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.