Manual Silencing Of Audible Signal Devices In Dwelling Units - Let’s Try To Resolve Confusion
Ark Tsisserev, Principal
This article is in response to the questions received by me on the referenced subject, after I wrote about the National Building Code of Canada (NBCC) requirements for audibility of alarm systems. Let’s show the NBCC requirement in its entirety, before we discuss the issue at hand. Article 3.2.4.18. of the NBCC states the following:
3.2.4.18. Audibility of Alarm Systems (See Note A-3.2.4.18.)
(1) Audible signal devices forming part of a fire alarm system shall be installed in a building so that (a) alarm signals are clearly audible throughout the floor area, and (b) alert signals are clearly audible in continuously staffed locations, and where there are no continuously staffed locations, throughout the floor area. (See Note A-3.2.4.18.(1).)
(2) The sound pattern of an alarm signal shall conform to the temporal pattern defined in Clause 4.2 of ISO 8201, “Acoustics – Audible emergency evacuation signal.” (See Note A-3.2.4.18.(2).)
(3) The sound patterns of alert signals shall be significantly different from the temporal patterns of alarm signals. (See Note A-3.2.4.18.(3).)
(4) The fire alarm signal sound pressure level shall be not more than 110 dBA in any normally occupied area. (See Note A-3.2.4.18.(4).)
(5) The sound pressure level in a sleeping room from a fire alarm audible signal device shall be not less than 75 dBA in a building of residential or care occupancy when any intervening doors between the device and the sleeping room are closed. (See Note A-3.2.4.18.(5).)
(6) Except as required by Sentence (5), the sound pressure level from a fire alarm system’s audible signal device within a floor area shall be not less than 10 dBA above the ambient noise level without being less than 65 dBA.
(7) Except as permitted by Sentence (11), audible signal devices located within a dwelling unit shall include a means for them to be manually silenced for a period of not more than 10 min, after which time the devices shall restore themselves to normal operation. (See Note A-3.2.4.18.(7).)
(8) Audible signal devices within a dwelling unit or a suite of residential or care occupancy shall be connected to the fire alarm system
(a) in a manner such that a single open circuit at one device will not impair the operation of other audible signal devices on that same circuit that serve the other dwelling units or suites of residential or care occupancy, or
(b) on separate signal circuits that are not connected to the devices in any other dwelling unit, public corridor or suite of residential or care occupancy. (See Note A-3.2.4.18.(8) and (9).)
(9) In a building or part thereof classified as a residential or care occupancy,
(a) separate circuits shall be provided for audible signal devices on each floor area, and
(b) audible signal devices within dwelling units or suites of residential or care occupancy shall be wired on separate signal circuits from those not within dwelling units or suites of residential or care occupancy. (See Note A-3.2.4.18.(8) and (9).)
(10) Audible signal devices shall be installed in a service space referred to in Sentence 3.2.1.1.(8) and shall be connected to the fire alarm system
(11) Audible signal devices within dwelling units that are wired on separate signal circuits need not include a means for silencing as required by Sentence (7) provided the fire alarm system includes a provision for an automatic signal silence within dwelling units, where
(a) the automatic signal silence cannot occur within the first 60 s of operation or within the zone of initiation,
(b) a subsequent alarm elsewhere in the building will reactuate the silenced audible signal devices within dwelling units,
(c) after a period of not more than 10 min, the silenced audible signal devices will be restored to continuous audible signal if the alarm is not acknowledged, and
(d) the voice communication system referred to in Article 3.2.4.22. has a provision to override the automatic signal silence to allow the transmission of voice messages through silenced audible signal device circuits that serve the dwelling units. (See Note A-3.2.4.18.(7).)
(12) If a 2-stage fire alarm system has been installed with an automatic signal silence as described in Sentence (11), the system shall be designed so that any silenced audible signal devices serving dwelling units are re-actuated whenever an alarm signal is required to be transmitted as part of the second stage. (See Note A-3.2.4.18.(7).)
This NBCC requirement is provided with numerous explanatory/clarification notes in Appendix A, and it would be also beneficial to show these Notes in conjunction with our discussion (see below):
Appendix A Notes on Article 3.2.4.18. of the NBCC
A-3.2.4.18.(1) Alert and Alarm Signals. Alert signals are part of a 2 stage fire alarm system. The intent of the first, alert, stage is to notify persons in authority of a potential threat to building occupants. If a continuously staffed location is available, the alert signal can be restricted to that location.
A-3.2.4.18.(2) Alarm Signal Temporal Pattern. The temporal pattern of an alarm signal relates to the time during which the signal is produced and the intervals between the individual signal pulses. The international standard ISO 8201, “Acoustics – Audible emergency evacuation signal,” includes a pattern that is becoming widely used in different countries and it is appropriate for this pattern to be adopted in Canada. The temporal pattern can be produced on most signaling devices. Most existing alarm systems can be modified, and this pattern could be phased in when the systems require modification. The characteristic of the pattern is a 3-pulse phase followed by an off phase. The 3 pulses each consist of an on phase lasting for 0.5 ± 0.05 s followed by an off phase lasting for 0.5 ± 0.05 s sounded for 3 successive on periods and then followed by an off phase lasting for 1.5 ± 0.15s. Figure A-3.2.4.18.(2)-A indicates the pattern that is intended.
