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.  

Low Frequency Sounders for Fire Alarm Evacuation

Are Low Frequency Sounders Being Enforced by your AHJ

Is your jurisdiction enforcing the new code mandated 520 Hz low frequency sounders for fire alarm audibility yet?  If so how are you tackling this new requirement?  And finally did you know that the smoke alarms within the sleeping rooms and guest units do not need to meet the 520 Hz requirement?

When did this start?

Not a lot of people are aware that this requirement was originally noted in the (2010) NFPA 72 National Fire Alarm Code section 18.4.5.3.  It states "Effective January 1, 2014, where audible appliances are provided to produce signals for sleeping areas, they shall produce a low frequency alarm signal that complies with the following:
(1) The alarm signal shall be square wave or provide equivalent awakening ability.
(2) The wave shall have a fundamental frequency of 520 Hz +/- 10 percent.

Now we fast forward to 2013.

Note that the (2013) NFPA 72 Fire Alarm and Signaling Code requirements are the same found in Section 18.4.5.3

Now lets break it down.  There are a lot of code sections so stay with me.

The Annex A of NFPA 72 (2013) section A18.4.5.3 lets us know that this section does not cover the audible requirements of single and multiple station smoke alarms and instructs us to consult chapter 29 for said requirements.

If you refer to Chapter 29 "Single and Multiple-Station Alarms and Household Fire Alarm Systems" section 29.3.6 it states the following: "All audible fire alarm signals installed shall meet the performance requirements of 18.4.3, 18.4.5.1, 18.4.5.2 and 29.3.8."  Please notice that this section does not include section 18.4.5.3. This may lead one to believe that single and multiple station smoke alarms for dwelling units do not need to meet the new 520 Hz low frequency requirements.

The key section to pay attention to here is section 29.3.8 which states "Notification appliances provided in sleeping rooms and guest rooms for those with hearing loss shall comply with 29.3.8.1 and 29.3.8.2, as applicable."

Section 29.3.8.1 "Mild to Severe Hearing Loss.  Notification appliances provided for those with mild to severe hearing loss shall comply with the following:

(1) An audible notification appliance producing a low frequency alarm signal shall be installed in the following situations:

    (a) Where required by governing laws, codes, or standards for people with hearing loss.
    (b) Where provided voluntarily for those with hearing loss.

(2) The low frequency alarm signal output shall comply with the following:

    (a) The waveform shall have a fundamental frequency of 520 Hz +/- 10 percent.
    (b) The minimum sound level at the pillow shall be 75 dba, or 15 dba above the average ambient sound level or 5 dba above the maximum sound level having a duration of at least 60 seconds, whichever is greater."

Section 29.3.8.2 "Moderately Severe to profound Hearing Loss.  Visible notification appliances in accordance with the requirements of 18.5.5.7 and tactile notification appliances in accordance with the requirements of section 18.10 shall be required for those with moderately severe to profound hearing loss in the following situations:

(1) Where required by governing laws, codes, or standards for people with hearing loss.
(2) Where provided voluntarily for those with hearing loss.

What does this mean?  

If we read section 29.3.8 very carefully you will notice the word "AND" between sleeping rooms and guest rooms for those with hearing loss.  This is telling us that the requirements of section 29.3.8.1 and 29.3.8.2 apply to ALL sleeping rooms including guest rooms for those hard of hearing.

How does this effect your design?

To this date there are no UL listed UBC smoke alarms that can produce an audible tone at 520 Hz.  In fact the only manufacture that has a UL listed 520 Hz low frequency sounder appliance is System Sensor.  This means no more mini horns in the sleeping rooms of R-1, R-2 and R-2.1 occupancies.  The only way to accomplish this is by installing a System Sensor HW-LF (low frequency sounder) or addressable smoke detector with low frequency sounder base in place of all mini horns.  This will give us the required 520 Hz in all sleeping areas during a general alarm condition.

How do we accomplish 520 Hz when the Single or multiple station smoke alarm is activated?

