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Four Costly Public-Safety DAS Mistakes You’re About to Make

Check out the digital article here  >> HetNet Magazine article

With public-safety DAS deployments costing upwards of a million dollars for large venues, overlooking the new code standards—even if they have not been adopted today by your jurisdiction—would be a costly mistake. But armed with a bit of knowledge, proper planning, and some creative problem-solving, you can be part of the 10 percent that get it right.

I know what you’re thinking: “He said impending code, but my deployment will be grandfathered.” Maybe, but many counties, cities, and municipalities don’t like the thought of first-responders losing radio coverage as they cross the threshold into a burning building. Therefore, many counties, like Summit County, CO, and municipalities like Schaumburg, IL, are enforcing codes retroactively.

To better understand the value of proactive code compliance and to fully gauge the impact of four significant code changes, we examine the ongoing efforts at Phoenix Convention Center (PCC) to bring their facility up to the latest fire safety standards, even though the city of Phoenix has yet to adopt the latest code.

In 2013, PCC was struggling to operate and maintain public-safety and cellular DAS equipment from Powerwave Technologies, who filed Chapter 7 bankruptcy the same year. To remedy the situation, PCC turned to their technology services provider, Smart City, to deploy and manage a new state-of-the-art public-safety and cellular DAS. In turn, Smart City engaged DAS integrator Connectivity Wireless to design, deploy, and maintain both the cellular and public-safety DAS. “In the past, Smart City relied on Connectivity Wireless to deploy cellular-only DAS­­­­­­, but the PCC project gave us the opportunity to leverage our public-safety expertise,” says Bryce Bregen, VP of sales and marketing at Connectivity Wireless. PCC and Smart City had the foresight to build the public-safety DAS to NFPA 2015 standards, but that decision presented a set of challenges the project partners would need to overcome.

Raelyn Thomas, Connectivity’s project manager, identified the greatest NFPA code challenges they encountered: circuit survivability, two-hour fire-rated IDF closets, two-hour fire-rated cabling, and system monitoring.

How Thomas’s team addressed these requirements provides a cautionary tale for others planning to deploy a public-safety DAS.

Editor’s note: NFPA and IFC codes are complex and ever-changing; the following lists, descriptions, and interpretation of fire codes should not be considered a substitute for obtaining a thorough and professional review of the fire code as it relates to your deployment:

1.    Pathway survivability: This section of the code epitomizes the motivation behind the code changes. Previous versions of the code focused entirely on the performance of the DAS, with no regard to how a network of cable, antennas, and electronics would operate in the early stages of a fire. Fortunately for PCC, their building was fully protected by an automated sprinkler system in accordance with NFPA 13. This meant that all transmission cables connecting the bi-directional amplifier (BDA) to the coverage antennas would need to be installed in metal conduit; otherwise these cable paths would need to meet a two-hour fire rating.

NFPA allows an exception for radiating cable, aka “leaky coax,” because radiating cable would not radiate inside metal conduit. Although radiating cable was a common, if not preferred, method of distributing RF signals back in the day, today its use is generally limited to subway and tunnel applications. If your intent is to deploy a state-of-the-art public-safety DAS, avoid its use if at all possible.

The requirement for metal raceway was the primary reason Connectivity Wireless decided not to combine the public-safety and cellular DAS. Many active DAS products were design to support cellular and public-safety DAS as a way to save money and mitigate channel interference. However, the survivability requirement of the new code frequently offsets the financial benefits of deploying a combined system. This was the case at PCC, so Connectivity Wireless designers chose to separate the systems and deploy a passive DAS for public safety. Despite separating the systems, over 5,500 feet of conduit was installed at substantial cost to meet this section of the new code.

2.    Two-hour fire-rated cables: NFPA is very particular about protecting the circuits running between the donor antenna and the BDA.  Because coaxial cable companies have yet to manufacture a two-hour fire-rated cable, Connectivity Wireless sought out a solution to transform the coax cable to meet the two-hour rating. Endothermic mat wrap (E-Mat) became the first choice. However, according to Thomas, “Hundreds of feet of riser cable and coax jumpers required E-Mat wrapping at $232/ft. So we turned to 3M to help find a less expensive solution, and they recommended their Fire Barrier Dust Wrap 615+, at a relative bargain price of $85/ft, to accomplish the job.”

PCC ended up using a bit more wrap than originally planned. Because one of the BDAs was in a distant location, it required a fiber-optic cable run and some analog-to-digital conversion to connect it to the donor antenna. Despite this long, horizontal cable run, the authority having jurisdiction (AHJ) did not consider this cable run to be part of the horizontal cable distribution allowed to be installed in a metal raceway/conduit. Therefore, this long run of fiber-optic cable also required the two-hour fire rating.

