Combined Domestic/Fire 2-inch Service OK?

10/31/2022

I'm dealing with a situation now where we are completely renovating an old mixed-occupancy property and the plans were drawn and approved with a 2-inch incoming service for both the residential domestic water and the fire suppression system.

Now that the fire sprinkler contractor is ready to install, and the fire chief reviewed plans for the 2-inch pipe, the fire chief says he won't approve it unless we install a minimum of 4-inch incoming pipe from the main.

The architect says the city already approved the pipe size. Fire Marshal says no.

Anyone have code/insight to support either way?

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

10 Comments

Dan Wilder

10/31/2022 08:07:12 am

First question is - Were the calculations performed with both the domestic supply and the fire sprinkler supply combined? (13-22 * 5.1.3.3).

If the calculations did include domestic and there are no amendments to the fire code, I would request a re-review of the decision and request what code/standard/amendment is being referenced to justify the redline.

If they didn't, comply with this section or have the UG size increased accordingly.

Unless there is a fire department approval, plans reviewed will not carry any credibility regardless of the other departments approving the plans (we fire protection contractors aren't the only red headed stepchildren, we just live in a different house).

Todd E Wyatt

10/31/2022 08:25:35 am

2022 NFPA 13 states :

Chapter 5 — Water Supplies
ENHANCED CONTENT
Chapter 5 contains the minimum requirements for the various water supply sources that provide water to sprinkler systems. The effectiveness of any sprinkler system design depends on the adequacy of its water supply in terms of its ability to provide the required demand for flow and pressure when needed. A failure of the system to control or suppress a fire can result in significant damage or loss of property and possible loss of life. Unless the sprinkler system discharge criteria can be satisfied by the water supply in terms of pressure, flow, and duration, the system will not perform as intended. Sprinkler system design considerations, such as sprinkler spacing, hazard classification, design density, and pipe sizes, will have little or no influence without sufficient water.

5.1 General.
5.1.2 Capacity.
Water supplies shall be capable of providing the required flow and pressure for the remote design area determined using the requirements and procedures as specified in Chapters 19 through 27 including hose stream allowance where applicable for the required duration.
ENHANCED CONTENT
As with all components critical to the effective operation of the sprinkler system, water supply sources must be reliable. The sources must be capable of meeting the system demand at all times. Regardless of how well the sprinkler system was designed and installed, if the water supply fails, the sprinkler system will fail. If the water supply is taken from a municipal waterworks system, potential future degradation of water supply conditions, as well as seasonal and daily fluctuations, must be considered.

Additionally, waterflow tests should be conducted on a routine basis to monitor the condition of the water supply. Over time, water supply systems are likely to be degraded by pipe corrosion, scale buildup, and inadvertently closed or partially closed valves. The impact of future users of the water supply also must be evaluated. In addition, if water supplies employ fire pumps or water storage tanks, that equipment is subject to certain requirements to maintain its reliability. NFPA 25 further requires that specific inspection, testing, and maintenance activities be conducted to ensure the integrity of the water supply.

Where a waterworks system serves as the sprinkler system’s water supply, 19.2.3 requires that the supply be of sufficient capacity to meet the sprinkler system’s discharge criteria, any inside hose demand where such equipment is provided, and a waterflow allowance for outside hose. Paragraph 19.1.6.2 requires the outside hose allowance to be added either at the connection to the water main or at a yard hydrant, whichever is closer.

Regardless of its arrangement, the underground supply must have sufficient capacity to satisfy the calculated system demand, based on the selected design approach from Chapter 19 or Chapter 24, the protection requirements from Chapters 20 through 23 and Chapter 25, and the occupancy requirements from Chapter 27. NFPA 13 requires fire pumps and water storage tanks to be sized based on the systems they serve, but in all cases, the supply must require no human intervention to operate and must be capable of supplying the system for the necessary duration.

5.1.3* Size of Fire Mains.
A.5.1.3
For typical combined domestic/fire sprinkler demands, systems with 4 in. (100 mm) pipe or larger typically do not need to include the domestic demand in the calculations because it is such a small fraction of the total flow that it does not make a significant difference in the results. But for situations where 4 in. (100 mm) pipe is used for the combined domestic/fire sprinkler systems and the domestic demand is considerable, then the domestic demand should be included in the calculations. Generally, pipe that is 6 in. (150 mm) or larger can carry combined domestic/fire protection demand without any consideration for domestic demand being necessary.

5.1.3.2
Sizes smaller than 6 in. (150 mm) for fire mains that do not supply hydrants shall be permitted, provided that hydraulic calculations show the main will supply the total demand at the appropriate pressure.
ENHANCED CONTENT
Private fire service mains must be at least 6 in. (150 mm) in diameter where they supply hydrants. In some cases, the use of a minimum 8 in. (200 mm) pipe for dead-end mains is advised. Where the fire service mains do not supply hydrants, they are permitted to be sized based on hydraulic calculations, or they are permitted to be as large as the riser under certain conditions. Fire mains need a water supply sufficient to meet the demands of the sprinkler systems, inside hose, outside hose, and other anticipated water demands.

5.1.3.3
Where a single main less than 4 in. (100 mm) in diameter serves both fire systems and other uses, the non-fire demand shall be added to the hydraulic calculations for the fire system at the point of connecti

James Phifer

10/31/2022 08:27:53 am

Agree with Dan, should be OK per code as long as you include the domestic demand in your calculations. You'd need good water pressure to be able to calculate NFPA 13 demand and domestic through a single 2" supply line though.

Dewayne Martinez

10/31/2022 08:42:51 am

Tyco dies make a RAPID RESPONSE Model RSV-1 Residential
Shut-Off Valve that is UL listed in 2" to be used for NFPA 13 installations. It eliminates the need to account for the domestic demand in your hydraulic calculations. Might be worth a look.

Alex

10/31/2022 08:34:26 am

Hi,

NFPA 13 (2013) 24.1.3.3 states that "a single main less than 4 inches in diameter serve both domestic and fire systems, the domestic demand shall be added to the hydraulic calculation.."

Can you confirm and prove that the system has been calculated with the domestic demand? If so, I agree with Dan in requesting the code reference.

Thanks,
Alex

Jesse

10/31/2022 09:39:08 am

I'm doubtful that a true demand calc was done.

Manny Rios

10/31/2022 01:09:41 pm

Regardless of the pipe size approved by the city, the AHJ is the Fire Chief/Fire Marshal and they have the last say, not the city/architect. Good luck!

Mike

10/31/2022 03:46:29 pm

Arguing with an AHJ is like wrestling with a pig in the mud. Pretty soon you learn the pig enjoys it. Why argue? Change it to 4", get a CO and move on. This is not the first time this has happened and won't be the last.

Chris

11/1/2022 02:27:05 pm

I agree, as long as the demand of the domestic is added at the point that the water supply splits; one side to fire and one side to domestic you are ok. But if the AHJ says that is a no-go then try to get a CO and press forward. Personally I don't like the water supply to be smaller than 4" since it gives you more flexibility in the future whether its use change or the city supply degrades.

sean

11/8/2022 07:22:11 am

early MEP plans probably did not include any calcualations. I can we why they are throwing a red flag unless there are sprinkler hydraulic calcs to back it up

Combined Domestic/Fire 2-inch Service OK?

Leave a Reply.

ALL-ACCESS

SUBSCRIBE

COMMUNITY

YOUR POST

PE EXAM

FILTERS

ARCHIVES

PE PREP SERIES