Mixing Speakers and Horns for Fire Alarm

Are we Allowed to Mix Voice Evacuation Speakers with Horns for Fire Alarm Occupant Notification?

This is a question that comes up from time to time and a lot of people have mixed feelings.  In a nutshell, the question in a more specific format is as follows: "Am I allowed to install voice evacuation speakers and standard temporal code-3 horns within the same fire alarm system?".  To make things fair, we will consult the Standards of NFPA 72 as well as the Code of the International Fire Code Section 907.

What code and standard sections relate to mixing audible signals for fire alarm evacuation?

Here are a list of codes and standards that dance around the topic:

NFPA 72 2016 Sections

• 10.10.7 
• 18.4.1.1
• 18.4.2.1

International Fire Code 2015

• Section 907 "Fire Alarm and Detection Systems"

NFPA 72 2016 Standard Dissection

NFPA 72 2016 - Section 10.10.7 states "Alarm evacuation signals shall be distinctive in sound from other signals and shall comply with section 18.4.2 and their sound shall NOT be used for any other purpose."

NFPA 72 2016 Section 18.4.2.1 States  "Distinctive Evacuation Signal" "To meet the requirements of section 10.10, the alarm audible signal pattern used to notify building occupants of the need to evacuate (leave the building) or relocate (from one area to another) shall be the standard alarm evacuation signal consisting of a three-pulse temporal pattern.  The pattern shall be in accordance with figure 18.4.2.1 and shall consist of the following in this order.

1. ON phase lasting 0.5 seconds +/- 10%
2. OFF phase lasting 0.5 seconds +/- 10% for 3 successive "on" periods
3. OFF phase lasting 1.5 seconds +/- 10%

This section in short describes the three-pulse temporal pattern of an audible EVAC signal. This temporal code-3 signal is generated by horns as well as speakers.  Remember with voice evacuation speakers, there is still a requirement to have the temporal code 3 whoops between the voice message.

What Does a Distinctive Signal Really Mean?

When the term "distinctive evacuation signal" is used, it's not meant to cover voice evacuation speakers versus horns or bells but to ensure that a temporal 3-pulse pattern or other approved audible tone is used for fire alarm evacuation and ONLY that.

Example: A 4-wire CO detector tied to the building FA system. If the CO detector activates, its internal sounder will alert nearby occupants of dangerous levels of CO via a temporal code-4 audible output.  These are typically tied to the FA system via a monitor module and activate a non-latching supervisory signal at the FACU. However for the sake of this post, lets say the CO detector activates speakers in the affected area. These speakers would need to produce the same temporal code-4 sound as it is not a fire alarm signal rather a CO alert tone.

A distinctive evacuation signal in the minds of NFPA 72 is simply put, a temporal code 3 or other approved audible tone.  Bottom line is the distinctive signal can ONLY be used for fire alarm evacuation and nothing else.

What about NFPA 72 2016 Section 18.4.1.1?

Another standard section that trips people up on this topic is NFPA 72 2016 - Section 18.4.1.1.  The standard states "An average ambient sound level greater than 105 dBA shall require the use of a visible notification appliance(s) in accordance with Section 18.5 where the application is public mode or Section 18.6 where the application is private mode."

Section 18.4.1.1 is not so much for horns and speakers but strobes in areas that have an average ambient sound level of 105 dB or greater. The reasons for this is 15 db over average or 105 + 15 = 120 dB (public mode) or 10 dB over average or 105 + 10 = 115 dB (private mode). This violates the Section 18.4.1.2 which sets a limit not exceed 110 dB for the FA audible appliances.

The language that hits home with this topic is actually found in the Annex.  A.18.4.1.1 states "The code does NOT require that all audible notification appliances within a building be of the same type.  However a mixture of different types of audible notification appliances within a space in not the desired method.  Audible notification appliances that convey similar audible signals are preferred.  For example, a space that uses mechanical horns and bells might not be desirable.  A space that is provided with mechanical horns and electronic horns with similar audible signal output is preferred."

When is Voice Evacuation Required in Place of Horns?

In order to find out WHEN something is required in the world of Fire Alarm, we have to consult a CODE.  Section 907 of the International Fire Code covers "Fire Alarm and Detection Systems".   This is the section where all the fire alarm requirements per occupancy group are broken down.

