Chis: Assuming 2000 sq ft, FM requires a 1.4 multiplier. So, the length down the branch line of the RA is 62.6'. If you have heads spaced at 10' on center along the branch lines, you would need 62.6 / 10 or 6.26 heads on the branch line. Since you can't have .26 heads, it has been standard practice to round up to 7 heads. 1.2 is the multiplier for NFPA 13. So per NFPA 13, you would need 53.6' along the line or 5.36 heads. This would be rounded up to 6. Using George's information, this seems to put NFPA & FM on the same criteria for the design area shape.
If you did not have George's information, on a FM job, you would be bidding 7 heads along the branch line. If each head is flowing 60 gpm, then you have 420 gpm in each branch line. Using George's information, you only need to flow 360 gpm / branch line. That could easily be the difference in 2?" v 2" branch lines. Thank you George for the information. Travis Mack -----Original Message----- From: [email protected] [mailto:[email protected]] On Behalf Of George Church Sent: Monday, June 29, 2009 3:23 PM To: [email protected] Subject: RE: FM rounding and other changes If I confused you, we're even now. glc -----Original Message----- From: [email protected] [mailto:[email protected]] On Behalf Of Chris Cahill Sent: Monday, June 29, 2009 5:40 PM To: [email protected] Subject: RE: FM rounding and other changes Except 13 is the predominant legal standard in the US. FM can do whatever they want but no where that I know of are they the legal standard. Perhaps you said that in your 3rd paragraph but where would FM exceed 13 but only need 2" lines vs. 2.5"? Do you mean to say FM has a higher density than 13 but rounding mathematically you get 2" lines and when you recalc per 13's lower density and rounding up you end up with 2" lines? Does this actually happen? Is this just a marketing trick by FM seeming to require a higher level of protection but in reality it's the same? Cynical I guess. Chris Cahill, P.E. Fire Protection Engineer Sentry Fire Protection, Inc. 763-658-4483 763-658-4921 fax Email: [email protected] Mail: P.O. Box 69 Waverly, MN 55390 Location: 4439 Hwy 12 SW Waverly, MN 55390 _______________________________________________ Sprinklerforum mailing list http://lists.firesprinkler.org/mailman/listinfo/sprinklerforum For Technical Assistance, send an email to: [email protected] To Unsubscribe, send an email to:[email protected] (Put the word unsubscribe in the subject field) __________ NOD32 4197 (20090629) Information __________ This message was checked by NOD32 antivirus system. http://www.eset.com _______________________________________________ Sprinklerforum mailing list http://lists.firesprinkler.org/mailman/listinfo/sprinklerforum For Technical Assistance, send an email to: [email protected] To Unsubscribe, send an email to:[email protected] (Put the word unsubscribe in the subject field)
