location/number of standpipes and selecting pump gpm 2

[Mech110]

Hello,

I am confused in selecting the required water supply demand and standpipe locations for firefighting system in a building. Building is partially sprinklered; 2 car parks and 3 commercial floors, remaining non-sprinklered are 7 residential floors. Occupancy is light and ordinary hazard 1.

Building has 6 stairways in total but 4 of them are emergency. Architectural layout is attached. I plan to use combined sprinkler system Class I using pipe calculation method.

1. Does all 6 stairways require standpipes? or I can use 4 stairways (which are circled in the attached layout). NFPA states that every stairway requires a standpipe, but thats only about emergency exits I guess. If I use the 4 standpipes, I do not need additional fire hose cabinets inside the building as 150 ft and 200 ft travel distances can be met using 4. However, these stairways start from the Ground floor till roof. The other 2 stairways (at the top side of building) run through all basements till roof.

2. Along with Q.1 as stated above, is there any other location(s) too which I must consider for FHCs or standpipes? What about the Entrance? (I read the section but did not get a clear picture of what NFPA wants)

3. Can I use 1250gpm pump for this arrangement (max. acc to NFPA 13) of 4 standpipes or I have to add 500gpm (for ordinary hazard, partially sprinklered buildings) to this? Wont 1750 gpm be too big for this scale of building?

3. Using 1250 gpm pump on the underground water tank, I plan on taking 8in main header/supply pipe and extract 6in standpipes from the main on required locations. Is it fine? If I have to use 1750gpm, how much should I increase the pipe sizes?

4. Building total elevation is approx. 150ft. Hence using 1250GPM and setting 120psi at the top most 2 1/2" valve of the remotest riser and using 500gpm for that riser to calculate friction losses plus the friction loss in the 8in main pipe, I get a required pump head of approx. 460'. Is this approach OK?

5. Using 460' pump head, I will have to install a pressure regulator on sprinkler pipe take off at only 1 floor to reduce pressure to lesser than 175 psi in the sprinkler system. But, if I set 100 psi instead of 120 psi at the top, I wont even have to use this regulator, but I used 120 psi to be on safer side. What do you suggest?

6. Lastly, 100 psi min. requirement is at the valve or end of hose pipe (at nozzle)? As I read somewhere, a 150ft hose pipe also induces considerable pressure loss should it be considered while doing pump head calculations?

Thanks in advance for all the help you people can give.

 

[crb7]

hi

7.10.1.1.5 in nfpa 14 (its about standpipes) said :"The maximum flow rate shall be 1000 gpm (3785 L/ min) for buildings that are sprinklered throughout, in accordance with NFPA13, Standard for the Installation of Sprinkler Systems, and 1250 gpm (4731 L/min) for buildings that are not sprinklered throughout, in accordance with NFPA 13"
so i guess maximum flow rate is 1250 gpm for your system.

 

[Mech110]

NFPA 14 required.
"7.10.1.3.2 For a combined system in a building equipped with
partial automatic sprinkler protection, the flow rate required
by 7.10.1 shall be increased by an amount equal to the hydraulically
calculated sprinkler demand or 150 gpm (568 L/min) for
light hazard occupancies, or by 500 gpm (1893 L/min) for
ordinary hazard occupancies, whichever is less."

is confusing me! 1250 gpm max. or 1750 gpm?

 

[TravisMack]

You state you have a partially sprinklered building. Therefore, it is not fully sprinklered. Because of this, the standpipe demand is 1250 gpm. You have at least 4 stairs..500+250+250+250.

I am assuming this is a combination standpipe system. So, you have 1250 PLUS the calculated sprinkler demand. What is your sprinkler demand? If you have not calculated the sprinkler demand, then add 500 gpm for a total of 1750 gpm.

Travis Mack
MFP Design, LLC

http://www.mfpdesign.com

"Follow" us at

https://www.facebook.com/pages/MFP-Design-LLC/92218417692

 

[crb7]

travis i have a question
in this project if we had 3 stairs, the standpipe demand would be 1000 gpm(500+250+250+250)? or we assume at least 1250 gpm for standpipe demand then split it in stairs?
what about small project? like 3 storey building?
tnx for your help

 

[Mech110]

Well according to NFPA support guys, I got this answer:

"I wouldn't apply the requirements of combined systems if the building is partially sprinklered. I would select the fire pump for the highest demand be that either the sprinkler system (per NFPA 13) or the standpipe system (per NFPA 14). Regarding the sprinkler systems, assuming the highest hazard is Ordinary I, the water demand would be ~250 GPM for sprinklers plus 250 GPM hose allowance. The standpipe system will demand 500 GPM for the most remote stairway plus 250 GPM for each additional stairway up to 1250 GPM for unsprinklered floors. Since the standpipe demand is higher than the sprinkler demand, the pump should be 1250 GPM (or 1000 GPM at a higher nominal discharge pressure)."

