System Sensor Smoke Detector Spacing on Level Ceilings with Beams and Joints

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September 1 2006 Paper Detector Spacing on Level Ceilings with Beams and Joists Detector Spacing on Level Ceilings with Beams and Joists Overview 72 The National Fire Alarm Code recommends using 900 square feet 30 feet center as a guideline for spacing spot type smoke detectors on smooth ceilings this is only a recommendation virtually all manufacturers of smoke detectors this guideline There has always been a question of how detector spacing to change when the ceiling is not smooth but is interrupted by beams or The language in the 2002 edition of NFPA 72 code was based on the fi re research reported in 1993 1994 and was considered the best available at that time However recent advances in computational uid dynamics CFD allowed fi re protection engineers to revisit the current guidelines and make recommendations for changes in NFPA 72 Challenges 2002 edition of NFPA 72 requires that when beams project more than 12 inches the ceiling and when ceiling heights exceed 12 feet each bay beam pocket by the beams should must be treated as a separate area That is each bay would one or more detectors depending upon its physical size When this requirement fi rst incorporated into the code it was backed by the best CFD data available at time Subsequent to this code change many fi re alarm system designers discovered following the literal code text could mean using a large number of detectors and exorbitant installation costs in many common building designs Historically part of the code has been a subject of contention in the fi re protection industry among NFPA 72 Initiating Devices Committee members Recommendations for Smoke Detector Spacing 72 requires different detector spacing depending upon whether the structural ornamental members on the ceiling fall into the defi nition of a beam or a joist the depth of those members The code defi nes solid joist construction as that are greater than 4 inches in depth and spaced 3 feet or less apart construction on the other hand is defi ned as members that are greater than inches in depth that are spaced more than 3 feet apart For the purposes of spot smoke detectors the spacing rules are the same for ceilings with beams and joist construction level ceilings NFPA 72 currently requires spacing smoke detectors at one half listed spacing perpendicular to the run of the beams on a ceiling less than or to 12 feet in height when the beams are less than or equal to 12 inches deep parallel to the beams NFPA requires standard spacing for smoke detectors this case the detectors may be mounted on the ceiling or on the bottom of the If the beams exceed 12 inches in depth or the ceiling height of the space 12 feet the detectors are required in every beam pocket on the ceiling April 2005 the Fire Protection Research Foundation funded new research using computer modeling to reexamine smoke detector spacing on ceilings with beams joists The CFD analysis was performed by Schirmer Engineering Corporation NFPA 72 2002 could result higher installation costs with beams joists affect detector Sensor Advanced Ideas Advanced Solutions Detector Spacing on Level Ceilings with Beams and Joists Vision Systems Ltd using Fire Dynamics Simulator and Smokeview Version developed by the National Institute of Science and Technology The results of research were published in a report entitled Detector Performance Level Ceilings with Deep Beams and Deep Beam Pocket Confi gurations The was issued March 28 2006 and was the basis for recommended changes to 72 on a variety of modeled aming re scenarios the results of this indicate NFPA 72 2002 edition requirement for placing smoke detectors every beam pocket when ceilings are greater than 12 feet in height beams are greater than 12 inches in depth is not supported by new study smooth ceiling 30 foot spacing guideline of NFPA 72 with permitted for narrow space geometry allows smoke detectors to extend approximately 41 feet on center and along a corridor For ceilings up to feet in height the deep beam confi gurations do not negatively affect performance This means that for corridor conditions spot detectors can be effectively used with deep beams at spacings for ceilings 900 square foot smoke detector spacing is adequate for waf e pan type ceilings up to 24 feet in height and for beams up to 24 inches depth that are spaced no greater than 12 feet on center recent analysis does support the spacing in the edition smoke detectors may be placed on the bottom of the beams or in beam pocket without any signifi cant difference in performance concern about mounting smoke detectors a minimum of 12 inches a ceiling beam corner per NFPA 72 is unsubstantiated The CFD showed no stagnant areas in the beam pockets that would smoke detector activation Although the modeling results no stagnant zones it does not suggest that spot detectors can installed in close proximity or contact to the wall or ceiling surface research report notes that such close mounting may impact the ow characteristics into and around the detector housing which have a negative impact on how smoke ows into a detector chamber The CFD software is available free of charge from the NIST web site www re nist gov fds The full report is available on the National Fire Protection Association web site www nfpa org Sensor Advanced Ideas Advanced Solutions Detector Spacing on Level Ceilings with Beams and Joists on these findings the report authors proposed language for addition to the body and annex of NFPA 72 language clarifies how smoke detectors shall be placed on ceilings with beams and joists These changes expected to be incorporated into the 2007 edition of NFPA 72 which will be released in late 2006 to quell of the debate surrounding the current requirements for smoke detectors on beam ceilings a part of the National Fire Protection Association mission to the worldwide burden of fire by updating their consensus codes based on the latest research available NFPA commissioned this study smoke detector spacing The results of this study and accompanying code changes are expected to reduce the cost of fire protection systems in beam ceiling applications while not comprising occupant safety document was written with guidance from Schirmer Engineering Corporation more information regarding Smoke Detector Spacing please contact Sensor Ohio Avenue Charles Illinois 60174 1 800 sensor2 9 06 1703 Sensor Advanced Ideas Advanced Solutions System Sensor

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