520 Hz Low Frequency for 120VAC Smoke Alarms IFC 2021

How is the new 2021 International Fire Code going to impact your fire alarm design and costs for Group R-1 and R-2 occupancies?

If you install fire alarm system in the residential vertical market, you need to keep reading.

When designing and pricing a new fire alarm system for group R-1 (hotels and motels) and R-2 (apartments, townhomes, and condos) you need to factor in 520Hz low frequency sounders for sleeping rooms. this is found in the 2021 International Fire Code (IFC) and 2022 NFPA 72 standard as follows:

2021 IFC Section 907.4.2.1.3
Audible signal frequency in Group R-1 and R-2 occupancies shall be in accordance with Sections 907.5.2.1.3.1 and 907.5.2.1.3.2

2021 IFC Section 907.5.2.1.3.1
In sleeping rooms of Group R-1 and R-2 occupancies, the audible alarm activated by the fire alarm system shall be 520-Hz low frequency signal complying with NFPA 72. 

2022 NFPA 72 Section 18.4.6.3*
Audible appliances provided for the sleeping areas to awaken occupants shall produce a low frequency alarm signal that complies with the following:

(1) The waveform shall have a fundamental frequency of 520 Hz +/- 10 percent.
(2) The notification equipment shall be listed for producing the low frequency waveform.

What does NFPA 72 consider a sleeping area?

To answer this question, you need to consult NFPA 72 2022 Annex A.18.4.6.3.

"The intent of this section is to require the use of the low frequency signal in areas intended for sleeping and in areas that might reasonably be used for sleeping. For example this section requires a low frequency audible signal in a bedroom of an apartment and also in the living room area of an apartment as it might have sleeping occupants. However, it would not be required to use low frequency signal in the hallways, lobby, an other tenantless spaces. In hotels, the quest rooms would require audible signals could use any listed audible appliances regardless of the frequency content of the signal being produced. This chapter of the code addresses notification appliances connected to and controlled by a fire alarm or emergency communications system. This chapter does not address dwelling unit protection such as smoke alarms and their audible signal characteristics. Requirements for single and multiple station alarms and household fire alarm systems can be found in chapter 29.  

To sum this up, NFPA 72 considers sleeping areas as bedrooms and living rooms.

Up to point, nothing has changed in the way we design and price new fire alarm systems in group R-1 occupancies and group R-2 occupancies. With that being said, lets get to the important code change noted above.

Here is where we get to the update!

2021 International Fire Code (IFC) Section 907.5.2.1.3.2

In sleeping rooms of Group R-1 and R-2 occupancies that are required by Section 907.2.8 or 907.2.9 to have a fire alarm system, the audible alarm signal activated by single or multiple-station smoke alarms in the dwelling unit or sleeping units shall be a 520-Hz signal complying with NFPA 72.

Where a sleeping room smoke alarm is unable to produce a 520-Hz signal, the 520-Hz alarm signal shall be provided by a listed notification appliance or a smoke detector with an integral 520-Hz sounder.

Here is the kicker. There are NO listed 120 VAC single or multiple station smoke alarms on the market with an integral 520 Hz sounder.

We all knew this was coming and surprise, here it is! If we simply the above code language, it states that the 120 VAC single and multiple station smoke alarms of group R-1 and Group R-2 occupancies must now produce a 520 Hz low frequency audible tone. 

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Based on the second paragraph of Section 907.5.2.1.3.2, there are two ways to tackle this new requirement:

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(1) Use a listed 520 Hz low frequency notification appliance

If this option is selected, you can utilize the wall or ceiling mounted 520 Hz low frequency notification appliances required by the 2021 IFC section 907.5.2.1.3.1 for occupant notification in group R-1 and and Group R-2 occupancies. These should already be captured by your minimum code design. However, with a standard design in mind, these appliances will only activate via a general alarm signal. This new 2021 code section 907.5.2.1.3.2 is requiring the single and multiple smoke alarms to sound these low frequency appliances. To accomplish this an addressable monitor module could be connected to a contact on the residential unit smoke alarms. This has been done for quite some time in Group R-2 occupancies used for university dorms or specific design criteria such a Marriott's Module 14.  In these cases, the addressable monitor module is in lace to supervise the in room smoke alarms. If these alarms activate, the fire alarm control unit (FACU) would receive a non-latching supervisory alarm without the activation of any occupant notification appliances. To insure the low frequency notification appliances activate via general alarm in addition to in-unit smoke alarm activation,  you would need an addressable control module to isolate each residential units notification appliance circuit (NAC). This way the system can be programmed to activate the in-unit NAC control module upon general alarm (corridor, smoke detectors, elevator lobby smoke detectorss, manual pull stations, waterflow, etc.) or the addressable monitor module connected to the 120 VAC single and multiple station smoke alarms. Remember to program the control module for latching upon general alarm activation and non-latching for the in-unit residential single and multiple station smoke alarms. 

