Smoke Detector above Fire Alarm Control Unit FACU

A question we see coming up more often is in regards to smoke detection above fire alarm control units.  The specific questions is, "Are you required to install a smoke detector above the fire alarm control unit (FACU) or fire alarm control panel (FACP)?".

Simply put the answer is YES and can be supported by the language found in NFPA 72 2022 edition section 10.4.5. (page #74).  This sections states the following:

"Unless otherwise permitted by 10.4.5.1 or 10.4.5.2, in areas that are not continuously occupied, early warning fire detection shall be provided at the location of each fire alarm control unit(s), notification appliances circuit power extenders, and supervising station transmission equipment to provide notification of fire at that location by one of the following means:

(1) An automatic smoke detector at the location of each control unit(s), notification appliance circuit power extender(s), and supervising station equipment.

(2) An automatic heat detector where ambient conditions prohibit installation of an automatic smoke detector."

Also note there is an Annex section related to this reference.  A.10.4.5 states that the equipment to be covered by this automatic smoke detection is a fire alarm control unit that is used to notify occupants and responders of a fire.

Here are a few other key items to keep in mind when dealing with this topic:

• The term Fire Alarm Control Unit (FACU) does NOT include annunciators or addressable devices.
• If the area where the FACU is located is continuously attended, a smoke detector is NOT required.  Keep in mind this is not intended for lobbies or offices where there are occupants coming and going throughout the day.  This is intended for areas such as lobbies with 24/7 security and security rooms where at least one guard is in attendance at ALL times.
• If the area where the FACU is located has full coverage smoke detection, then an additional smoke detector dedicated to the FACU is NOT required.
• If the single smoke detector intended to protect the FACU per 10.4.5 does not cover the entire space where the control equipment is located, then additional smoke detection is NOT required.

Now here is were it may become confusing for the designer or AHJ.  Section 10.4.5 as well as A.10.4.5 clearly state that the FACU to be protected is a control unit that is in place to notify occupants and first responders of a FIRE.  As you may or may not be aware, there are additional systems we deal with in this industry known as Dedicated Function Fire Alarm Systems.  

Building Fire Alarm System vs. Dedicated Function Fire Alarm System

As defined by NFPA 72 2022 edition Section 3.3.118 (page #29)

Building Fire Alarm System.  A protected premises fire alarm system that includes any of the features identified in section 23.3.3.1 and that serves the general fire alarm needs of a building or buildings and that provides fire department or occupant notification or both.

Dedicated Function Fire Alarm System.  A protected premises fire alarm system installed specifically to perform emergency control function(s) where a building fire alarm system is not required.  

Here is the code section that indicates when a Dedicated Function Fire Alarm Alarm Systems can be installed in place of a building fire alarm system per NFPA 72 2022 edition section 23.3.3.2.1. 

"In facilities without a building fire alarm system, a dedicated function fire alarm system shall be permitted and shall not be required to include other functions or features of a building fire alarm system."

The two most common dedicated function fire alarm systems typically used are:

• Dedicated function sprinkler monitoring system:  This is a system installed when a particular building does not require a building fire alarm system BUT still has an automatic fire sprinkler system employing more than 6 heads.  Example could be a small strip mall (Group M) with under 100  occupants but more than 6 automatic sprinkler heads.  Although this system is not in place to notify occupants or responders of a fire, a smoke detector is required above the panel since this system is in place to monitor the sprinkler system.  Per NFPA 72 2022 section 10.4.5 a smoke detector is required to protect "supervising station transmission equipment".

• Dedicated function elevator control system:  This is a system installed strictly and specifically to control the emergency functions of an elevator such as elevator recall and shunt trip.  These systems will typically have your elevator lobby/equipment room smoke detectors, heat detectors, relays and modules to perform the emergency control functions found in NFPA 72 2022 chapter 21.  Note this system would not be required to be monitored as it is not in place to monitor the status of an automatic sprinkler system.  In this case a smoke detector is NOT required above the control unit as it is not monitored nor is it in place to notify occupants or responders of a fire.

FACU Smoke Detector Installation Location

NFPA 72 2013 Smoke Detector Mounting Diagram

Pay attention to your applicable code as the installation location of this smoke detector changed
between NFPA 72 2010 and 2013 editions.

NFPA 72 2010 (A10.15 #1 and #2) state if the ceiling height is 15' or less, the smoke detector shall be installed on the ceiling or wall within 21' of the centerline of the FACU.  If the ceiling height exceeds 15', the smoke detector should be installed on the wall no more than 6' above the top of the FACU.

NFPA 72 2013 (A10.4.4) states the smoke detector shall be installed in accordance with section 17.7.3.2.1.  Section 17.7.3.2.1 states "Spot-type smoke detectors shall be located on the ceiling or, if on a sidewall, between the ceiling and 12 inches (300 mm) down from the ceiling to the top of the detector."

Help Out Your Local Fire Fighters With a Dry Riser Now!

