On March 12, 1994, a fire broke out in a retirement community apartment in Deleware, Ohio. Smoke detectors located near the common area detected the fire, and the fire alarm systems actuated. However, the fire quickly impinged on the surface-mounted metal raceway and damaged the fire alarm wiring inside — ultimately silencing the audible fire alarm signal. Because the fire alarm stopped operating shortly after starting, some residents believed a system malfunction sounded the alarm, so they didn’t evacuate. By the time the resident realized there was an actual fire, it had grown large enough to block their exits. Two residents died — one from smoke inhalation and one from a heart attack — and seven were injured.
Fire department notification often depends on the proper operation of fire detection and alarm systems. In buildings where total evacuation is impractical, emergency voice communications systems help coordinate the safe evacuation of occupants in the affected areas, which is one reason the Code requires them. When fire detection and alarm systems fail, smoke can block egress paths before occupants even know there’s a fire. This makes safe and efficient evacuation difficult, if not impossible. All of these failures — and their consequences — can happen when fire damages the fire system cabling. Thus, it’s necessary to ensure fire alarm systems will function when needed. To do so, critical circuits need added protection. Protection schemes involve fire-rated enclosure assemblies and/or fire-rated cable.
For decades, fire-rated cable, or MIcable, has provided this added protection. MI cables use copper conductors with a magnesium oxide insulation covered by a copper sheath. Each cable may include anywhere from one to several insulated solid conductors. The cable is available with a 2-hr fire resistance rating and is intended for emergency power circuit feeds for fire pumps and emergency generators. Because of its difficult installation characteristics, MI cable has not been widely used in low-voltage fire protection and emergency voice system applications, but thanks to recent developments in wire technology — and changes in national codes and standards — an alternative to MI cable is now available.
Circuit integrity (CI) cable is typically soft-jacketed with solid conductors and is listed for use in fire alarm and voice communications systems. The cable’s soft and flexible insulating material changes state when exposed to high temperature conditions, creating a fire resistant insulator to protect the conductors. However, until subjected to high temperatures, CI cable is as flexible as standard fire alarm cables, which makes it as easy to install as nonfire-rated electrical wiring. You can pull it through standard raceways and conduit and install it without special tools or hardware. And you don’t need special training to handle or install it.
NEC 760.31(F) requires CI cable used to ensure survivability of critical circuits be listed for that function and states that listed cable may be used to comply with the survivability requirements in the 1996 edition of NFPA 72, Secs. 3-2.4, 3-4.4, 3-12.4, and 3-12.4.3.
Engineers have specified CI cable for fire fighter elevator controls, pressurization/smoke exhaustion fans, and fire alarm notification systems. To assure their compatibility with today’s sophisticated fire alarm circuits, manufacturers have tested CI cables for their capacitance levels and distortion-free transmission of high-speed data pulses.
Conformance to the Code requirements of circuit survivability will ensure the performance of the fire alarm system during a fire emergency. CI cable provides you with flexibility in planning cable routing, while minimizing wall and shaft construction.