Phantom Flow for a 750 sqft Paint Spray booth?

12/11/2024

Does Phantom Flow apply to a 750 sqft Paint Spray booth?

Currently acting as AHJ for a spray booth sprinkler submittal. We commented that their hydraulic calculations must comply with 2022 NFPA 13 Sections 28.2.4.2.4 and 28.2.4.2.5.

Are we correct in our interpretation that Section 28.2.4.2.5 requires an additional flow to be added, like a secondary hose stream allowance, so that the design discharge meets the minimum required discharge?

In this specific submittal, it would require an Extra Hazard Group 2 (EH2) spray booth (approximately 750 square feet in area) to add additional flow in the calculation to meet the minimum EH2 design discharge of 1,000 gpm? (ie: 0.40 x 2500 = 1,000 gpm).

The Appendix material seems to confirm this interpretation. It seems like overkill, but I cannot find an NFPA Section that would allow the minimum design area (2500 sqft) to be reduced for calculation purposes, even if the spray booth itself is only 750 sqft.

Thanks in advance.

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6 Comments

Brett

12/11/2024 06:28:35 am

Phantom flow is specific to the density/area method. If the density/area method is being used then phantom flow is required. If the room design method is being used then phantom flow is not required.

Dan Wilder

12/11/2024 07:11:59 am

I would argue that if the booth falls under NFPA 33 (per 13-22 27.5), then the design provisions of the calculation area as defined within 33-19' 9.5.1 would not require it. If it referenced back to NFPA 13 for hydraulic calcs then I would apply it as you have stated.

33-19'-9.5.1.2 does define the booth spray areas as EH2

33-19'-9.5.1.2.1 states the design area shall not be required to exceed the area of the booth or room where the application is being conducted.

So if the calculation area is only the booth per 33, then the EH2 minimum design area within 13 does not apply, nor would the sections 28.2.4.2.4 & 28.2.4.2.5 for not meeting that minimum.

Jaymie

12/11/2024 08:29:38 am

I think you're talking about two different things. Your design area would be .40 for 750 square feet. Your hose stream allowance for extra hazard is 500 gpm for 90 minutes so water needed when combined is 72,000 gallons.

Jesse

12/11/2024 08:58:54 am

I don't think phantom flow applies here, or at least I would pursue avennues for it not to apply. Further, I don't think the spirit of phantom flow would be appalicable.

First, if room design method is being used, phantom flow wouldn't ever apply as phantom flow is specific to CMDA designs.

Secondly, I think 33 would be a more appllcable code which doesn't require phantom flow.

Anthony

12/12/2024 09:04:09 am

I agree with Jesse here. the phantom flow for a fixed known hazard like a spray booth would not require enlarging the main to carry the added capacity.

My guess is that this section of the standard is to allow for convenient future expansion of the high hazard area. For a fixed paint booth in a small shop, I'd ask for variance. Seems counter productive and costly. I would hope this item is removed or given an "if allowed by an ahj this item will not be required" in the future editions of 13

Jay

12/11/2024 09:24:08 am

I had this same situation last Fall in an electric vehicle collision repair/body shop facility. I sent the questions to the NFSA, about whether or not the EH2 spray booth design was required to extend 15ft outside the booth (adjacent hazards) and if a phantom flow was required to be added due to the spray booth size (about 400 sqft) the design flow was well under the minimum 1000gpm of an EH2.
Here is their response (design area extension not required and phantom flow not required):

The answer to your question is yes, only the sprinklers within the spray booth or room are required to be calculated.

As you mentioned section 9.5.1.2.1 states “ The sprinkler design area shall not be required to exceed the area of the booth or room in which spraying or resin application is conducted”.
Section 9.5.1.3 states that “the water supply shall be sufficient to supply all sprinklers likely to open in any one fire incident without depleting the available water for use in hose streams.”
The Annex material for section 9.5.1.3 further clarifies the intent by stating “Building areas outside of the spray area or paint booth are not included in the demand calculations, as the fire suppression systems and booth/spray area construction are intended to contain a fire until manual fire-fighting efforts can achieve final fire extinguishment.

While NFPA 13 does provide a larger area for these densities, the fact that NFPA 33 provides specific design area constraints takes precedence.

Section 5.2 of NFPA 33 requires spray rooms to have a 2 hour rating. Additionally Section 5.3.2 requires walls and ceilings of spray booths constructed of sheet metal to have no thinner than 1.2 mm or two layers no thinner than .09 mm.

So long as these areas meet the requirements for a spray booth or spray room, the calculations are not required to extend beyond that area.

Phantom Flow for a 750 sqft Paint Spray booth?

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