Dry Pipe Automatic Sprinkler Systems

Fire fighters are there to help you. When a fire breaks out they are rushing out to the fire to stop it before it can cause too much damage. Help them out by getting a dry riser. The dry riser is something that can be fitted into your building to help fight fires as soon as they break out. The outlet that exists outside the building can aid fire fighters further by making sure that they have a source of water they can use.

Dry Sprinkler Pipe System - How It All Works

The dry riser works on the principle of compressed air. Compressed air is what differentiates it from the dry riser’s counterpart; the wet riser, which utilises water-filled pipes. The compressed air works by pressing the valve shut that prevents the water from entering the pipe. Once the air is released the valve opens up and the water can shoot through the pipes. 

At the end of the pipe is a sprinkler system. Sprinklers open up when a fire has been detected. Naturally, once the sprinkler opens the compressed air disappears and the water can then attack the flames. They may not necessarily be able to eliminate the fire, but what they can do is to make sure that it’s limited. Think of it as giving fire fighters some additional time to get to the scene of the incident.

Dry Pipe Sprinkler Systems - Help Your Local Fire Fighters!

Your local fire fighters are not always going to be in the best position when confronted with a fire. Due to rapid urbanisation, it’s now harder than ever to find a suitable water outlet that can provide the supply that’s needed to combat the most serious fires. Dry risers have to get their water from somewhere, and that comes in the form of an inlet valve. Fire fighters are able to attach their tools to this valve and draft the water from there.  

So you don’t have one of those things and they are forced to look elsewhere. Those extra minutes spent looking for a suitable supply of water could mean the difference between your property burning down and the structure being saved. Surely the desired outcome is going to be obvious here?

If you suspect the valve in your high rise has been tampered with ring the dryriser theft hotline.

Dry Pipe Sprinkler System - Where are they Fitted?

From a glance, it seems as if the dry riser system is quite vulnerable. Once the fire takes hold it can attack the pipes and cut off the supply. This is not the case at all. All of these systems are required by law to have their main pipes in a place that’s resistant to fire. Escape stairways are the number one places where these can be found. Note, these fire-resistant areas are not necessarily going to protect it forever. On the contrary, sooner or later the fire will burn through. 

Primarily, it’s to combat minor fires before they spread. If a major fire breaks out, or even worse an explosion, then nothing can be done until the fire fighters arrive.

Dry Pipe Sprinkler System - How Expensive Are They?

If you are looking to install one of these systems then one of the things you will be looking at is the price. Of course, the price is very important because nobody wants to invest a great deal of money in anything. Small businesses may also have trouble meeting large costs, so affordability is perhaps the most important factor. The good news is that companies are offering these systems at a cost-effective price. Regular deals are constantly being employed to encourage people to invest in these systems. 

Fire Sprinkler - Wet Pipe Systems

With fewer components and less installation time, a wet pipe fire sprinkler system is the most common system you will come across.  A wet pipe fire sprinkler system has a series of piping systems or branches that are fed from the main riser.  The term wet pipe system comes from the fact that the fire sprinkler system is always filled with water.  Behind each sprinkler head is water waiting to be released upon activation.  With that said, you will not typically see wet pipe fire sprinkler systems in areas exposed to freezing temperatures such as parking garages, etc.

The operation of a wet pipe fire sprinkler system is rather simple.  The sprinkler heads contain either a fusible glass bulb or metallic heat sensor.  Heat from a fire will cause the fusible glass bulb to burst or the metallic heat sensor to separate which then opens the small valve on the fire sprinkler head causing water from the piping to discharge and extinguish the fire.

Wet pipe fire sprinkler systems are a fixed temperature type installation, meaning each sprinkler head is is activated only if exposed to a predetermined temperature as low as 155 degrees F or as high as 286 degrees F.

Below are three types of wet pipe fire sprinkler systems with additional information on their operation.

Wet pipe fire sprinkler system with and Alarm Check Valve

When water enters the fire sprinkler system it becomes non-potable and unsuitable for drinking.  To keep this water from entering back into the city water system, an alarm check valve is used.  An Alarm Check Valve is a small and simple device consisting of a spring, valve clapper and an alarm port.

Withing the alarm check valve, the spring holds the valve clapper closed allowing water to flow in only one direction.  Once the system is filled, the water remains in the piping until an individual or multiple sprinkler heads are activated.  Once a sprinkler head is activated, water is discharged and needs to be replaced within the piping.  In order for this to happen, the valve clapper opens allowing the water to flow in to the system and out of the activated sprinkler head.  As the alarm port becomes exposed to water pressure, it causes a water motor gong, mechanical horn or audible/visual device to sound.  A more common way to initiate an electric bell or fire alarm horn/strobe, is a water flow device.

To prevent city water surges from causing false alarms, a retard chamber is used.  A retard chamber is a metal reservoir that holds the water during a brief city water surge.  A drip valve at the bottom side of the reservoir allows the water from the surge to slowly drain out.  If a true fire activates a sprinkler head, the drip valve is unable to drain the water fast enough causing the flapper on the water flow device to move thus activating an alarm condition.

