Sprinkler coverage?

[mtlogcabin]

Mercantile occupancy quick response heads. The store has 7 package units and the 5 ft X 5 ft (25 sq ft) combination supply/return duct protrudes 30 inches below the bottom of the bar joist and all the sprinklers are uprights located within the bar joist. The owner does not want anything protruding below the bar joist.

The sprinkler contractor is saying he has to put a head under the combination supply/return grille to provide proper coverage because the duct is more than 3 ft wide. I am familiar with what he is talking about but I am not sure he is applying it correctly and my sprinkler guru inspector is on vacation.

Questions

1 Is this a problem? The heads are spaced on about 12 ft centers.

2 Would 1 or 2 side wall heads properly placed provide the coverage under the area in question in lieu of 1 under the grille.

3 Do you even want a head under a package AC grille or 30 inches below the other heads? I don't think it would perform properly.

 

[Insurance Engineer]

Yep he needs protection since it is over 4' wide.

8.5.5.3.1* Sprinklers shall be installed under fixed obstruc- tions over 4 ft (1.2 m) wide.

 

[tmurray]

What is the occupancy classification?

Depending on the occupancy classification and the distance from the sprinkler heads to the obstruction it might not be required. If the duct is 4' or more wide they will need one regardless. My feeling is that it is likely that they will need one.

 

[cda]

Agree with IE

1 Is this a problem? The heads are spaced on about 12 ft centers.

Yes a problem, especially if the sprinkler company sees it and has to put their name on it.

2 Would 1 or 2 side wall heads properly placed provide the coverage under the area in question in lieu of 1 under the grille.

Not sure the question. A head is needed below the duct. More than likely cannot be a sidewall .

3 Do you even want a head under a package AC grille or 30 inches below the other heads? I don't think it would perform properly.

If positioned under the duct and not out in mid air should collect enough heat to activate

You are trying to get water under the duct, because spray if the head at the deck is obstructed by the duct

 

[FM William Burns]

Like InsEng says..........> 4' only!

No on the side walls (upright)

The sprinkler is required under the obstruction due to the capacity of the area deflecting heat from reaching the uper level uprights in the vicinity of the obstruction. We typically allow the contractors to paint the piping orange (listed paint) to prevent the fork lift guys and gals from not seeing the piping and causing water damage....

 

[mtlogcabin]

This is what I am having a problem with. A head under this does not seem like it would work. The floor layout for the store has each of these units directly over the main aisles so there would not be a fire load directly under these units. The GC has a call into the sprinkler designer for a solution. I just want to dot the I's and cross the T's and not get fed something that will not perform properly.

 

[steveray]

Agreed with the "working" thing......but it would be required.....someone smarter than me hopefully designs it to work...maybe adjust head temp or something like that....

 

[JPohling]

leave the return up high with a separate grille. use a dedicated supply diffuser down low. Then your less than 4' and no special sprinkler manipulation required.

 

[cda]

now you show the picture

Have the fire sprinkler company look at the obstructions rules and adjust heads at deck around the unit, so there is protection underneath.

If standard heads have them look at maybe 8.6.5.1.2 and table 8.6.5.1.2 NFPA 13 2010 or similar if they find some other similar section that would apply

That should be able to handle the problem if the sprinkler company has a good designer

is this a big box store with either ten foot spacing or esfr's??

four thousand nine hundred and ninty eight bottles of threads on the wall

 

[mtlogcabin]

42,000 sq ft box store. The system was designed under the 2010 NFPA 13 using ESFRS heads. I think Table 8.12.5.1.1 might be some help here but I am afraid if they add more heads then there might be a possible "skipping" if there is a fire.

 

[cda]

if they have to add it would maybe be one or two

they may be able to adjust per Table 8.12.5.1.1 and not have to add.

the idea is that you get the head far enough away, and up and down from the obstruction to get water under it.

it should be a no brainer for a good designer

Skipping, now where is that in 13?? I do not think you have to worry about that. main problem is you are dealing with esfr and threre is a little less that you can play with those.

Just put it on the sprinkler comapny and tell them to design to 13 for obstructions. in this case I do not see adding a head under the unit the way to go, unless last resort.

four thousand nine hundred and ninty nine bottles of threads on the wall

IE agree but that section allows """"""(3)

Additional sprinklers shall not be required where sprinklers are positioned with respect to the bottom of obstructions in accordance with 8.12.5.1.""""""""""

8.12.5.2* Isolated Obstructions Below Elevation of Sprinklers. Sprinklers shall be arranged with respect to obstructions in accordance with one of the following:

(1)

Sprinklers shall be installed below isolated noncontinuous obstructions that restrict only one sprinkler and are located below the elevation of sprinklers such as light fixtures and unit heaters.

