Municipal Water Distribution Residual Pressures - NY 1

[Tibbs01]

I am evaluating a water distribution system on a college campus in New York and am struggling with pointing to a regulation that stipulates required residual pressures that need to be maintained during fire events. In particular - maintaining residuals in the system while a fire is somewhere else nearby (i.e. not maintaining a residual in the building on fire).

10 State Standards specifies a water system needs to maintain 20 psi "at ground level" under all flow conditions (including fire flows).

My concern is that providing only 20 psi at ground level will result in draining the upper portions of taller buildings on the campus. It seems to me that the intent of the regulations are to not create a health hazard resulting from a siphoning/back flow condition, however that is what would happen in taller buildings if pressures are reduced to 20 psi at ground level.

It seems that a prudent recommendation would be to install domestic booster pumps in the taller buildings to maintain positive pressure in the building's plumbing system during periods when the external water system's residual pressure is not sufficient to maintain adequate residuals in the building.

Can anyone help by directing me to a regulation/code that specifies that?

 

[cvg]

10 state standards are generally interpreted to apply to the publicly owned part of the water system. That is, the system up to the point of delivery to the customer (meter). Once you get beyond the meter your standards are generally controlled by various building codes or owner / developer standards. Tall buildings often use booster pumps. 20 psi delivery pressure is generally acceptable only for 1 - 2 story buildings.

 

[Tibbs01]

Thanks cvg. I understand that 10 States generally applies to municipal systems, but I am of the opinion that this campus is really in and of itself somewhat of a municipal system.

It doesn't have a treatment works, but it certainly has miles of distribution piping, large industrial and domestic demands and pump stations. It is significantly larger than many small communities I have worked for in the past that are held to 10 State Standards. The owner doesn't have any standards to speak of, and they really want a hard regulation or code to stand by to justify the cost of improvements. I need help finding that code.

 

[bimr]

It will be listed in the building code. Here is an example from the International Building Code:

FIRE-FLOW. The flow rate of a water supply, measured at 20 psig residual pressure, that is available for fire fighting.

http://www2.iccsafe.org/states/oreg...ix B_Fire-Flow Requirements for Buildings.pdf

You will have to determine the building code that has been adopted in the location of your project. Search through the building code.

 

[Tibbs01]

Thanks bimr. The requirements for providing fire flows and pressures to a building on fire are clear to me. What I am struggling with is providing adequate pressure to upper floors of high rises while a nearby low rise fire is occurring and its(low bldg) fire flow demand is lowering residuals available to the high rise. High fire flows adjacent to the high rise will cause upper floors of high rise to have no pressure, creating a health hazard.

 

[bimr]

One would want to maintain a minimum 20 psig pressure at all times, so you would design for 25-30 psig pressure. A plumbing engineer would typically design the building plumbing system with pressure zones throughout the building.

The link should clarify the issue.

A well-designed building is usually divided into pressure zones between eight to 10 floors per pressure zone depending on the floor-to-floor height. Given a 50-story building, the 50th floor usually has a governing pressure around 25 to 30 PSI and each story height of 10 feet adds 4.33 PSI to the pressure as you go down in the building from the top.

http://www.plumbingengineer.com/sept_09/code.php

 

[cvg]

the water department can only provide water to the point of delivery and thus can only be responsible for meeting the standards at that point. Even though you are working on a "public" project, the water department cannot be responsible for anticipating how high the buildings will be on campus or how many miles of waterline will be installed or anything else that is done on campus. As the site engineer / developer that is your responsibility and you will have to follow building codes. You may be able to get some good information on local requirements if you contact the fire marshall.

 

[bimr]

Another link:

http://www.newcomb-boyd.com/pdf/high-rise article.pdf

 

[Tibbs01]

Great input everyone. I agree that once on the "building side" of the regulations, that the building code will govern. As I look at the NYS plumbing code - it states that a booster pump is required when "public water main is insufficient to supply minimum pressures specified in the code" (based on the fixtures being served). The question becomes: do you consider the substantial pressure drop in a 'public' water system associated with a nearby fire as the 'public' system being unable to provide adequate pressure? The campus has monitored pressures at top floor fixtures during periods of peak DOMESTIC demand and they are around 30 psi. However, modeling of large fire demands in the system shows that the buildings will have no pressure at top floor of high rises during a fire nearby.

 

[coloeng]

Each individual building should have a back flow preventer. This will prevent the water from flowing out of the building due to the fire fighting at another building on campus. It won't prevent water from being drawn from the higher floors because of usage on the loweer floors.

 

[cvg]

the 20 psi residual is measured at the nearest public fire hydrant attached to the "city" side of the property line or at the meter. This does not guarantee that you will have any pressure at the top of your buildings during a fire or at any other time. Your analysis shows that the "private system" has inadequate pressure to supply water to the top of the buildings.