Another scenario that will come up with this approach is audible tones synchroning as well as conflicting tones. If this method is used, an activated smoke alarm would sound it's internal sounder as well as the in room 520 Hz low frequency sounders. This would produce both the standard 3 KHz and 520 Hz tones in the space. Not sure if it is possible to disable the local piezo or sounder on a 120 VAC smoke alarm as this would rectify the conflicting tone issue. To top this off the new 2022 NFPA 72 standard requires audible tones to be synchronized. See section 18.4.3.3. We feel as though this could definitely produce an issue as the audible tones are produced from two different sources. Synchronizing the audible tones may be difficult or impossible.  

Key takeaways for option number one:

• Requires at least one addressable monitor module for each residential unit.
• Requires one addressable control module for each residential unit
• Requires a signaling line circuit (SLC) ran to each residential unit monitor module and control module.
• Requires a 24VDC power circuit to the addressable control module.
• Design the system so that each residential unit receives a separate isolated notification appliance circuit (NAC) fed from the control module noted above. 
• Confirm the electrical contractor is providing 120VAC single and multiple smoke alarms with dry contacts for the the capability to trip the addressable monitor module noted above. 
• Possible need for additional power supplies and signaling line circuit (SLC) cards depending on the base system.
• Ensure the audible tones from the single and multiple stations smoke alarm internal piezo and the fire alarm system low frequency Sounders are synchronized. Per 2022 NFPA 72 section 18.4.3.3
• Look into the issue of conflicting audible tones. As stated above there may be a method to disable the local piezo or sounder on the single or multiple stations smoke alarms. 

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(1) Use an addressable system smoke detector with an integral 520 Hz low frequency sounder base.

If this option is selected for your design, you can replace the standard ceiling or wall mounted 520 Hz low frequency notification appliances with a low frequency sounder base connected to an addressable system smoke detector. As noted above per 2022 NFPA 72 Section A.18.4.6.3, these smoke detectors and 520 Hz low frequency sounder bases will be required in all sleeping areas which are considered bedrooms and living rooms. Like any other sounder base installation, make sure to account for the addition of a signaling line circuit (SLC) and sounder base notification appliance circuit. With this option, the electrical contractor can remove all power wiring, back boxes and single or multiple smoke alarms from their bid and installation. 

Key takeaways for option number two:

• Requires at least one addressable smoke detector with integral low frequency sounder base in each bedroom and Livingroom.
• Requires a signaling line circuit (SLC) ran to each residential unit smoke detector.
• Requires a 24VDC power circuit or notification appliance circuit (NAC) to the integral low frequency sounder base.
• Depending on your fire alarm system, you may need end of line power supervision modules to supervise the loss of sounder base power. 
• Confirm the electrical contractor is NOT providing 120VAC single and multiple smoke alarms, 120 VAC power circuits and back boxes as this will be covered in your fire alarm design. 
• Possible need for additional power supplies and signaling line circuit (SLC) cards depending on the base system.

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Author note: Make sure if option number two is selected for you redesign, you still incorporate the necessary 110CD or 177CD visual appliances in the ADA (Americans with Disabilities Act) units. 

This is a HUGE change to the code and we suggest you start the conversation with your architects, general contractors and electrical contractors so everyone is on the same page moving forward. 

NICET FAS Certifications by State

If you are certified by the National Institute for Certification in Engineering Technologies (NICET) in Fire Alarm Systems (FAS), you may be interested to see how your state ranks up. The cart below has been provided to me by NICET to help show the country how you stack up. I was surprised to see which state came out on top in the most NICET FAS certified technicians. Its also great to see the tail number is up to 17,046 certifier individuals. Keep it up!

