How long do the cables need to function to warn occupants to egress safely and continue to report conditions to firefighters throughout an emergency? How much heat does it take before the wires are compromised and can no longer deliver signals and voice messages to occupants and first responders? These are all questions and concerns discussed in recent NFPA technical committee meetings.
In NFPA 72, National Fire Alarm and Signaling Code ®, which addresses protection requirements of cables, defines ‘pathway survivability’ as the ability of any conductor, optic fibre, radio carrier, or other means for transmitting system information to remain operational during fire conditions. However, this term alone does not provide a one-size-fits-all solution as there are five different levels of pathway survivability and many life-safety systems require some level of pathway survivability.
Following are the five levels of pathway survivability:
- Level 0 does not contain any provisions for pathway survivability, so essentially this is just an unprotected cable.
- Level 1 consists of pathways in buildings that are fully sprinklered 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 protected by metal-armoured cables.
- Level 2 provides a 2-hour fire rating through 2-hour fire-rated circuit integrity (CI) or fire-resistive cable, 2-hour fire-rated cable system, or a 2-hour fire-rated enclosure or protected area. The standard does allow performance alternatives, where approved by the Authority Having Jurisdiction (AHJ).
- Level 3 is essentially adding the protection requirements of Level 1 and 2 together.
- Level 4 is new to the 2022 edition of NFPA 72 and contains essentially the same provisions as Level 2, except with 1-hour fire-rated requirements.
A few key factors determine the required level of pathway survivability for a given system. Cables are generally protected consistent with the construction classification of the building in which they are installed. However, additional protection can be required based on the installation standard such as NFPA 72. In addition, the structural components of buildings are designed with a specific fire-resistance rating depending on the construction type. These ratings allow the building to withstand a fire for an expected period that may be 0 to 4 hours, which also allow increased time or protection for evacuation.
Certain building types permit one-hour fire-resistance ratings, but in prior editions of NFPA 72, there was no protection level that aligned with a 1-hour rating. However, the new pathway survivability level 4 includes a one-hour fire-rated cable, system, or enclosure requirements, which fills the gap that existed in previous editions.
There is a potential concern that a substantial fire incident could compromise fire alarm or signalling cables or systems that would prevent occupants from being notified of a fire incident in the building, even though egress pathways would still be maintained given the construction classification. An example of a life-safety system that requires pathway survivability includes emergency voice/alarm communication systems (EVACS), which are one-way systems. In buildings with partial evacuation or relocation plans, EVACS are required to have a Level 2 or Level 3 survivability pathway.
Another example of a life-safety system that requires a higher level of pathway survivability is in-building wired emergency services communication systems and Emergency Responder Communication Enhancement Systems (ERCES), which are two-way systems. First responders depend on two-way communication to protect people and property in emergencies. Fire department radio systems may not operate properly when signal strength inside a building is impaired by building materials such as steel and concrete. ERCES provide radio coverage in buildings by using a Bi-Directional Amplifier (BDA) which boosts the signal to ensure the performance for public safety radio systems.
So how protected do these life-safety systems truly need to be? That is the question many industry stakeholders are grappling with. In order to thread the needle on this topic, a project idea was submitted to The Fire Protection Research Foundation (FPRF), NFPA’s research affiliate, to determine if temperature impacts the transmission and the functional and operational quality of alarm/data signals and voice messages in a fire-rated and non-fire-rated environment. If it was found that temperature does have an impact, the critical temperature and time at which the transmission of alarm/data signals and voice messages are no longer understandable also needed to be identified.
This project idea evolved from an NFPA Technical Committee with the goal of providing the necessary information to the technical committees responsible for writing NFPA 72 and NFPA 1225, Standard for Emergency Services Communications.
The report, titled ‘Evaluating Data and Voice Signals in Pathway Survivable Cables for Life Safety Systems’, was published in April of 2022. This project consisted of a literature review and development of a research plan. The literature review documented types of life-safety systems that require pathway survivability, identified cable failure incidents, reviewed existing codes that require some level of pathway survivability and dug into the technical substantiations for those provisions. A review of technical literature on the transmission and functional operational quality of alarm/data signals and voice messages was included as well.
