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FPE Corner Continued from page 32


perature, blood carboxyhemoglobin (COHb), or a combi- nation of factors. Stated in quantitative terms these become the performance criteria. Examples of perfor- mance criteria would be maintain visibility of a least 25 feet, a smoke layer 8 feet above the walking surface, limit occupant exposure to temperatures not exceeding 120 degrees F, or a COHb concentration in the blood less than 12%.


Once performance criteria is established design fire sce-


narios are developed. A typical design scenario would be an arson fire set in stacked-stair storage in an exhibition room. All reasonable design fires and design scenarios must be considered. Examples of general design scenarios can be found in Chapter 5 of NFPA 101, The Life Safety Code, 2009 edition. Many in the sprinkler industry are a little suspicious


about performance-based design. This was probably due to the experience with PBD in other countries where the PBD effort was often directed at figuring out how to avoid providing sprinkler protection. This view is not widely held among U.S. fire protection engineers who in my experience consider sprinklers an essential part in the PBD process. A major advantage of sprinklers is that by reducing or controlling the size of a potential design fire the rate of heat release is reduced resulting in lower temperatures and less smoke production. It is common practice in PBD to take a conservative approach to the affect of sprinkler pro- tection on the fire. At the moment of sprinkler operation the growth of the fire is stopped and the fire output (heat release rate, smoke production) is held constant for the remainder of the analysis. In the sprinklered condition fire size can be further


reduced by decreasing the time to sprinkler activation. Sprinkler activation times can be calculated using the techniques contained in Annex B Engineering Guide for Automatic Fire Detector Spacing of NFPA 72, National Fire Alarm Code, 2010 edition. For a given design fire size or growth rate sprinkler operation times can be decreased by reducing spacing, using sprinklers with a lower temperature rating or RTI, or lowering room ceiling height.


Returning to our RSET/ASET example, sprinklers can


used to justify increases in the available safe egress time resulting from reduced fire output. Sprinklers are also considered critical in the PBD of


smoke management systems. Design fires without sprin- kler protection can grow to be very large producing quan- tities of smoke which cannot adequately be “managed” by a smoke management system. Sprinkler protection can also be used in PBD to supple-


ment building fire resistance. Increased sprinkler densities can be used to limit impact of fire on structural elements, with the result of reducing or eliminating the requirement for passive fire protection measures. It has long been rec- ognized by building codes that “closely spaced” sprinklers used in conjunction with fixed glass partitions can be con- sidered an alternative to one hour fire resistance rated wall in atrium separation. It has also long been a provision in NFPA 13 for rack storage that sprinklers can be used to


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provide steel columns the required one hour fire resistance rating in lieu of passive protection. Sprinklers can play a large role in the PBD for existing building renovations. It is often said sprinkler protection “cures a lot of ills” as they are frequently used to com- pensate for various code deficiencies. NFPA® 101A Guide on Alternative Approaches to Life Safety, 2010 edi- tion is a document that contains “Fire Safety Evaluation Systems” (FSES) for several occupancies. The FSES’s are indexing methods used to perform qualitative risk assess- ment of a given occupancy to aid in determining equiva- lency with NFPA 101. In each of the indexes the presence of complete building sprinkler protection is given the highest point score. For example in the FSES for a health care occupancy the presence of total system smoke detec- tion coverage is given a point value of 4 while total build- ing sprinkler protection using quick response sprinklers is assigned a value of 10. Sprinkler protection can also be factored into PBD


when assessing firefighting forces in addressing required response times and manpower needs. Now we must be cautioned that sprinklers do not “cure


all ills”. A common criticism from certain quarters of the industry is that too much reliance is placed on sprinklers at the expense of other proven fire protection measures. This criticism applies to both performance-based design and to use of sprinkler trade-offs in prescriptive design. Though these complaints are often voiced by those with a vested interest in passive fire protection products, they should not be completely ignored. Fire protection engi- neers are trained to consider the use of multiple safeguards so that the failure or ineffective performance of one fire protection feature does not result in failure of system. The concept of multiple safeguards must be part of any PBD. This brings us to an important issue in PBD with respect to sprinklers, which is, their effectiveness and reliability. That will be the subject of next month’s article. For those interested in more information about PBD the following publications can be found at www.sfpe.org SFPE Engineering Guide to Performance Based Fire Protection, 2nd edition, SFPE and NFPA SFPE Code Official’s Guide to Performance-Based


Design Review, published by SFPE and ICC, 2004 Introduction to Performance-Based Fire Safety, Richard


Custer and Brian Meacham, SFPE and NFPA, 1997 Have a fire safe New Year. n


Sam Dannaway, P.E., is a registered fire protection engineer and mechanical engineer with bachelor’s and master’s degrees from the University of Maryland Department of Fire Protection Engineering. He is past president and a Fellow of the Society of Fire Protection Engineers. He is president of S.S. Dannaway Associates, Inc., a 15-person fire protection engineering firm with offices in Honolulu and Guam. He can be reached via email at sdannaway@ssdafire.com.


The views and opinions expressed in this column are those of the author and do not reflect those of Plumbing Engineer nor its publisher, TMB Publishing.


January 2011


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