Fire alarm systems stakeholders increasingly raise questions concerning the acceptability of using Ethernet and other networks for fire alarm and signaling systems applications. NFPA 72 2013, National Fire Alarm and Signaling Code, made an attempt to address these questions using a concept called “shared pathways.” Unfortunately, the code did not directly address the actual issues of using the Ethernet or other networks.
During the code-revision process, the use of Ethernet and other networks presented the NFPA Technical Committee members with concerns about ground detection, system management, availability, software control and more. Because of these questions and the rapidly changing technology affecting the industry, the NFPA Technical Correlating Committee on Signaling Systems for the Protection of Life and Property formed a task group to address the risk analysis, design, application, installation and performance of networks and networking equipment that fire alarm systems, fire emergency voice alarm communications systems (EVACSs) and mass notification systems (MNSs) might use.
The task group’s work resulted in proposed changes for NFPA 72 2016. These proposed changes remain in the comment phase for public review.
The task group used the shared pathway concept to build on the use of networks and the Ethernet, and I present some of the proposed changes here to whet your appetite.
First, a new class of circuit is proposed, titled Class N (for network), and that is a pathway that performs as described:
1. “It includes two or more pathways where operational capability of the primary pathway, and a redundant pathway to each device shall be verified through end-to-end communication. Exception: When only one device is served, only one pathway shall be required.”
2. “A loss of intended communications between endpoints shall be annunciated as a trouble signal.”
3. “A single open, ground, short or a combination of faults on one pathway shall not impact any other pathway.”
4. “Conditions that affect the operation of the primary pathway(s) and redundant pathway(s) shall be annunciated as a trouble signal when the system’s minimal operational requirements cannot be met.”
5. “Primary and redundant pathways shall not be permitted to share traffic over the same physical segment.”
Class N circuits are similar to Class A and X circuits as described in the current code in that the primary and redundant, or outgoing and return conductors, exiting from and returning to the control unit, respectively, are routed separately.
Additional requirements for Class N pathways include that “a single fault on a Class N pathway connected to the addressable devices cannot cause the loss of more than one addressable device” (exactly like a Class X circuit) and that no area or zone can “be serviced solely by a single device when deploying Class N pathways, such that a single device failure would render an area or zone incapable of initiating input signals, or receiving output signals.”
The only exception to this last requirement reads, “when a risk analysis is performed to determine areas where a single device is sufficient and acceptable to the authority having jurisdiction.”
As you can tell just from this initial set of requirements, the reliability of the Ethernet and other networks remains of paramount concern.
The use of the Ethernet or networks for fire alarm or mass notification systems will radically change the installation of these systems. You should note that Chapter 12 (Circuits and Pathways) will not contain the requirements for Class N pathway transmission equipment. Rather, other chapters in NFPA 72, such as “Emergency Communications Systems” or “Protected Premises Fire Alarm Systems,” will contain these requirements.
The code will also address circuit integrity (CI) cable in a new way. The code has required CI cable for fire EVACS cable risers since NFPA 72 2002. The requirements for CI cable had the performance goal of meeting the survivability requirements for speaker riser circuits to ensure they would remain useful for communications during the fire. Every edition of the code through the 2013 edition has required the survivability of circuits.
Readers who have had an involvement with high-rise fire EVACS know that Underwriters Laboratories (UL) pulled the listing for all CI cables in 2013. Industry experts hoped that UL would develop a quick response to formulate a new testing standard that would allow the CI cable manufacturers to re-enter the market. Sadly, that has not happened. Only one option remains. To meet the code requirements for survivability, an installer must use listed Type MI cable. This offers a much more costly alternative than listed Type CI cables formerly provided.
The NFPA Technical Committee on Emergency Communications Systems has struggled with this issue ever since UL removed CI cable’s listing. The technical committee still intends to require survivability. In an attempt to provide some semblance of survivability and system reliability, the technical committee has added two exceptions to proposed NFPA 72 2016. The first exception intends to ensure that the code does not require Level 2 or 3 survivability for any building that has less than 2-hour fire-rated construction. The technical committee never intended to make a fire alarm system more survivable than the building it served. The proposed exception now permits the use of Level 1 survivability in buildings where the code would normally require Level 2 or 3 survivability and where notification or evacuation zones are separated by less than 2-hour fire-rated construction. And, of course, the code defines pathway survivability Level 1 as consisting of “pathways in buildings that are fully protected by an automatic sprinkler system in accordance with NFPA 13, Standard for the Installation of Sprinkler Systems, with any interconnecting conductors, cables, or other physical pathways installed in metal raceways.”
The second proposed exception to the Level 2 or 3 survivability requirements recognizes the inherent reliability of Class X and the new Class N circuits. It does this by permitting Level 1 survivability “where there are at least two pathways provided that are separated by at least one-third the maximum diagonal of the notification or evacuation zones that the pathways are passing through and the pathway is Class X or Class N.”
This last exception presents the first time the technical committee has essentially reduced the survivability requirements by not requiring the use of 2-hour rated cable, such as Type CI. Obviously, the intent remains the same, namely maintaining a suitable level of reliability of operation during the time the fire EVACS must provide critical communications capability.
Even when the various technical committees of the NFPA Signaling Project embrace new technology—albeit often at what appears to outsiders as a glacial speed—they must remain diligent and aware of the market trends, such as the changes that occurred with the Type CI cable.
The addition of Class N circuits could have the potential to radically change the installation practices for fire alarm systems. You must review NFPA 72 2016 very carefully when it becomes available in late 2015. The proposed changes include numerous examples and a large amount of annex material to help designers, contractors and authorities having jurisdiction understand how these circuits intend to operate.
The proposed changes to the cable survivability requirements will also affect your installations that you may need to know about these changes before NFPA publishes the new edition of the code. To meet the required use of 2-hour rated cable in systems you will soon install, you may present the forthcoming performance alternatives to the authority having jurisdiction for review and approval.