Issue 9: Top 10 Changes in the 2007 Edition of NFPA 13
By Chris Dubay, P.E.
Now that the 2007 edition of NFPA 13 has been published, it is a good time to review some of the changes that directly affect the fire protection engineering community. This article will review ten specific changes; these changes by no means represent an all-encompassing list of changes but have been selected to highlight some of the major areas of change.
The definition of the term "compartment" was revised to limit the size of openings in walls and to permit certain openings to have no lintel. Permitting a single opening with no lintel was in response to the common use of full-height doors, and calculations were completed to ensure that the single opening with no lintel would not have a detrimental effect on the activation time of sprinklers within the room. These same changes were made to the definition of "small room" (Section 3.3.15) and the room design method (Section 188.8.131.52.5).
The definition of "ordinary hazard (Group 2)" occupancies was modified to address proper classification of stockpiles of contents having moderate or high rates of heat release. These changes were made partially in response to a Fire Protection Research Foundation Report1 addressing protection of shelf storage arrangements. Additionally, annex material was added to A.5.3 for the purposes of defining ordinary hazard (Group 1) and (Group 2) as follows: "Class I, Class II, Class III and Class IV would be considered to have moderate rates of heat release, while Group A plastics would be considered to have high rates of heat release."
The allowable methods for determining water delivery time for dry pipe sprinkler systems were modified to permit use of an inspector's test connection, a test manifold or water delivery calculations utilizing a listed program. This change eliminated the small system exemptions for 500-gallon (1.9 m3) and 750-gallon (2.8 m3) systems with quick-opening devices where protecting dwelling units.
Annex material was added to address concerns that sprinklers were omitted from certain high bay areas and therefore did not meet the requirements of NFPA 13. The following text was added to Section A.8.1.1: "Based upon experience and testing, sprinklers have been found to be effective and necessary at heights in excess of 50 ft (15 m). For a building to meet the intended level of protection afforded by NFPA 13, sprinklers must not be omitted from such high ceiling spaces."
The situation of multiple small attached buildings was addressed to determine when and where a completely separate fire sprinkler system is required. Where the buildings are not attached, NFPA 13 still requires a separate fire sprinkler system. However, the following text was added to address multiple buildings that are attached by canopies, covered breezeways, common roofs or a common wall(s):
After several editions containing differing requirements between NFPA 101 and NFPA 13, the requirements for closely spaced sprinklers and draft stops for protection of vertical openings were modified to require draft stops and sprinklers only where they are provided as an alternative to enclosure of the vertical opening.
The paragraph that permitted omitting sprinklers from bathrooms where a thermal barrier was used (Section 184.108.40.206.1) was modified to only require the thermal barrier for the walls and ceilings behind any shower enclosure or tub. Previously, the thermal barrier was also required in walls and ceilings behind all fixtures. While not a specific code change, one major issue that was raised during the committee discussions was that common design take-outs for shower and tub units do not account for the thermal barrier, and once on-site, the thermal barrier will often be removed in order for the shower or tub to properly fit between the studs. Where this occurs, sprinklers would then be required within the bathroom regardless of its size.
NFPA 13 no longer requires small-hose connections for storage occupancies. The text of Section 12.2.1 was modified to indicate that small-hose connections are only required where specifically required by the Authority Having Jurisdiction. Additionally, the specific statements that small-hose connections shall not be required for the protection of Class I, II, III and IV commodities stored 12 feet (3.7m) or less in height (Section 12.2.2) and for the protection of miscellaneous storage (Section 13.1.1) remain for the 2007 edition.
For storage applications that have ceiling heights exceeding 30 ft (9 m), modifications were made to address the proper design criteria for the sprinkler system protecting that space where the distance between the ceiling and the top of storage exceeds 20 ft (6.1 m). Additionally, a new annex section B.3 was added to provide not only additional information, but to provide an extensive reference list on this subject.
Several changes were made to systems that utilize antifreeze solutions. One major area addressed was the underprediction of friction loss for antifreeze solutions at low temperatures by the Hazen-Williams formula. Where antifreeze systems having a volume greater than 40 gallons (0.15 m3) are utilized, NFPA 13 now requires a second set of friction loss calculations utilizing the Darcy-Weisbach formula to account for the solution's actual viscosity. Additionally, changes were made to ensure that the minimum required concentration of antifreeze was utilized based upon the anticipated minimum temperature (Section 220.127.116.11) to avoid excessively high concentrations of antifreeze solutions, which are combustible.
