A Guide to Fire Alarm Basics - Supervision
A fire alarm system is a crucial part of the overall fire protection and life safety strategy of a building . A fire alarm system serves many functions and the differences between the functions can be a bit confusing, so I created a visual guide to fire alarm basics. The objective of this blog series is to discuss some of the major components and functions of a fire alarm system. For an overview of the entire system take a look at my Guide to Fire Alarm Basics Blog. This blog will take a deeper dive into the supervision portion of a fire alarm system.
It is common and often required to utilize a fire alarm system to monitor the condition of other systems, processes, or equipment that are related to the building’s fire and life safety or other systems that the owner would like to monitor. Supervision can include but is not limited to valves on fire protection systems, other fire protection systems such as kitchen hood suppression systems, valve room or storage tank temperatures, and fire pump condition. Issues with these systems would provide a signal to the fire alarm control unit via an initiating device circuit (IDC) for conventional systems, or a signaling line circuit (SLC) for addressable systems and would create a supervisory condition at the fire alarm control unit (FACU).
Conventional supervisory devices are devices that are used on an initiating device circuit and use a switch contact to short both sides of the device circuit together. By doing so, the device causes an increase in current flowing through the circuit, which the FACU interprets as a supervisory signal. Once one device shorts the circuit, no other device on that circuit or “zone” can send a signal. Because of this, any device on the circuit or “zone” will put the entire zone into a supervisory state. Zones are typically designed to enable someone to easily identify an area where the supervisory is located, for example, you may have all of the valve supervisory switches for one system on its own zone so the supervisory comes up as “supervisory wet pipe system 1”.
Addressable supervisory devices are capable of communicating a unique identification number or address to a control unit via a signaling line circuit. This identification consists of a binary string of 1s and 0s that indicate the address or location of that device on the circuit. When the FACU polls a supervisory device, the device responds with its status (Normal, supervisory, etc.) and address. The device address allows for the location to be identified at the FACU. When one supervisory device is activated on a signaling line circuit, the FACU is still able to poll the other devices unlike a conventional initiating device circuit.
Additionally, some addressable supervisory devices are also able to transmit to the FACU a range of values such as temperature, water level, pressure, and other variables, and then the control unit software determines the set points for initiation of a supervisory signal. These types of supervisory devices are known as analog addressable as they are able to tell the FACU their address and their value.
Valves that can shut off the water supply for a fire suppression system such as a sprinkler system are required to be supervised to ensure that they are not closed while the system is in service. One way of supervising these valves is the use of the fire alarm system. This is done by installing a switch, which will send distinct signals to indicate that either a control valve has been moved from its normal position (typically meaning that the valve has been shut) or that the control valve has been restored back to its normal position.
Water-based fire suppression systems are required to be maintained above a temperature of 40O F (4O C) where the system piping is filled with water. One way to ensure that these systems are not subject to freezing temperatures is to utilize the fire alarm system. This is done by placing temperature devices that can send a signal to the fire alarm control unit when the temperature in a space has dropped below 40O F (4O C) and for when the temperature has been restored to a temperature above 40O F (4O C).
If a building has a fire suppression system other than a sprinkler system such as a kitchen hood suppression system, or an inert gas system, it may be required to be monitored by
a fire alarm system. Based on the system type and the building occupancy, some of the signals may appear on the fire alarm control unit as a supervisory signal, which indicates that either the system has actuated or there is an issue with the suppression system that must be addressed. The other suppression systems may be connected directly to the building fire alarm control unit, or the other suppression system is controlled by its own fire alarm control unit (known as a releasing panel) that is then connected to the buildings main fire alarm control unit.
Some water-based fire suppression systems such as a dry pipe or pre-action sprinkler system may require the use of pressurized air or nitrogen within the system piping. In some cases, the pressure within the piping is required to be supervised by the fire alarm system. This is done using pressure transducers or pressure switches that are connected to the fire alarm control unit. A supervisory condition may then be created if the pressure in the piping is too high, or too low.
If the building has a fire pump that supplies a water-based fire suppression system such as a sprinkler system or a standpipe system, the fire alarm control unit is connected to the fire pump controller to monitor for the following conditions:
- Pump or engine running
- Controller main switch off normal
- Trouble with the controller or engine
- Main power to electric fire pump disconnected
- Phase reversal on electric fire pump
- Loss of phase on electric fire pump
For more information on fire pumps take a look at this blog.
If a water tank is used to supply a water-based fire suppression system, the water level in the tank and the temperature of the water may need to be monitored. This is done by installing water level sensors within the tank that can send a signal if the water level drops by a specified level, and the installation of water temperature sensors that can send signals if the temperature drops below 40O F (4O C) and for when the temperature has been restored to a temperature above 40O F (4O C).
Want to Learn More?
Like I noted in the beginning of this blog, if you are interested in learning more about fire alarm basics, take a look at my Fire Alarm Basics Blog I will be updating this series over the next few months to add a deeper dive into different portions of the fire alarm system. If you found this article helpful, subscribe to the NFPA Network Newsletter for monthly, personalized content related to the world of fire, electrical, and building & life safety.