Bluebeam for Fire Alarm Design

 What is Bluebeam?

Bluebeam is a glorified PDF editing software that reaches beyond your expectations. At least in the world of fire alarm design. This software is much like Adobe or Foxit but way more in depth. If setup correctly, Bluebeam can work wonders for your fire alarm take accuracy and efficiency.  

What is different with Bluebeam?

Bluebeam offers and mazing platform that can be setup for quick navigation and access of toolkits, templates, scales and layers. This software allows you to scale a drawing and work with accuracy much like AutoCAD. When laying out a fire alarm system, it is crucial to to make sure your automatic detection initiating devices and notification appliances are spaced properly. When working in scale with custom fire alarm device and notification appliance spacing templates, you can rip though a design in no time at all. 

Did you know the 2021 International Fire Code now requires 120 VAC single and multiple station smoke alarms to produce a 520 Hz low frequency audible tone? 

Bluebeam Software Demonstration

If you are interested in using Bluebeam, I highly recommend watching our YouTube video linked below. This is a quick run through of all the features specific to fire alarm designs and take-offs. 

Bluebeam Profiles and Toolkits

Bluebeam is great in the sense that you can create your own custom profiles and toolkits. Profiles allow you to setup the interface in a way that suits your specific needs Toolkits, allow you to compartmentalize different device and equipment symbols for use in performing take-offs or fire alarm design. If you want to save your self the headache, time and trouble, of creating your own toolkits, we have you covered. The very same setup you saw in our YouTube video are now available for sale right her on our site. 

Bluebeam Profile/Toolkits

Digital File Download $200.00 USD

Bluebeam Demonstration Video

Fire Service Access Elevator FSAE Training Class

Fire Protection Education is hosting a 2 day online virtual seminar covering the new code revisions pertaining to fire service access elevators and occupant evacuation elevators. Read below for a quick overview of the class, pricing, contact info and how to signup.

Fire Service Access Elevator Introduction 

Fire Service Access Elevators or FSAEs were first required in the 2009 edition of the International Building Code or IBC Section 403.6 for all high-rise buildings over 120 feet. At that time only one Fire Service Access Elevator FSAE was required with 3,500lb capacity, serving all floors and sized to accommodate an ambulance stretcher per IBC Section 3002. This was just a standard electric passenger elevator (could not be hydraulic or freight) which was required to serve all floors of the building. This fire service access elevator could have a simplex operation or be a part of a group automatic operation and it required significant building protection around the elevator hoistway and the FSAE car per IBC Section 3007. The building protection features included: large lobbies (150SF in size with a minimum 8 feet dimension), protection of the hoistway and lobbies from Smoke, Heat, Fire and Water, hoistway lighting activated upon fire service activation, pathway survivability for control wires and a monitoring system to monitor the smoke and temperature conditions in the FSAE lobbies and Elevator Machine Room (EMR) or Elevator Control Room (ECR)

This one traction FSAE was just a regular passenger elevator or a service passenger elevator which could be used by the building occupants during the normal operation of the building. 

During fire and non-fire emergencies, the trained firefighters had the ability to choose this elevator for their firefighting emergency operation using Phase II in-car emergency operation. The responding firefighters had available information about the lobbies and EMR/ECR from the FCC and they could make a decision if they want to use this elevator or not to conduct their emergency firefighting and rescue operation. This one elevator had a much greater level of protection than all other elevators in the building and the firefighters were trained to select this specific elevator which was identified with a Fire Helmet symbol on the hoistway door jambs of the FSAE car.

Within the following 4 Code cycles of the IBC (2012, 2015, 2018 and 2021) another FSAE was added and since the 2012 IBC - TWO FSAEs are required in each high-rise building over 120 feet.  This additional FSAE was required for redundancy (in case the other FSAE was out of service or on inspection, etc.) but not for additional firefighting operation. Both FSAEs are required to be sized to accommodate an ambulance stretcher  per Section 3002 and both are required to have 3,500lb capacity.

What is changing with Fire Service Access Elevators?

There are many requirements included in the International Building Code (IBC) regarding these elevators however, no requirements are included for FSAEs in the A17.1/B44 Elevator Safety Code (current edition is 2019). 

