Two Sprinkler Types, RTI, Hazard for Mezzanine?

12/28/2023

We have a showroom with an open mezzanine that takes up around 30% of the floor area. The bottom and the top of the mezzanine are office areas. The showroom has a ceiling height of 23-ft while the mezzanine has a ceiling height of 11-ft.

We designed the the showroom as Ordinary Hazard using standard response, extended coverage sprinklers (18' x 18') on the ceiling with the top part of the mezzanine also being protected with standard response, extended coverage. There are no walls on the top side of mezzanine.

On the flip side, we designed the bottom part of the mezzanine using Quick Response, Light Hazard (15' x 15' ) spacing since it's an office (Light Hazard occupancy).

However, since this is an open mezzanine with no walls separating between the two spaces, this means that both these areas would be considered one compartment. Under NFPA 13, sprinklers in the same compartment should be the same response type and hazard levels.

However, would the elevation difference and the mezzanine floor separating the two make it okay to have two different type of hazard level and response type?

If not, what about adding draft curtains?

Thanks in advance.

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9 Comments

R Jackson link

12/28/2023 08:34:34 am

I have never been accused of being smart, but I was taught, whenever possible, (and it is almost ALWAYS possible), to place outlets on mains 12 feet apart and sprinklers 10 feet apart. This uses less mains and more lines. Less mains and more lines=quicker install. Using extended coverage heads, when standard coverage will work, would be less heads, but longer pipes sizes. I am unable to wrap my feeble old brain around this. And yes, when I started designing, it was pencil and paper.
Based on the information given, is it not possible to space the heads like this?

Anonymous

12/28/2023 08:37:48 am

Is there a reason you cannot use QR EC at the deck and have the same head type throughout?

Franck

12/28/2023 08:49:28 am

Yes you can have different sprinklers at ceiling than the ones below the mezzanine. It is not good to mix sprinklers at the same level (below the ceiling, for example) as a single fire will operate different sprinklers.
This is not the case with a mezzanine: a fire below the mezzanine will operate the mezzanine’s sprinklers, and a fire not below the mezzanine will operate the ceiling’s sprinklers. So no confusion and no mix. But a draft curtain is necessary (and beneficial) to be sure you will keep the heat plume below the mezzanine and avoid the activation of the ceiling sprinklers.
This situation is not unusual with ESFR protection at ceiling and standard sprinklers below a mezzanine. And again, draft curtain to be provided.

Pete H

12/28/2023 08:51:45 am

In my opinion, no, you can't mix response types and because it's an open mezzanine, this is the same compartment.

Frankly even with draft curtains, the definition of compartment in NFPA 13 (2016 edition) 3.3.6 reads very specific rules on openings and their sizes and being completely enclosed.

The easiest fix since the ceiling protection is existing would be a 1:1 switch of the heads below the mezzanine for standard response heads.

But this is just my opinion, take with a grain of salt.

1/2/2024 08:47:58 am

Can't install SR sprinklers in LH unless it's a retrofit.

Agreed with Pete on the compartment definition.

Jesse

12/28/2023 10:08:57 am

You can mix these sprinklers protecting the ceiling level and below the mezz. We do this a lot in Storage where we have ESFR at the ceiling / deck and K=8 sprinklers below a mezz. area containing picking shelves to 8-feet or so. The picking area is a different hazard class, in this case OH2.

Fred Walker

12/28/2023 11:06:42 am

Concur with all sprinklers at the ceiling height being the same. Sprinkler below mezz deck may be a type appropriate to the occupancy below the mezz.
Code is not definitive on this so you still have to present the case to the AHJ and get their acceptance.

Dan Wilder

12/28/2023 12:44:42 pm

Firstly, above the mezzanine is described as office but it's stated that EC SR sprinklers are used? All light hazard areas require quick response (minus some exceptions that do not seem to apply here) so that will need to be addressed.

If the sprinkler is listed as both QR & SR (typically, the SR listing comes into play with the larger spacing and higher density), it would be allowed per 9.4.3.5 to be installed in the same compartment as the other QR sprinklers.

Interestingly enough, I cannot find a specific section on using a draft curtain for separation of response types outside of ESFR, and even then, use of a draft curtain or other means to trap heat is discussed only for a higher hazard design extension into a lower hazard area. The intent seems to be there, just not the language that I can find?

2019 Referenced
3.3.38 - Compartment, walls and a ceiling, lintel may be required based on opening size

9.4.3.1 - QR for light hazard (with exceptions)
9.4.3.2 - QR required within compartment (no exceptions apply)

14.2.5 - For ESFR & draft curtains

19.2.2 - Extension of high hazard

20.6.5.3.1 & 3.2 - ESFR & control mode sprinkler separation within storage

20.10.1 - Adjacent design hazards

sean

12/31/2023 06:19:19 pm

I think that being in the same compartment no matter the level still has to face the same issue. We don't want to mix different heads as the response times could have heads outside the expected area to activate sooner then over the fire.

Lets think the opposite. if QR at the ceiling would you permit SR heads below the mezz? No it could result in the QR heads activating sooner. There are just too many factors to take into account.

Two Sprinkler Types, RTI, Hazard for Mezzanine?

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