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Benefits of Public Safety DAS

Have you ever walked into a building and noticed you have “no bars” on your cell phone? Radio frequency (both radio and cellular) signals are greatly reduced when passed through dense building materials such as concrete and metal. This problem was evident during 9/11, when first responders were not able to effectively communicate inside the World Trade Center towers. Since 2009, the International Code Council and the National Fire Protection Association have added first responder radio coverage requirements to their book of fire codes. Many states and municipalities have begun enforcing these codes.

What You Need to Know About Public Safety DAS

System Coverage

Our DAS design will need to meet the system coverage requirements of both the National Fire Protection Association (NFPA) and the International Fire Code (IFC). While IFC dictates that 95% coverage is needed in all areas, NFPA dictates that 99% coverage is required in areas of vital importance, such as those designated by your local fire department. In addition to this, 90% coverage is needed in general areas according to the NFPA. While areas that are being used during the day are usually covered in a DAS design, these aren’t always the areas where emergency responders are during a crisis. For instance, first responders aren’t always in the office, the break room, or conference room. Many times they’re trying to get to hard-to-reach and uncommon places such as equipment rooms, basements, stairwells and elevators.

 

Implementing these minimum coverage standards into your next DAS project requires more effort and a closer look at your materials and the final design. You’ll also need to take advantage of a comprehensive initial radio frequency (RF) survey. The radio frequencies used by local public safety personnel (UHF/VHF 700 and 800 MHz) must be considered. Also, the building’s location and layout are factors in determining adequate coverage.

NEMA-4 Enclosures

When a fire is responded to, what’s one of the most prominent things you’re able to see? The fire hoses pumping out water on the building—as much as hundreds, if not thousands, of gallons-per-minute (GPM)! This means there’s an ample amount of water that’s likely getting on sensitive radio gear. When this happens, communication is compromised. The National Electrical Manufacturer Association (NEMA) specifies that communication must be watertight, weatherproof, and “exclude at least 65 GPM of water from a one-inch nozzle delivered from a distance not less than 10 feet for five minutes”.

 

This is where NEMA-4 enclosures come in. The NFPA and IFC dictate that all equipment supporting the public safety network needs to be housed in a NEMA-4 compliant enclosure. This includes equipment such as radios and power systems. Consider that when designing your next DAS project, it is necessary to include material and installation costs of a NEMA-4 enclosure that will comply with standards of the NFPA and IFC. These enclosures will ensure the lifespan of your equipment in the event of a crisis during which equipment integrity can be compromised due to the emergency measures being taken.

System Monitoring Alarms

Is your system ready in the event of a crisis? How can you know? System monitoring alarms provide real-time monitoring of your system to let you know if it’s ready. Your systems need to be monitored for power or battery failures, antenna network malfunctions, and even battery capacity. How will this impact your next DAS design?

 

Consider that the information system monitoring alarms needs to be sent back to a centralized monitoring point. This means that all alarms need to communicate to the central fire alarm panel. While both the NFPA and IFC require an alarm system, they’re different in their requirements. It all depends on your local jurisdiction, having the final say on what your requirements are in regard to monitoring. Consider that a system monitoring alarm is necessary and will provide you with information on how ready your system is in the event of a public safety emergency.

-95 dB Minimum Signal Strength

-95 dB is the minimum signal strength required within the coverage area, as dictated by both the NFPA and IFC code. Regardless of frequency the analysis and design must take into account the signal strength which needs to be a minimum of -95 dB!

 

What are the frequencies that will be used? Consider that 700 and 800 MHz frequency won’t have the same signal strength as very high frequency (VHF). If 700 or 800 MHz is used, it will require greater antenna density to achieve coverage at the required signal strength of -95dB.

Battery Backup

Is your battery backup system sufficient? Oftentimes in the event of a crisis, especially in a building, a power failure is imminent sometimes the power needs to be cut off in order to prevent hazards from affecting emergency responders. The equipment that supports the public safety radio system needs to function for a full 24 hours on a backup battery meet code. You can meet this requirement by carefully selecting the proper solution for your DAS design and considering your power requirements, which can range from AC to 12 volts or -48 volts DC.

Frequency Updates

Does your system accommodate frequency updates? Systems that support the public safety emergency responder radio coverage need to be able to support updates to frequency requirements. Your current platform will need to support UHF, VHF, 700 MHz, and 800 MHz in order to meet this requirement, which both the NFPA and IFC support.

 

When designing your DAS, you need to take these frequency changes into account. The adoption of new frequencies needs to be factored into your design in order to meet requirements and be fully functional.

Antenna Isolation

The NFPA dictates that your antenna isolation requirement needs to be 15 dB higher than the gain of the amplifier. Although your design may incorporate this, consider that public safety coverage may need to be upgraded in order to include more antennas as you consider coverage and signal strength for your public safety solution.

 

Consider a directional antenna rather an omnidirectional one in order to achieve proper coverage, signal strength, and antenna isolation for your DAS design.

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