The new 2022 edition of the A17.1/B44 will include provisions for the Fire Service Access Elevator FSAE controllers to provide a signal to the building electrical system to activate the FSAE hoistway lights upon Elevator Fire Service (FEO) activation. 

Significant changes are included in the 2021 edition of the IBC and detailed information about the FSAE Lobbies EMR/ECR temperature monitoring system via the building FA system is included in the 2019 edition of NFPA 72 Section 21.5 and A.21.5.

What is changing with Occupant Evacuation Elevators? 

A very significant change regarding the interface between the building fire alarm system and the Occupant Evacuation Elevators (OEE) is included in the 2022 edition of NFPA 72 Section 21.6 which will greatly affect the Fire Alarm system design and interface with the building elevator system.

Class Information

Class is a covered over two sessions as follows:

• Session #1 (4 Hours): Thursday August 12, 2021 from 9:00am - 1:00pm PST
• Session #2 (4 Hours): Friday August 13, 2021 from 9:00am - 1:00pm PST
• Be sure to log in at 8:30am each day to verify connection
• Course includes PDF color copy of class slides, completion certificate, color PDF flow chart for occupant evacuation elevator and fire alarm sequencing.

ICC Preferred Education Provider

• ICC Course No 19708
• Approved for 8 Hours - 0.8 ICC-CEUs

Course cost

• General Public = $400.00
• Active AHJs = $350.00

How to enroll

• visit www.fireprotectioneducation.com
• email info@fireprotectioneducation.com
• call 510-589-6286

    

Fire Alarm Wiring Based on NEC Article 760

A common topic for discussion in the fire alarm industry involves fire alarm wiring. This article will cover all aspects of fire alarm wiring including but not limited to separation, conduit fill, strapping, mechanical protection and marking.

Fire Alarm Circuits

Did you know the 2021 International Fire Code now requires 120 VAC single and multiple station smoke alarms to produce a 520 Hz low frequency audible tone? 

The definition of a fire alarm circuit is as follows: "The portion of the wiring system and connected equipment powered and controlled by the fire alarm system. Fire alarm circuits are classified as either nonpower-limited or power-limited."

I'm sure you have heard these two terms in the industry before so let's break them down.

Non-Power Limited Fire Alarm Circuits

A non-power-limited fire alarm circuit commonly referred to as NPLFA, can operate at up to 600V and the power output isn't limited.

Power-Limited Fire Alarm Circuits

A power-limited fire alarm circuit commonly referred to as PLFA, must have the voltage and power limited by a listed power supply that complies with NEC 760.121. Based on this section, a power source can be either (1) a listed PLFA or Class 3 transformer, (2) a listed PLFA or Class 3 power supply or (3) listed equipment marked to identify the PLFA power source. A few examples of listed equipment would be fire alarm control panels with integral power sources and circuit cards listed for use with PLFA sources.

The two tables below provide the listing requirements for power-limited fire alarm circuit sources:

Power Sources for Power-Limited Fire Alarm Circuits

Power-Limited fire alarm equipment must be supplied by a branch circuit that supplies no other load and is NOT GFCI or AFCI protected. The branch circuit overcurrent device (breaker) must be identified in red, accessible only to qualified personnel, and identified as "FIRE ALARM CIRCUIT". The red markings cannot damage the overcurrent protective device or cover any manufacturer's markings. The lock pictured below is available from Space-Age Electronics.

Equipment Marking for Power-Limited Fire Alarm Circuits

The fire alarm equipment that supplies power-limited fire alarm cable circuits must be marked to indicate each circuit that is a power-limited fire alarm circuit. Per NEC article 760.30, the fire alarm circuits must be marked at terminal and junction locations.

Wiring Methods for Power-Limited Fire Alarm Circuits

Power-limited fire alarm circuits shall be installed in accordance with NEC article 760.46 and conductors shall be solid or stranded copper.

