Time Calculations 1

[desnov74]

A requirement for hospitals keeps coming up. Inspectors are asking us to ensure that water will get to the area in time for a pre-action system. Often there is quite a bit of distance from the pre-action valve, air-compressor, etc, and the hazard area being protected.

How can I calculate the time for water to reach the hazard in these type of systems?

How can I do it utilizing software?

What can I solve this with fundamentals?

Thanks in advance.

 

[cdafd]

I would ask for a reference out of NFPA 13 showing where the time requirement is required for a pre action system.

Do not think it is there.

are you talking about a dry pipe?? and if so the time does not kick in till a certain gallonage system.

 

[desnov74]

thanks cadfd,

I know this isn't a nfpa13 requirement but rather a an additional requirement from the public health department of my local state.

Any thoughts?

 

[TravisMack]

You would need to purchase the FDT program from Tyco to calculate the delivery time. It is a pain to input, but very effective.

Travis Mack
MFP Design, LLC

 

[cdafd]

desnov74

1. is the requirement in wrinting/ code???

2. what is the requirement??

 

[LCREP]

My guess is they do not know the difference between a dry pipe and a preaction system, a very common mistake, both have air in them. That is about all they have in common, besides putting wet stuff on the red stuff.

What state is this requirement in?

****************************************
Fire Sprinklers Save Firefighters’ Lives Too!

 

[desnov74]

Sorry to take so long to respond. Just got too busy.

I researched the code, in 2002 in 13 section 7.4.5 the states that the period of time for water to reach the most remote sprinkler is 60sec. for each 400ft of common feed from the main, from the time a heat response element responds. Section 7.4 pertains to combined dry and preaction systems.

From what I understand,the only way to do predict this reliably is with software. (as mentioned by TravisMack)

I wonder if there is a way to determine this from first principles. This could help verify software simulations and submittals.

thanks and sorry for the delay again

desnov

 

[LCREP]

Section 7.4 pertains to combined dry and preaction systems.



Unlikely u have one of these things installed, u most likely have a preaction system, so the time thing does not apply.

****************************************
Fire Sprinklers Save Firefighters’ Lives Too!

 

[DonPhillips]

It has been about 20 years since I worked mass flow rate type problems but if I remember correctly, first principals involved solving differential equations - like the second derivative of a function plus a function equals a constant and solving for the function. Hated those problems then - would rather purchase the software now.

Don Phillips

http://worthingtonengineering.com

 

[Oremus]

Don, What?


I'll just take your word for it...

 

[desnov74]

NFPA 2002 7.3.2.2.3 For Pre-action systems if the volume is over 750 gallons, then the pipe must reach the last sprinkler within 6-sec.

I also looked up the software and got a quote, the price was somewhere in the range of 5000 USD!

Thanks to all again

 

[SprinklerDesigner2]

Don likes that sort of thing, functions of functions, but just thinking about it makes my eyes glaze over and my teeth hurt.

Used to be in Ohio, when they were operating under the Ohio BOCA Fire Code, all dry and preaction systems had to meet the 60 second rule regardless of size. Not all jurisdictions knew about this, but the state fire marshal certainly did, but it was absolutely there and part of law having been adopted by the state legislature.

I had one job near Napoleon, Ohio where I had huge troubles with a 250 gallon dry system. One of those with a static pressure of 90 psi, residual of 20 while flowing 520 gpm. Would work, would calc but when it came to meeting the 60 seconds you had to be real cautious.

Is BOCA still around?

 

[stookeyfpe]

BOCA is gone. It's part of ICC.

 

[DavidCR]

I think that beside the flowing time, depending on the size of the system, the most important time issue could be the response time of the control devices involved.

 

[FFP1]

You guys might want to read Section 7.3 of NFPA 13 a little closer. The 60 sec requirement only applies for standard preaction systems when the system has a "double interlock" design.

If single interlock preaction systems are designed properly, water will enter the sprinkler piping prior to any sprinkler head operation. NFPA 13 essentially considers the system to be wet with no 60 sec requirement as long as water has filled the system prior to sprinkler head operation.....the inevitable air pockets and minor delay prior to water discharge is ignored by NFPA 13 for the single interlock designs.

Double interlock systems and Combination systems (preaction & dry systems) do have the minimum time requirements discussed on this forum; however, the requirements are different for each.

Sections 7.3 & 7.4 are relatively clear, but you must make sure you apply the minimum time requirements depending on the appropriate system.

 

[desnov74]

FFP1:

You are correct, I've should have been more clear with this in the post.

Thanks everyone for the comments good feedback.