Does a Pendent (Horizontal) Meet NFPA 409?

1/11/2024

We have a steel aircraft storage hanger Group 1. It's approximately 50-ft high with exposed steel columns requiring a fire rating per NFPA 409-2022 Edition.

The steel will not be fireproofed but will be protected with sprinklers in accordance with NFPA 409 5.6.3.4.

Can pendent sprinklers, installed sideways, be used to satisfy NFPA 409 for column protection?

In the past we have protected the columns with sidewall sprinklers spaced according to 409 and on alternating sides of the column. Then the sidewalls were changed to pendent sprinklers installed horizontally to provide better spray distribution on the columns as the sidewall spray tended to (in theory at least) bounce the spray back in stead of vertically.

This approach has been accepted by EOR and AHJs alike.

NFPA 409 states that "wetting of the lower sprinkler should be considered" although multiple level sprinklers were never used. I'm not sure how this plays in.

I recall reading that pendents installed horizontally could be used for column protection due to better spray distribution, however, I cannot find that in code.

The client is not open to fireproofing or intumescent paint; column sprinkler protection is in the bit and is going to be used.

All is appreciated!

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7 Comments

Dan Wilder

1/11/2024 07:54:48 am

There are several sections within NFPA that state "Sidewall" specifically, others just reference nozzles or open-head sprinklers along with the GPM requirements based on area of coverage. I'm not seeing a 409- 5.6.3.4? You did not specify if the sprinkler protection was a closed or open sprinkler design. IMO, if closed, stick with a sidewall, if open, allowable in any orientation. If the EOR/AHJ has bought off on the AMM approach, document appropriately and pipe-on!

13-22'
20.14.2.2.4.1 - indicates sidewall
20.15.2.1 - indicates sidewall

409-22' - Only indicates "discharge devices" within 7.7.3 (and subsections) but requires the 10' vertical distance AND the 0.25 GPM/FT² wetted area. The intent is wetting in a downward direction hence the 10' max vertical requirement and I'm not onboard with providing coverage "upwards" from a pendent installed sideways or what benefit that has unless there are obstructions internal to the webbing (stiffeners) that are trying to be accounted for.

There is reference to NFPA 15 (22') where 7.4.3.4 applies and you have described within the question for protection.

The advantage of a sidewall would be the nearly 180° coverage at the top of the boss fitting allowing the sprinkler to essentially be buried within the flanges of the column and still available to provide the 100% wetting (pipe outlet right to a sprinkler instead of addition pipe/fittings for positioning). A pendent would need to be further out to provide the same 100% wetting coverage within an "I-Beam" configuration due to the conical distribution pattern.

Kimberly Olivas

1/11/2024 09:37:52 am

So, would a horizontal sidewall with the deflector to the side be the best, then you get the 180 degree spray going up and down on the column, is that you were envisioning?

1/11/2024 01:22:17 pm

No, but I can see that inference.

The HSW would be installed normal with the water spray in a horizontal direction into the webbing. Let gravity handle the rest.

The only function of this is to make sure the steel stays at a reasonable temperature via the cooling effect of the water thus keeping its integrity.

When installing these in the past, we used a vertical pipe attached to 3¼" unistrut that sandwiched the beam. The outlet faced into the webbing and the HSW was installed directly onto the pipe outlet...protected the sprinkler and was a quick install.

Fred Walker

1/11/2024 08:41:08 am

NFPA 409 is open on this, leaving compliance to NFPA 13 with the limited guidance in Chapter 7. Don’t read more into 409 than is there, if the column protection complies with NFPA 13 and the limited requirements of NFPA 409 Chapter 7 then 409 is satisfied.
From there it engineering judgement and AHJ approval.

Jesse

1/11/2024 09:31:31 am

Agree with everything here thus far. Its easy to read too much into standards.

Personally, I'd go with the sidewall.

O.P.

1/11/2024 11:10:53 am

As I originally posed the question, I was more inclined to go with the pendent in the horizontal position, due to anticipated "bounce back" from a horizontal discharge, However, as Dan stated, " The intent is wetting in a downward direction".

With that in mind, I feel that using a sidewall now is the better option as the water will certainly wet the column web

A few items inadvertently omitted in my original post.
1- Overhead Wet system to be installed ( No foam)
2- Column sprinklers located in between flanges on opposite sides, spaced 10 ft vertically.

The answer as to whether the pendent could be used horizontally can be found in NFPA #13 (2016) 8.2.1.2

Thanks for the insight everyone - very informative.

Patrick Drumm

1/11/2024 01:09:57 pm

O.P. I appreciate your original question because although you observed something in the field that had been previously installed (swapping of sidewall to pendents in horizontal position), you still want the code back-up to perform that type of installation in the future. I sometimes find others simply see things in the field and assume they were done properly and that is a dangerous game to play.

In regards to your requested code-path. I start in Chapter 5 of NFPA 409 at Section 5.6.3. In the appendix it states that "Additional guidance pertaining to fixed water spray systems can be found in NFPA 15" as well as stating that "The design of such protection should take into account factors such as the shape of the column, wetting of lower sprinklers, obstructions, and type of discharge device." Obviously, the last item being the most important to us.

I think the code section your looking for to get the buy in from AHJ's would be NFPA 15 Section 6.2.1.4. - "Where approved, sprinklers shall be permitted to be used in water spray systems and installed in positions other than anticipated by their listing to achieve specific results where special situations require." The text of this section is very similar to NFPA 13 Section 8.3.1.2.

I agree with your follow-up post though. I like horizontal sidewalls installed per their listing at 10 feet max intervals. It's a similar installation to what is required in storage occupancies where column protection is needed - See NFPA 13 Sections 16.1.4 & 17.1.4.

NFPA 13 & NFPA 409 References are 2016 Editions.
NFPA 409 References are 2017 Edition.

Does a Pendent (Horizontal) Meet NFPA 409?

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