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Fire Protection requirement for a Wooden Structure.

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hussainsayz

hussainsayz

Mechanical
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I have a light hazard building, wooden structure with small basement, level-1 and level-2 total area of the building is 4650sft and 20 ft maximum height, the nearest city water pressure test available is Static 51 psi, residual 38 psi and 890 gpm, the main water line is 6 inch. does building requires a fire pump for sprinkler system or the city water pressure is enough to cater the needs of the system.
 
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What do your calculations tell you?

You make no mention if wet / dry system. Is the attic a flat attic or sloped? There are a lot of questions to just say yes/no on something like this.


Travis Mack, SET, CWBSP, RME-G, CFPS
MFP Design, LLC
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its a dry system as temperature reaches -13 F, and level-2 with sloped attic.
 
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So, to my first question: What do your calculations tell you? Have you done calculations? At least a preliminary set? You don't give the slope. Is it >2:12? Is it ≥4:12?

What is your attic structure spacing? These are all required to determine the answers to your questions. Do you have a lot of experience in fire sprinklers? Are you looking to confirm your answer, or are you looking to take a $50k gamble on a response from an internet forum?

Depending on how you design your attic, you could have a demand around 500 gpm with a dry system and sloped attic. Assuming you have ±45 psi at system demand, you need to deduct the following approximations:

Elevation pressure: ±9 psi
End sprinkler pressure: 7 psi
10% safety margin: ±5 psi - I would probably take this to 10 psi.
Backflow preventer losses: ±5 psi

This leaves you with ±14-19 psi for friction loss in a dry system. Are you willing to gamble that you can do a dry system with less than ±14-19 psi in friction losses? I have no idea what your building looks like to know if that is even possible. You may want to seek help of someone that you compensate for their time, skills and opinion to assist you with this.

Travis Mack, SET, CWBSP, RME-G, CFPS
MFP Design, LLC
"Follow" us at
 
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Building Type: Museum or exhibition center.
Hazard Classification: Light Hazard as per NFPA 13 chapter 5.2
For a light hazard occupancy with a design area of protection of 1500 square feet, using pendant sprinkler/upright sprinkles.
Protection Areas and maximum spacings of sprinklers for a noncombustible obstructed and unobstructed and combustible unobstructed spaces. Hydraulically calculated Q=225 ft2
Q= 225 ft2 x 0.10 gpm/ft2
= 22.5 gpm minimum for each sprinkler head
Water Demand.
Light Hazard Density curve= 1500 x 0.10 = 150 gpm, calculate hydraulically 7 heads at 22.5 gpm which would produce 22.5 x 7 =157.5 gpm
Water Pressure Demand
Minimum water flow for a sprinkler head in this system is 22.5 gpm, therefore
P = (22.5 x 5.6)2
P= 16.1 PSI
 
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Based on that, you need to hire a fire sprinkler consultant to guide you.

In your combustible concealed attic space, assuming you have combustible construction with members less than 3' on center, you are limited to 130 (or 120) sq ft.

Do yourself a huge favor and hire a consultant to assist you. You could make a very costly mistake with this situation. Also, you mentioned a dry system and don't account for the dry system penalty.

I am trying to offer you the best advice. Hire some one to help you. This does not appear to be in your area of competence at this time. It may be in the future, but not right now.

Travis Mack, SET, CWBSP, RME-G, CFPS
MFP Design, LLC
"Follow" us at
 
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Thank you very much Mr. Travis Mack, it was a very helpful suggestion.
 
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