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Hung Up on Seismic Issues?

Informal Interpretations Save Members Time, Money

The informal interpretations featured in this issue of Sprinkler Age address obstruction concerns. AFSA’s informal interpretations are provided to AFSA members by Vice President of Engineering & Technical Services Roland Huggins, a P.E. registered in fire protection engineering; Director of Technical Program Development Phill Brown, a NICET IV certified automatic sprinkler technician and NFPA Certified Fire Protection Specialist (C.F.P.S.); and Senior Engineer Tom Wellen, P.E., senior fire protection engineer. These opinions are provided for the benefit of the requesting party, and are provided with the understanding that AFSA assumes no liability for the opinions or actions taken on them.

Subject: Clearance Hole Penetrating A Sidewalk

QUESTION: “When a riser is on the outside of the building and the underground stub up is coming up in a sidewalk, is the annular clearance required around the piping? The underground stub up flange is 6 in. above the concrete slab. A flange by groove piece is installed on the stub up with an elbow. The pipe is installed on the elbow to enter the building for an inside riser. Is the clearance hole required for the pipe rising up through the sidewalk?”

ANSWER: In response to your questions we have reviewed NFPA 13, Standard for the Installation of Sprinkler Systems, 2013 edition as the applicable standard. Our informal interpretation is that clearance would be required around the pipe penetrating the floor or the sidewalk surface if seismic design applies per the building code.

The building code would specify when seismic design is applied to systems. The purpose of the clearance is to prevent breakage of the fire sprinkler pipe during a seismic event. The holes for the clearance should be nominally 2-in. larger than the pipe for 1 in. through 31/2 in. and 4-in. larger for pipe sizes 4-in. and larger according to Section 9.3.4.2. The clearance around the pipe does not have to be annular or in other words, the pipe does not need to be located in the exact center of the opening. An exception to providing clearance is the use of flexible couplings within 1 ft on both sides of the opening. The problem is that since the piping is located underground, it would not be feasible to install a flexible coupling under the floor or sidewalk surface. Thus the clearance should be provided for underground piping at the penetration. Note that the piping is not limited to sprinkler risers and can include drains, fire department connections, and other auxiliary piping.

Subject: Rods Less Than 6 in. to Omit Lateral Bracing

QUESTION: “Section 9.3.5.5.10 indicates that pipe individually supported by rods less than 6 in. from point of connection to top of pipe do not require lateral sway bracing. However, the Sprinkler Systems Handbook indicates that the 6-in. rod rule doesn’t apply to feed mains and cross mains and must be lateral braced regardless of rod length. Is it required to laterally brace all feed mains and cross mains with rods less than 6 in.?”

ANSWER: In response to your question we have reviewed NFPA 13, 2013 edition as the applicable standard. Our informal interpretation is that the text in the handbook is an error and should not be applied.

Section 9.3.5.5.10 states, “The requirements of 9.3.5.5 shall not apply to pipes individually supported by rods less than 6-in. long measured between the top of the pipe and the point of attachment to the building structure.” There is no other supporting information excluding cross mains and feed mains from this section. As such, the handbook text addressing Section 9.3.5.5.10 is incorrect that states, “For the 2013 edition, cross mains as defined in 3.5.5 cannot use this exception and will need lateral braces even if short hangers are used. The concern is that if the lateral sway braces are omitted then the hangers in this situation would have to carry the load of the main and the attached branch lines, which in many applications could be a tremendous horizontal force.”

The text for the 2016 edition of NFPA 13 also shows the handbook text to be in error. The new wording will indicate that the lateral sway bracing required by 9.3.5.5 shall be permitted to be omitted when 9.3.5.5.10.1 for branch lines or 9.3.5.5.10.2 for mains is met. Section 9.3.5.5.10.2 will require mains to comply with 6 criteria as: (1) The main piping shall be individually supported within 6 in. of the structure, measured between the top of the pipe and the point of attachment to the building structure. (2) At least 75 percent of all the hangers on the main shall meet the requirements of 9.3.5.5.10.2(1). (3) Consecutive hangers on the main shall not be permitted to exceed the limitation in 9.3.5.5.10.2(1). (4) The seismic coefficient (Cp) shall not exceed 0.5. (5) The nominal pipe diameter shall not exceed 6 in. (152 mm) for feed mains and 4 in. for cross mains. (6) Hangers shall not be omitted in accordance with 9.2.4.3, 9.2.4.4, or 9.2.4.5.