Cable splices or terminations shall be made in listed fittings, boxes, enclosures, fire alarm devices, or utilization equipment. If the circuits are installed exposed, the cables shall be adequately supported and installed in such a manner that maximum protection against physical damage is afforded by building construction. The thought here is that nails from baseboards, door frames, drywall, etc. may penetrate deep enough to damage the wire. To avoid this, make sure to install your fire alarm cables no closer than 1 1/4" from the edge or the framing.  If this is not possible, use 1/16" thick steel plate for protection [NEC 760.24(A)]. Where cables are installed within 7 feet of the floor, said cables shall be fastened in an approved manner at intervals of not more than 18 inches.

Power-limited fire alarm cables are NOT permitted to be strapped to the exterior of any raceway as a means of support. Exposed cables must be supported by the structural components of a building so that the cable will not be damaged by normal building use. Cables must be supported by straps, staples, hangers, cable ties, or similar fittings designed and installed in a manner that will not dame said cable. If the calves or raceways are installed above a suspended ceiling, they must be supported by independent support wires attached to the suspended ceiling.

Cables passing through a wall or floor. Both Power-Limited and Non Power-Limited Fire Alarm Cables shall be installed in metal raceways or rigid nonmetallic conduit where passing through a floor or wall to a height of 7' above the floor, unless adequate protection an be afforded by building construction. Keep in mind if the cables pass through a fire barrier, you must provide fire caulking to insure the integrity of the barrier.

Power-Limited Fire Alarm Circuit Separation

This is a topic that a lot of designers and technicians constantly go back and forth on.  To better understand the separation requirements, I believe it is important to know what the 3 different circuit classification are.

Class 1 Circuits. 

Class 1 remote-control and signaling circuits typically operate at 120V, but the NEC permits them to operate at up to 600V [725.21(B)]. You must install these circuits within a wiring method listed in Chapter 3 of the NEC, which includes raceways, cables, and enclosures for splices and terminations [725.25]. Remote-control circuit. These circuits, which control other circuits through relays or equivalent devices, are commonly used to operate motor controllers in moving equipment, mechanical processes, elevators, and conveyors.

Class 2 Circuits.

Class 2 circuits typically include wiring for low-energy (100VA or less), low-voltage (under 30V) loads such as low-voltage lighting, thermostats, PLCs, security systems, and limited-energy voice, intercom, sound, and public address systems. You can also use them for twisted-pair or coaxial local area networks (LAN) [725.41(A)(4)]. Class 2 circuits protect against electrical fires by limiting the power to 100VA for circuits that operate at 30V or less, and 0.5VA for circuits between 30V and 150V.

Class 3 Circuits. 

Class 3 circuits are used when the power demand for circuits over 30V exceeds 0.5VA, but is not more than 100VA [Chapter 9, Table 11]. We often see Class 3 signaling circuits for security systems and public address systems; voice, intercom, and sound systems; and some nurse call systems.
Higher levels of voltage and current are permitted for Class 3 circuits (in contrast to Class 2 circuits).

Fire Alarm Cable Separation based on Circuit Classifications

PLFA with Class 1 Circuits

NEC 760.136 (A) Power-limited fire alarm circuits must not be placed in any enclosure, raceway or cable with conductors of electric light, power or class 1 circuits.

NEC 760.136 (B) If the circuits are separated by a barrier, power-limited fire alarm circuits are permitted with electric power conductors.

NEC 760.136 (D) Power-limited fire alarm circuits can be mixed with electric light, power and class 1 circuits in enclosures where these other conductors are introduced solely for connection to the same equipment and a minimum of 1/4" separation is maintained from the power-limited fire alarm cables.

Power-limited fire alarm circuits shall be separated by not less than 2" from insulated conductors of electric light, power or Class 1 circuits. Exception: If the electric light, power, class 1 circuit or power-limited fire alarm circuits are installed in a raceway, metal-sheathed, metal-clad, nonmetallic-sheathed or underground feeders.

PLFA with Class 2 and Class 3 Circuits

NEC 760.139 (A) Two or more PLFA Circuits. Power-limited fire alarm circuits, communications circuits or Class 3 circuits can be installed in the same cable enclosure, cable tray, raceway or cable routing assembly.

NEC 760.139 (B) PLFA and Class 2 Circuits. Power-limited fire alarm circuits and Class 2 circuits can be within the same cable, cable tray, cable routing assembly, enclosure, or raceway provided the Class 2 circuit insulation is not less than that required for the power-limited fire alarm circuits.

