NFPA 13 has other restrictions on orifice size in OH occupancies, and even 5.6K heads that are listed for OH cannot be used for design densities over 0.30 GPM/SF (From memory, could be wrong #) Specifically because small drops don't make it to the seat of the fire before they turn to steam.(4.2K heads have even smaller droplets.) Steam is good for some fires like residential, low ceilings knocks smoke down for occupant egress, indicates a good heat exchange, ect. But in OH what good does it do if the droplet size is so small that the steam forms 20'-0" AFF and the water never reaches the seat of the fire. That's why we see more of the large orifice Special Application Storage Sprinklers. K11.2, K14, K16.8, K22, K25. BIG Droplet Size penetrates the fire better. In this case "Bigger is Better."
Thom McMahon, SET Firetech, Inc. 2560 Copper Ridge Dr P.O. Box 882136 Steamboat Springs, CO 80488 Tel: 970-879-7952 Fax: 970-879-7926 -----Original Message----- From: [email protected] [mailto:[email protected]] On Behalf Of Fletcher, Ron Sent: Tuesday, December 01, 2009 7:21 AM To: [email protected] Subject: RE: Calcs-How much margin If the heads "are not as effective in controlling a fire" then how do they get UL Listed? If it is Listed and I would assume tested it should be okay to use. If it is OH-I and the spacing requires an EHP less than 7 psi why not use the UL listed 4.2k head? Ron Fletcher Aero Automatic Phoenix, AZ _______________________________________________ Sprinklerforum mailing list [email protected] http://fireball.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)