The 2016 edition text will specify limitations on the size of the feed main and cross main, but in no way does it require that lateral bracing be provided on all feed mains and cross mains. The handbook commentary regarding this subject area should not be applied. The disclaimer provided in the front of the handbook under the heading Notice Concerning Code Interpretations that states, “The commentary and supplementary materials in this handbook are not a part of the NFPA document and do not constitute Formal Interpretations of the NFPA (which can be obtained only through requests processed by the responsible technical committees in accordance with the published procedures of the NFPA). The commentary and supplementary materials, therefore, solely reflect the personal opinions of the editor or other contributors and do not necessarily represent the official position of the NFPA or its technical committees.”

Subject: Net Vertical Reaction Forces

QUESTION: “The AHJ is requiring rod stiffeners for the all thread rod hangers on a sprinkler system which is to be seismically braced in accordance with NFPA 13. The seismic coefficient is Cp=0.35. Braces (longitudinal and lateral) are install between 30 degrees and 44 degrees. Are rod stiffeners required for this application?”

ANSWER: In response to your question we have reviewed NFPA 13, 2013 edition as the applicable standard. Our informal interpretation is that providing additional support for the net vertical reaction forces is not required.

Your application has a Cp of 0.35 where the requirements of net vertical reaction forces do not apply. The concern is with the pipe moving in a vertical direction. The bracing attached in a horizontal orientation may not resist the vertical movement of the pipe for higher Cp seismic loads. Section 9.3.5.10 states, “Where the horizontal seismic loads used exceed 0.5Wp and the brace angle is less than 45 degrees from vertical or where the horizontal seismic load exceeds 1.0 Wp and the brace angle is less than 60 degrees from vertical, the braces shall be arranged to resist the net vertical reaction produced by the horizontal load.” The NFPA 13 Handbook further clarifies this section indicating this requirement was first introduced in the 1996 edition of NFPA 13 addressing the need to protect against upward vertical movement of the pipe as a result of a strong horizontal load in combination with a limited brace angle from vertical. Previous editions did not specifically address such vertical movement. When needed, this additional support could take the form of hanger rods located in close proximity of braces and reinforced against buckling by use of pipe sheathing or other means. This does not apply for your application.

Subject: Drain Line and Seismic Separation

QUESTION: “Does a drain pipe that passes through a seismic separation require a seismic separation assembly if the piping in question is beyond the drain valve?”

ANSWER: In response to your question we have reviewed NFPA 13, 2013 edition as the applicable standard. Our informal interpretation is that the requirements under seismic separation do not apply to drain lines.

Section 9.3.3.1 indicates that an approved seismic separation assembly shall be installed where sprinkler piping, regardless of size, crosses building seismic separation joints at ground level and above. This sentence references “sprinkler piping” and not all piping. As such, this section would not apply to drain lines passing through a seismic joint. The references used throughout the standard to “sprinkler piping” refer to pipe that supplies sprinkler heads. Other pipe or components are referenced when the requirements are applied. An example is Section 9.3.4.1 that states, “Clearance shall be provided around all piping extending through walls, floors, platforms, and foundations, including drains, fire department connections, and other auxiliary piping.” As such, the drain piping for this application would be required to meet clearances, but would not be required to have a seismic separation assembly.

Subject: Sprinkler Clearance Hole in Walk-in Cooler

QUESTION: “Is it the intention of 9.3.4.2 to require the nominal 2-in. hole clearance on a 1-in. dry drop head penetrating a walk-in cooler ceiling in addition to the sprinkler manufactures listed escutcheon hole requirement?”

ANSWER: In response to your question we have reviewed NFPA 13, 2013 edition as the applicable standard. Our informal interpretation is that the intent for a larger clearance hole for a single sprinkler is not required for this application.

