How Fire Panel Know my Detectors are OK?

How Fire Panel Know my Detectors are OK?

Wishing you a very Happy New Year 2022.

The exact design of a commercial fire alarm system is determined by the commercial space’s occupancy classification and the local codes mandated by the Authority Having Jurisdiction (AHJ) for that specific occupancy classification. But regardless of the system design, all commercial fire alarm systems must have a Fire Alarm Control Panel (FACP).

An FACP is the “brain” of the fire alarm system to which all other devices are connected. When an initiating device (such as a smoke detector or a manual pull station) transmits an alarm signal to the FACP, it activates the notification devices to alert the occupants via audible and visual alarm devices.

An FACP also has a digital display that provides the current status of the fire alarm system. In modern “addressable” fire alarm systems, every device connected to the FACP has a unique address (for example: “57 - smoke detector basement electrical room”) which allows the FACP to display the specific device that initiated the signal. This level of detail allows the authorized personnel to quickly locate the source of the alarm. The building’s authorized personnel also use the FACP’s functional switches to acknowledge signals, silence alarms and reset the system once the alarm condition has been cleared by fire department personnel.

It's assumed that fire alarm systems have to work all the time because fires happen anytime... but, then again, this is the real world. Problems with the fire alarm system do occur, and that's when it may not go into alarm. To know when it needs to be fixed, the whole fire alarm system needs to be supervised. 

Smoke detectors look for the presence of smoke. The most common type used today are photoelectric smoke detectors. A photoelectric smoke detector operates by projecting a small beam of light across an internal chamber. If that beam of light becomes obscured beyond a preset threshold (a percentage of light obscuration) by smoke, dirt or other small particles, the detector will transmit an alarm signal to the

If there's trouble inside the fire alarm panel, the panel does its self-diagnostics and indicates trouble. However, when there's a problem in the wiring or devices outside the panel, that's another story. 

Addressable Supervision is the Fire Alarm Control Panel polling or asking a device "Are You OK?", and the device answers "I'm OK!"

Polling is an I'm OK Check

Conventional Class A and Class B wiring directly supervises only the wires; it does not really supervise the devices. The Signaling Line Circuit (SLC), on the other hand, is different; it supervises the devices. 

Unlike the conventional methods, the SLC is a kind of two way street. To supervise, the SLC uses Polling of the Devices. Polling is similar to an I'm OK survey of the entire fire alarm system outside the panel. 

To Poll the devices, the panel uses a signal to say 'device 27 report', and device 27 reports back with a signal that says essentially, 'I'm OK.' If device 27 doesn't report back, or if it does report back but says it isn't working correctly, the message on the fire alarm panel indicates trouble on device 27. 

Failure of the device to report back could be trouble with the device, or trouble with the wiring. However, because the panel specifies the device in trouble, the troubleshooting process of the fire alarm system is sped up. 

Supervising the Wire

With conventional Class A or Class B wiring methods, in order to directly supervise the wire, a current is passed through the entire wire loop. 

The devices connected to the loop aren't supervised; the panel never checks the devices to see if they work. Unless a detector in the field opens the loop, or a horn or strobe shorts (almost never happens), the fire alarm panel won't indicate trouble. 

On the other hand, with the exception of Styles 6 and 7 (equivalent to the conventional Class A), the wires in an addressable loop aren't directly supervised. 

Instead of passing a current through the wire, the SLC wiring is indirectly supervised. If, during the polling process, the returning I'm OK signal is received at the panel, the panel assumes that the wiring is complete. That's the indirect supervision of the wire in the loop. 

Alarm Signals -- Input and Output Device

For input devices, of course, if smoke detector 27 goes into alarm, the panel gets the signal from device 27, and using words on the display, identifies smoke detector 27 as the source of the alarm.

Then again, to turn on the horns or strobes is a specific area, the panel can also send signals along the same SLC to the specific output modules it needs to turn on. 

Addressable I'm OK Supervision -- It's All About Confidence

Using the "I'm OK" signals of the polling process, the addressable fire alarm system directly supervises the devices on the SLC. With this direct supervision of the devices, the fire alarm system has confidence the building wiring is intact.

According to NFPA 72, fire alarm initiating devices are defined as devices used to manually or automatically signal a fire alarm system to initiate responses from equipment and people. These devices connect to the alarm system’s control panel and are under the control panel’s surveillance. When triggered, the control panel identifies the location and then goes into the alarm stage, sounding alerts throughout the building and sending commands to emergency responders.

SSA Integrate offers NFPA inspection programs to our customers. Regular fire equipment inspections will ensure the ongoing reliability and safety of your fire protection systems. As part of the fire protection inspection process, detailed reports will be provided identifying any system deficiencies and recommended action to bring the system back up to applicable fire codes.
We provide a comprehensive selection of fire protection inspection services through our Preventive Maintenance Agreement (PMA). Your company can save valuable time and money by having your fire safety needs addressed with one PMA.