Using fire alarm systems for special applications
Fire protection designers may use fire alarm systems for special applications in many building and fire protection scenarios. In most of these applications, the fire alarm system interconnects to some form of fire suppression or special notification system within the building. When a contractor reads the fire alarm system specifications, he or she may not always know or realize that the fire alarm system will serve “double duty.”
Common interconnections to a building fire alarm system include the connection of the automatic sprinkler system water flow and control valve position supervisory switches and the switch that indicates system actuation from a kitchen hood fire suppression system. In each case, the fire alarm system simply monitors the status of these systems and performs no control functions.
In addition, the National Fire Alarm Code, NFPA 72-2002, requires these connections. In fact, the Code requires that protected premises fire alarm systems must include, in addition to manual and automatic alarm initiation and alarm notification, the ability to accommodate the following:
1. Monitoring of abnormal conditions in fire suppression systems
2. Activation of fire suppression systems
3. Activation of fire safety functions
4. Guard’s tour supervisory service
5. Process monitoring supervisory systems
6. Combination systems
7. Integrated systems
For example, a particular project may require an electrical contractor to install a fire alarm that will connect to a combined dry-pipe pre-action automatic sprinkler system or a deluge sprinkler system. The former employs regular sealed automatic sprinklers attached to a piping system containing air under pressure with a supplemental detection system installed in the same areas as the sprinklers. Operation of the detection system actuates tripping devices that open dry pipe valves simultaneously and without loss of air pressure. Operation of the detection system also opens listed air exhaust valves at the end of the feed main, which usually precedes the opening of sprinklers. It also serves as an automatic fire alarm system.
Similarly, a deluge system employs open sprinklers attached to a piping system connected to a water supply through a valve that opens when actuated by the operation of a detection system installed in the same areas as the sprinklers. When this valve opens, water flows into the piping system and discharges from all the open sprinklers attached to the piping system.
These applications will require either heat detectors or smoke detectors to actuate the fire alarm system. The fire alarm system will then actuate the valve that permits water to flow into the piping. In addition, on the combination dry pipe pre-action system, the sealed sprinkler heads must each fuse before water discharges onto the fire. The supplemental detection system, keeps water out of the piping until an appropriate fire signature, such as heat or smoke, is detected.
Obviously, the electrical contractor must understand how such integrated systems operate. In addition, he or she must communicate with the sprinkler contractor to ensure the system will operate properly. Also, if the electrical contractor intends to perform the system layout, he or she must understand the need to include detection devices in all areas protected by these special application automatic sprinkler systems.
A fire protection design may also require the fire alarm system to control fire safety functions. These include building and fire control functions that increase the level of life safety for occupants or limit the spread of the harmful effects of fire. Common connections include fire door or smoke door release, fire damper or smoke damper operation, fan shut-down and elevator recall. But the interconnection of other fire safety functions could include the release of a fire resistant curtain in a theater or the initiation of a stairwell pressurization system or a smoke control system in a high-rise building.
The electrical contractor must understand the operation of these special applications and the Code requirements associated with their installation. For example, Chapter 4 of NFPA 72 requires the fire alarm system to monitor the integrity of the method(s) of interconnection between the fire alarm system and controlled electrical and mechanical systems. Such interconnections must comply with the applicable provisions of the National Electrical Code, NFPA 70, Article 760.
The fire alarm system may actuate valves that cause the foam concentrate to inject into the flowing water. Or, it may actuate a pump that forces foam concentrate into the flowing water. In either case, a detection system, usually either heat detectors or flame detectors, will actuate the fire alarm system.
The prudent electrical contractor must consider the stability of the fire alarm system and its resistance to unnecessary actuations. This will help prevent accidental discharge of the foam, when a fire has not occurred, that could damage an open engine compartment of an aircraft parked in the hangar.
Fire protection designs may use fire alarm systems in many special applications. The contractors involved in these applications must understand the operation of the fire protection system to ensure a correct application of the fire alarm system. EC
MOORE, a licensed fire protection engineer, frequent speaker and an expert in the life safety field, is a co-editor of the current National Fire Alarm Code Handbook. Moore is a principal with Hughes Associates Inc. at the Warwick, R.I., office.