Thursday, August 31, 2017

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%

Temporal Code 3 Pattern NFPA 72

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:


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".