One of the most significant areas of change within the 2007 edition of NFPA 131 is related to requirements for earthquake protection. NFPA 13 has included provisions for the protection of sprinkler systems against earthquakes since 1947, a time at which many building codes didn't even address the subject. But major changes in building code requirements for earthquake protection have come in the past 20 years with funding from the Federal Emergency Management Agency, leading to the development of the National Earthquake Hazards Reduction Program2 (NEHRP) provisions. The NEHRP provisions initially found their way into the codes through direct adoption, and now through reference to the American Society of Civil Engineer's standard ASCE/SEI 7.3 The 2007 edition of NFPA 13 includes major changes intended to correlate with the NEHRP/ASCE/SEI provisions.
The NFPA Committee on Hanging and Bracing of Water-Based Fire Protection Systems has been trying to keep pace with a moving target as successive editions of ASCE/SEI 7 address protection of architectural and mechanical systems. There is a difficult transition period taking place right now involving the seismic provisions of NFPA 13 and the 2003 edition of the International Building Code4® (IBC). Because of the reference to ASCE/SEI 7, the 2003 IBC does not contain the detailed seismic requirements that had been included in the 2000 edition of the IBC. Although general reference to the 1999 edition of NFPA 13 is contained in the 2003 IBC, a section of ASCE/SEI 7 that made special reference to the use of NFPA 13 for earthquake protection was omitted during the adoption process, leading some to believe that sprinkler piping must be protected the same as other mechanical piping. However, sprinkler system piping is not arranged like other mechanical piping systems, and some of the requirements of NFPA 13 have been specifically developed to prevent system damage during earthquake movement.
Several structural engineers who helped write the NEHRP provisions have been participating in the NFPA 13 amendment process, trying to eliminate areas of conflict. Among the areas of concern were the fastener requirements for bracing, specifically anchorage allowances that were outdated. These were addressed with a TIA (emergency amendment) to the 2002 edition of NFPA 13 that became effective August 6, 2003. That TIA can be viewed at the nfpa.org Web site and is officially part of the 2002 edition of the sprinkler standard, but was not issued on the 1999 edition referenced by the 2003 IBC.
The 2003 TIA to NFPA 13 reduced the allowable fastener loads to match current industry standards, limited the maximum spacing of lateral braces to 40 ft (12.2 m) on center and provided clarification of how NFPA 13 could be used in conjunction with the seismic design force formula contained in ASCE/SEI 7 for use with nonstructural components:
Fp = 0.4 ap SDS Wp (1+2(z/h)) / (Rp / Ip)
The design acceleration, SDS, for any part of the United States is found in widely available maps developed by the U.S. Geological Survey (USGS), and some of the other factors are directly assigned for fire sprinkler systems in ASCE/SEI 7. While the importance factor, Ip, has always been 1.5 for sprinkler systems, assigned values for some of the other factors changed between the 2002 and 2005 editions of ASCE/SEI 7. The TIA issued on the 2002 edition of NFPA 13 suggested the use of component response modification factor, Rp, of 3.5, correlating with the 2002 edition of ASCE/SEI 7, which also specified a component amplification factor ap of 1.0. In the 2005 edition of ASCE/SEI 7, the Rp for a steel piping system (with joints made by something other than welding or brazing) is 4.5, and the ap is 2.5 (regardless of how joints are made).
While the 2002 edition of ASCE/SEI 7 was referenced for use by the 2003 editions of the IBC and NFPA 50005® building codes, the 2005 edition of ASCE/SEI 7 is referenced by the 2006 editions of those codes. As such, compliance with the 2003 or earlier editions of these codes would produce an ap/Rp ratio of 1.0/3.5 = 0.29, whereas compliance with the 2006 editions of these codes produces a ratio of 2.5/4.5 = 0.55, resulting in significantly higher forces. To some extent this has been offset by the clarification that the calculated design force can be reduced by a factor of 1.4 due to the fact that ASCE/SEI 7 is based on strength design, whereas NFPA 13 uses allowable stress design. Prior to the 2007 edition, all loads in NFPA 13 were at allowable stress levels with the exception of the buckling loads for brace members. In the 2007 edition, tables that contained the allowable loads on braces have been reduced to add a factor of safety appropriate to the use of allowable stress design.
