Where is "Bottom of Riser" for 7-Story Building?

4/17/2023

I'm working on an existing system in a seven-story building. There is an existing pump and piping which snakes its way through the building.

There is a pressure gauge at the inlet and outlet of the pump, but none afterward until 200' away from the pump room. The pipe branches off with a zone valve assembly with pressure gauge serving that floor area, and then upwards through the remaining floors with no gauge.

Zone valve assemblies with gauges are located on the floors above.

Now for my question - when performing hydraulic calculations, where would you indicate the "bottom of riser"?

Thanks in advance.

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24 Comments

Glenn Berger

4/17/2023 08:09:43 am

Typically the base of the riser is where the water supply enters the building.

I am curious to know - - you stated that the existing piping "snakes its way through the building." Does this mean prior to the fire pump and just the existing configuration in general? Regardless you need to insure that all piping and fittings are included in the calculations from the conducted hydrant flow test to the most remote hydraulically demanding area.

4/17/2023 09:30:55 am

The service comes into the building and runs for more than a hundred feet before the DCVA, then probably around 75 feet to the pump inlet, then the 200 feet stated earlier begins.

My calculations do take into account this piping as well, with information based on previous calculations.

Josh

4/17/2023 08:13:49 am

I'm with Glenn here. Typically I consider the base of the riser to be a standard 3' - 5' below where the base of the riser is from the supply in calcs to be safe. The frost lines I mostly work in are pretty shallow so it typically covers that too.

Eric R

4/17/2023 08:20:55 am

So going by the book, NFPA 13 considers each zone control assembly as the starting point for a "sprinkler system" assuming they have a control valve, gauge, flow-switch, and drain. If that is true then by the book you are required to hang a hydraulic placard at that location and that location would be your base of riser point.

In my opinion this is not a good policy as there is generally no test equipment to verify the hydraulic design installed at these zone controls, so having a placard that tells you the characteristics at that point is basically useless. My opinion is that your base-of-riser would be the outlet flange of the fire pump as it allows you to easily validate that any design changes you have made actually work.

In this case you would still want to hang a new hydraulic placard at the zone control for the system you modified to be in compliance with NFPA 13, and make sure to include a note on the placard stating that the flow and pressure on the placard are based on the fire pump outlet.

Dan Wilder

4/17/2023 08:30:28 am

Definition of a sprinkler system within 13

3.3.216* Sprinkler System.
A system, commonly activated by heat from a fire and discharges water over the fire area, that consists of an integrated network of piping designed in accordance with fire protection engineering standards that includes a water supply source, a control valve, a waterflow alarm, and a drain.

So the BOR of an individual system (which is what is typically calc'd) is that control valve (in my mind). Nothing is saying that there isn't a "main riser" controlling the building, but making a calc plate ladder at an individual riser that controls an entire building gets difficult.

I've seen it both ways, especially since some of those risers are open to the public and things go missing.

chad

4/17/2023 08:46:11 am

Agreed and to add to that:

3.5.10 Risers. The vertical supply pipes in a sprinkler system.

So as soon as goes from aboveground to underground is also a good reference point, though usually its the first control valve on the BFP.

Franck

4/17/2023 08:45:06 am

As indicated by Dan and Eric, Base of Riser (BOR) is at the alarm check valve, where you put the placard

I don’t like hydraulic calculation at BOR, and always ask to have it to the place you make the water flow test (connection to the city water grid or at discharge side of the fire pump).
That way you can check if your water supply is sufficient for your demand, despite possible fluctuations / degradations.

BOR is typically a US approach as it defines your sprinkler system downstream the alarm check valve and if you modify the connection upstream, it doesn’t change your hydr. calc. results.
But it does not help to make an analysis of existing installations with water flow (pump curve) results as you don’t have the friction losses from your BOR to the water supply testing point.

4/17/2023 09:37:10 am

There are also no alarm check valves in the entire system, just water flow switches at the zone assemblies.

Ryan Page

4/17/2023 08:56:27 am

I mostly agree with Eric, except I would not use the pump outlet as the BOR. As he stated, by the book, the BOR would be at the supply side of the control valve serving the system you are calculating.

That being said, an ADDITIONAL placard should be placed in the pump room on the discharge side of the fire pump. This additional placard would correlate with your most demanding calculation and reference the pump outlet instead of the BOR.

Because there is a fire pump, I have to ask, is there a standpipe or just a riser feeding all of the floors? If there is a standpipe, the standpipe calc placard would serve as the “additional” placard mentioned above.

4/17/2023 09:52:29 am

There is a standpipe as well that is served by the pump. The pipe tees off, and the standpipe routing is completely unrelated to the sprinkler piping. They don't share chases, or routes.

Eric R

4/17/2023 09:03:07 am

Longer Rant Incoming:

As someone who handles a significant volume of both NFPA 25 inspection work and design work for existing system modifications the way hydraulic placards, general information signs, and the un-defined location of "base-of-risers" are currently handled drives me batty.

