Sprinklers Needed Below Multiple Small Clouds?

11/5/2020

I have a project where there are multiple cloud ceilings with minimal gaps in-between. The clouds are 3'-6" wide, and the gaps between them are approximately 3-inches. Below is an image of the reflected ceiling plan.

Are sprinklers required below these cloud ceilings? Thanks in advance.

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13 Comments

Dan Wilder

11/5/2020 07:35:03 am

Referencing 9.2.7 of the 13'-19 ed.

If this honeycomb pattern had extended to the perimeter wall, this may have qualified but due to several gaps against the walls, within the pattern, and the separation between patterns, protection would be required above and below.

This does not comply with the below section:
9.2.7.1(1)-Combined total area of opening is less than or equal to 20% of the area of the ceiling
Table 9.2.7.1 for the maximum area of open width due to entire honeycomb units being left out and the gaps against the walls.

Your layout also needs to comply with 9.2.7.2.5 for protection below the honeycombs.

Rosstan Snow

11/5/2020 10:40:32 am

Does this percentage differ between the 13-13' and 13-19' edition. Has the section been revised? This jurisdiction is under 13-13'

Franck

11/5/2020 11:56:23 am

For your information, requirements for cloud ceilings have been added to the 2016 edition of NFPA 13 following a Fire Protection Research Foundation (FPRF) project studying the behavior of heat and smoke.
Prior to this, sprinklers were generally required both above and below cloud ceilings.
The requirements of 9.2.7 in the 2018 Edition is to omit sprinklers above the cloud ceiling. In no way you can omit sprinkler below : in all cases, sprinklers need to be provided below the cloud ceilings as they create an obstruction.

In your case, I'm afraid you need sprinkler both above and below the cloud ceiling, as indicated by Dan (you don't fulfill the requirements of 9.2.7.1(1)).
In case of fire in your building, because of large openings in your "cloud ceiling system" (around it), the heat will first collect above the cloud ceiling and it would take time before you can activate the sprinklers located below the cloud ceiling.

For the sprinklers located below the cloud ceiling, you just need to provide them to cover the area below them with the min/max spacing specification as if it was a ceiling protection.
And avoid sprinkler located where there is no tile (you still need to collect the heat, i.e., you need a "cloud ceiling" above your intermediate sprinkler level of protection).

For the sprinklers located above the cloud ceiling, it is normally preferred to center them as much as possible above the obstruction tiles.

If you have access to NFPA 13 handbook, you will find a lot of interesting information on that topic.

Franck

11/5/2020 12:33:07 pm

In addition to my above comment, note that if sprinklers could be omitted above the could ceiling, then the position of sprinklers below the cloud ceiling should be based on table 9.2.7.1, which give a maximum coverage area per sprinkler, depending on the width dimension of the clouds and the opening width compared to ceiling height.

On the Clock

11/5/2020 02:03:01 pm

Thanks, Franck. Am I understanding you correctly that once it is determined that sprinklers are required BELOW the cloud array, then normal sprinkler spacing below the ceiling would apply? One does not need to make sure the gap between clouds will not "stop" the heat from jumping one cloud to the next? Would it be prudent to follow the same maximum gap-width formula for omitting sprinklers above the ceiling (A9.2.7.1) when placing sprinklers in say, every third or fourth cloud, skipping the clouds in-between?

When the architect will not allow penetration of the cloud, do you think a sprinkler with intermediate shield off to the side per 9.5.5.3.1.2 / Fig. A.9.5.5.3.1.2 is an option?
Thanks in advance.

Franck

11/5/2020 02:40:18 pm

Just matter of interpretation and whether you want to be conservative or not.

NFPA 13 in chapter 9.2.7 is regarding sprinkler spacing (and other requirement such as the provision of quick response sprinklers...) when you may omit sprinkler above the cloud ceiling.

The following is just my point of view.

If you have sprinkler both above and below, you can still follow the requirements (if they are more restrictive than the minimum requirements from other chapter), or not, for the sprinkler located below the cloud ceiling.
You can choose the most restrictive requirement just to be sure.

Note that 9.5.5.3.1.2 is to provide additional sprinklers below the obstruction, but does not prevent to provide sprinklers at the ceiling level. In other words, because the heat plume from the fire will collect anyway at the ceiling level, you may (and in most case will) operate sprinklers above the obstruction.
The protection below the obstruction is just in case the fire is so bad, and not controlled by the ceiling sprinklers because of the obstruction, that the sprinkler underneath will operate if the fire is located below.
Sprinklers do not operate with radiant heat from the heat plume if they are not located directly inside the heat plume.
Sprinklers operate at the ceiling level, because the ceiling collect the heat at the sprinkler location.
Sprinklers with shields (as within in-racks) are not collecting heat. The shield is just to avoid that water from the ceiling sprinkler can wet the fusible element (bulb) of the sprinkler underneath and thus delay its activation.

Whatever the size and shape of the shield, they are of poor benefit.