A simplified approach to determining seismic forces on sprinkler systems has also been developed for the 2007 edition of NFPA 13, involving a number of conservative assumptions. For example, the approach assumes poor soil conditions, leading to higher earthquake forces on the piping. The user of the standard always has the option to determine lateral forces in accordance with the actual equation of ASCE/SEI 7, but the simplified approach allows the determination of loads without the use of the equation. Table 18.104.22.168.2 contains a series of "seismic coefficients", factors that are simply applied to the design acceleration, SDS, taken from the USGS maps to arrive at the earthquake design-force levels.
Because of the changes in ASCE/SEI 7, AHJs and others should be aware that the appropriate criteria for use in conjunction with the 2000 and 2003 editions of the model building codes are those found in the 2002 edition of NFPA 13, including the TIA. The appropriate criteria to be used with the 2006 editions of the model building codes are found in the 2007 edition of NFPA 13. Designers and AHJs do need to be aware that the building code references a specific edition of the standard. Generally, this does not preclude designers from using newer editions, especially if such revisions work better technically, as long as the use of newer editions is specifically documented and justified.
The new changes to the 2007 edition of NFPA 13 bring the standard fully in line with the latest thinking of the earthquake experts. In fact, the 2007 edition of NFPA 13 was unanimously approved as "deemed to comply" with the seismic requirements of ASCE/SEI 7 without exception at the IBC Structural Committee Hearings in Orlando in September of 2006.
The 2007 edition of NFPA 13 also contains a number of individual changes of significance relative to the installation of seismic bracing and restraint, including the following:
Where seismic separation assemblies are provided, four-way bracing must be provided on piping within 6 ft (1.8 m) of both sides of the separation.
To limit piping deflections, a new table limits maximum load per lateral brace based on spacing from 20 ft to 40 ft (6.1 m to 12.2 m) along with size and type of pipe; the allowance for maximum lateral brace spacing over 40 ft (12.2 m) has been eliminated.
The distance between the last lateral brace and the end of a pipe being braced must not exceed 6 ft (1.8 m).
Except where branch lines are supported by rods less than 6 in. (150 mm) in length, restraint of all branch lines is required, with maximum distance between restraints ranging from 27 ft to 55 ft (8.2 m to 16.7 m) depending on the size of the branch line and the force level. Branch lines 2-1/2 in. (65 mm) and larger continue to require lateral bracing.
Additional hangers used at an angle of not less than 45 degrees from vertical fulfill the requirements for branch line restraint, provided the hanger rod slenderness ratio does not exceed a value of 300.
One of the issues not addressed within NFPA 13 that is an important design consideration relates to clearance around sprinklers penetrating ceilings. The 2005 ASCE/SEI 7 as adopted by the 2006 building codes requires a 1-in. clearance around sprinkler penetrations of ceiling membranes in high-risk seismic areas. Some sprinkler manufacturers have developed larger escutcheon plates to cover these holes; flexible drops can be used as an alternative.
The special earthquake protection criteria of NFPA 13 have been developed over decades, making use of both laboratory findings and real earthquake experience. The new changes bring NFPA 13 into conformance with the latest standards in the field of earthquake engineering. Attempts to bypass the NFPA 13 approach and treat sprinkler system piping like other mechanical systems is not advised, since it will produce the worst of both worlds: more cost with less actual protection against earthquakes.
Russ Fleming is with the National Fire Sprinkler Association.
1NFPA 13. Installation of Sprinkler Systems, National Fire Protection Association, Quincy, MA, 2007. 2FEMA 450, "NEHRP-Recommended Provisions for Seismic Regulations for New Buildings and Other Structures", National Institute of Building Sciences, Washington, DC, 2003. 3ASCE/SEI 7, Minimum Design Loads for Buildings and Other Structures, American Society of Civil Engineers, Reston, VA, 2005. 4International Building Code, International Code Council, Washington, DC, 2003. 5NFPA 5000®, Building Construction and Safety Code, National Fire Protection Association, Quincy, MA, 2003.
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