcement may not be for a fire but related to chemical, environmental or criminal/terrorist threat. In addition to wiring methods to ensure survivability of the notification circuits, consider duplicate or redundant control units and pathways. The survivability of the main control panel, power boosters, cellular backup panel and other essential control panels require protection from direct water spray. Survivability measures are also required if the fire command center’s emergency voice/alarm control equipment is separate from the rest of the fire alarm control equipment (panel). If a generator is used for secondary power, then survivability is also required for the generator’s power supply circuit feeding the fire and emergency alarm system.
The four levels of survivability are Levels 1, 2 and 3. But there’s also a Level 0, for which all conductors must be installed in accordance with the applicable requirements of the National Electrical Code (NEC). If no other special protective measures are taken, the circuitry is assigned Level 0. A Level 0 installation should not be considered sub-standard; this is the level for installations where circuit survivability is not mandated. There is no need to state a circuit has Level 0 survivability, since compliance with Article 760 of the NEC is required in every installation.
Level 1 is the first actual survivability level. This first level requires the building to have a code-compliant sprinkler system and you are permitted to use any of the standard fire alarm wiring methods and conductors (i.e. either FPL run exposed or cables in conduit, etc.) described in Article 760, the same as required in Level 0. However, all of the circuits required to have survivability must be installed in either metal conduit or metal raceway to attain a Level 1 rating.
Level 2 is for buildings without sprinklers. This second level requires that all circuits requiring survivability use the two-hour rated cable (CI) method or another two-hour rated system. Otherwise, you would have to install those conductors in a two-hour rated enclosure or run them only through two-hour rated areas of the building.
If the building is sprinklered, the same Level 2 installation is bumped up to a Level 3. Unfortunately, NFPA 72 reduces the specific requirements of Levels 2 and 3 to mere guidelines by allowing exceptions for using any two-hour, performance-based alternatives approved by the AHJ.
Wiring rules and requirements are designed to protect the premises from the ravages of fire and there are new things to learn from the 2010 Code.