NEC.139 (C) PLFA and Low Power Network Communication. Low-powered network powered broadband communication circuits hall be permitted in the same enclosure, raceway, cable assembly, or cable tray.

NEC 760.139 (D) PLFA and Audio System Circuits. Power-limited fire alarm circuits and audio system circuits using Class 2 and Class 3 wiring methods shall not be installed in the same raceway, enclosure, cable routing assembly or cable tray. Please not this does not apply to voice evacuation and mass notification speaker circuits controlled by a fire alarm control unit or amplifier.

Fire Alarm Cable Substitutions

NEC 760.154(A) The following fire alarm cable substitutions are permitted as long as the wiring requirements of NEC Article 760 Parts I and III apply.

FPLP (Fire Power-Limited Plenum) ------------> CMP
FPLR (Fire Power-Limited Riser) --------------> CMP, FPLP, CMR
FPL (Fire Power-Limited) -----------------------> CMP, FPLP, CMR, FPLR, CMG, CM

Fire Alarm Conductor Size

NEC 760.142. Conductors of 26 AWG shall be permitted only where spliced with a conductor listed as suitable for 26 AWG to 24 AWG or larger conductors that are terminated on equipment or where the 26 AWG conductors are terminated on equipment listed as suitable for 26 AWG conductors.

Single conductors shall NOT be smaller than 18 AWG.

How to Figure Conduit Fill

Conduit fill requirements can be found in the NEC Annex Table C.  This is toward the back of the book and is broken up into different sections based on the type of raceway being used.  In this example, we will use table C.1 for EMT (Electrical Metallic Tubing).  Take a look at the table below and try to locate the maximum number of 14 AWG THHN conductors permitted in 2 1/2" EMT raceway. The answer is 241.

NICET Facebook Group Post Answers

If you are looking for the answers to the NICET for Fire Alarms Facebook group posts, then you are in the right place!  If you have stumbled upon this article and want to have these questions pushed to your phone or PC instantly, then please by all means join the greatest Fire Alarm forum online.

If you have a questions you want dissected, email us and we will throw it out there.

Question from post on 5-15-19

Based on the International Building and Fire Codes, a fully sprinklered two story office building with a group B occupancy and 11,000 sq' of floor space per level requires what type of fire alarm system?

The 2015 International Building Code table 1004.1.2 states that business type occupancies requires 100 sq' of space per occupant.  11,000 sq' divided by 100 = 110 occupants per floor. The 2015 International Fire Code section 907.2.2, a group B occupancy with greater than 100 persons on a floor above or below the level of exit discharge, a manual fire alarm system shall be required. Since this facility is sprinkled, only one manual pull box would be required in an approved location IF the waterflow activates the occupant notification appliances.

Smoke Detector Spacing with Beams

Smoke Detector Spacing for Smooth Ceilings

Let's start with the basics of smoke detector spacing.  Based on 2022 NFPA 72, there is not a listed spacing for smoke detectors. Instead, you are instructed to consult with the smoke detector's published documentation.  However, NFPA 72 2022 edition section 17.7.4.2.3.1 states the following, "In the absence of specific performance based design criteria, one of the following requirements shall apply:

1. The distance between smoke detectors shall not exceed a nominal spacing of 30 feet and there shall be detectors within a distance of one-half the nominal spacing, measured at right angles from all walls or partitions extending upward to within the top 15 percent of the ceiling height.
2. All points on the ceiling shall have a detector within a distance equal to or less than 0.7 times the nominal 30 foot spacing.

What does this mean?

Number 1 above states you must have a smoke detector within one half the nominal spacing from walls.  One half of 30 feet is 15 feet.  In the image below you will see a total of six yellow circles each with a 30 foot diameter.  These circles represent the area covered by a spot type smoke detector based on a nominal spacing of 30 feet. As required by the 2022 NFPA 72, we have spaced each detector at 15 feet from walls and 30 feet apart.    

Smoke Detector Spacing with a Smooth Ceiling

What about the white areas not covered?

If you notice in the image, there are areas not covered by the yellow circles representing the smoke detector coverage.  This is where NFPA 72 2022 edition section 17.7.4.2.3.1 criteria number two comes into play.  