(2)

Additional sprinklers shall not be required where the obstruction is 2 ft (0.6 m) or less in width and the sprinkler is located horizontally 1 ft (0.3 m) or greater from the nearest edge of the obstruction.

(3)

Additional sprinklers shall not be required where sprinklers are positioned with respect to the bottom of obstructions in accordance with 8.12.5.1.

(4)

Additional sprinklers shall not be required where the obstruction is 2 in. (51 mm) or less in width and is located a minimum of 2 ft (0.6 m) below the elevation of the sprinkler deflector or is positioned a minimum of 1 ft (0.3 m) horizontally from the sprinkler.

(5)

Sprinklers with a special obstruction allowance shall be installed according to their listing.

 

[Insurance Engineer]

Oh ESFR YES you need them under the unit, see below, from 13, 2013 Ed but the same as 2010.

8.12.5.2* Isolated Obstructions Below Elevation of Sprin- klers. Sprinklers shall be arranged with respect to obstructions in accordance with one of the following:

(1) Sprinklers shall be installed below isolated noncontinuous obstructions that restrict only one sprinkler and are located below the elevation of sprinklers such as light fix- tures and unit heaters.

(2) Additional sprinklers shall not be required where the ob- struction is 2 ft (0.6 m) or less in width and the sprinkler is located horizontally 1 ft (0.3 m) or greater from the near- est edge of the obstruction.

Also I believe in 2010 Ed of 13 you have to add the addition ESFR head to the calculations, so calculate 13 heads instead of 12. The 2013 Ed of 13 did away with this as well as FM.

I know you can not use FM Data Sheets but good stuff on obstructions in data sheet 2-0 look for storage sprinklers section.

This is a common problem with ESFR sprinklers. You really have to make sure you look at each head and make sure you have nothing obstructing 1' on either side of the head and 2' down if the obstruction is less than 12" wide, if the obstruction is greater than 24" wide then the 1' on either side of the head does to 2'. Obstructions can include bar joist, bridging, lighting , electric conduit, overhead doors etc etc.

I do not find many ESFR jobs that do NOT have obstructions. It only takes one ESFR obstructed head to cause the entire system to fail. Some of the full scale test video I have reviewed show this happening within the first 1-2 minutes of the fire staring, and out of control within 5 minutes of the fire starting.

 

[steveray]

Do you have a link for the FM info?....Thanx!

"I know you can not use FM Data Sheets but good stuff on obstructions in data sheet 2-0 look for storage sprinklers section.

This is a common problem with ESFR sprinklers. You really have to make sure you look at each head and make sure you have nothing obstructing 1' on either side of the head and 2' down if the obstruction is less than 12" wide, if the obstruction is greater than 24" wide then the 1' on either side of the head does to 2'. Obstructions can include bar joist, bridging, lighting , electric conduit, overhead doors etc etc."

 

[Insurance Engineer]

Here you go

FM Global Data Sheets

 

[cda]

42,000 sq ft box store. The system was designed under the 2010 NFPA 13 using ESFRS heads. I think Table 8.12.5.1.1 might be some help here but I am afraid if they add more heads then there might be a possible "skipping" if there is a fire.

Hay I was looking for something else and found "skipping"

1.5 Sprinkler Skipping

Sprinkler skipping is what happens when a sprinkler operates prior to another sprinkler that is closer to the fire plume, the sprinkler closer to the fire plume is then deemed to have skipped.

Two types of skipping behaviour exist temporary skipping (where the skipped operates after an adjacent sprinkler that is further from the fire plume) and residual skipping (where the skipped sprinkler does not activate at all).

Sprinkler installation standards generally require that a minimum distance is maintained between adjacent sprinklers to prevent operating sprinklers from wetting the thermal element of adjacent non-operating sprinklers causing them to skip.2 Different minimum differences are prescribed for different sprinkler types due to the differences in water spray pattern of the sprinklers. For standard pendant and upright spray pattern sprinklers the minimum distance is in the order of 1.8m (the minimum specified by NFPA132) to 2.0m (the minimum specified by NZS45418).

Skipping has the consequence of creating a region which receives a lower water discharge density from the sprinklers, resulting in less effective fire control and the potential for greater fire growth in this area.

As the design criteria used for the installation of fire sprinkler systems is generally developed from large scale fire testing, if there has been significant skipping in the fire tests then the resulting regions of low water discharge density will have allowed more fire

growth than if the sprinklers did not skip. This additional fire growth can result in a greater number of sprinklers operating overall and a greater amount of water (a higher density) being need from the adjacent sprinklers to control the larger fire. The overall impact of this is an increased density and or area of operation being prescribed in the installation, and subsequently larger pipes and water supplies being required which increases the cost of installing sprinkler protection.

http://www.civil.canterbury.ac.nz/fire/pdfreports/J%20Dyer%20report.pdf