What is the required duration for a Secondary Water Supply within Seismic Zone?

IBC Section 403.3.3:
​
"The secondary water supply shall have a duration of not less than 30 minutes as determined by the occupancy hazard classification in accordance with NFPA 13."

Does this mean minimum 30 minutes, with the gpm/demand determined by NFPA 13?

Or the minimum duration is also determined by NFPA 13, such that the secondary water supply could require an even longer duration, like 60 minutes?

​​​​​​​​​​​​​​​​​​​​​​​​​​​Sent in anonymously for discussion. Click Title to View | Submit Your Question | Subscribe

I'm looking at a few projects that have fire pumps and above-ground cylindrical storage tanks for fire protection.

Some projects I have seen have recirculation after the fire pump discharge underground and back into the storage tank. Frustrated I can't find much on this in NFPA 22 or elsewhere.

Is this part of a means for freeze-protection, or to keep the water from getting stagnant, or for pump testing (in which case I guess it would have to branch off from the flow meter)?

Or is it likely engineer preference? Is it a military requirement?

Thanks in advance.

​​​​​​​​​​​​​​​​​​​​​​​​​​Sent in anonymously for discussion. Click Title to View | Submit Your Question | Subscribe

Is there any NFPA provision for forbidding a fire pump to start in the event a water storage tank has a water level that is too low?

I'm wondering what might happen if the water storage gets down to ~25% of the design level, or lower, and the potential need to shutdown the pump before it runs dry. 

​​​​​​​​​​​​​​​​​​​​​​​​​Sent in anonymously for discussion. Click Title to View | Submit Your Question | Subscribe

We are bidding a job that may possibly need a 1,250 gpm rated fire pump due to not enough flow from the city. Our test was 43 psi static, 35 psi residual at 872 gpm. We will need to include a ground suction tank.

How do I correctly include or simulate a ground suction tank in my hydraulic calculations?

We use the Sigma Hydraulic Calculation program.

Thanks in advance.

​​​​​​​​​​​​​​​​​​​​​​​​​Sent in anonymously for discussion. Click Title to View | Submit Your Question | Subscribe

​We're looking at a fire protection system, Ordinary Hazard Group 2, that requires primary fire protection water from a storage tank.

We are looking at three options, (1) above ground insulated with a heater, (2) underground concrete and (3) underground fiberglass.

I am curious what the community here sees around the industry as being the most common choice here?

The job site already has substantial excavation going on and the job is located in the north east so freezing is a concern. There will be no private hydrant so we don't see the need to carry hose allowance in our tanks sizing.

​Thanks in advance.

​​​​​​​​​​​​​​​​​​​​​​​​​Sent in anonymously for discussion. Click Title to View | Submit Your Question | Subscribe

Can a commercial pool be used as the required secondary water supply to a high-rise sprinkler system?

The 2019 IBC/CBC Section 403.3.3 requires an automatic secondary water supply in certain seismic design categories. This is typically met by installing a dedicated tank that meets the minimum demand for 30 minutes.

I have a developer asking if they can run a feed line to their 100k +/- gallon commercial pool so it can serve this purpose.

Outside of the engineering challenges and value engineering their team must address, I'm wondering if this arrangement is even allowed. I cannot find anything in IBC/CBC, NFPA 24, NFPA 13, etc. that wouldn't allow this. Any help is appreciated.

​

Section 903.3.5.2 (IBC 2012)/Section 403.3.3 (IBC 2015) requires and automatic secondary water supply. I am an FPE and I work in a jurisdiction (Hawaii) that has never required this secondary water supply due to local code amendments to IBC. Recent code revisions now require this secondary supply, and I now have my first project subject to this requirement. I'm planning to meet this requirement as as follows;

• Secondary Water Supply: Provide an underground storage tank capable of supplying the sprinkler system + Hose Stream demand for 30-minutues per IBC requirement (min. 12,000 gallons). A vertical turbine fire pump will sit on top of the tank and pull water from below. Pump will be sized to supply full sprinkler system and standpipe system pressure demand (750 gpm @ 250 psi).
• Primary Water Supply: The city water main will flow directly into the water storage tank at a rate equal to the standpipe system demand. The tank will serve as a "break tank" as long as the city water supply is viable. Although the city water supply will fill the tank at an equal rate to the system demand, the minimum break tank size will be 750 gpm x 1.5 x 15 min = 16,875 gallons.

Am I on the right track here? Is this primary/secondary supply arrangement viable? Does anyone foresee any code or other issues that may be a problem with this arrangement?

​​​​​​​​​​​​​​​​​​​​​​​​​Sent in anonymously for discussion. Click Title to View | Submit Your Question | Subscribe

We have a water storage tank that is leaking but cannot find the leak.

They have scoped the pipes, used dye to try to track with no luck.

Does anyone know if ground penetrating radar or some other thing that we can try to locate this leak?

