Sprinkler and fire alarm interconnections
NFPA Journal®, November/December 2010
The Life Safety Code® and building codes allow for certain modifications in their construction requirements when a "supervised" automatic sprinkler system protects a building. The Life Safety Code states that "supervisory attachments shall be installed and monitored for integrity in accordance with NFPA 72®, National Fire Alarm and Signaling Code, and a distinctive supervisory signal shall be provided to indicate a condition that would impair the satisfactory operation of the sprinkler system. System components and parameters that are required to be monitored shall include, but shall not be limited to, control valves, fire pump power supplies and running conditions, water tank levels and temperatures, tank pressure, and air pressure on dry-pipe valves. Supervisory signals shall sound and shall be displayed either at a location within the protected building that is constantly attended by qualified personnel or at an approved, remotely located receiving facility." The code goes on to state that "waterflow alarms shall be transmitted to an approved, proprietary alarm-receiving facility, a remote station, a central station, or the fire department."
These requirements initiate the shared responsibilities between the automatic sprinkler and fire alarm systems. NFPA 72 does not, by itself, require the facility to connect waterflow and valve supervisory switches to the fire alarm system. Once the Life Safety Code or building code requires a supervised sprinkler system, however, the 2010 edition of NFPA 72 allows the connection of alarm and supervisory devices to the control unit of a building fire alarm system or dedicated-function fire alarm system. The use of a dedicated-function fire alarm system allows the supervision of an automatic sprinkler system without requiring the installation of a complete fire alarm system in the building.
NFPA 72 restricts the number of supervisory devices and waterflow switches that may connect to an initiating device circuit to 20 and 5, respectively. These restrictions are intended to reduce the number of specific initiating devices that individuals responding to the signals must investigate before they find the precise sprinkler system or valve that has initiated the signal. For example, upon receipt of a waterflow alarm signal, the responding fire department should not have to deal with excessively large zones. Nor should maintenance personnel responding to a signal from a closed sprinkler control valve have to search many valves to find the closed one.
Ideally, in order to more accurately pinpoint the source of a signal, the facility will connect even fewer alarm or supervisory switches than the maximum allowed.
To provide even more accurate information about the location of the source of an alarm or supervisory signal, switches may connect to a signaling line circuit interface (SLCI). This interface will transmit multiple signals with signal-specific addresses to an addressable fire alarm system control unit.
The initiating device circuits that extend from the switches to the SLCI module must meet the same limitations as other initiating device circuits. In order for the fire alarm system to then transmit the alarm signal off-premises, NFPA 72 requires that the actuation of the waterflow initiating device must occur within 90 seconds of the beginning of a flow of water equal to, or greater than, that from a single sprinkler of the smallest orifice size installed in the system. The built-in time delay helps avoid false alarms from the movement of water due to waste, surges, or variable pressure in the water supply system.
Understanding the shared responsibilities between the automatic sprinkler and fire alarm systems becomes an important factor in ensuring that these systems provide the benefits expected by the fire protection community and building owners.
Wayne D. Moore, P.E., FSFPE, is a principal with Hughes Associates and immediate past chair of the NFPA 72 Technical Correlating Committee.