Please note that the following is a summary of information regarding these systems and does not include a comprehensive overview of the subject matter. Please refer to applicable codes for complete information.
What is DAS?
DAS stands for Distributed Antenna System, it is a system of strategically placed antennas throughout a building that amplify the signal for public safety radios (mainly the Fire & Police Departments). DAS can go by many names in specifications – BDA (Bi-Directional Amplifier), ERRCS (Emergency Responder Radio Communication System), Radio Enhancement System, Two-Way Radio Communication Enhancement System, and more.
How does it work?
There are two types of systems, either passive or active. A passive system takes an outside signal through a donor antenna, sends it through coax cable, to an amplifier, then to a splitter and sent to each broadcast antenna. An active system takes the outside signal from the donor antenna through coax cable to a digital conversion unit, then through fiber to a remote unit, through coax cable, and finally to the broadcast antennas. A passive system is best for buildings less than 100,000 square feet and active systems are better for buildings greater than 100,000 square feet.
Is it required by code?
According to the 2015, 2018, and 2021 International Fire Code Section 510.4.1, every building shall have acceptable signal coverage when strength measurements are at 95% in all areas and 99% in critical areas as denoted by the AHJ. The system itself is not required but if your building does not meet code, the AHJ could require one to be installed.
Where can I find it in the code?
NFPA 72 – 2013, 2016, 2019
IFC – 2015, 2018, 2021
NFPA 1221 – 2016, 2019
What can cause interruptions in signal?
There are many reasons that signal can be interrupted for public safety radios. Certain construction materials such as concrete, fiberglass, low-e glass, and more can cause disruptions in the signal. Obstructions outside of the building can also affect the signal like tall trees, hills, new buildings, and storms.
What are considerations when designing these systems?
It is most important to know the frequencies that the local fire and police departments operate at. Generally, public safety operates in the 700/800 MHz Public Safety band, VHF band, or UHF band. Often, they will operate within multiple bands which may require more than one system. While it is important to know the central frequency, it is important to also know the frequency band that is required to be amplified and if there are separate uplink/downlink frequencies.
Also, the lead designer and installation personnel must have (at least) a valid FCC-issued General Radiotelephone Operator License and certification of in-building systems issued by an approved organization or manufacturer of the equipment.
How do I know if I need to install a DAS?
In general areas, 95% coverage is required and in critical areas 99% coverage is required. The inbound/outbound signal must be sufficient to provide no less than a DAQ (Delivered Audio Quality) of 3.0.
Within existing buildings, the owner can verify coverage by a Grid Test. A Grid Test works by dividing each floor into a grid of 20 equally sized test areas. A fully calibrated portable radio is utilized at the center of each grid to measure the signal strength at each. If more than one grid fails, the building does not meet the 95% coverage requirement. If two grids fail, the floor will be divided into 40 equally sized test areas and if no more than two nonadjacent grids fail, the system passes. If your system fails, a DAS will need to be installed as required by the AHJ.
Within new buildings, you cannot fully know if there is limited coverage until construction is underway and the shell is complete. Then, it is required as designated above. Typically, though, larger buildings like hospitals, malls, large schools, campuses, convention centers, and stadiums usually require additional coverage.
What are the inspection requirements?
The building must be tested annually and when there are structural changes. Testing includes the Grid Test as described above, all amplifiers must have their gain measured, recorded, and stored with the building owner, 1 hour load testing of all batteries and power supplies, and verifying operation of all active components. Once testing is complete, a report must be sent to the fire code official.
What are the battery backup requirements?
Either 12 hours or 24 hours depending on what year IFC is locally adopted. IFC 2015 requires 24 hours and IFC 2015 & 2018 require 12 hours.
Does this need to connect to the Fire Alarm System?
Yes. The FACP must monitor the system and provide a supervisory alarm for the following –
A dedicated annunciator shall also be provided for annunciating the status of –
What other terms should I be aware of?
See NFPA 1221 for more definitions