Work done at Factory Mutual showed that convective heat typically supplies more than 80 percent of the heat sprinklers need for activation.
Convective heat needs a flow of air past the sprinkler. Testing has shown that heat collectors with edges, such as inverted boxes, can actually delay sprinkler response, presumably because they create dead air space. Flat heat collectors are only effective where the edge of the heat collector picks up the fire plume and acts like a small ceiling. To work effectively, the combined areas of heat collectors need to make up a large percentage of the floor area.

A study performed in 1990 (“A Study of the Utility of Heat Collectors in Reducing the Response Time of Automatic Fire Sprinklers Located in Production Modules of Building 707,” prepared for the U.S. Department of Energy Rocky Flats Plant by Hughes Associates, Inc. (HAI)) stated the following:
• Heat collectors with the edges turned down around the side produced a dead air space and the sprinklers had longer response times than sprinklers with a flat heat collector

Different types of heat collectors (with or without edge)
• The heat collector must be in the plume to be effective. If the centerline of the fire is more than 1 to 2 feet from the edge of a flat heat collector, a standard-response sprinkler may take longer to respond, regardless of its thermal sensitivity.
• If a fire is midway between two sprinklers, the sprinklers may not respond at all (regardless of the size of the heat collector) because the sprinklers are not exposed to the convective heat flow of the ceiling jet.
• Quick-response sprinklers activate more quickly than standard-response sprinklers only if the fire was directly underneath the heat collector.

Franck

11/5/2020 02:41:30 pm

Sorry for being sometimes so late to answer... but I am living in France, with time difference :)

On the Clock

11/6/2020 10:48:34 am

Thank you for you time, expertise, and perspective, Franck - Have a good evening!

On the Clock

11/5/2020 10:47:39 am

I’m following this, as I am running into variations of this all the time. I feel NFPA #13 concentrates more on whether or not sprinklers are required above, but is lacking in what is required for protection below, unless extrapolating from similar sections. I often encounter several smaller clouds that individually, would not require sprinklers below, but if several are arranged side-by side, with only a small gap in-between, does this constitute one large obstruction based on ceiling height and width of gap, kind of applying in reverse the allowable gap with of 8.15.24.1(1) (2016) (A9.2.7.1(1) (2019)? And what if each cloud would individually require sprinklers, would several side-by-side require a sprinkler in each cloud, or could you utilize maximum sprinkler spacing and skip clouds based on the paragraphs mentioned above? ID the gap is no more than 6-inches, can you center a pendent sprinkler with shield in the gap itself if complying with the 3-inch rule of 8.5.5.3.1.2 (2016) and 9.5.5.3.1.2 (2019)? As in the original post, I’m running into this with ceiling cloud arrays and sound reflectors in performing arts centers.

Franck

11/5/2020 12:20:44 pm

This is a difficult question and the answer, as very often, is... it depends

You have to consider the smaller clouds as obstructions from the ceiling sprinklers and make a technical judgement whether it creates an obstruction or not.
It may depend on the width of the obstruction and the distance below your sprinkler head.

Check §10.2.7.2 Obstructions to sprinkler discharge pattern development in NFPA 13 (2019).

It is just like with ducts or cable trays or pipes.
One cable tray (less than 4 ft wide) may not be an obstruction, but 3 cables trays running in parallel may create an obstruction.
It is the same with pipes or ducts.
Remember, for example, that with upright sprinklers, you need a riser nipple to limit the obstruction from the branch line if the size of the piping is 3" or more, for example... (§10.2.7.2.1.8).

Figure 10.2.7.2.1.3(b) is quite explanatory for small obstructions below the deflector that create obstruction to sprinkler discharge. If your deflector at the ceiling level is less than 3 times the width of the obstruction and the obstruction located less than 24 in. from the deflector, then you have an issue (and need to provide sprinkler protection underneath).

The only permission is for obstruction less than 4 ft and located more than 18 in. below the deflector's plane (which is a result of 10.2.7.3.2).

Franck

11/5/2020 12:00:33 pm

Note that in the MeyerFire tool kit, you have an interesting Cloud Ceiling Calculator

Rosstan Snow

11/5/2020 03:54:11 pm

It does but for this application its impossible to determine given the various opening between clouds, the wall...etc. There is no doubt protection below is required based on condensed spacing. Overhead protection is a given. If the edge to edge spacing of the clouds were 6" or more, then it would interesting to see what sum the calculator would advise. Nevertheless; everyone's feedback has been impeccable. In Houston, the adopted code is still 2010 NFPA 13; Harris County is 2013 NFPA 13. Very few jurisdictios have adopted 2016 much less 2019. However, I have submitted a variance in code between 2013 and 2016 and Harris County accepts certain design approaches based on the newest code. Houston? Not a chance

Franck

11/6/2020 01:11:57 am

My life is easier :)
Working in loss prevention for an insurance company based in Europe, we don’t have your IBC (which is not “international” but “north american”) and I can use the latest version of NFPA to recommend improvement.
This way, we can improve situations based on the latest evaluation and modernization.

On the other hand, each country may have its own regulation and it is sometimes a hard job to convince them to do more than the minimum legal requirement and to follow an “american” standard

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