Does 52,000 SF System Area Apply Horizontally?

12/18/2023

We have a car park area which is part of a bigger development that we are sub-dividing into different pressure zones due to it being a very tall building. The three levels of car park in total are less than 65-ft (20 m) high, but they are very long and wide. My question is about sprinkler control valve areas.

I know for ordinary hazard the restriction per floor from one riser is 52,000 sqft (4830 sqm) with no restriction as you go up.

Does that mean for a wide, low-level building, say on 1 level, do we need a system riser for each 52,000 sqft?

This seems pretty onerous to me, as FM Global do not even insist on this. Here in England, the restriction is 12,000 sqm x 10 floors per valve.

I'm being asked by the authorities to allow the valves, but is that restriction of 52,000 sqft (4830 sqm) per valve set on a single floor set in stone?

Can we do something based on hydraulic calculation that is more user friendly?

Thanks in advance.

13 Comments

Glenn Berger

12/18/2023 08:10:59 am

The 52,000 square feet is published in NFPA 13, as such that is the closest to being "set in stone" as possible.

franck

12/18/2023 08:26:00 am

No deviation allowed.
And I would fully discourage to go further with occupancies like a car park.
If you are in the UK, you should be aware of the big car park fire at Sylvester a few years ago in Liverpool.

David Kendrick

12/18/2023 09:36:30 am

Researching the reason for the 52,000 square feet might give reason to consider modification.
Originally pipe schedule systems were calculated using pencil, paper, slide rules and logarithmic tables.
There were two spacing rules for fire sprinklers, 130 square feet and 100 square feet.
The maximum number of sprinklers calculated was 400. So Light Hazard, Ordinary hazard I, II & III at 130 square feet times 400 heads is 52,000 square feet.
Extra hazard I & II is 400 heads times 100 square feet for a total of 40,000 square feet.
At the time calculating a system was labor intensive using the technology of the day.
With today's technology that really isn't an issue if the pipe layout is known. However insurance companies risk / loss data is structured around the system size limits.

I was privileged to have worked for two of the men that did a lot of work to creating computer programs that sped up system calculations. Linwood McCool and Hasu Doshi were acknowledged in the NFPA handbook several years ago for their work along with others on the hydraulics committee.

52,000 and 40,000 aren't magic numbers. They're the result of the practical limitations at the time system size limits were set up.

Kim O

12/18/2023 09:52:06 am

Yes, 52,000 square feet is as large as a system can be on one level. It is in NFPA 13. That's for Light and Ordinary Hazards. It's 40,000 for Extra Hazard.

Casey Milhorn

12/18/2023 09:55:37 am

I believe there is a proposed change coming to NFPA 13 to increase the areas by 150%. I haven't seen an update on this in the last month or so. Not sure where it currently stands.

I agree if you can calculate it, it should be allowed. The only concern I would have is when a system has to be down for maintenance or modification purposes. There can definitely be an argument about limiting area for that. I like where NFPA 13 currently falls on zoning by floor.

But until NFPA 13 is changed and adopted by the local AHJ (as part of the applicable building code) then you will more than likely be required to keep it under the required sqft area.

Dan Wilder

12/18/2023 09:59:06 am

As allowed, and depending on which edition year being referenced, yes 52K ft² is the maximum for any single zone regardless of building height or breadth of a structure for the occupancy you stated.

If the zones need to match the ventilation zones, that is more a performance-based approach. This would very likely lower the total system areas to match the ventilation zones which is a common approach for several large footprint occupancies I have worked on in the past.

As Franck was alluding to, anything with car lifts and/or stackers including those newer automated retrieval units, EV parking and/or EV storage should all be reviewed heavily for design approaches including egress, ventilation, suppression, water supply, and drainage.

