spacing reduction for cross zoned detectors on preact sprinkler sys?

[pipesnpumps]

The subject line says it all. Is there any spacing reduction for fire/smoke detectors which are serving a preaction sprinkler with cross-zoned detectors? i.e. two detectors are required to open the preaction valve.

Logic and reason is telling me the detectors should probably be spaced closer, but I can't find a code/standard passage that requires that.

BTW, this contractor designed a cross-zoned system (two detections to turn on the water), but only put one detector in the small rooms... so basically the fire could go past flashover before the sprinkler even saw water. I could not find any code/standard discussing that, so I pulled out the AHJ card.

Appreciate any insight on the spacing

 

[cdafd]

Not sure but do not think so

Seems like regular spacing depending on size of room


Love it they do cross zone and put one detector in the room

I like it better when they put none

 

[cdafd]

Think about if they did not cross zone and used only one to trip
You would do normal spacing

 

[cdafd]

nfpa 13
7.3.1.6 Location and Spacing of Releasing Devices.
7.3.1.6.1 Spacing of releasing devices, including automatic sprinklers used as releasing devices, shall be in accordance with their listing and manufacturer's specifications.
7.3.1.6.2 The release system shall serve all areas that the preaction system protects.
7.3.1.6.3 Where thermal activation is utilized, the activation temperature of the release system shall be lower than the activation temperature of the sprinkler.


7.9.2.8 Fire Detection for Preaction Release.
7.9.2.8.1 Detectors for Preaction Systems.
7.9.2.8.1.1* The release system shall be designed to operate prior to sprinkler operation, unless detectors meet the requirements of 7.9.2.8.1.2. Detectors shall be electric or pneumatic fixed temperature type with temperature ratings less than that of the sprinklers. Detection devices shall not be rate-of-rise type.
7.9.2.8.1.2 Where the system is a double interlock preaction system or single interlock preaction antifreeze system, detection devices shall be permitted to be any type specifically approved for use in a refrigerated area if installed in accordance with their listing requirements and NFPA 72, National Fire Alarm Code.
7.9.2.8.2 Detector Location at Ceiling. Under smooth ceilings, detectors shall be spaced not exceeding their listed spacing. For other than smooth ceilings, detectors shall not exceed one-half of the listed linear detector spacing or full allowable sprinkler spacing, whichever is greater.

 

[DM2]

You need to have a look as NFPA 72 and spacing reductions due to air changes. Most will forget to consider the air changes in a room with respect to reduced spacing of smoke detectors.

The manufacture of the releasing control panel also has "Recommended Guidelines" for releasing service, which will use a spacing of about 250 sq. ft. per smoke detector. Many AHJ's will force this requirement. Having said that, I suspect you'll find that the air changes in the room dictate a spacing somewhere close, maybe 300 sq. ft., to 250.

Obviously the installation of a single smoke detector in a protected space, with logic requiring 2 detectors to initiate a release goes against the release logic.

Lastly, you'll not find anything in NFPA 72 2007 edition, which requires spacing reduction for releasing applications. The 2010 edition may have changed.


Regards,
Dan Marr

"Real world Knowledge isn't dropped from a parachute in the sky but rather acquired in tiny increments from a variety of sources including panic and curiosity."