How well do you understand the NFPA 72 requirements for pathway survivability? Like many other fire alarm applications, the code is not always clear, and there are quite a few different interpretations on this subject. Having spent many years on the NFPA 72 Protected Premises technical committee, I will try to explain what the intent of the code is.
Writing code is a challenge because sentence structure and word choice can dramatically affect interpretations. For any fire protection system, three entities are usually a factor in the end-result: the authority having jurisdiction (AHJ), the designer and the installer. When you are not sure of a requirement, I strongly recommend communicating to the other two entities, regardless of which one of the three you are. It is better to do this as soon as the issue comes up, not at the final inspection and test. I have personally found that the great majority of disagreements can be easily resolved through good communications.
You do not have to provide pathway survivability for all fire alarm circuits and pathways. You must provide it when laws, codes, standards or design documentation tell you that you must do so.
Although NFPA 72 Chapter 12 describes the four levels of pathway survivability, it does not tell you when one or more must be provided. The only requirements I have found are in Chapter 24 of NFPA 72, Emergency Communications Systems. In the 2019 edition, Section 24.3.14 provides requirements for pathway survivability. This section states that pathway survivability shall be provided for systems employing partial evacuation or relocation and requires either a Level 2 or Level 3 survivability level to be used. You do not need to provide it when you have general alarm throughout the building.
The intent is to ensure the pathways will survive a fire long enough that emergency messages can still be sent to areas that did not receive the initial message. You provide pathway survivability from the control equipment to the notification zones they serve. For example, if you have a 10-story high-rise, you provide pathway survivability from the control panel, up the riser, to each floor. You are not required to provide survivability throughout each notification zone.
In 2019, two new paragraphs were added that provided some modifications to the thresholds. One new paragraph states that if notification zones are separated by less than 2-hour fire-rated construction, you are permitted to use Level 1, 2 or 3. The other new paragraph states that where Class X or N pathways are installed and the incoming and outgoing pathways are separated by a least one-third the maximum diagonal of the notification zone, you are permitted to use Level 1, 2 or 3.
Other new or modified requirements were made for two-way, in-building wired communications systems (fire phone systems) and area of refuge emergency communications systems. If installed in areas with a minimum of 2-hour fire-rated construction, Level 2 or 3 is required. If installed in less than 2-hour fire-rated construction areas, you are permitted to use Level 1, 2 or 3.
A question that keeps coming up is whether or not the junction boxes or control equipment on each floor also need to be in a 2-hour fire-rated enclosure. Some people think they do, others don’t. Section 220.127.116.11 of NFPA 72 provides information about protection of items other than the notification pathways. Review this section when you plan to provide pathway survivability. In particular, paragraphs 18.104.22.168.4 through 22.214.171.124.6 address protection of circuits that run through junction boxes, terminal cabinets or control equipment where the separation of in-building fire emergency voice/alarm control equipment locations results in the portions of the system controlled by one location being dependent on the control equipment in other locations. In these cases, all of that equipment must be in a 2-hour fire-rated enclosure or room, or other equivalent method approved by the AHJ.
As a review of the survivability levels found in Chapter 12, Level 0 pathways do not require any pathway survivability. Level 1 consists of pathways in buildings fully protected by sprinklers, and all conductors must be installed in a metal raceway or metal armored cables. Level 2 consists of pathways installed using 2-hour fire-rated cables or cable system, or pathways installed in a 2-hour fire-rated enclosure, or per performance alternatives approved by the AHJ. Level 3 is a combination of Level 1 and Level 2.
This information should help get you heading in the right direction when providing pathway survivability.