As noted in the report, there are several codes that reference pathway survivability:
- International Building Code
- International Fire Code
- NFPA 70, National Electrical Code®
- NFPA 72, Fire Alarm and Signaling Code®
- NFPA 101, Life Safety Code®
- NFPA 1225, Standard for the Emergency Services Communications
- NFPA 5000, Building Construction and Safety Code
- UL 2196, Fire Test for Circuit Integrity of Fire-Resistive Power, Instrumentation, Control and Data Cables
Many of these codes reference NFPA 72 and NFPA 70 for requirements associated with emergency communication of voice or data signals. NFPA 72 refers to NFPA 1225 for emergency communication of voice or data signals. NFPA 72 also refers to the UL 2196 test standard for fire tests for circuit integrity of a specific class of cables.
At the time of this article, a working task group is developing proposals to modify the language in the existing UL 2196 test standard to include communication cables and a thermal resistance test. The intent is to create a more rigorous data-quality standard, rather than just the presence of a signal.
The literature review identified the potential for fire-related impacts exists, but evidence of impacts in EVACS or ERCES was not found. As a result, it remains unknown whether there is a serious potential problem. Cable failure incidents that resulted from a fire or effects from fire that were reviewed in this study include the NY Telephone Exchange fire (1975), Browns Ferry Nuclear Plant fire (1976), the World Trade Center fire (1993) and recent Grenfell fire (2017). A survey was shared through NFPA’s networks asking those in the industry if they were aware of any operational cable for life-safety systems that failed due to a fire or fire effects, but no additional information was provided for the purpose of the study. In addition, there were no scientific studies found that illustrate fire-rated enclosures or building fire-sprinkler systems specifically mitigate thermal-induced data or voice signal degradation in cables. However, fire-rated enclosures and/or building fire-sprinkler systems can reduce the temperature to which cables are exposed, which could be expected to help, but the extent of that protection is unknown.
With the knowledge gaps from the literature review documented and a research plan developed to determine if temperature impacts the transmission and the functional and operational quality of alarm/data signals and voice messages in a fire-rated and non-fire-rated environment, the research road map to address this issue moving forward identifies five future research initiatives:
1) Establish a testing series to investigate the potential for thermal effects on signal degradation. This would include a cable exposed to a specified high temperature for a specified time while transmitting voice/data signals. Various types of cables would need to be tested for thermal exposure via a furnace until thermal impact is achieved.
2) Study impact from other factors such as mechanical stress and water impact on communication systems would expose various cable types to mechanical stress via impact and water exposure by a hose stream.
3) Evaluate different test method(s) for pathway protection and suggest improvements focuses on the evaluation of potential mitigation measures, aimed at preventing unacceptable thermal exposure for a variety of scenarios for pathways that are in fire-rated and non-fire-rated enclosures, pathways located within or not in a metal conduit or raceway, pathways without physical protection but in an area with protection from an automatic sprinkler system.
4) Develop engineering models for performance-based approaches that would involve the development of engineering models to predict the performance of a whole system based on the performance of each component either by analytical modelling or by using probabilistic methods.
5) Publish/disseminate research outcomes for standardization would be given for improvement and changes in current available standards and the dissemination of the engineering tools.
Download the report or check out the one-page summary to review the highlights of this project. In addition, there has been expressed interest in launching a Phase II of this project to conduct testing in the research areas identified in this report. If you have interest in becoming a project technical panel member or becoming a project sponsor for this effort, please contact the Fire Protection Research Foundation
You can also continue tracking the progress on this subject by following the proposals to the UL 2196 test standard, as well as code changes to NFPA 72 and NFPA 1225.
Lastly, if you have a research need, please let us know by submitting a project idea.
For more information, go to www.nfpa.org/foundation
About the Author
Jacqueline R. Wilmot is a licensed fire protection engineer and a research project manager with the Fire Protection Research Foundation.
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