Last month’s Ask Our Experts question was, “What are pathway survivability and circuit pathway classification in regards to life safety systems?” In our blog post we covered classifying the levels of protection for the connections between life safety system components and their control panels, a topic extensively discussed in Chapter 12 of NFPA 72: National Fire Alarm and Signaling Code. As you may remember, class designations highlight the importance of the type of wiring method chosen, when it comes to detecting fires and other hazards, and notifying building occupants of a hazard before it becomes life threatening.
So now that we’ve covered the classification of wiring pathways, we want to expand on this topic and take a more specific look at pathway survivability, what’s keeping those wires safe. The NFPA designates pathway survivability based upon level of protection, which are as follows:
Level 0: The lowest level, Level 0, does not have any provisions required for survivability. At this level, only compliance with NFPA 70 is mandatory.
Level 1: The next level of survivability, Level 1, requires that a building be fully sprinkled, as well as have “any interconnecting conductors, cables, or other physical pathways installed in metal raceways.” Taking this first step in survivability makes a life safety system significantly more resistant to damage from a fire by ensuring that a sprinkler system will deploy water in any areas afflicted with excessive heat from flames. The secondary requirement of installing conductors, cables and pathways in metal raceways prevents conductors from being directly exposed to open flames, adding to their ability to resist damage and remain operational.
Level 2: When graduating to Level 2 of pathway survivability, requirements move beyond water-based protection mechanisms, and include direct fire-rated protection of circuits and pathways. This is typically accomplished in one of three ways; two-hour fire-rated enclosures, two-hour fire-rated circuit integrity (CI) cable or two-hour fire-rated cable systems. Fire-rated enclosures are fairly straight forward; circuits are installed with properly rated enclosures so that they can resist direct flames for at least two hours by being physically shielded from them. Circuit integrity cable protection typically jackets conductors in an insulation formed from minerals that when exposed to extreme heat reacts by creating an insulating barrier for the internal copper conductors. Cable systems are essentially a combination of different techniques that when applied alongside an appropriately rated cable will achieve the required two-hour rating. There is a less common fourth option, that allows any two-hour fire rated performance alternatives to be used provided that they are previously approved by the authority having jurisdiction.
Level 3: The most secure of all pathway survivability options is Level 3, which takes all of the requirements of Level 2, and additionally states that the building must also be fully sprinkled. This level of survivability both directly protects circuits and pathways from flames with a physical barrier and simultaneously attempting to extinguish the fire.
When considering the different levels of pathway survivability as applicable to your business or organization, it is critical to remember that when a situation is at its worst is when life safety needs to able to perform at its best. Making sure that everyone is able to get out of a burning building safely is always the primary function of a life safety system, and choosing the highest level of appropriate protection for it is the best chance to do so, especially in the worst of conditions.
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