Starting with the Hydraulic Placard:
NFPA has always utilized the "base-of-riser" as the location that the system flow and residual pressure should be calculated to FOR DOCUMENTATION ON THE PLACARD ONLY. This however is generally not the end point of a new system calculation as we are required to calculate back to a point where the water supply is known, which is generally a fire hydrant flow test for systems on public water.

Because of this inconsistency a vast majority of hydraulic placards we see during our inspection work have the incorrect flow and pressure data on them. This can be very problematic when you come across a system with no previous inspection records, and the 2" main drain test indicates a static pressure of 100psi, residual of 65psi and the hydraulic placard states that the system needs 350gpm at 75psi at the base-of-riser. Do I suddenly have an impaired sprinkler system, or simply bad data? Unfortunately this little mistake can cost quite a bit of money to investigate if I can't get my hands on the original hydraulic worksheets.

A very easy way to fix this would be for NFPA 13 to require that hydraulic placards state the flow and pressure needed at both the base-of-riser and at the calculation end-point. Most sprinkler design software provides this information already, and if both locations were required on the placard then the likelihood of using the wrong data would drop significantly.

For the Base-of-Riser Location:
In my opinion the value of documenting the hydraulic characteristics at a base-of-riser is that it gives a point where the design can be validated through flow-testing at a location generally accessible to a private inspector or designer.

With this in mind, I feel that the base-of-riser should be a point on the system that has the ability to perform a flow test. This could be the outlet flange on a fire pump as indicated above, or with the (relatively recent) advent of backflow forward-flowtest manifolds, directly after said backflow preventer.

Having both a previously documented hydraulic base-line on a placard, and a way to validate that the water supply at that point then allows a designer to make modifications up-stream of the point without having to worry about obtaining water supply testing on public utilities that could significantly slow down a design process. (actually not quite as there is still an issue of how the base-of-riser flow/pressure interacts with the water source flow/pressure when taking outside hose into account)

Having "base-of-riser" not be a defined term in chapter 3 of NFPA 13 should be corrected if for no other reason to make a determination on if the point should be located before or after the pressure loss of a backflow preventer. (the correct answer is after)

Lastly the General Information sign:
To go along with my above point on having the ability to measure flow/pressure at the backflow preventer test header. I think that this flow test, which is required to be performed at system commissioning, should be documented on the general information sign along with the original main-drain test results. These two pieces of data go hand in hand in allowing validation of the available water supply for as long as the system stays in service.

Ryan Page

4/17/2023 09:21:27 am

The flow and pressure needed at the calculation endpoint would be that of just one sprinkler. Calculations are based off demand, not supply.

Eric R

4/17/2023 10:43:00 am

Ryan,

I think this might just be lingo confusion. When I say calculation endpoint I mean the point where the total system demand meets the known water supply point.

As opposed to the calculation start point being the single most demanding sprinkler head in the design area.

Ryan Page

4/17/2023 09:27:56 am

Sorry, forgot to add that flow tests are required to be done within one year of submitting plans to the AHJ (I don’t currently have a copy of 13 in front of me so I cannot quote what section that’s from). So yes, you can do a preliminary design, but you will not be able to submit it for a permit.

Eric R

4/17/2023 09:41:24 am

I don't necessarily disagree with you, which is why I commented on the issue of base-of-riser flow testing not accurately taking into account outside hose requirements.

However as far as I can tell, performing system modifications that do not increase the system demand above the currently documented values on the hydraulic placard has generally been accepted by AHJs without requiring updated flow test data.

Dan Wilder

4/17/2023 11:47:07 am

Not sure how you're using a main drain to justify hydraulics...that test is to only show history of the water supply and trigger an investigation to a water supply piping obstruction/closed valve or possibly a new hydrant flow test. At that point there is enough information to start reviewing hydraulics within the building.

Jumping straight to fixing the above ground piping without understanding what is going on between the public supply and the main drain location isn't the intended route.

Eric R

4/17/2023 01:50:06 pm

(Dan, this wall of text isn't particularly aimed at you minus the aboveground piping part :) , it's just a hot topic of mine at the moment)

When we perform an NFPA 25 inspection for a new customer, any main drain results that show a residual pressure below the pressure on the hydraulic placard gets noted down as potentially needing review unless we have other historical data like an initial acceptance test result or some other documentation(generally previous inspection tags from within a year or two of the system age) that make it clear the reading is acceptable. We don't label this as a deficiency, but as a simple comment for review.

I realize that this goes beyond the strict scope of 25, but it makes sense to document the disparity to protect our liability. If there was ever a fire event and the system performed poorly the owner's lawyer would have a field day going all "As an industry expert didn't you realize that reading could have indicated a problem?!?" if we didn't.

I'm not sure where you are getting us jumping straight to changing aboveground piping though. When we find these disparities we will try to get access to the original contractor's certificate or hydraulic worksheets because quite frequently the placard is simply documenting the wrong node and can be easily corrected with a few minutes of review.

