Low Frequencies

Low Frequencies

Historic Dallas hotel gets a fire alarm system makeover

Known for offering big comfort and style, SpringHill Suites Dallas Downtown/ West End delivers on the motto “Everything is Bigger in Texas.” Located in the historic West End of downtown Dallas, the 10-story hotel features 148 guest rooms with a sophisticated and contemporary cowboy ambiance. The hotel recently needed a new fire system panel, which in turn required the entire fire system to be brought up to current code.

Fire and Life Safety America (FLSA), located in Euless, Texas, was asked to evaluate the existing fire panel, but the city of Dallas requires fire systems to be brought up to code when any component is replaced. Because the city recently adopted the 2013 Edition of NFPA 72 and the IBC 2012/IFC 2012, it was necessary to upgrade the voice system and notification devices in addition to the fire alarm control panel.

“The city of Dallas’s new building code requirements stated that with any fire system upgrade or replacement, the entire building fire system has to be brought up to current code,” said Carl Ball, alarm and special hazards sales and design for FLSA. “Recommending the replacement of the existing, obsolete fire panel triggered this requirement to bring the entire building up to current NFPA code.”

This fire system upgrade made Springhill Suites one of the first buildings in Dallas to comply with the NFPA 72:2013 low-frequency requirements for sleeping spaces for protected premise fire alarm systems.

The new requirement covers how to alert sleeping people in commercial sleeping areas, such as hotels. The requirement specifies that an audible device in the space must produce an alarm tone at a lower frequency centered on 520 Hz, and must be of a square wave form. NFPA research found that a lower frequency, specifically 520Hz and of a square wave form, was more effective in waking individuals, including those with mild to severe hearing loss.

A square wave is different from a pure tone signal in that a square wave consists of a specific fundamental frequency and an infinite number of subsequent peaks at odd-numbered harmonics. The low frequency tone benefits not only the hard of hearing, but also children, deep sleepers, and people impaired by alcohol or medications. The tone gives these individuals a higher chance of waking when a fire occurs.

It’s important to remember that fire alarm systems and smoke alarms are just as valuable for people when they’re asleep as they are for when they’re awake. This is illustrated in a 2010 study by the U.S. Fire Administration, which determined that 50 percent of deaths as a result of residential fires occur between 10 p.m. and 6 a.m. This emphasizes the importance of maximizing those crucial seconds between the initial sounding of an alarm and waking individuals so that they can react appropriately when there is a building emergency.

Specifically, the low frequency sleeping space requirements within NFPA 72:2013 edition are discussed in the following NFPA 72 chapters:

  • Chapter 18 (Protected Premise Fire Alarm Systems) – Requires low frequency notification in every sleeping space
  • Chapter 24 (Emergency Communication Systems) – Requires a low frequency signal in sleeping areas to be followed by a voice message in sleeping spaces
  • Chapter 29 (Household Fire Alarm Systems) – Requires low frequency notification only in sleeping spaces for those classified as having mild-tosevere hearing loss, where governed by law or code, or volunteered to provide a means for such individuals.
  • Many jurisdictions in the United States such as Dallas have adopted IBC and IFC 2012, which indirectly reference NFPA 72: 2013, which requires a low frequency tone in certain newly constructed Group-R occupancies. These are the applications that may be impacted:
  • Transient lodging spaces/hotels/ motels.
  • College and university dormitories.
  • Assisted living facilities.
  • Apartments and condominiums.


In order to meet this important code requirement, SpringHill Suites chose the Honeywell Farenhyt Series IFP 2000ECS intelligent fire alarm control panel with voice system and corresponding UL low frequency listed devices, such as Honeywell Farenhyt Series amplifiers with incorporated low frequency tones, System Sensor high-fidelity speakers and speaker strobes, and Farenhyt intelligent low frequency sounder bases.

“To meet the new low frequency code requirement we had to have low frequency sounder bases on the detectors in each room, as well as speakers,” said Dennis Piekarski, ASH operations manager at FLSA. The low frequency sounder bases are designed to be aesthetically pleasing, making them ideal for applications like hotels where appearance is critical.

Two sounder bases were installed in each room, a total of 296 low frequency sounder bases, which required careful wiring consideration. To cut down on some of the conduit without interrupting wire requirements and circuit integrity, the FLSA fire and life safety system design called for the placement of a power supply and an amplifier on each floor.

“The system was designed so that if a detector in an individual room went into alarm, only the sounder base in that room will activate,” Peikarski said. “If an alarm condition is triggered by any device in the common areas of the hotel, the voice system activates on the floor of the alarm as well as the floor above and below the alarm.

“The system also has capacities of an ‘all call’ manual page throughout the entire hotel, including all guest rooms and all common areas,” Piekarski said.


With the comparatively high current draw of low frequency 520 Hz devices, the selection of the power supply and accurate voltage drop calculations are critical to ensuring adequate current to the loop. The code does not preclude the use of low frequency devices throughout a building, including nonsleeping spaces, but the high current draw of the devices can make this a higher cost approach.

Having a power supply on each floor helped to distribute power throughout the building.

“The low frequency bases consume more power than standard bases,” Ball said. “When there are many in a building, the main design criteria are to be aware of how much power they pull collectively. In this case, having a power supply on each floor worked out really well.”

System Sensor and Honeywell Farenhyt Series low-frequency solutions worked well for this project because they provided the required audible notification while also being easy to install. Due to the quantity of devices, ease of installation was a critical feature in this case. The System Sensor low frequency sounders, sounder strobes, and sounder bases meet the NFPA 72: 2010/2013 low frequency requirements for commercial sleeping spaces, and they can be interconnected with our non-low frequency sounders to provide synchronization throughout the notification zone.

What’s more, when the hotel installed a sprinkler system in 2011, the corresponding sprinkler piping was placed in the soffits.

“Although it posed a design challenge, this was the perfect space to run our wires so we wouldn’t have to run exposed wires and conduit throughout the building,” Piekarski said, “making it more aesthetically pleasing.”

This article originally appeared in the June 2016 issue of Security Today.

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