Fireflow model with sprinklers and hydrants 1

[atxeng]

I am modelling a private line with two hydrants and a fire sprinkler system for a newspaper press building here in Texas. I am having trouble reaching the pressure required for the sprinkler system and the MEP for the project (located in Colorado) told me the demands for the sprinkler and the hydrants are not concurrent and can be modelled separately. Of course I did not believe him, so I rushed to mylocal code and the IFC, but could not find anything on the subject.

Can any of you tell me that this is allowable per a certain ordinance because it makes no sense to me.

 

[LHA]

I can't imagine a scenario where one would use a fire sprinkler and not a fire hydrant at the same time, or vice versa.

I always have, and would, design for their concurrent uses, unless you find something in writing which allows you not to. Aphone call from some Mech Eng in another state don't cut it.

Keep in mind the MEP who seals is only liable for the sprinklers/plumbing working as spec'd. YOU (or the Civil who seals) are liable for there being enough h2o for adequate fire flow.

There might be something here:

http://www.nfpa.org

Engineering is the practice of the art of science - Steve

 

[CarlB]

I don't believe you would need to sum the maximum hydrant flow and the sprinkler flow, as they would not typically be concurrent. Or need to be concurrent. See

http://www.eng-tips.com/viewthread.cfm?qid=170610&page=3

for a discussion with code citations.

 

[cvg]

I would be interested in hearing about the scenario where they are not concurrent. I cannot imagine a case where the fire department would arrive, turn off the sprinklers first and then begin hosing it down. Seems counterproductive to me. Am I missing something?

 

[CarlB]

Did you read the discussion I linked? As the OP requested, can you cite a code or ordinance?

I don't do sprinkler design, but the little I understand the sprinklers are effective in putting out a fire when it is small & contained. This is what the flow calculations, affected areas, sprinler heads are designed for. And for hydraulic design, the (nearly) full available pressure of the water mains are used, plus some hose allowance. If building is ablaze with the Fire Department directing multiple streams on it, then the design hydrant capacity comes into play (1000 GPM +). And the main residulal pressure is much less than sprinklers were designed for.

As mentioned in the linked post, they are 2 different scenarios. The water mains are designed to achieve the required hydrant flows, which probably do include some domestic uses. But not full sprinkler demand.

 

[LHA]

Don't feel bad, I'm missing it too, cvg.

I read the other thread, and I believe the two main responders are more knowledgeable than me on fire demand. So, I believe their claim that cumulative sprinkler and FH flow is not REQUIRED to be provided.

But I still can't see why you would ever WANT to design to that. Even the one explanation of "it should be mostlyout/contained by the time the FD gets there", is a little risky for my blood. I am pretty sure I will continue to use both.

Even when Architects/MEPs supply me with a demand, it always comes similar to this actual one from my files:
"The fire protection system demand inside each building is 225 gpm. There will also be two fire hydrants on the site. The inside and outside hose stream is 250 gpm for a total of 475 gpm"

Engineering is the practice of the art of science - Steve

 

[edwards1800]

Ok, I am trying to figure this stuff out too. Reading over the linked post, I found the following relevant paragraphs (slightly edited):

[ul square]
[li] NTTT (Civil/Environme) 14 Nov 06 14:50 [/li]
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[li] Water used to extinguish fire in a sprinklered building consists of:
[/li]
[li] 1. Fire flow, for fire hose streams connected from hydrants around the building?, obtained from IFC table, 2750 gpm reduced to 1500 gpm in the above example.
[/li] [li] 2. Sprinklers and hose allowance boosting the sprinkler system?, = (discharge density x design area) + hose allowance (250 or 500 gpm).
[/li]
[/ul]
[li] TravisMack (Mechanical) 14 Nov 06 19:47
[/li]
[ul circle]
[li] If you have the non sprinklered building..say an industrial park, you must have a minimum flow at any hydrant of 2000-3500 gpm at stookey stated above.

If you have the sprinklered building, for example with ESFR heads, you would need around 1750 gpm (12 heads flowing at 1500 gpm + 250 gpm hose allowance

Now, based on my understanding, here is how the scenario works and may help you understand....

Fire occurs in an unsprinklered building. By the time the FD gets there, the fire is raging pretty heavy and the FD will be drawing a lot of water from the municipal supply - say at 3000 gpm to attack the fire. That is where the fire flows come in to play.

Fire occurs in SPRINKLERED building. Let's assume there are ESFR sprinklers to stay with the example above. By the time the FD gets there, the fire is suppresed or contained to a relatively small area (1200 sq ft or less) and the FD only needs to draw a small amount of water (to complete the final knockdown on the fire). The hose allowance that is mentioned above accounts for the relatively small amount of water that the FD will be taking from the supply in addition to the demand from the sprinklers. So, in this case there would be about 1500 gpm flowing from the sprinklers and about 250 gpm for the FD to finish the attack.

The scenarios are 2 completely different situations to try so show how the numbers are really independent of each other.

Hopefully that helps to clear up some of the differences for you.
[/li] [/ul]


[li] TravisMack (Mechanical) 23 Mar 07 15:39
[/li]
[ul circle]
[li] The sprinkler demands will typically include a hose allowance, and will also be at higher pressure requirements than the site fire lines. For example, a sprinkler system may need 300 gpm at 50 psi at the base of the riser, and 550 gpm @ 55 psi at the city tap. The extra 250 gpm is the hose allowance you are required to account for in calculations.

The site fire line demands are required flows at 20 psi. Since most water purveyors don't like the water main pressures to fall below 20 psi, this will insure that the FD has adequate water to go through the FD pumper truck while maintaining the pressure in the city water mains.

