Water Mist Fire Suppression Systems Theory and Applications By Robert M. Gagnon, P.E.
Life Safety Applications -- Living Quarters Water spray efficiency in living quarters dates back to the earliest uses of sprinklers as a life and property saving tool. An awareness of drop size occurred in the early 50s with the development of the standard spray sprinkler as a replacement to the "old style" sprinkler. It was noted during testing that the smaller droplets provided a greater available surface area for cooling and heat absorption. It was decided to make the "teeth" on the sprinkler deflector more closely spaced than the old style head, thus breaking the water spray into finer drops. Subsequent tests, related to sprinklers installed in corridors outside of a living unit, were conducted by the National Institute of Standards and Technology in 1977.1 Full scale tests, bench scale test, and mathematical modeling were employed to determine the best nozzle placement, nozzle diameter and water droplet size. It was determined that large droplets were an inefficient method of distributing water to a fire hazard in a living occupancy. The findings clearly showed that the smaller droplets, as predicted by intuition and mathematical modeling, were significantly more efficient in absorbing heat, evaporation and in cooling of the fire plume. Additional studies indicated that velocity and droplet trajectory were also significant factors in the rate of evaporation. Full scale studies confirmed the bench studies, and resulted in the conclusion that smaller orifice nozzles, and their associated smaller droplet sizes, achieved a greater plume temperature reduction, resulting from more efficient evaporation. Testing is now being performed at the Maryland Fire and Rescue Institute of the University of Maryland to test water mist systems for sleeping quarters. 2,3 A new 24 foot by 48 foot building was constructed that includes a control center for data collection, a 12 foot by 12 foot room with a table and ladder, and a 12 foot by 12 foot room with an underfloor area. One room contains a residential system installed in accordance with NFPA 13R, the standard for installation of sprinkler systems in one and two family dwellings and mobile homes. The other room is equipped with a water mist system of varying piping configurations and with nozzle sizes of varying orifice diameters. Tests that were viewed featured a test room with a table in the center and a ladder in the corner of the room. Four containers of Heptane were situated at the quarter points of the room, with one additional container under the table, and three containers at varying elevations on the ladder. Two primary piping configurations were tested -- the cornice protection system, with nozzles surrounding the room at the ceiling perimeter, and the ceiling configuration, with two lines of nozzles installed at the ceiling. Nozzle outlets were about 6 inches on center, installed into pre-tapped outlets on stainless steel pipe. Other tests are being performed to test the effectiveness of water mist on underfloor applications. Halon has been the protection method of choice for this application in the past. Thorough tests, over the period of a year, will be conducted to test both Heptane fires and wood crib fires with a wide variety of nozzle orifices, piping configurations, and design applications. http://www.utcfireandsecurity.com/utcfs/Templates/Pages/Template-79/0,11708, pageId%3D75200%26siteId%3D70,00.html http://www.montgomerycountymd.gov/apps/News/press/PR_details.asp?PrID=2715 -----Original Message----- From: [email protected] [mailto:[email protected]] On Behalf Of [email protected] Sent: Friday, May 28, 2010 2:29 PM To: [email protected] Subject: Re: Mist Systems Considered Option for Inside Homes Where can we find more information on these systems. Phil _______________________________________________ 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) _______________________________________________ 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)