Any help is appreciated!

​​​​​​​​​​​​​​​​​​​​​​​​​Sent in anonymously for discussion. Click Title to View | Submit Your Question | Subscribe

We design fire protection systems for large industrial plants with a large area network running in the kilometers.

In such case there could be chances of surge due do sudden closure of a deluge valve, check valve, or fire pump. We do not have time/expertise to carry on surge analysis on software.

I have heard about using tanks for surge.

How would we go about sizing an anti-surge tank?

Is there any basic guidelines based on fire water flow rate/pump discharge pressure to get first cut sizing of a surge  protection tank?

​​​​​​​​​​​​​​​​​​​​​​Sent in anonymously for discussion. Click Title to View | Submit Your Question | Subscribe

We have a water storage tank and a diesel fire pump on our project.

Is there any requirement for the pressure relief valve discharge pipe, when connected to a supply tank, to be extended below the lowest possible water level?

​​​​​​​​​​​​​​​​​​​​​​Sent in anonymously for discussion. Click Title to View | Submit Your Question | Subscribe

We have a fire sprinkler system with a 550 gpm total sprinkler demand (including hose allowances). The supply duration is 60 minutes. There is no city water supply and we are only utilizing a storage tank.

Is the tank required to have a minimum capacity of 33,000 gallons?

Or, could we rely on fire department response, potentially reduce the tank size, and have a manual fire department connection for tank refill?

​​​​​​​​​​​​​​​​​​​​​​Sent in anonymously for discussion. Click Title to View | Submit Your Question | Subscribe

We have a project with a limited water supply that makes it impossible to automatically replace the required fire water in 8-hours. 

Could a larger (1.5 x the required fire flow) water storage tank be an option?

​​​​​​​​​​​​​​Sent in anonymously for discussion. Click Title to View | Submit Your Question | Subscribe

Our fire water demand capacity is 60,000 gallons, but our current water tank storage capacity is 30,000 gallons. We don't have any space near our current fire water storage tank. 

Is it possible to make another (second) tank with a capacity of 30,000 gallons and connect it to the old tank through pipe?

​​​​​​​​​​Sent in anonymously for discussion. Discuss This | Submit Your Question | Subscribe

​I am currently working on an existing high rise building that requires a fully automatic sprinkler system to be added and the AHJ is requiring a water tank to be added on the property to serve as a secondary supply.

There is no room for a secondary supply.

Can a pool be used to substitute a water storage tank that will supply the building through fire pumps?

What codes could back up this option?

​​​Sent in anonymously for discussion. Discuss This | Submit Your Question | Subscribe

How can we prevent the formation of algae or microorganisms in water storage tanks for fire protection due to the water being stagnant?

​​​Posted anonymously for discussion. Discuss This | Submit Your Question | Subscribe​

I'm putting together design-build requirements for a new single-story construction building. The flow test pressure is borderline in my opinion so I'll be calling for a fire pump.

When is a water storage tank required with a pump?

I don't think the system needs one, but I just want to be sure.

​​Posted anonymously for discussion. Discuss This | Submit Your Question | Subscribe

Is it permissible to consider the refill supply for a water storage tank when sizing the tank?

The supply would come in above 20 psi. Thanks in advance.

​​​​Posted anonymously for discussion. Discuss This | Submit Your Question | Subscribe

NFPA 22, 2018 Edition regarding filling requirement and duration - 

Section 4.2.1.4. states "The water supply shall be capable of filling the minimum required fire protection volume within the tank in a maximum of 8 hours" and at the same time Section 14.4.3 states "The tank shall be kept filled, and the water level shall never be more than 4 in. (102 mm) below the designated fire service level."

If I understand correctly, as soon as the water goes below 4-inches from the normal filled level in the tank (HHL), the makeup water supply should be starting to replenish and the pipe sizes should be provided in such a way that the tank can be filled within 8-hours.

In a fire, as the water is going down, the tank will always start full.

What is the case where the tank would be emptied out (except maintenance) and need to be refilled within 8-hours?

What if we store water in two tanks to allow maintenance - would we not need to meet this 8-hour requirement?

I'm unsure of how these two requirements work together. Appreciate any feedback.

​​​​​​​​​​​​​​​​​Submitted anonymously and posted for discussion. Discuss This | Submit Your Question | Subscribe

I’m working in the construction of 4-star hotel. The water storage tank is underground made from concrete and the pump room is located above the water tank. The designer specified the fire pumps to be vertical split-case type! In order to follow code, I proposed to install vertical turbine pumps instead of the specified vertical-split case.

The supervisor Engineer is insisting to follow the specification of the fire pump and pushing me to create an underground pump room in order to install the specified pump set.

Any recommendations to avoid this directive?

I have a bad flooding experiences with this this type of subgrade pump rooms.

​​​​​​Submitted anonymously and posted for discussion. Discuss This | Submit Your Question | Subscribe