Since there is no such thing as a low frequency LISTED smoke alarm, I propose installing addressable system smoke detectors in all sleeping rooms and guest rooms.  On top of this an addressable control module will need to be installed for each residential unit.  The control module will then need to be wired so that it controls an individual NAC (Notification Appliance Circuit) for that particular unit.  Through programming we can activate this individual control module upon activation of any smoke detectors within the unit.  Lastly the control module for each unit will need to be mapped to activate during a general alarm condition.  This way we are activating the in room low frequency sounders via the in room smoke detectors as well as any building wide general alarm device.  This method allows us to accomplish the requirements of section 18.4.5.3 as well as 29.3.8 with listed equipment and methods.

How does this effect your final cost?

Obviously there is a lot more equipment needed to perform this requirement such as addressable system smokes and control modules.  On top of this the low frequency sounders are more expensive than mini horns.  Also note that the new low frequency sounders draw more current than mini horns which will decrease your total allowable appliances per NAC ultimately increasing the number of required remote power supplies.

This is going to be a huge adjustment for our industry which will ultimately comes with a large learning curve.  I suggest your contact your local AHJ (Authority Having Jurisdiction) and find out what their interpretations on this subject are.

It is Illegal to Tamper with Fire Alarm Systems

Today I rode along with some of our technicians to perform an annual fire alarm inspection of a three story apartment complex with approximately 140 units. The system comprised of a Gamewell IF610-252 addressable fire alarm control panel with Wheelock notification devices. On the first floor there were 20 handicap units with addressable system smoke detectors (Apollo XP95-P) which activated a signal module for the notification appliance circuit within its designated unit.

Now, the addressable system smoke detectors in the handicap units were programmed to supervisory events for the purpose of central station monitoring and common area notification of the facility. However, the individual notification devices within the unit were supposed to activate if the photoelectric smoke detector was activated. Needless to say, this system was messed up. Some of the smoke detectors failed to activate the NACs and other actually activated the common corridor devices. We also found that the installing fire alarm company did not design the system with SYNC modules.

How this facility passed it original acceptance test is beyond me.

On top of all of this we came across 4 units where the occupant had tampered with the fire alarm system mini horn within their living room. We had to remove the tape, cotton, plastic and whatever else they could find to suppress the sound from the devices and warn the occupants that it is a crime to tamper with fire alarm equipment. For your reference, the California Penal Code section for this is 148.4

It reads:

a) Any person who does any of the following is guilty of a misdemeanor and upon conviction is punishable by imprisonment in a county jail, not exceeding one year, or by a fine, not exceeding one thousand dollars ($1,000), or by both that fine and imprisonment:

(1) Willfully and maliciously tampers with, molests, injures, or breaks any fire protection equipment, fire protection installation, fire alarm apparatus, wire, or signal.

(2) Willfully and maliciously sends, gives, transmits, or sounds any false alarm of fire, by means of any fire alarm system or signal or by any other means or methods.

(b) Any person who willfully and maliciously sends, gives, transmits, or sounds any false alarm of fire, by means of any fire alarm system or signal, or by any other means or methods, is guilty of a felony and upon conviction is punishable by imprisonment in the state prison or by a fine of not less than five hundred dollars ($500) nor more than ten thousand dollars ($10,000), or by both that fine and imprisonment, if any person sustains as a result thereof, any of the following:

(1) Great bodily injury.
(2) Death.

If you are interested in taking the NICET CBT exam for fire alarms, then we have you covered!  We are now selling our CBT Levels 1 - 3 practice exam DVDs.  These DVDs are packed with tons of NICET CBT practice exams along with all code references as to where to find the answers.  We have also supplied the DVDs with all of the necessary NICET applications, CBT calculator demonstrations, links and more.  If you need more information, feel free to send an email.  You can find the link to purchase our DVDs on the top left section of each page on this site.

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Fire Alarm Wiring NAC Circuits Diagram

In the fire alarm industry there are three types of fire alarm wiring circuits. Below is a circuits diagram that displays the circuit styles of a Notification Appliance Circuit (NAC). This would be your horn/strobe or speaker circuits off of remote power supplies, addressable fire alarm panels, signal modules, bell cards, etc.

Click here for information on fire alarm wiring IDC Initiating Device Circuits.
Click here for information on fire alarm wiring SLC Signaling Line Circuits.