Wet pipe fire sprinkler system with Maintained Excess Pressure

In this type of wet pipe fire sprinkler system, excess pressure is pumped in just above the alarm check valve to hold the clapper down even during a city water surge.  This type of wet pip fire sprinkler system eliminates false alarms caused by city water surges.

There are two ways to measure pressure loss in this type of system.

1.  Connect a pressure switch to the system above the alarm check valve.  If as sprinkler head is activated, the pressure switch will detect a loss in pressure and sends an alarm.  Usually a supervisory pressure switch is used to monitor if there are leaks within the system.

2.  Connect a pressure switch to the alarm port on the alarm check valve.  If a sprinkler head is activated, the alarm check valve opens.  When the valve opens, the alarm port is exposed to the incoming water supply.  The pressure switch will detect a change in pressure and will send an alarm.

Wet pipe fire sprinkler system with a straight pipe riser

This type of system will have a straight pipe riser located downstream from the check valve or backflow preventer and are the most common type of wet pipe system.  The vertical supply pipe or riser, does not have a retard chamber or alarm port like others.  Instead you will find a riser check valve.

A riser check valve utilizes a vane type water flow switch to monitor water flowing within the wet pipe fire sprinkler system.  When continuous flow of water equal to 10 gallons per minute occurs, the water flow switch activates an alarm condition after a predetermined amount of time.  This time delay can be selected on the actual water flow device.  This time delay is to help eliminate false alarms caused by city water surges.


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Fire Sprinkler - Dry Pipe Systems

A deluge and pre-action fire sprinkler system are both part of the dry pipe family.  Dry pipe systems are typically installed in areas where water is subject to freezing such as unheated facilities and parking garages.  Unlike the wet pipe fire sprinkler system (filled with water) a dry pipe system is filled with compressed air from a source such as an electric compressor or nitrogen bottle.

Like wet pipe fire sprinkler systems, dry pipe systems also have a valve clapper and alarm port.  The dry pipe valve clapper is held closed by a pressure differential between air pressure and water pressure.  Supervisory pressure switches are typically used to measure the pressure on the system side.  These pressure switches can send either a low or high pressure signal to the panel.  The fire alarm control panel or pre-action panel will then turn on a pump or release pressure depending on the signal (low or high pressure).  This ensures that the correct amount of pressure is present in the system at all times.

In the event of an actual fire and a fire sprinkler head activates, the air pressure in the system is released.  When the air pressure drops to the trip point (usually around 10 psi below normal), the dry pipe valve opens and allows water to flow in from the main source to fill the distribution pipes and out of the activated fire sprinkler head.  Once the water is flowing through the clapper valve, the alarm port is exposed to the water.  At this time a pressure switch senses the increase in pressure and sounds an alarm.

Dry Pipe Valve

A dry pipe valve is located above the main system control valve and must be installed in areas not subject to freezing.  The whole purpose of the dry pipe valve is to ensure water does not enter the distribution piping and freeze.  It is a one way clapper that has a small amount of water covering it known as the priming water.  This priming water helps to seal the valve seat and has an immediate chamber that connects the valve to the alarm line.

Pressure Switches

There are alarm pressure switches and supervisory pressure switches both used in dry pipe fire sprinkler systems.  Both of these pressure switches monitor air pressure on the system side of the dry pipe valve.  The alarm pressure switch measures pressure change within a system and sends alert signals the the main fire control panel or pre-action system panel.  The supervisory air pressure switches monitor air on the system side of the dry pipe valve and perform two different functions.

1.  Monitor low air pressure and prevents accidental operation of the dry pipe valve due to low air pressure from an air compressor failure or leaks in the system.

2.  Monitor high air pressure to prevent damage to the clapper and gaskets in the dry pipe valve.


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Fire Sprinkler - Deluge Fire Sprinkler System

A deluge fire sprinkler system works similar to a wet pipe system, however, the deluge system uses open fire sprinkler head or nozzles that do not operate individually.  The pipes are dry in normal operation and the water is held back by an electronic solenoid.  The solenoid is connected and control by a compatible releasing fire control panel.  An initiating device such as a smoke detector or heat detector sends a signal to the releasing panel which in turn energizes the releasing circuit and opens the solenoid.

These types of deluge systems are typically installed in high hazard areas such as power generating stations, aircraft hangers, chemical plants, and other areas that main contain chemicals and or flammable liquids.  Water is not always adequate to control fires in areas where chemicals and flammable liquids are stored.  Often you will find that a foam concentrate is mixed with the water in a part of the system known as the proportioner.  The foam is known as Aqueous Fire Fighting Foam or better known as AFFF.  This foam when mixed with water causes expansion when released through the sprinkler head which in turn deprives the fire of oxygen.

Read more about dry fire sprinkler systems here.


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.

Make sure to join our Fire Alarms Online Facebook Group HERE.