With a nominal spacing of 30 feet, you must insure that all areas of the ceiling have coverage within 0.7 times this 30 foot amount.  To find this distance, simply multiply 30 feet by 0.7 to get 21 feet.

If you use Pythagorean's Theorem you will come up with a surprising result.  Remember Pythagorean's Theorem is used to find the unknown side of a right triangle and is expressed as A squared + B squared = C squared.  In this case we have a right triangle in each quadrant of the yellow circles.  Each quadrant is 15 feet our and 15 feet up.  We can write this equations as:

15 squared + 15 squared = C squared 

225 + 225 = 450 squared

450 squared = 21.2132 feet

In the image below you will see a cleared depiction of how this all comes together. With this, it is clear that we have met the intent of the standard by mounting our smoke detectors 15 feet from the walls, 30 feet apart and still achieve 0.7 times the nominal spacing (21 feet) coverage at all points of the ceiling.

Smoke Detector Coverage for 30 Feet

NFPA and Smoke Detector Spacing Distances

The Annex of NFPA 72 provides us with a diagram to assist in smoke detector spacing. Note that smoke detectors are not listed for spacing.  Use the smoke detector's published installation documents and the spacing breakdown below to assist in your design.

For areas/corridors 10 feet wide, smoke detectors can be spaced at 41 feet.

For areas/corridors 15 feet wide, smoke detectors can be spaced at 39 feet.

For areas 20 feet wide, smoke detectors can be spaced at 37 feet.

For areas 25 feet wide, smoke detectors can be spaced at 34 feet.

For areas 30 feet wide, smoke detectors can be spaced at 30 feet.

Smoke Detector Spacing with Beam Construction

If your ceiling configuration involves beams, your smoke detector coverage can get a bit more tricky.

NFPA 72 2022 edition section 17.7.4.2.4.2 deals with level ceilings with beams. In a nutshell, this is how it breaks down:

• If the beam depth is LESS than 10% of the overall ceiling height, then smooth ceiling spacing for smoke detection can be applied.  Also note that in this scenario, you can choose to install the smoke detectors on the ceiling or the bottom of the beams. Reference the above text and images for smooth ceiling spacing.
• If the beams are are equal to or greater than 10% of the overall ceiling height, two scenarios are possible:
• If the beam depth is equal to or greater than 10% but less than 40%, use smooth ceiling spacing PARALLEL to the beams and one half spacing PERPENDICULAR to the beams.  With this scenario, the smoke detectors can be mounted on the ceiling or the bottom of the beams.
• If the beam depth is equal to or greater than 40%, a smoke detector shall be placed on the ceiling within each beam pocket.  Keep in mind that more than one smoke detector may be required to cover a given beam pocket.

How to Calculate Smoke Detector Spacing with Beam Construction 

Did you know the 2021 International Fire Code now requires 120 VAC single and multiple station smoke alarms to produce a 520 Hz low frequency audible tone? 

To calculate the beam depth for smoke detector spacing, convert your overall ceiling height into inches.  For example, if your ceiling is 12 feet it would convert to 144 inches.  Take 144 and multiply it by 0.1 to get 10%.  144" x 0.1 = 14.4".  In this case, ant beam depth of 14.4" or more would require an altered smoke detector lay out.  If you want an easier way to work this calculation and remember what spacing requirements go with the different percentages, we have you covered.  Download a FREE copy of our Excel Fire Alarm Calculation Tool and use the "SD BEAMS" tab.  All you need to do is input your ceiling height and beam depth in inches and the calculator will give you a color code for which spacing requirement is required (see image below).  Email us with any questions.   

Smoke Detector Spacing in Corridors with Beams 

What do you do if you have a corridor that is equal to or less than 15 feet in width with beams running perpendicular to the length of the corridor?  Consult NFPA 72 2022 section 17.7.4.2.4.2 (4).  This section of the standard allows you to use smooth ceiling spacing and the smoke detectors can be mounted on the ceiling, bottom of the beams or on the sidewall.

Smoke Detector Spacing in Rooms 900 Square Feet or Less

NFPA 72 2022 section 17.7.4.2.4.2 (5) allows the use of smooth ceiling spacing for smoke detection coverage in rooms that are equal to or less than 900 square feet.  You can also install the smoke detector on the ceiling or bottom of the beam.