open web beam?

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GKramer

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can heat detectors be installed on the bottom of open web metal beams? They are approx. 24" deep, the cieling material is some sort of corragated metal. The solid portions of the beams (top and bottom) approx. 4" or less.
The spacing of the beams is 5'.
I'm a journeyman electrician, now working for a company that installs low-voltage security/fire systems.
Thanks
 
I think that this meets the definition of a smooth ceiling because the joists are not solid allowing air and heat to circulate. This means that according to NFPA 72 you will need to be mounted within 12" form the ceiling. I will say however that I know what you are talking about and have been allowed to put detectors on the bottom side of the joist. It will be the local AHJ's call.
 
I'm not a F/A Nut but the best I could find is that the heat detector has a signal alarm at 135?, and depending on the host panel can be part of of other devices.
 
GKramer said:
can heat detectors be installed on the bottom of open web metal beams? They are approx. 24" deep, the cieling material is some sort of corragated metal. The solid portions of the beams (top and bottom) approx. 4" or less.
The spacing of the beams is 5'.
I'm a journeyman electrician, now working for a company that installs low-voltage security/fire systems.
Thanks
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FWIW,,,,,(not much),,,,,I just finished a 10,000 sq ft production area and the security/ low voltage was done by another company. He mounted his heat/ smoke detector in the exact location you are speaking of. Again,that doesn't mean much, but it passed in Louisa County. There were 4 in this building
 
GKramer said:
can heat detectors be installed on the bottom of open web metal beams? They are approx. 24" deep, the cieling material is some sort of corragated metal. The solid portions of the beams (top and bottom) approx. 4" or less.
The spacing of the beams is 5'.
I'm a journeyman electrician, now working for a company that installs low-voltage security/fire systems.
Thanks
Click to expand...

Robertson deck?
 
GKramer said:
can heat detectors be installed on the bottom of open web metal beams? They are approx. 24" deep, the cieling material is some sort of corragated metal. The solid portions of the beams (top and bottom) approx. 4" or less.
The spacing of the beams is 5'.
I'm a journeyman electrician, now working for a company that installs low-voltage security/fire systems.
Thanks
Click to expand...

Based on your information, the short answer is "NO".

Mounting on the bottom of the beam is for solid beam construction and the beam can't be deeper than 12" with spacing 8' on center or less (NFPA 72-2002 5.6.3.1.2). Your 24" depth is too great, even if you had a solid beam.

You can treat the ceiling as "smooth" if the solid portion of the top plate is 4" or less in depth. In this case, you must mount at the ceiling. The reason for this is that the hot air needs to accumulate around the detector for it to operate as listed. If the air rises past the detector and has to build "down" to the 24" elevation you may not get timely activation of the fire alarm system.

While we're at it, heat detector spacing has to be de-rated for mounting heights above 10' (NFPA 72-2002 Table 5.6.5.5.1). It sounds like you may be in a warehouse or other space with a high ceiling.

Also, don't assume that the detector has a 30' listing. Many are listed for 50'. They can also be dual listed, say 25' for FM and 50' for UL. This information will be in the package on the detector's installation sheet.
 
Factory Mutual is thier own set of rules and have rules and one pays to join the club to get your stuff certified, that pertain to Roof systems, Bar joist and metal decking, and pressure vessels like sprinklers and I'm sure other things...
 
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