The issue of how to address a sprinkler pipe penetrating the ceiling of a cooler or freezer is not well presented in NFPA 13. There are two problems contributing to the confusion. First, section 9.3.4 on clearance explicitly states that this section applies to pipe extending through walls, floors, platforms, and foundations. Despite the fact that ceiling are not part of the scope, text in the annex (A.9.3.4) discusses the possible need for larger clearances in drop ceiling unless rigidly braced. Although we refer to the top of the freezer as a ceiling, it is not treated like a drop ceiling and Section 9.3.4 does not apply. In actuality, 9.3.2.4 provides the requirements for drops to freestanding structures within the building. We typically think of this section for addressing drops to racks but as discussed in A.9.3.2.4, freestanding structures include but are not limited to freezers, coolers, paint booths, and offices. I must confess that offices are typically part of the building structure so this is a bad example unless the committee meant re-locatable offices. Section 9.3.2.4 states that drops are required to have flexible couplings. The casual use of the term drop implies that this requirement also applies to drops supplying a single sprinkler. Fortunately, we do get some clarification from A.9.3.2 where it indicates piping 2 in. and smaller in size are pliable enough so that flexible couplings are not usually necessary. As such, a coupling should not be required. As for the clearance, follow the manufacturer’s requirements for the boot seal (an issue that addresses the concern for ice build-up caused by airflow induced by the pressure differential created by the temperature difference between the interior and exterior of the freezer).

Subject: Branch Line Restraints

QUESTION: “Regarding the minimum length of a branch line to be restrained, I still do not see a minimum length specified. Is the starting point when there are two sprinklers on a branch line?”

ANSWER: In response to your question we have reviewed NFPA 13, 2013 edition as the applicable standard. Our informal interpretation is that restraints are provided when there are two sprinklers on a branch line.

Historically, the primary concern being addressed by branch line restraint was to keep long branch lines from whipping around (restrain the end of the branch line) and to avoid damage to the sprinkler if it were to strike something. Restraint has a minimum possible spacing of 26 ft and a maximum of 53 ft. Restraint is intended to address branch lines (which feeds more than one sprinkler, thus must have some length) and not armovers or drops. An armover is defined in Section 3.5.3 as a horizontal pipe that extends from a branch line to a single sprinkler or a sprinkler above and below a ceiling. There is no limitation on the length of the arm-over. Thus, an armover is defined differently from a branch line; it is not part of Section 9.3.6 and does not require restraint per Section 9.6.3.7. The only pipes feeding a single sprinkler that must be restrained are sprigs greater than 4 ft as per Section 9.3.6.6.

Subject: Pipe Clearance When Penetrating a Structural Member

QUESTION: “Is clearance required on fire sprinkler pipe that penetrates a steel structural member such as a steel I-Beam? Are flexible groove couplings required to be located within 1 ft of each side of the steel structural member?”

ANSWER: In response to your questions we have reviewed NFPA 13, 2013 edition as the applicable standard. Our informal interpretation is that clearance and couplings are not required for pipe that penetrates steel structural members.

Section 9.3.4.10 specifically addresses your issue. It states, “No clearance shall be required where piping is supported by holes through structural members as permitted by 9.1.1.6.3.” Section 9.1.1.6.3 allows for holes through solid structural members to serve as hangers for the support of system piping provided such holes are permitted by applicable building codes and the spacing and support provisions for hangers of the standard are satisfied. This method secures the pipe to the structure and keeps the pipe from moving differently from the structure thus satisfying the seismic requirements. As such, the pipe should contact the beam where clearance requirements of Section 9.3.4.1 through 9.3.4.3 are not applied.

This is also supported by Section 9.3.4.9 that says clearance from structural members not penetrated or used, collectively or independently, to support the piping shall be at least 2 in. Flexible couplings are not required since the structural members serve as lateral bracing and branch line restraints. Flexible couplings provided on each side of the structural member where the pipe penetrates is equivalent to providing a flexible coupling before and after each lateral restraint. Requiring flexible couplings at these penetrations would defeat the purpose seismic design.

EDITOR’S NOTE: These interpretations were prepared by AFSA’s Technical Services Department in answer to specific questions from contractors and/or AHJs. These opinions are provided for the benefit of the requesting party, and are provided with the understanding that AFSA assumes no liability for the opinions or actions taken on them. AFSA members can access over 7,600 informal interpretations online. Click here to access the informal interpretations.

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