In part I of this series, we explored the 2013 edition of NFPA 72 Chapter 12 Circuits and Pathways. We noted that the old “Class” and “Style” assignments have been changed to reflect a performance-based description of fault tolerance using the term “Class” only, with “Style” now being deleted. We provided a few tables that will help you make the transition from the old “Class” and “Style” to the new NFPA 72 Chapter 12 Class A,B C,D,E,R, S and X designations.
Over the past week we have had a few questions regarding the “R” and “S” designations. Class “R” is provided for redundant circuits that utilize metallic conductors, but are not afforded with ground fault detection. Similarly Class “S” provides a single path supervised circuit that utilizes metallic conductors, but is also not afforded with ground fault detection.
In this week’s post we will explore the second part of Chapter 12 regarding the survivability of circuits. We should note that Chapter 12 does not prescribe survivability. This Chapter simply describes the survivability level designations. We must reference Chapter 24 which describes the different levels of survivability per the application.
Each level of pathway survivability offers options for the designer and installer to meet the requirements. Some users of the code have been confused and assumed that, if a contractor installed a circuit in conduit, that circuit would have survivability. Wire or cable in a raceway, such as conduit, certainly has mechanical protection, but the conduit or raceway cannot preserve the integrity of circuits when attacked by fire.
Level 0, 1, 2 and 3 in Chapter 12 identify the “levels” of survivability. Let’s take a deep dive into each level.
Level 0 pathways have no required survivability. With electronic redundancy through various LAN and WAN networks, Ethernet is a good example of Level 0.
Pathway Survivability Level 1 consist 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.
Pathway survivability Level 2 consists of one or more of the following:
- 2-hour fire-rated circuit integrity (CI) cable
- 2-hour fire-rated cable system [electrical circuit protective system(s)]
- 2-hour fire-rated enclosure or protected area
- 2-hour performance alternatives approved by the authority having jurisdiction
Pathway survivability Level 3 is identical to Level 2, except the pathways include those installed in buildings fully protected by automatic sprinkler systems in accordance with NFPA 13, Standard for the Installation of Sprinkler Systems.
Bases on current Codes and Standards we will typically see most fire alarm circuits serving low rise buildings with non-voice fire alarm systems to be Level 0 or Level 1 survivability designation. For high-rise buildings that provide emergency voice paging fire alarm systems will use a pathway survivability of Level 2 or 3 for where the occupants will either be either totally or partially evacuated or even relocated to a non-fire area within a building.
The revisions and updates to Chapter 12 are a great improvement to our every expanding use of Internet Protocol (IP) technologies to save lives and protect property. Today as buildings become more integrated and intelligent, IP-based life safety building networks will continue to be used to support a range of safety functionality providing unified, real time, security and fire incident information.
As a result, this approach allows enhanced monitoring of properties and improved co-ordination with the internal and external emergency response teams. IP network enabled fire alarms and safety alerts reduce emergency services’ response time in the event of fire, terrorist threat or other emergencies.
This coupled with networked security systems will for example – automatically release emergency exit locks, broadcast pre-recorded status messages, display exit paths on bright LCD screens, and enable ventilation systems for smoke extraction.
Chapter 12’s revisions enable all industry stakeholders to leverage the best in class technologies to save lives and protect property. This is why it is so important that we all become familiar with these new Class and Level designations.
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