# Nfpa 13 q&a nfsa



## Insurance Engineer (May 7, 2014)

13 Q&A see link below, could not fit it all in.

http://www.readyshare.com/Users/seminars@nfsa-org/UploadMails/technotes15_5_2014_50723_PM.htm

This month, we have selected the following baker’s dozen (13) questions as the “Best of April 2014” answered by the engineering staff as part of the NFSA’s EOD member assistance program.  If you have a question (and you're a member of the NFSA), you can send your question to eod@nfsa.org and we'll answer it as soon as we can.

It should be noted that the following are the opinions of the NFSA Engineering Department staff, generated as members of the relevant NFPA technical committees and through our general experience in writing and interpreting codes and standards.  They have not been processed as a formal interpretation in accordance with the NFPA Regulations Governing Committee Projects and should therefore not be considered, nor relied upon, as the official position of the NFPA or its Committees.

Question 1 – Hydraulic Calculations for Sprinklers Under Obstructions

We have a situation where we have sprinklers at the ceiling and obstructions more than 4 ft wide, so we are putting sprinklers under the obstructions.  How do we handle the hydraulic calculations?  Do we include all of the sprinklers in 1500 sq ft including the sprinklers at the ceiling and the sprinklers under the obstructions?

Answer: No.  You only need to calculate the sprinklers at one level, the sprinklers at the ceiling or under the obstructions, whichever are most demanding.  Section 23.4.4.6.3 (and its two subsections) cover this subject (similar sections in previous editions).  Typically, the sprinkler system at the ceiling will be the most demanding.  However, the sprinklers under the obstruction might be more demanding if a small diameter pipe is used to feed many sprinklers.  In the 2013 edition of NFPA 13, the committee has expressly stated that sprinklers under obstructions are assumed to be less demanding as long as the same pipe sizes and lengths are used under the obstructions as at the ceiling (23.4.4.6.3.2).

Question 2 – ESFR Sprinkler System Design Area

In older editions of NFPA 13, ESFR sprinklers had a minimum design area of 12 sprinklers, but also 960 sq ft.  So, if sprinklers were installed at their minimum spacing, there may have been more than 12 sprinklers in the design area.  We have a situation where we are installing ESFR sprinklers at 64 sq ft spacing in one portion of the building in accordance with the 2013 edition of the standard, do we need to calculate the system with 15 sprinklers (960/64=15)?

Answer: No.  There was a minimum design area in NFPA 13 for ESFR sprinklers up to the 2007 edition.  When preparing the 2010 edition, the committee eliminated the minimum area requirement with the following statement:

Analysis from Factory Mutual has determined that the 960 sq ft design area is not necessary as long as the minimum spacing rules are followed.

Question 3 – Protecting Storage at Different Ceiling Elevations

We have a situation with a storage occupancy and a sloped ceiling (the slope is less than 2 in 12, so we can use NFPA 13) where the height of the building at the peak is 30 ft.  We’ll use sprinklers at the peak that can protect storage at that building height, but further down the slope, can we switch to the sprinklers that can handle the lower ceiling height like 25 ft?

Answer: Yes, but if there is no vertical barrier to the hot gasses from a fire under the higher ceiling area, you have to use the sprinklers for the higher area at least 15 ft horizontally beyond the point where the roof comes down to 25 ft above the floor in order to meet section 12.3. The following figure might be helpful to summarize the rules.

Question 4 – Dry System Protecting Rack Storage

For a dry-pipe or preaction system protecting rack storage with control mode density area protection at the ceiling and in-rack sprinklers, does the increase in the design area apply to the ceiling sprinklers only or do we need to increase the in-rack sprinkler protection area as well?

Answer: The increase in the design area only applies to the ceiling sprinklers.  No increase is required for the in-rack sprinklers.


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## cda (May 7, 2014)

Fantastic

I have a connection with NFSA and thought the eod was open to ahj's ????


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