Figure A-3.2.4.18.(2)-B Temporal pattern imposed on a single stroke bell or chime
Note to Figure A-3.2.4.18.(2)-B:
(1) The on phase represents the time that the striker mechanism is actuated. The sound produced by the bell or chime will continue at a level that decreases until the striker mechanism is re-actuated.
A-3.2.4.18.(3) Audibility of Alarm Systems. It is very difficult to specify exactly what types of sound patterns are considered to be “significantly different” from one another. The intent is to ensure that there is a noticeable or measurable difference between the alert signals and the alarm signals such that it reduces the possibility of confusion.
A-3.2.4.18.(4) Sound Pressure Level. For the purposes of this requirement, an audible signaling device should not produce a sound pressure level more than 110 dBA when measured at a distance of 3 m.
A-3.2.4.18.(5) Residential Sound Level. In a building in which corridors or hallways serve more than one suite or dwelling unit, there will be situations in which an audible signal device cannot be placed in the corridor or hallway to alert persons sleeping in suites and dwelling units, because the sound level in the vicinity of the device would exceed that permitted by Sentence 3.2.4.18.(4). In these situations it will be necessary to supplement the building fire alarm system with an audible signal device in the suite or dwelling unit. These devices could be piezoelectric devices similar to the sounding units in many smoke alarms, subject to the device emitting the appropriate temporal pattern required by Sentence 3.2.4.18.(2).
A-3.2.4.18.(7) Disconnect Device for Dwelling Units. In order to minimize the annoyance caused by false and unwanted alarms, the disconnect will permit a person to silence the local audible device within the dwelling unit. At that time the person would be aware of sounds from devices in common spaces and could plan appropriate action. The disconnect will reduce the possibility of tampering with the audible devices.
A-3.2.4.18.(8) and (9) Signal Circuits. Clause 3.2.4.18.(8)(a) permits Class A wiring, or Class B wiring with signal circuit isolators located outside of the suites, to serve audible signal devices within residential suites. Clause 3.2.4.18.(8)(b) permits a separate signal circuit to serve each suite without the need for signal circuit isolators or Class A wiring. Open circuits and Class A and Class B wiring circuits are terms defined in CAN/ULC-S524, “Installation of Fire Alarm Systems.
As could be seen from the referenced NBCC provisions, the subject of audibility of alarm systems has many interesting aspects, and most of these aspects have been discussed in my earlier articles on this topic.
However, the objective of this specific article is to clarify application of Sentence 3.2.4.18.(7) which states: (7) Except as permitted by Sentence (11), audible signal devices located within a dwelling unit shall include a means for them to be manually silenced for a period of not more than 10 min, after which time the devices shall restore themselves to normal operation. (See Note A-3.2.4.18.(7).), as some electrical designers and electrical contractors are of the opinion that exception for installation of manual silencing means allowed by Sentence (7) applies when audible signal devices of all dwelling units on a typical floor are connected to a common signal circuit, and this circuit serves only audible signal devices in dwelling units (e.g. it does not extend to the devices located in corridors and other areas).
It should be noted that Sentence 3.2.4.18.(8) sets very specific conditions for connection of audible signal devices located in dwelling units to the building fire alarm system, and condition (8)(b) of this Sentence states the following:
(b) on separate signal circuits that are not connected to the devices in any other dwelling unit, public corridor or suite of residential or care occupancy. (See Note A-3.2.4.18.(8) and (9).)
Appendix A Note on Sentence 3.2.4.18(8)(b) further explains that a signal circuit is deemed to be “a separate” circuit, if such circuit serves only audible signal devices of a particular dwelling unit or suite (see below):
Clause 3.2.4.18.(8)(b) permits a separate signal circuit to serve each suite without the need for signal circuit isolators or Class A wiring.
And only when such wiring connection is done, and all conditions (a) to (d), listed in Sentence (11) are met, manual silencing means may be omitted for audible signal devices located in dwelling units, and automatic silencing of these devices by the fire alarm system could be sufficient.
Diagram A in Appendix A10.3 of ULC S524-2019 below depicts a wiring configuration for audible signal devices in dwelling units, when manual silencing means are required. Accordingly, Diagram B shows a wiring arrangements, when such manual means for audible signals devices in dwelling units would not be required, provided that all conditions of Sentence 3.2.4.18.(11) of the NBCC above are met.
A10.3 EXAMPLES OF WIRING CONFIGURATIONS FOR RESIDENTIAL NOTIFICATION DEVICES
A. ADDRESSABLE SIGNAL DEVICES
B. SEPARATE SIGNAL DEVICE CIRCUITS
NOTE 1. Circuits wired back to control unit or transponder.
Hopefully, this article clarifies existing confusion on the referenced subject. However, as usual, local AHJs should be contacted to discuss specific conditions of installation.
This article was originally featured in Electrical Line Magazine.