How to Meet Highrise Second Supply Req'ment?

8/1/2024

Our high-rise facility consists of apartments, condominiums, retail on the bottom floor, restaurant tenants on the top floor, and (3) levels of underground parking. We are 9 stories tall out of the ground.

They have great water pressure at the site with 140 static and 118 residual, flowing about 1,900 GPM, but with our floor-to-floor distances, I cannot get 100 PSI at the top of my standpipes. The building footprint is spread out, so I will need (8) standpipes to cover the hose lay inside the building (fully sprinklered). I'm assuming one 1,000 gpm pump will cover all the standpipe demand.

To complicate matters, this is in a seismic area D classification, and with it being a high rise, I am required to have a secondary on-site water supply. The intent was to install an underground tank to supply the fire pump or pumps, if necessary.

My thought was to supply water directly from the city main to the tank, and if there is ever a break in the city supply line, the pump would be served from water in the tank, which would have enough capacity to serve the facility for 30 minutes.

Is 30 minutes the duration I need?

What do you think about how I plan to serve the building? Would that meet the requirement for a secondary water supply?

Do I consider the standpipe demand when sizing the underground tank, or just the most demanding area of my sprinklers?

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4 Comments

Dan Wilder

8/1/2024 09:02:23 am

The secondary water supply will need to be able to meet the sprinkler demand + hose stream per 914.3.2...it does not state the need to be sized to meet standpipe demands....this would also correspond to the duration (based on hazard classification). With the OH areas of the restaurants on the upper floor, this may trigger the 60 minute duration vs the 30 min.

As he building is below 420', 2 separate water supply connection requirements are not in effect.

The primary water supply and duration (sprinkler, standpipe, fire pump) will need to be able to meet full standpipe or sprinkler required floor and pressures (this looks to be several calcs per your description of "spread out") but will likely need to follow NFPA 14-19' 7.10.1.2.1.1 and 7.10.1.2.3.1 (these stick out to me) for the standpipes and also looking at the OH restaurant areas on the top floor.

Some previous discussion
https://www.meyerfire.com/daily/required-duration-for-secondary-water-supply

Anthony

8/1/2024 09:44:44 am

Dan, IBC 403.3.3 does require a secondary supply as this building is in a class D seismic design category. the 420'-0 designation is only referenced in 403.3.1 and 403.3.2.

Otherwise, I agree with your comments.

8/1/2024 11:39:29 am

Yes, I was referring to the 2 water main connections on different streets for 403.3.2, 403.3 is just a secondary water onsite water supply (i.e. the tank).

Following this conversation
https://www.meyerfire.com/daily/does-tank-meet-secondary-supply-in-ibc

Jack G

8/2/2024 11:31:21 am

914.3.2 Secondary water Supply:
An automatic secondary " on site" water supply having a capacity of not less than the hydraulically calculated sprinkler demand plus hose streams for seismic categories " C-D- E-F ". ( in this case sized for OrdH- 1 or 2, plus hose s for 60 minutes) ad their the design includes mech rooms, maybe retail, and commercial kitchens etc..
The secondary supply shall be on site and thus would preclude an addional connection to the munucipal water supply. SOME municipalities have an exception and will allow a connection to a water main from another municipal main and/ or supplied from another municipal zone. ( philadelphia being one).
An additional fire pump shall not be required, unless the secondary supply cannot deliver the minimum intake pressure to the primary pump.
This would require the primary pump to be sized to supply the building with the " street pressure and boost alone" included in the design of the primary pump, and would over pressure the design when connected to the primary munucipal supply. Additional PRVs would/may be required for hose valves and sprinkler supplys to the floor. The total cost could be huge if a lot of hose and sprinkler valves are in the over pressurized zones.
" the secondary supply shall be automatic"( as opposed to manual).
Generally the intent is a Secondary pump would be required if the secondary supply cannot deliver the necessary pressure to the intake side of the primary pump.
So.....could the Ord Haz areas on the low floors be designed without the pump ?. Talk to the AHJ.
The rest of the building/ floors / standpipe with the primary fire pump? ( AHJ)
The secondary supply sized for light hazard? ( size of tank ) and the street pressure and / or built into the fire pump?( AHJ)
A second municipal supply pressurizing the tank ?
Like a break tank that would supply the tank with additional gpm to meet OH demand.
I m thinking " not" .
The tank should be sized for OH, and the primary pump over sized to include the street pressure and the OH design.
The pump '( if horizontal and not vertical) should be provided with 3-5 feet of head, 'to allow it to wotk properly) meaning the tank bottom being above the suction of the pump. ( otherwise a vertical fire pump.required ).

How to Meet Highrise Second Supply Req'ment?

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