The reply can be seen at this link:

https://community.nfpa.org/message/56689?commentID=56689&et=watches.email.thread#comment-56689

So, I am going with 1250 GPM as 1750 GPM was already too much!


@crb7 Though you haven't asked me but since I am sure on this thats why I am replying to your question. 500GPM is taken for the most remote stairway (see which stairway is farthest from the fire pumps or water reservoir) and then for each additional stairway 250 GPM is added. So for 3 stairways, 500+250+250 = 1000 GPM is fine for you according to NFPA 14. About storeys, check of it is a high-rise building (a high-rise is where a floor is 75 feet higher than where a fire truck access can stand on ground). Different clauses apply for high-rise and non high-rise buildings. For example NFPA 14 5.4.1.2 "Class I standpipe systems in buildings classified as highrise
buildings shall be automatic or semiautomatic." while it can be even of dry type or any other type in a non high-rise according to clause "5.4.1.1* Class I standpipe systems shall be permitted to be automatic dry, automatic wet, semiautomatic dry, manual dry,
or manual wet in buildings not classified as high-rise buildings."

Now if anyone could help me with my other questions!!!!

 

[crb7]

tnx mech110
good luck

 

[UFT12]

Mech110,

the reply you got seems to clearly violate NFPA 14, par. 7.10.1.3.2 which mandates what basically Travis told you. I believe the most prudent here for you it to clarify with your AHJ.

As far as concern the rest of your questions, you will need to seek for help other than simply an engineering forum, maybe a consultant or a colleague engineer more experienced on this. However I will try to help a bit on your questions.

1. As long as your staircases meet the definition of "exit staircases" or "exit stairs" of your applicable building code and serve as exits, all of them require connections, even if some of them are side by side. Note the word "connection", not necessarily standpipes. See 7.3.2.1 & 7.3.2.1.1 of 14.
You want a reason? Stair exits are protected and they access the floors to fight the fire. Where would a fire start and from what side would be the best to attack it? Nobody knows. Only Firefighters on location. Connections must be available.

2. All other locations are also found in NFPA 14, 7.3.2. So yes, main entrance requires a connection too. See 7.3.2.6.

3. I believe you got the answer for this.

4. Hydraulic calculations will give you the answer but why would you want to go up to 120 psi for your least favorable connection? Unless you have something that mandates such requirement, 100 psi should be the pressure you would be solving your system for.

5. If there is a case where it satisfies your design standard (e.g. NFPA 14) without the need of pressure regulators then this is the way to go.

6. Review 7.8.1 of the standard carefully. "... at the outlet of the hydraulically most remote... connection". But pressure drop from the connection itself (valve) should be included in your calculations.

 

[Mech110]

@UFT12 Thanks a lot for your help. Yes it violates, that is why I had contacted NFPA and mentioned the same clause you referred to. Generally speaking, by your experience, 1250 gpm will be fine or not?

1:
"7.3.2.1 Hose connections shall be provided at each main floor landing of required exit stairs." ok the word "connection" but what about: "7.4 Number of Standpipes. Separate standpipes shall be provided in each required exit stairway." Could you please take a look at the following layout and clarify my confusion? I plan to put standpipes in the encircles locations. The other approach could be that I use 2 standpipes at opposite ends and take fhc connections to the adjacent stairway but if it does not violate clause 7.4.

https://files.engineering.com/getfi...sc=212727627.1.1531215767504&__hsfp=122536126

2. OK I got it. Just to make sure, a connection is required here even though the floor is sprinklered and even though the travel distance from nearest standpipe is lesser than 150ft.?

3. 4. 5. Yes points closed. Thanks a lot!

6. It means that 100 psi should be the design basis at the end of hose which means including friction loss in the hose pipe (200-300 ft. length) + friction loss in the hose valve (2 1/2in) which is 31ft equivalent length of steel pipe acc. to table 8.3.1.3 . If this is the case then setting 120 psi at the hose connection will approximately bring the same result. Is it fine?