Ray Hardy link

12/18/2023 10:10:08 am

Thanks to everyone for your responses- much appreciated. Just to clarify, can a sprinkler control valve set serve risers in individual stair cores, with zone valves on, each covering 52,000 ft2 or is the restriction on the control valve itself covering 52,000 ft2 per floor? If we had one set of control valves covering 2 risers in a stair could we allow 52,000 ft2 x 2 on the same floor with a branch from each riser? Hard to put into words so I hope I’ve made it clear. Thanks again.

Connor R

12/18/2023 12:44:39 pm

NFPA-13-2019 4.5.1 states "The maximum floor area on any one floor to be protected by sprinklers supplied by any one sprinkler system riser" shall be 52,000 sq ft for Ordinary Hazard.

NFPA-13 defines System Risers as "The aboveground horizontal or vertical pipe between the water supply and the mains (cross or feed) that contains a control valve (either directly or within its supply pipe), a pressure gauge, a drain, and a waterflow alarm device."

This means that if you have exceeded the maximum area that can be fed from any one system riser on a given floor, an additional riser must be provided back to the water supply. The point of connection to the water supply is typically adjacent to the building water service entrance, although some sites will have underground or aboveground water supply loops to feed the fire protection systems.

You could potentially argue for an "express main" type situation where you have one larger riser control manifold at the water service entrance which splits to feed both stairs, although that would leave the whole system vulnerable to being taken offline if anything happens to that single riser. If you're already running a riser up each stair, it is prudent to run them both all the way back to the water service entrance and have separate control valves, waterflow alarms, pressure gauges, and drains for each riser.

In general, if the area per floor exceeds 52,000 sq ft, an additional sprinkler riser is provided back from the water service entrance or from a site water supply main. This would allow up to 52,000 sq ft to be protected by each riser for a given floor for Light and Ordinary Hazard occupancies, for a maximum of 104,000 sq ft split across two systems. Areas beyond that would require additional risers.

12/18/2023 10:16:46 am

The size limitation is not only for technical reasons related to layout and optimized pipe sizing. Of course systems are better designed today than in the old time of pipe schedule installations. But there is still a financial or risk limit.
As indicated above, it is not uncommon to have a sprinkler system impaired. If your sprinkler system is impaired on 52 000 sq ft (or less) it is a lesser financial / risk exposure than with a much larger installation.
Many insurance companies in the US make loss estimates based on a ´Normal’ scenario (what if there is a fire and everything works as it should), called NLE (Normal Loss Expectancy), and a more critical scenario where one system is impaired (pump, sprinkler riser…), called PML (Probable Maximum Loss).
The larger the sprinkler system, the bigger the PML and the more expensive the insurance premium.

Jesse

12/18/2023 12:49:39 pm

Yep, the 52,0000 is pretty solid. And all of the reasons described in replies above mine are why

Dwight Havens

12/18/2023 04:01:14 pm

I think an explanation of the reason for the size limitations would help. This will require research in the NFPA codes and standards, and the building codes that were in effect at the time this requirement was established. My understanding is that the area limitations were based on a desire to minimize the risk presented to the building and the occupants, should a system be out of service. From a code perspective, this limits the resource needed to establish a fire watch, or the need to shut down the use of that portion of a building while the system is out of service. I also seem to remember, early in my career, that the 52,000 square feet, (or 40.000 square feet in some cases) corresponded with the maximum allowable fire area at that time, thus subdivision to limit loss potential was also used.

Pete D.

12/19/2023 09:20:41 pm

It's per level.
If your structure is 53ksqft per level and 3 levels, you will need 2 risers. If you have a long, narrow structure, and you're slightly over the maximum area allowed per system, it may play in your favor that you're required to add a second system riser from a hydraulic design standpoint. Shorter runs will keep the pipe diameter down.

sean

12/31/2023 06:06:13 pm

anytime you go over 52k sq.ft. you need to have another system.
Many times once you hit 3 floors you need to start looking at floor control systems from one of the many requirements. It also depends on what version, there have been some recent changes.

Does 52,000 SF System Area Apply Horizontally?

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