Pre-Action Systems
Q: I hope you can help me out. During an inspection of a fire alarm system, we found pre-action systems tied into the fire alarm system. We found that the heat detectors for the pre-action system activated the general fire alarm, but if a low-air signal was received (as in an open sprinkler head) a trouble alarm was sent. The sprinkler contractor has raised the question that the signals received should be the same. What do the codes say about this issue?
—S. Mixalot, LA.
A: If the only way the air could escape from a sprinkler pipe was for it to exit from an open head, then your contractor would have a point. There is a big “but” however, regarding this statement. The air in these pre-action pipes is not holding back water as in dry-pipe systems. Dry-pipe systems use the air to keep these systems from freezing.
Secondly, they make sure the piping isn’t disconnected or tampered with in any way. Pre-action systems use the supervisory air (or nitrogen) to make sure the piping remains undisturbed and connected. Unlike the dry-pipe system, releasing the air from a pre-action system will not cause water to enter the piping.
Both deluge systems and pre-action systems utilize an electric solenoid valve to keep water out of the overhead sprinkler pipes, but for different reasons. In a deluge system, all the sprinkler heads are open and will flow large amounts of water upon the activation of these early warning detectors. These suppression systems are normally used in high-hazard areas.
On the other hand, pre-action sprinkler heads are normally closed, and only open when they reach their listed temperature. In operation, water only flows from heads actuated by the fire, in order to minimize water damage. Pre-action systems are usually installed to protect areas where the client has great concern over leaking pipes or broken heads: for instance, large computer rooms or laboratories.
NFPA 72 (2002 ed.) 6.8.5.5.1 only requires an alarm signal when water has entered the dry-pipe section of the pre-action system. Except for vane-type systems, both deluge and pre-action systems use a pressure switch to activate an alarm when tripped.
Smokes in Dorm Bedrooms
Q: Are college dorms required to have smoke detectors in all the bedrooms or just the common areas?
—W.E. from PA.
A: Dormitories are in the same category as hotels and motels, which is R-2. This means smoke alarms are to be installed in the sleeping areas and outside each sleeping area if there is another room between it and the hallway.
Smoke detectors are to be installed in the halls and other similar (common) areas of the building. You will also have to install manual pull boxes at the entrance to each exit, with audible notification throughout. Don’t forget the duct detectors, sprinkler devices or any other code-required extinguishing systems. ADA might apply…Void where Prohibited.
Greg Kessinger, SET, CFPS, president of an alarm installing company since 1981, teaches NICET training classes to fire alarm system designers and installers and continuing education seminars for Ohio’s fire alarm inspectors. You can reach him at 888-910-2272; e-mail: [email protected]; or visit his website at www.FireAlarm.org.
