Campus Network Fiber Cut and Monitoring Impairment
A university has five buildings connected by a proprietary fire alarm network over a single 12-strand single-mode fiber. The network is configured as a daisy chain from the head end in Building A through Buildings B, C, D, and E. Each node has its own addressable panel and can operate in local mode if the network fails. At 9:15 a.m. a landscaper cuts the fiber between Buildings C and D. Buildings D and E continue to detect and sound locally, but the head end in Building A receives only a network trouble and cannot identify which buildings are isolated. The campus has a 24/7 dispatch center in Building A. The AHJ requires compliance with NFPA 72 network requirements and asks for a written impairment plan.
1. Classify the network pathway and assess the installation against NFPA 72 network requirements for a campus of this size. What is the consequence of the single fiber path?
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The single daisy-chain fiber is a Class B pathway: one path, no redundancy. A single cut disconnects D and E from the head end. NFPA 72 network requirements include supervision and annunciation of pathway faults. A general network trouble at the head end may satisfy basic supervision but does not tell responders which buildings are isolated. Class X would provide redundant, diverse paths and fault isolation so that one cut does not stop communication.
For a five-building campus with a 24/7 dispatch center, the loss of monitoring for two occupied buildings is a significant impairment even though local detection still works. The AHJ should require either Class X or a documented, approved alternate means of monitoring each node.
2. List immediate actions for the first hour, including notifications and fire watch.
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Within the first hour: confirm whether Buildings D and E can still send alarm signals to the central station by any alternate path, such as cellular or IP. If not, notify the AHJ, the central station, and the building managers. Implement a fire watch or interim wireless monitoring in D and E, and verify that local alarms still sound and that occupants can hear them. Dispatch technicians to locate and repair the cut. Tag the network and log the impairment.
Do not remove the network from service until interim monitoring is in place. The impairment coordinator should document the time, affected buildings, and fire watch patrol intervals.
3. Recommend a permanent correction and the documentation required.
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Reconfigure the campus network as Class X with redundant, diverse fiber routes, or provide an independent communication path from each building node to the central station. Update the network drawings, sequence of operations, and as-built documentation. Perform a network acceptance test that includes a single-point fault at each segment and verifies annunciation at the head end and central station. Provide battery and voltage-drop calculations for any added equipment, train dispatchers on the new trouble indications, and obtain AHJ approval. If Class X is not feasible, submit a risk assessment and a listed alternate monitoring method for approval.