a requirement from NFPA 13 bothers me a lot since I want to know the fundamental reason of it

[yamete389]

It says in NFPA 13 that the air supply shall have a capacity capable of restoring normal air pressure in the system within 30 minutes.So where does this "30-minutes" comes from?? is it a time interval relevant to the time of fire duration or this "30-minutes" just exists in this code for nothing?

 

[cdafd]

Get the dry pipe system back in service with in a given time.

 

[yamete389]

So this given time just poped up from the NFPA guy's head one day and then was written into code.thought any rules or requirment in NFPA must have a solid reason(apparent or compelling) behind them.

 

[cdafd]

Well the group decided that was a good time period instead of maybe 24 hours ?


I take that the group wanted the fire sprinkler back in normal service, rather fast.

It also gives an ahj an enforcement tool, to ask the owner to give his building fire protection.

The 30 minute rule has been there for a long time

 

[LCREP]

As a past member of an NFPA committee it probably went something like this....

The code section said that the air should be available as soon as possible. Joe recalls in the past when a system took too long to get back into service and resulted in a large loss. Jeff also recalled something like that but was not a big deal. Joe said all systems should have air and in service in 10 minutes. Jeff said that is not possible how about 2 hours. So they had 4 hours of discussion, 29 different votes on various times with no agreedment on the time. Then they formed a special committee to come up with a solution. The special committee meet 45 times and spent 109 hours on the topic. The special committee came back to the group with a proposal for 45 minutes. The group then had a vote and in the end it was 30 minutes........ Oh yea then they spent another 2 hours deciding on where a period should go in the sentence!!!!

Got to love the code makeing process

 

[SprinklerDesigner2]

Because it always was.

In 1974 we had OH 1, OH2 and OH3 and other than an increase from 250 to 500 hose stream there was very little difference between OH2 and OH3. A density of .19 vs .21 and where was it decided .21 was better than .19? Any testing done for this? Not that I can discover.

Some reasons for the way things are are lost in the fog of history. Why 52,000 sq ft on a system and not 50,000 sq ft, 60,000 sq ft or 100,000 sq ft? The way it was explained to me back in the dawn of time systems were limited to 400 sprinklers. 400*130=52,000 so now you know where the 52,000 comes from. Same with EH where 400*100=40,000.

My favorite is anyone want to guess where the drawing of the escalator having sprinklers spaced 6'-0" around the opening came from? Anyone want to guess as to all the testing that went into the scheme and why it is still there? It's been in "the book" forever but seeing how often it is used does it warrant a whole half page?

 

[stookeyfpe]

My favorite is anyone want to guess where the drawing of the escalator having sprinklers spaced 6'-0" around the opening came from? Anyone want to guess as to all the testing that went into the scheme and why it is still there? It's been in "the book" forever but seeing how often it is used does it warrant a whole half page?

Since you asked the basis for design is founded on a series of fire tests performed by the National Bureau of Standards (now known as NIST) in 1981.