PSI at top of standpipe

[FireSprinkler]

NFPA 14 (2000ed) Chapter 5-7(1) Exception No. 1 allows the AHJ to permit a hydraulically calculated standpipe to provide 65PSI at the top (rather than 100psi). Fine.
BUT... Exception No. 2 starts off: In other than high rise buildings...
Does anyone know why Exception No. 1 would NOT be allowed in high rise buildings??
Especially since, in a large city with full-time personel and pumper trucks, the Fire Department will pressurize the (in this case a class I) standpipe to whatever they want anyway. It almost makes the PSI at the top redundant because a class I standpipe is for F.D. use only anyway.

Any thoughts??

 

[louis]

It might be due to the special design of high-rise buildings. I understand that they may be equipped with pressure-reducing valves at the hose connections. I also note that the exemptions are missing from the 2003 edition. Perhaps the reason for the exemptions has gone or lost its voice on the committee.

 

[FireSprinkler]

Well, My first post was a misunderstanding of the code. I thought that Exception #2 was an Exception to Exception #1. That is not the case. NFPA would not write "Exceptions to Exceptions". Exceptions ONLY refer to the main paragraph which they occour under.
Yes, I also understand that the exceptions are not included in NFPA 2003. I believe it has to do with the difference between the smooth bore nozles and combination fog nozzles that are use in some City Departments but not others. But, that's an entirely different matter.

 

[Slowzuki]

It may be related to the problems of multi-stage standpipes and exceeding working pressures of fire trucks with high buildings.

I worked on a project where we could hardly stay under the 175 max on the lower piping and meet 65 at the top.

Ken