I can't think off the top of my head where you will find the quote to show they are not additive, but you will not find a quote that says they aren't. If you check the appendix B in the IFC, it indicates the site fire flow requirements. It does not say that you are also to incorporate the sprinkler demand to these.

I hope Stookey checks in on this. Since he is the resident ICC expert, he can likely give you a better point to look in the I-codes.
[/li]

[/ul]

[li] stookeyfpe (Specifier/Regul) 25 Mar 07 21:54 [/li]
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[li] See 2006 IFC section B105.2, exception.
[/li]
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[/ul]


So, to summarize, when looking at NFPA 13 for sprinklered buildings, there is a Sprinkler Demand added to a Hose Allowance . This should NOT be added to Fire Flow , which is the number calculated using the relevant building codes for the area and is independent of buildings and their sprinklers.

1. Sprinkler Demand = water supplied to sprinklers
2. Hose Allowance = water supplied to fire dept from building’s sprinkler supply
3. Fire Flow = water supplied to community hydrants for fire dept use

Is this correct?

 

[equimo]

According with NFPA 13, you must calculate the sprinkler system following the reasonable steps: 1. Choose the critical area (NFPA 13 establish the size of the area and the flow required according with the level risk), usually is the most remote area from the riser or from the feeding pipe i.e 1500 sf with 0.5 gpm/sf for low risk, look for your risk; 2. With the area and flow given by NFPA 13, make calculation for the sprinkler system loss pressure and find the required pressure at the Feeding point; 3. Add 500 gpm for hoses, (NFPA 13) or 1000 gpm if you have a large warehouse; 4. The hydrants are part of a large system that you should use in case of a large conflagration outside of the building, then you should not add more flow for those hydrants and its calculation can be done separately from the sprinkler system.

 

[TravisMack]

Equimo:

You are right in theory, but the numbers are off.

NFPA 13 says to calculate the most demanding area. This may not be the most remote from the supply. I have done several projects where the most demanding area is right by the supply, and there is a less demanding area at the end of the system. The calculations must be done to support the most demanding area.

Establishing your risk is determining the hazard in "sprinkler-ese." A low risk would be light hazard and would be 0.10 gpm / sq ft coming from each sprinkler in the demand area. You can get into some higher storage demands where the sprinklers will be putting out 100 gpm or more each.

Hose allowances vary from 100 gpm for an office (light hazard) to 750 gpm for tire storage.

A key thing to remember is that the size of the facility has nothing to do with the hose allowance or sprinkler densities. I could have a 1 million sq ft office with 10' ceilings and only figure a calculated area of 0.10 gpm / sq ft over the most demanding 900 sq ft with a hose allowance of 100 gpm (190 gpm total demand). You could also have a 2000 sq ft building storing grp A plastics to 20' and you would have a design density of 0.6 gpm / sq ft over the most demanding 2000 sq ft with a 500 gpm hose (1700 gpm total demand). So, as you can see the size of the facility has nothing to do with sprinkler demands. It is the occupancy of the building that drives the sprinkler demands. I only bring this up because I had to do ALOT of education with a building owner this past week on this very issue. Actually, it comes up quite often, so I often use the same scenario above to help educate owners about the sprinkler systems.

 

[edwards1800]

TM:

I understand your point about the size of the building.

I don't quite follow your calcs:
I am looking at NFPA 13 Figure 11.2.3.1.5. In your first example (1 million sq ft office with 10' ceilings and only figure a calculated area of 0.10 gpm / sq ft over the most demanding 900 sq ft with a hose allowance of 100 gpm (190 gpm total demand)) why did you use 900 sq ft instead of 1500 sq ft? Does paragraph 11.2.3.1.8.1 require you to use 1500 (making total demand 250 gpm)?

In your second example (2000 sq ft building storing grp A plastics to 20' and you would have a design density of 0.6 gpm / sq ft over the most demanding 2000 sq ft with a 500 gpm hose (1700 gpm total demand)) why did you use .6 gpm over 2000 sq ft instead of .4 gpm over 2500 sqft (the extent of the figure, and in accordance with paragraph 11.2.3.1.8.2)?

Am I reading that figure and its limitations incorrectly?

 

[TravisMack]

Sorry. I took several liberties there...

Ex 1: Using listed Quick Response sprinklers, you can reduce the design area by up to 40% based on ceiling height. In a light hazard area, you are required to use QR sprinklers. If you have a 10' ceiling, the design area can be reduced to 900 sq ft. Therefore, you get the 0.10 gpm / sq ft over the most demanding 900 sq ft.

Ex 2. I assumed 20' of storage in single / double / multiple row rack using specially listed sprinklers (example: Tyco ELO-231). This allows a design density of 0.60 gpm / sq ft over the most demanding 2000 sq ft with 500 gpm hose.

As you can see, there are multiple scenarios that drive the sprinkler requirements. This just goes to further illustrate that it depends on what is in the building instead of the size of the building.

I hope that clarifies.

 

[PCU]

Sprinklers are to stop the fire from spreading. Once the FD shows up and hooks to the hydrant, the sprinkler flow can be ignored since the FD will be using the hydrant to extinguish the fire and, if they want to, will hook a pumper up to the FDC to maintain flow to the sprinkler system.

 

[TravisMack]

"Sprinklers are to stop the fire from spreading"

This is something that I think most people forget, or don't know. Fire sprinklers have been very successful in fighting fires, but a sprinkler system (unless it is ESFR) is designed to control / contain a fire to a certain area. Sprinklers do well at suppressing the fire, but that is just an added bonus. The majority of sprinklers are known as control mode and are simply to contain a fire to a area to mitigate property damage and provide for life safety. The suppression is left to the responding fire dept.