Some examples of voice evacuation requirements are as follows:

• IFC Section 907.2.1.1 Group A occupancies with 1000 or more requires voice evacuation
• IFC Section 907.2.3 Exception #2  Group E occupancies with more than 100 persons requires voice evacuation
• IFC Section 907.2.13 High-Rise Buildings require voice evacuation.
• IBC Chapter 3008 Occupant Evacuation Elevators require voice evacuation

The following is a good example of two separate types of fire alarm occupant notification methods being used for one facility.  Prior to the newer versions of the International Fire Code, it was typical to have Group E occupancies (schools) with horns in corridors, restrooms, classrooms, etc.  However if the auditorium or gym (Group A) has an occupant load of 1000 or more, voice is required. In these cases you would have a standalone voice panel triggered to activate the speakers in the gym/auditorium on general alarm. Currently the 2015 IFC is requiring voice throughout E occupancies if the occupant load is greater than 100 so this is no longer an issue.
To circle back to the original question, "Am I allowed to install voice evacuation speakers and standard temporal code-3 horns within the same fire alarm system?" YES, by code, you are allowed to install different methods of audible tones used for evacuating occupants as long as they have ONE "distinct evacuation signal".  Referencing NFPA 72 2016 A.18.4.1.1, it is not desirable to have different types of audible appliances producing conflicting tones.  This is based on the different audible appliances being installed in one area where they could both be heard at the same time.  For example it would not be desirable to have horns in classrooms and voice evacuation speakers in the common corridor where larger groups of occupants come together.  During an evacuation, the classroom doors would be opened to the corridor and the temporal 3 output from the horns would drown out the speakers thus eliminating any sort of intelligibility.  Even if you provided the correct digital audio file to mirror the horn's temporal sound output through the speakers, the voice portion of the evacuation message would still be played during standard code 3 cycles on the classroom horns.

Additional VOICE requirements for speakers can be seen in NFPA 72 2016 Section "18.4.1.5".

Low Frequency Sounders for Sleeping Areas

What are Low Frequency Sounders for Sleeping Areas?

Anyone in the fire alarm design and installation industry has more than likely heard the term low frequency sounders.  These newer sounders first appeared in the NFPA 72 2010 edition under section 18.4.5.3 and stated an effective date of January 1, 2014.  In short these are re-designed audible appliances for sleeping areas only!  Multiple studies have been performed on sleeping parties to see how they react in different scenarios.  Some of the scenarios involved older individuals who have a difficulty with their hearing,  others were individuals who are under the influence of narcotics.  The original thought was that these people would have a difficult time awaking from a sleeping state via the standard 3 Hz sound put out by a typical mini-horn commonly found in apartment and hotel sleeping areas.  The newer low frequency sounders have a square wave signal with 520 Hz plus or minus 10 percent.  Below are two links to show you the difference between the two sound outputs:

Listen to a 520HZ Low Frequency Tone

Listen to a 3 KHz Standard Tone 

Now that it is 2024, most of the country is currently enforcing the NFPA 72 2022 edition.  If your AHJ is enforcing the 2013 version of this standard, you have been required to provide these low frequency appliances in all sleeping areas for nearly 4 years.

Are you Installing Low Frequency Sounders Correctly?  

Now the same installation factors found in the NFPA 72 standard apply to low frequency sounders. They shall have a sound level of at least 15 dB over average ambient, 5 dB or maximum sound level (duration of at least 60 seconds) or 75 dB whichever is highest.  Now seeing that NFPA 72 2013 has been nice enough to provide us with a chart depicting average ambient sound levels for different types of occupancies, this cannot be used in lieu of actual readings taken at the site.  However we can take away from this chart that a residential occupancy has an average ambient sound level of 35 dB.  If we use this as an example and tack on the additional 15 dB per NFPA 72 2022 18.4.5.1, we only come up with 50 dB.  This is 25 dB lower than the required 75 dB per the same standard section.  An example of the only time you would be going higher than 75 db is a sleeping area with an average ambient sound level of 61 dB.  61 dB plus 15 dB = 76 dB.  In short, 99 percent of the time, a designer will be aiming to achieve 75 dB.

NFPA 72 Occupancy Average Ambient Sound Levels

Tips to keep in mind:

• If you double the power to the sounder, you will gain 3 dB
• The dB from the appliance is measure at 10' away.  Every time you double the distance from the appliance, you loose 6 dB.  Read more here.

What Exactly is a Sleeping Area?

Seems like a pretty easy question to answer right?  Well I'll have you know this comes up a lot and more often than not, designers get it wrong!  A sleeping area is obviously associated with a bedroom and a bedroom is not classified as such unless it has a closet.  However, as defined by NFPA 72 2022 A.18.4.6.3, low frequency sounders are required for use in areas intended for sleeping (bedrooms) as well as areas that might be reasonably used for sleeping (Living Rooms).  Most apartments or hotel rooms are outfitted with a comfy couch in the living room.  It's not uncommon to find yourself falling asleep in this area.  This is what has prompted the requirement for low frequency sounders to be installed in not only the bedrooms but the living rooms as well. 

How Does this Affect my Design?  

It is pretty common knowledge that these 520 Hz low frequency sounders draw a lot more current than the standard 3 Hz mini-horns.  You will need to take this into effect when calculation voltage drop and battery calculations for the remote power supplies serving the areas in question.  Depending on the size of the project, this may mean you need additional notification appliance circuits and remote power supplies.