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".

Final Answer: Can You Mix Horns and Voice Evacuation Speakers?

Yes. You are allowed to mix voice evacuation speakers and temporal Code-3 horns within the same fire alarm system, provided that:

• A single, consistent evacuation signal is used for fire events

• Conflicting audible signals are not heard in the same space

• Intelligibility is not compromised

• The design aligns with NFPA 72 Annex guidance

What Is Not Recommended

• Horns in classrooms and speakers in adjacent corridors where both can be heard simultaneously

• Designs where horn output overwhelms voice intelligibility during evacuation

• Multiple audible signals competing during a single fire event

Even if speakers replicate a horn’s temporal tone digitally, the voice message would still conflict if horns are active in the same acoustic space.

Voice Intelligibility for Accurate Occupant Notification

Do you know the reason behind modern fire alarm systems?  They are intended to recognize a potential life threatening fire situation such as smoke, flame or heat.  It is then their responsibility to alert the masses.  If the whole point to a fire alarm system is to alert and inform occupants, then what good does it do if these occupants can not understand the evacuation message?  This is what prompted the National Fire Protection Association or NFPA to change the title of NFPA 72 from the National Fire Alarm Code to the National Fire alarm and Signaling Code first seen in the 2010 edition.

Side note:  Did you know that NFPA 72 is not a Code reference rather a Standard?  Learn more in this article title Fire Alarm Codes vs. Standards.

I am sure seasoned fire alarm system designers have had this pounded into their heads by now but news flash, fire alarm notification signals are no longer the priority in some scenarios.  We have always been taught that our occupant notification alert or evacuation messages were to take precedence over any other audio or tone.  To an extent this is still correct including outputs such as Musak, Public Address or P.A.,  Concert or Performance Audio, etc.  There are now and have been for some time, fire alarm systems incorporating additional features that make up what is known as Mass Notification.  The alert tones, voice messages and canned message instructions of a mass notification system are to take priority over any fire alarm notification output.  This was the reason behind the revision and extended title of NFPA 72.  The National Fire Protection Association added the word "Signaling" to the title of NFPA 72 as well as chapter 24 covering Emergency Communication Systems (ECS).  NFPA 72 does not cover every aspect of Mass Notification system design.  If you are seeking additional information on the requirements of these systems, you will need to obtain a copy of the Unified Facilities Criteria (UFC) document titled "Design and O&M: Mass Notification Systems"

If you research the document above, you will become aware that Mass Notification adds a lot of new criteria to the design and engineering of a given fire alarm system, however this article will serve to inform readers on the importance of a term known as Voice Intelligibility.  If you consult the Annex D of your 2013 NFPA 72 (starts on page 311) you will find all the information pertaining to voice intelligibility.  Below we are going to touch on some of the important factors to keep in mind when up against a mass notification system that must meet specified voice intelligibility measurements.

1. What exactly is voice intelligibility?  Voice intelligibility is a measure of how comprehensible speech is in given conditions.  Voice Intelligibility is affected by the quality of speech signal, the type and level of background noise, reverberation, and for speech over communication devices, the properties of the communication system.  The concept of voice intelligibility is relevant to several fields, including phonetics, human factors, acoustical engineering and audiometry.
2. In order to meet the criteria of NFPA 72 as well as the UFC, you will need to have what is known as a risk analysis drafted up by a fire protection engineer.  A risk analysis is an individual plan for a specific facility.  This plan includes a multitude of criteria based on potential risks and threats at the given facility.  This risk analysis will breakdown segregated areas of the building and how to evacuate or hold occupants based on individual threatening scenarios.  The risk analysis will also explain acoustically distinguishable spaces or ADS.  As defined by NFPA 72 2016 D.2.3.1.1 - An acoustically distinguishable space can be an emergency communication system notification zone, or subdivision thereof, that can be enclosed or otherwise physically defined space, or that can be distinguishable from other spaces because of different acoustical, environmental, or use characteristics such as reverberation time and ambient sound pressure level.  The ADS might have acoustical design features that are conductive for voice intelligibility, or it might be a space where voice intelligibility could be difficult or impossible to achieve.
3. Once evacuation or staging areas of the facility are understood, we will need to design the audio potion of the mass notification system.  This is where voice intelligibility comes into play.  Keep in mind the differences between audibility levels (dB) and Voice Intelligibility.  For lack of better terms, one defines the sound pressure and the other defines the clarity and comprehension of the audio.  Just because you meet the intent of NFPA 72 chapter 18 in regards to dB levels does not mean you have accomplished an acceptable measurement of voice intelligibility.
4. How do you measure voice intelligibility?  Unlike the use of a dB meter for audibility, voice intelligibility is a little more tricky.  There are two scales used to measure intelligibility.  One is the CIS scale which stands for Common Intelligibility Scale and the other is STI or Speech Transmission Index.  To acquire this reading you will need..... You guessed it, a Voice Intelligibility meter.   
5. What is a passing measurement for voice intelligibility?  The voice intelligibility of an emergency communication system is considered acceptable if at least 90 percent of the measurement locations within each ADS have a measured STI of not less than 0.45 (0.65 CIS) and an average STI of not less than 0.50 (0.70 CIS).  The measurement shall be taken from an elevation of 5 feet or any other elevation deemed appropriate based on occupancy.  In areas of the facility where sound levels exceed 90 dB, it may be impossible to meet these voice intelligibility measurements.  In these cases other methods such as LED signage, etc. may be used.  For reference the STI scale can be converted to CIS via the following calculation:  CIS = 1 + log (STI).

There are a ton of factors to take in when designing a mass notification system to meet the voice intelligibility requirements of NFPA 72 and the Unified Facilities Criteria.  This article is meant to touch on the main points and get you going in the right direction.

If you are in the market for a dependable voice intelligibility meter, I highly recommend the VOX01 from SDi.  This unit is compact, sturdy, very easy to use and comes packed with tons of features and abilities.  Here is a direct link to SDi's webpage containing information on the VOX01.  Below is a video of me revealing the VOX01 when it first came to market.  Feel free to check it out and let us know if you have any questions.