I have had similar situation happen occasionally (not to this dramatic degree) in warehouses where the last bay is a different dimension than the others. If we go by the strict NFPA 13 definition of sprinkler spacing, distance along branch lines times distance between branch lines, then the spacing does not fall under 130 sqft. Since spacing dictates end head pressure and is mandated by 13, it needs to be followed. Add two sprinklers to the System A line adjacent to the boundary and decrease the distance between them to 10 ft. Now you have a maximum of 112.5 sqft throughout the space.
At 07:58 PM 11/1/2009, you wrote: >Skip reading this post if you prefer to avoid wasting grey matter. >Have paper and pencil handy if you do. > >Imagine a room 30 feet by 60 feet where the 30 foot dimension is left >and right and the 60 foot dimension is up and down. This room requires >OH spacing. We will examine three different sprinkler layouts. The >branch lines run in the 60 foot direction in all the layouts. The >hydraulics are not to be an issue in this exercise. > >The first layout, A, uses four branch lines spaced 7.5 feet apart, >starting at 3.75 feet from the long wall, with sprinklers spaced on 15 >foot centers, starting at 7.5 feet from the short wall. System A uses >16 sprinklers. The sprinkler operational area, 112.5 square feet, is >less than 130 square feet per sprinkler. The miraculous hydraulics in >the imaginary system A delivers the correct water density. > >The second layout, B, uses two branch lines spaced 15 feet apart, >starting at 7.5 feet from the long wall, with sprinklers spaced on 7.5 >foot centers, starting at 3.75 feet from the short wall. System B uses >16 sprinklers. The sprinkler operational area, 112.5 square feet, is >less than 130 square feet per sprinkler. The miraculous hydraulics in >the imaginary system B delivers the correct water density. > >Both system A and system B appear to be identical with respect to >sprinkler design density. Each uses the same number of sprinklers for >the same total area and each sprinkler in both systems operates the >same operational area of 112.5 square feet. Both system A and system B >are also bilaterally symmetrical. You can split each into two equal >sized sprinkler systems right down the middle in the up and down >direction. You would have a 15 foot wide by 60 foot long, two branch >line system A Left and and an identical system A Right. You would >have a 15 foot wide by 60 foot long, one branch line system B Left and >an identical system B Right. All these Left and Right systems also >appear to be identical with respect to sprinkler density. > >The third layout C, which as stated before is for the same 30 foot by >60 foot room, is comprised of the 15 foot wide by 60 foot long, two >branch line system A Left abutted to the 15 foot wide by 60 foot long, >one branch line system B Right. Each of these Left/Right pieces is one >half of two equal design density sprinkler systems that covered the >same area. > >Logically system C appears to be equal with regard to sprinkler design >density to system A and system B. (Remember that hydraulics are not to >be an issue in this exercise.) The logic required to consider this >equality involves considering the operational area for each individual >sprinkler, which we happen to be accustomed to doing for sprinklers >occurring at boundaries, but which is considered by some as blasphemy >when applied in this exercise. > >The "blasphemy" for system C occurs at the boundary between the two >equal sprinkler design density systems A Left and the system B Right >pieces. Here the distance between the branch lines is 11.25 feet. >Therefore according to the rules the spacing between OH sprinklers >cannot exceed 11.55 feet and thus the maximum distance the end >sprinklers can be from the wall is 5.77 feet. That is fine for the >system B Right where the end sprinkler is 3.75 feet from the wall but >it is not fine for the system A Left. Its sprinklers are 7.5 feet from >the wall. > >What made system C work logically as the addition of to equal systems >is that the dividing boundary between the system A Left and system B >Right occurs at 3.75 feet from the last system A Left branch line >which is 7.5 feet from the first system B Right branch line. This line >is at the blasphemous sprinkler operational area extents for the 7.5 x >15 spaced sprinklers and the 15 x 7.5 spaced sprinklers, not at >halfway between the 11.25 spaced branch lines. > >This is enough wasted matter. > >Allan Seidel >St. Louis, MO > > > >_______________________________________________ >Sprinklerforum mailing list >[email protected] >http://fireball.firesprinkler.org/mailman/listinfo/sprinklerforum > >For Technical Assistance, send an email to: [email protected] > >To Unsubscribe, send an email to:[email protected] >(Put the word unsubscribe in the subject field) Todd G. Williams, PE Fire Protection Design/Consulting Stonington, Connecticut www.fpdc.com 860.535.2080 _______________________________________________ Sprinklerforum mailing list [email protected] http://fireball.firesprinkler.org/mailman/listinfo/sprinklerforum For Technical Assistance, send an email to: [email protected] To Unsubscribe, send an email to:[email protected] (Put the word unsubscribe in the subject field)
