Pre-Action Fire System

[Gategator37]

This is more of a Fire Alarm question, but i'm sure some of you have worked with this system. The Designer gave a basis of design for a Pre-Action System and informed us to provide a Cross Zoned Fire Alarm System with Photoelectric and Ionization Smoke Detectors. Here is my question... Since NFPA 72 requires a maximum spacing of 30 ft between heads, in this scenario does that mean 30 feet between the photo an ion heads or do I have to install a photo an ion next to eachother then at 30 ft install another smoke and ion? Are the photo and ion detectors supposed to be on separate zones from one another?

Any code references would help a bunch.

Thanks in advance.

 

[ron]

No code references are available that I know of.

Typically the photo and ion are 30' apart. It would take a smoky (photo) and flaming fire (ion) to activate the detection portion of the pre-action. If it is single interlock, then water flows after the detection portion is activated. Double interlock also requires supervisory air pressure loss in the pipe for the valve to open. Those definitions are in NFPA 13.