Calc Shoe Store Remote Area by Ignoring Walls?

1/3/2022

We have submitted plans for a new shoe store in an existing mall. The entire space is about 4,400 sqft and the stock room is 840 sqft with full-height walls.

The plans reviewer is requiring us to revise and resubmit using the calculation method in NFPA 13, 2016 Edition, citing Section A.23.4.4.2.

We are coming up short and the main (distribution pipe) is limited to 6".

Does this requirement seem reasonable?

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7 Comments

Dan Wilder

1/3/2022 07:32:14 am

I'm under the assumption that Room Design was the original hydraulic approach (I don't see an annex section for 23.4.4.2)? Does the space comply with the Room Design approach as defined in 11.2.3.3 & 12.10?

Even if it does, I would think if the main sales floor would require a full 1500 FT² design area and the HMRA would be just as bad?

Mike L

1/3/2022 08:02:38 am

A little more information is needed to give a complete, definitive response/advise.

My guess is you were calculating the Stock Room only utilizing the Room-Design Method of hydraulics. That is acceptable if the stock room is separated from the rest of the space by rated partitions. I would agree with that approach as Stock Rooms are generally more hydraulically demanding than the Sales Area. BUT the separations and the use of the Room Design method need to be communicated on the drawings so the AHJ is aware of that approach.

If the AHJ is recommending the Density Area method, then the 1,500 sf area is selected for the most hydraulically demanding area and ignoring walls. As you mentioned, your calculations do not work doing so. (retrofits of existing systems can be problematic that way), then perhaps you can utilize the area reduction allowance under section 11.2.3.2.3.

Whichever method you use, all the pertinent information needs to be indicated on the plans so it's clear to the AHJ what's being presented.

Travis Mack link

1/3/2022 08:13:54 am

What is the design density you are shooting for in the shoe storage area. Since many of these contain expanded plastics, you may be hitting the criteria for EH2. I have seen this many times in shoe stores. It is quite the challenge for a typical OH2 shell design. However, if you don't meet the criteria for room design, then you would need to extend past the walls and get the proper design area.

But, there is one option you may be able to use. Look at 23.4.4.2.4. This will require you to calculate the entire area and add a "phantom flow" to make up the difference if any. So, if you are EH2 criteria, then you could use high temp sprinklers and get the design area to 2000 sq ft. You then calculate the 846 sq ft. If the demand is <800 gpm, then you need to add a phantom flow to make up the difference to get to 800 gpm. Also, there is a 500 gpm hose allowance for that.

If you are able to use OH2, then you could possibly do a QR reduction and still apply the criteria for 23.4.4.2.4 since you are still less than the minimum design area for QR reduced OH2.

Hopefully that helps some.

Glenn Berger

1/3/2022 08:15:25 am

More information is required. Is there a fire rated separation between the spaces? What was originally submitted to the AHJ for approval?

Anthony

1/3/2022 08:20:57 am

Any mercantile space will be OH2 minimum, I'm assuming this store room has storage less than 12' high. So you'd be looking at similar hazard. Even if you are using room design the sales floor should require the same density over the whole floor thus the 1500 sq ft would be best used in this scenario.

Alex

1/3/2022 09:02:38 am

Very common approach having the stock room designed utilizing the room design method. Make sure its clearly shown that the room is rated. Shouldn't be a problem if the information is portrayed correctly.

Thanks,
Alex

Jesse

1/3/2022 09:03:52 am

You're in a tough spot.

Room design is challenging because you may not have adequate listed fire separation. I rarely see adequate listed separation between these areas. As such, a CMDA approach and full design area is indicated.

The sales floor is OH2 at best. But the stock room may indeed be a higher hazard class. We get wrapped up in the magic 12-foot number, but remember that only is a benchmark for Class I-III. Class IV, Group A, and Expanded Group A is lower. You may very well have expanded Group A so your threshold is 5-ft and you'll need to protect as EH2

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Calc Shoe Store Remote Area by Ignoring Walls?

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