Fire alarm systems have two jobs. It must detect a potential fire in a facility, and then notify its occupants. It’s that simple. Getting the system to work properly and meet local life safety codes; that’s not so simple. This article is the first in a series that will explain fire alarm systems to personnel that need to design them, as well as those that will interact with them after the facility is occupied.
Who’s In Charge Here?The fire alarm control panel (FACP) is the origin of all fire alarm activity. Depending on the size of the installation, there may be a number of FACP’s in a system that talk to each other, but the basic premise is the same. The FACP controls all devices connected to it. What makes up an FACP? First, there must be a main control board. This board processes signals from the devices on its field circuitry and supervises all subcomponents for proper operation. These subcomponents include:
- Circuit boards
- Power supplies
- System CPU
- Initiating devices
- Notification appliance circuits
We’ve discussed the two jobs of the FACP, detection and notification. Detection devices are also referred to as ‘initiating’ devices. An initiating device initiates an output of some type on the fire alarm system when activated. Examples of initiating devices are:
- Smoke detectors
- Heat detectors
- Manual pull stations
- Dry contact monitoring devices
+ Sprinkler waterflow
+ Sprinkler shut off valve
+ Fire pump status
The status of other building systems, such as fans and stairwell door locking systems, can by monitored via dry contacts as well.
Grabbing your attention
The output associated with the activation of an initiating device may be the activation of the internal sounder on the panel, a relay that will shut down the ventilation system or audio/visual devices. Audio/visual devices are referred to as ‘notification’ appliances and reside on notification appliance circuits (NACs). Examples are:
- Horns
- Speakers
- Strobes
- Combination audio/visual (A/V) devices
Other types of notification devices are those that alert the fire department via phone lines or radio and annunciation devices. It may be helpful to remember that everything connected to an FACP is either initiating events or notifying someone about an event.
On the lookout for trouble
Initiating devices are supervised by the FACP in two manners. The first is referred to as ‘conventional’. Conventional initiating devices operate on low voltage only and initiate alarms by shorting their connection circuitry. This circuit is referred to conventional zone. The number of conventional devices that are on a single zone is determined by a combination of:
- Number of electrically operated devices that can be powered by the zone
- Area of coverage – fire codes limit the square footage of a zone
- Type of conventional devices – some types of initiating devices cannot share zones with other types
Logically, if the FACP has only conventional zones, it is referred to as a conventional panel. In the 1990’s, these panels began to give way to ‘addressable’ panels and devices. Addressable technology utilizes digital data transmissions rather than voltage to monitor initiating devices. This allows for point identification, or addressing, of these devices. Instead of annunciating the alarm as a general zone, systems can now identify exactly where the alarm was generated. Other advantages of addressable devices are:
- Lower installation costs
- Customization of the detector’s sensitivity to smoke or heat
- Software grouping to allow specific outputs per group
- Required by most fire departments for new installations
Be sure to look for our next newsletter that will touch on the effectiveness and intelligibility of mass communication messages. For additional information on this and many other life safety topics, contact Gene Rowe at Affiliated Customer Service, Inc., at generowe@affiliatedinc.com or (630) 434-7900
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About Gene Rowe
good morning sir Gene,
i have a problem in my project about generator room fire alarm components, i noticed that there are no smoke detectors mentioned in the drawing plan in the ceiling or wall of the room… but there is monitor module which is designate as M inside a square box, is there a chance that this is referring to a smoke detector or sensing device that could give an alarm to FACP ? should i insist to my client to order some smoke or heat detectors or which is required ?
thanks a lot.
mr rodolfo