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Author Topic: Sprinklers don't stop the fire!  (Read 9152 times)

Martin

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Sprinklers don't stop the fire!
« on: October 18, 2012, 10:06:16 am »

Hello,

I modeled a fire wit a HRR of 586 kW/m² and a spread rate of 0,4 m/s. 7 m above the fire there are several sprinklers. They are activated when the temperature ishigher then 57 °C. When I simulate the fire, the sprinklers start after a while, but the effect on the fire is not that big. There are still temperatures of 250 °c after 15 min. What do you think, is it mote a problem of the sprinkler (too less or the HRR for the amount of water is to high) or is there an option in PyroSim that allows me to kill the fire with the water and I just didn't activate that?

Thank you for any reply!

Greetings
Martin
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Charlie Thornton

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Re: Sprinklers don't stop the fire!
« Reply #1 on: October 18, 2012, 02:01:47 pm »

Could you share your model so we can see how you are setting up your fire?

The usual problem with extinguishing is trying to extinguish a burner type of surface (i.e. a SURF namelist with HRRPUA set). This type of surface cannot be extinguished by a sprinkler. You need to ignite a layered surface, then your sprinkler can put it out. Here is a similar question on the FDS discussion group forum:

https://groups.google.com/forum/?fromgroups=#!topic/fds-smv/cwtTzI-o4EE
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Martin

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Re: Sprinklers don't stop the fire!
« Reply #2 on: October 19, 2012, 02:42:07 am »

OK, just checking if I understand correctly:
1) I can not extinguish a fire that arises from a burner surface
2) The only way to model a fire that spreads out with a certain spread rate and a heat release rate is a burner surface  isn't it? With the layered surfaces I can just simulate fires that either start to burn immediately with a certain HRR in full size or I can define that they start burning at a specific temperature.
3) So it is not possible to simulate the extinction of a fire that spreads out with a certain spread rate, correct?
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Bryan Klein

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Re: Sprinklers don't stop the fire!
« Reply #3 on: October 19, 2012, 03:11:31 pm »

OK, just checking if I understand correctly:
1) I can not extinguish a fire that arises from a burner surface
...

You can diminish HRR with burner surfaces by specifying a value for the 'Extinguishing Coefficent' (E_COEFFICIENT) on the Burner surface properties dialog.  The empirical E_COEFFICIENT is used to decrease the HRR according to HRR = HRR_specified * exp(-E_COEFF*t).  You must decide what value of E_COEFF to use, based on experimental data.

Best Regards,
-Bryan Klein
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Martin

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Re: Sprinklers don't stop the fire!
« Reply #4 on: October 22, 2012, 02:35:12 am »

OK, thank you Bryan! It is quiet hard to find that kind of value in papers etc. Does anyone have a suggestion what he/she already used in former simulations?
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Bryan Klein

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Re: Sprinklers don't stop the fire!
« Reply #5 on: October 22, 2012, 11:06:05 am »

Hello Martin,

I do not have reference values for this parameter.  It also looks as if there have been some bugs found in the 5.5.3 release of FDS related to sprinkler extinguishing burners, that have been resolved in FDS 6.

In the meantime, I recommend posting your request to the FDS-SMV discussion group.
https://groups.google.com/forum/?fromgroups#!forum/fds-smv

While we try to answer FDS support related questions, you will probably get much better results by asking the developers directly.

Best Regards,
-Bryan Klein
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Bryan Klein

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Re: Sprinklers don't stop the fire!
« Reply #6 on: October 22, 2012, 11:07:23 am »

Here is a thread about this issue on the fds-smv issue tracker.
http://code.google.com/p/fds-smv/issues/detail?id=1210
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