Ponds and the wrong pump problem

[maudedog]

Here's my problem....I've got a client that purchased a really nice booster pump system on skids. One diesel and one electric pump, each rated for 3,000 fire flow. I didn't do it, but I inherited the two horizontal split case pumps that is comes with. It was designed and purchased when they were going to put in a 1MG steel tank and boost from that to the fire system. The booster is sitting on site in the wrapping, looking for a home.

Now somebody changed their mind and they write the checks so they get to do that. The don't want a steel tank anymore, they want to build a lined reservoir. You can already see the problem coming.....

The reservoir will be earthen and then lined with an HDPE geomembrane...no big deal. However, I'm dealing with a flat site and the booster I have. If I balance the earthwork, I end up having to put this booster in a below grade vault as the pumps require about 3' of submergence. The other option is to keep the booster at grade and import material to the site (about a 1/4 million for that).

I think its an easy decision, bring in the dirt and keep that pump station at grade.

Most of the problems the vault creates can be dealt with (HVAC, Electrical, etc.). These are just engineering problems. My question is, is there a problem with NFPA in setting the booster below grade. I can't seem to find any references to this. I think its a horrible idea regardless of NFPA, but would like to know if its prohibited.

To me the obivious problem is what happens under flood conditions. We are not in the 100 year floodplain, but the potential pretty much always exists in some form. Flood and fires go together. I don't see a way to have the booster operate in a vault for any significant time if there is a flood and fire simultaneously.

I don't want to be the guy that put the back-up generators in the hospital basement in new orleans. we all know how that turned out. However, the client may want to pursue this as the "cheaper" option despite my feelings on it. I'd really like to have something to point to and say "what you want is not allowed". Any thoughts?

As a back-up plan to NFPA, I'm looking to the insurance carrier. I believe that some carriers for plants, Facotry Mutual, specifically won't insure a system with pumps below grade. Still trying to root that one out with their carriers.

 

[LCREP]

Looks like you will need some elevation on your reservoir based on the sections below.

From NFPA 20, 2010

4.14.3 Suction Size.
4.14.3.1* Unless the requirements of 4.14.3.2 are met, the size of the suction pipe for a single pump or of the suction header pipe for multiple pumps (operating together) shall be such that, with all pumps operating at maximum flow (150 percent of rated capacity or the maximum flow available from the water supply as discussed in 4.6.2.3.1), the gauge pressure at the pump suction flanges shall be 0 psi (0 bar) or higher.

4.14.3.2 The requirements of 4.14.3.1 shall not apply where
the supply is a suction tank with its base at or above the same elevation as the pump, where the gauge pressure at the pump suction flange shall be permitted to drop to ?3 psi (?0.2 bar) with the lowest water level after the maximum system demand and duration have been supplied.

Regarding flooding, see below

4.12.1* General Requirements. The fire pump, driver, controller, water supply, and power supply shall be protected against possible interruption of service through damage caused by explosion, fire, flood, earthquake, rodents, insects, windstorm, freezing, vandalism, and other adverse conditions.

Regarding insurance companies, you can always find one that will write the coverage for the correct $$$$, getting them to pay when you have a loss, well that is another thing!

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[b1ueshift]

There are lots of pumps in basements.

You should be able to have life safety equipment in the basement of a building provided that the buidling was not providing an essential service. You don't have to design for a fire and a flood to occur simultaneously when the building is fully occupied.

If your building is an emergency services building (hospital, police etc), then the building will need to remain occupied after a natural disaster so the building services will need to be kept running without interuption.

If you have a non-essential building (like a process plant for example) then, the building will have to be taken out of service if the fire pumps are damaged in a flood untill such time as the building can be repaired.

I wouldn't be too worried about insurance - having a building seriously damaged in a natural disaster should be less than a 1 in 1000 year event.

 

[chicopee]

Did you get the pump characteristic curves which include graphs of the NPSH. From that info, you should be able to make an engineering determination.

 

[b1ueshift]

I'm not contradicting what LCREP is saying regarding the standards, but the standard leaves a lot open to interpretation.

Your pumps should be protected to an appropriate standard, but what standard is appropriate? That will be different depending on how essential your building is. A hospital is more essential than a warehouse and requires a higher standard of protection.

 

[DavidCR]

I saw two similar cases with pumps bellow grade.

In one, an industrial plant, they build a dike wall around the pump to prevent flooding, one positive aspect was that they put the controller outside this dike for easier operation access. In the other, an office building, they installed a small pump for the flooding case.

I didn´t liked both solutions but they got the AHJ approval. I agree that the NFPA 20 is not clear enough, even FM sheet gives you room for interpretations in an obvious risky condition.