3.    Two-hour fire-rated rooms: No public-safety BDA or fiber-based DAS electronic equipment meets a two-hour fire rating, and because the electronics typically reside in an intermediate-distribution-frame (IDF) closet, the IDF closets/rooms require the two-hour rating. The good news at PCC was that all of their IDF closets met the code requirement; the bad news was that there was no IDF closet near a remote location where one BDA needed to be installed. The deployment team at PCC considered multiple options, but in the end they were required to build a new fire-rated IDF closet to house the remote BDA.

It appears to me that the code was drafted around the assumption that passive DAS is the predominate choice for in-building radio coverage. Passive DAS works for small to midsize buildings, but it is not technically and financially practical for larger buildings. “NFPA did consider active/fiber DAS deployments when drafting the 2016 code,” says Minfei Leng of Bird Technologies, a principal on NFPA’s Emergency Communications Systems (ECS) Technical Committee.

In my experience, where there was confusion in applying certain aspects of the code to the realities of active/fiber DAS deployments, the AHJs have been able to apply the intent of the code to resolve matters. As a general rule of thumb, consider the fiber-based remote units as BDAs, then apply the code appropriately. This effectively means that your fiber runs (jumpers too) from the fiber-DAS headend unit to the remote units will need to meet the two-hour fire rating. Of course, all rooms housing fiber electronic equipment will need to meet the two-hour rating as well.

4.    System monitoring: This is where it gets interesting. As previously mentioned, the code committee appears to have overlooked the need for active/fiber-based DAS products. (I suppose one could argue that the active/fiber DAS manufacturers have not kept up with the code.) The code requires that the “system” include automatic supervisory signals for malfunction. Items that require supervision are associated with the BDA and power source. This part of the code is not new, so it’s not difficult to source BDAs and backup power systems with dry-contact relay ports to communicate the information to a dedicated monitoring panel (2016 NFPA 1221 Section 9.6.13.2).

The trouble arises when one tries to apply this requirement to an active/fiber DAS product. Most active DAS solutions include some dry-contact alarm ports on their remote units, but most of the alarming is software based, as well as proprietary, making communication to the dedicated monitoring panel, as defined by code, virtually impossible.

Prior  to defaulting to a passive DAS solution for PCC, Connectivity Wireless engineers had debated how to meet the system-monitoring requirement when deploying an active/fiber DAS. These systems are monitored and controlled via a computer terminal with an IP address. In an appeal to the City of Phoenix, the AHJ acknowledged the conundrum and agreed a terminal and monitor was the only option. (My personal experience is that AHJs are reasonable people; if there is not a commercial solution that meets the letter of the code, the AHJs will work with you to achieve the objective, as long as it meets the intent of the code.)

According to author H. Jackson Brown, Jr., “Nothing is more expensive than a missed opportunity.” And fortunately, PCC didn’t miss the opportunity to properly upgrade their public-safety radio coverage. Can you imagine the inconvenience and cost of reinstalling all of your cable in conduit, building out new fire-rated IDF closets, wrapping all of your fiber runs, and potentially scrapping your entire active/fiber DAS?

PCC worked with their partners to overcome four major code challenges, and then some. With proper education, the right deployment partners, and some creative problem-solving, you can also find yourself in the category of the lucky 10 percent who won’t need to worry when the city council votes to adopt the latest edition of NFPA or IFC code.

Additional impending code items you’ll want to consider:

  • Permits for the DAS: Local fire officials may not be aware of the code—I’ve experienced this many times. Make sure your originating source of information is the AHJ.
  • Testing: There are very specific test procedures that must be followed.
  • Minimum qualifications of personnel: Most often the system design requires sign-off by an FCC Licensed Radio Operator. Almost all DAS integrators lack this person.
  • As-built drawings: Specific formatting is required.
  • Power backup: NFPA requires twelve hours; IFC is considering twenty-four hours.
  • Network operations center (NOC) monitoring: Your system will require 24/7/365 monitoring.
  • Channelized BDA: It is often required by the AHJ. Broadband BDAs have the potential to cause adjacent-channel interference. PCC has deployed CommScope’s Node-A channelized BDA.
  • Obstruction by new building: In some jurisdictions, including Sunnyvale, CA, building a new structure that blocks the RF signals into a building that previously had adequate coverage means that you will be picking up the tab for your neighbor’s DAS.