Mechanical Protection vs. Survivability

Know the terms before you bid:

There seems to be a confusion among contractors regarding the term “survivability” as it relates to fire alarm system circuits; some use it to discuss the circuit’s inclusion in a metal raceway and assume that installing wire in a metal raceway adds to its fire rating. That is not true. Survivability is defined using the performance requirements of Section of NFPA 72-2007, which states, “Fire alarm systems used for partial evacuation and relocation shall be designed and installed such that attack by fire within an evacuation signaling zone shall not impair control and operation of the notification appliances outside the evacuation signaling zone.”

So survivability really refers to the floor above the fire floor’s capability to operate for some time in a fire. The NFPA 72-2007 Protected Premises Technical Committee has determined that time to be two hours.

How did the confusion happen? For many years contractors have installed fire alarm circuits in raceway. Many fire officials looked at wire in raceway as better protected and started to misuse the term survivable to describe these installations.

Another term misuse is the assumption that circuits will be more survivable if they are installed in a Class A fashion.

NFPA 72-2007 defines the class of fire alarm circuits in section 6.4.2 as “Initiating device circuits, notification appliance circuits and signaling line circuits shall be designated by class or style, or both, depending on the circuit’s capability to continue to operate during specified fault conditions.”

Class A circuits must meet the performance requirements that “allow all connected devices to operate during a single open or a non-simultaneous single ground fault on any circuit conductor.”

Also, they must be installed so that “the outgoing and return conductors, exiting from and returning to the control unit, respectively, are routed separately.” The outgoing and return (redundant) circuit conductors must also not be run in the same cable assembly (i.e., multiconductor cable), enclosure or raceway.

The code does not dictate a separation distance but does offer some guidance in Annex A that states the goal of the requirement “is to provide ‘adequate’ separation between the outgoing and return cables to help ensure protection of the cables from physical damage. The recommended minimum separation to prevent physical damage is 305 mm (1 ft.) where the cable is installed vertically and 1.22 m (4 ft.) where the cable is installed horizontally.” The only problem with the separation requirement is that it is not always possible to install the cable or raceways in compliance with the guidance provided. However, in the strict interpretation of the code, the fire official cannot enforce the Annex material because it is explanatory only. In theory, a contractor can install the cables or raceways side by side and meet the intent of the code. However, some federal jurisdictions incorporate the Annex material as requirements for their projects; then the separation distances are mandatory. The important factor in the requirement is to prevent physical damage to the fire alarm circuits. The requirement also means that the raceways or cables cannot cross over each other.

The code does offer some exceptions to the separation requirements that state “[t]he outgoing and return (redundant) circuit conductors shall be permitted to be run in the same cable assembly, enclosure, or raceway under any of the following conditions:

1. For a distance not to exceed 3 m (10 ft.) where the outgoing and return conductors enter or exit the initiating device, notification appliance or control unit enclosures
2. Single conduit/raceway drops to individual devices or appliances
3. Single conduit/raceway drops to multiple devices or appliances installed within a single room not exceeding 92.9 m2 (1,000 ft2) in area.”

In most cases survivabiliy actually applies only when installing speaker circuit riser cables. Section requires that “[a]ll circuits necessary for the operation of the notification appliances shall be protected until they enter the evacuation signaling zone that they serve. Any of the following shall be considered to meet the requirements of this subsection:

1. A two-hour fire rated circuit integrity (CI) cable
2. A two-hour fire rated cable system (electrical circuit protective system)
3. A two-hour fire rated enclosure
4. Performance alternatives approved by the authority having jurisdiction
5. Buildings fully protected by an automatic sprinkler system installed in accordance with NFPA 13, Standard for the Installation of Sprinkler Systems, and with the interconnecting wiring or cables used for the operation of notification appliances installed in metal raceways and in accordance with Article 760 of NFPA 70.”

Contractors who bid on projects that require either Class A or survivable circuits need to understand these two areas of the code. Don’t lose money on an installation simply because you have not read and understood the codes.     •

MOORE, a licensed fire protection engineer, frequent speaker and an expert in the life safety field, is a co-editor of the current National Fire Alarm Code Handbook. Moore is a principal with Hughes Associates Inc. and is located at the Warwick, R.I., office.

About the Author

Wayne D. Moore

Fire/Life Safety Columnist
Wayne D. Moore, a licensed fire protection engineer, frequent speaker and an expert in the life safety field, is a principal member and past chair of NFPA 72, Chapter 24. Moore is a vice president with JENSEN HUGHES at the Warwick, R.I., office. He c...

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