If these documents aren't available then determining if the main drain test is acceptable can not be resolved, and it should be left up to the AHJ on if they want further investigation to occur. From my experience they generally want it investigated, which costs money.

I agree that not having a good understanding of what is happening between the public supply and the main drain is the issue at hand. The question is how do you resolve whether or not the system is capable of functioning properly when the placard is potentially incorrect and there is limited ability to verify the water supply without having to involve the public utility.

I've been told that one should just assume the placard is correct. I'm not willing to accept that when my experience has been they are wrong more often then they are correct. Heck I have pictures of placards with negative pressures on them because the system included a fire pump, and whoever created the sign just pasted in the topline water supply residual pressure without any introspection at all.

Requiring two sets of data on the placard, one for the base-of-riser, and one for the water source would force people to at least recognize there is a difference between the two.

Dan Wilder

4/17/2023 10:03:38 pm

No issue documenting an issue on a separate form in addition to the standard NFPA 25 form however the main drain test does nothing to verify overhead design....it's there to be an easy check of possible underground or supply issues. Now with the forward flow testing for backflows, I would love to see the hydraulic BOR be placed there in the future (for in building or dedicated single building riser feeds at least).

I've got inspector's and fire officials that jump straight to needing overhead fixes with main drain tests when there is no correlation to a measured flow, even a diminished flow doesn't paint the correct picture as the error % is huge when comparing the two on a chart...now, after we exhaust the observation and confirmation phase for anything between and consult the water department for historical data in the area, there may be a water supply issue identified.

https://www.meyerfire.com/blog/advantage-of-flowing-more-water-in-a-flow-test

Jessica L

8/20/2024 02:29:21 pm

"Base-of-Riser" terminology awareness is much-needed. I'd love for the term to be more clearly defined by both NFPA, and FM.

Anthony

4/17/2023 09:17:53 am

The point of the BOR hydraulic point is so that your hydraulic placard that is hung on that riser can be examined and compared to the current pressure gauge on the system. When you preform your quietly main drain test/ water flow alarm test you can see if the residual pressure is greater than the system placard shows required. If the residual pressure is less than 10% of the requires system pressure then you have an impairment.

For that reason, I like the BOR node at the riser where you're going to test the system. You're way more likely to have the inspector actually look at the riser, placard and gauge and care if all the information is right in front of them. Compared to having to do math or think about where the BOR system incoming is.

Eric R

4/17/2023 09:52:10 am

Anthony, you are on the right track, but it is important to clarify that technically you should not be comparing main drain results to the hydraulic placard.

Main drain tests in NFPA 25 should be compared to the initial main drain test performed at system acceptance and then to prior main-drain tests performed at previous NFPA 25 inspections. A 10% reduction in this comparison is what creates the deficiency.

You can't compare the main drain test directly to the hydraulic placard (even if it is showing the correct data) as the main drain test does not have a GPM component, and also does not take into account any additional residual pressure reduction that would occur if outside hose allowance was applied to the water supply.

However flows of a main-drain that indicated a residual pressure below what is stated on the placard should be noted as such on the inspection report as it may require further investigation. In multiple instances that this has happened to me we have performed water supply validation testing and then supplied signage at the riser with an updated "initial main drain test result" that can then be used for NFPA 25 purposes going forward.

This is why more clarity on the system signage is so important, and why full BOR flow tests should be performed and recorded at system acceptance for future referencing.

James Art

4/19/2023 11:19:20 pm

Yes, a 2" drain is intended just to watch the water supply, and compared to previous tests.
I have found several partly closed valves, sometimes key valves, paved over, and some obstructed pipes.
In one case there were 3 parallel systems, and one was much lower, but no one did anything, just wrote it in the tally. for several years.

Factory Mutual, and other insurance companies had charts for Long Drains and Short Drains to estimate the flow from a 2" drain test.
We used these to do a quick and dirty analysis of the water supply,which can then be compared to the required water supply,

Another thing that can be done is add a piece of straight 2" pipe and use a pitot tube to get the flow.

In Ca, AHJ's are supposed to retain plans and calcs for most buildings as long as the building lasts. But many do not, and getting that info is often not possible after a few years.

Another recurring problem in CA is AHJ's that force the addition of backflows, and then the system needs to be upsized.
State law and the CaBC prohibit this in most cases, but the water cos just ignore that law, and are bigger than each client.

Peter H

4/17/2023 10:34:23 am

For the full building? At the pump outlet.

For the individual systems in the zones? At the fitting on the supply side before the alarm valve in the respective floor control valve assemblies.

After that, I'm just echoing what Eric R has already posted.

Cory

5/25/2023 03:44:55 pm

I typically consider the base of riser as the zone control valve assembly as that is where you put the NFPA 13 calc plaque. Which would be after a fire pump, at the inlet to BFP or individual risers if you have multiple. I usually don't see base of riser's outside of the building/riser room.

Where is "Bottom of Riser" for 7-Story Building?

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