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Vertical separation between standard sidewall sprinklers

Vertical separation between standard sidewall sprinklers


We have an existing electrical transformer room (wet transformers) in a healthcare occupancy that is protected by a preaction system. Our facility management dept. has a project to replace the transformers. The contractor is proposing to remove some of the existing sprinkler piping (standard uprights with standard pendants beneath duct obstructions) and replace with standard sidewall sprinklers. They need to temporarily remove ductwork in order to remove and replace the transformers. Their layout sketch shows two sidewall sprinklers to cover the area where the existing standard uprights were removed, and one additional sidewall sprinkler 2-ft 11-in directly beneath one of the new sidewall sprinklers to cover the area beneath the duct obstruction.

Is there is minimum vertical separation between sidewall heads in NFPA 13 (my facility requires NFPA 13, 2013 edition)? Does the 6-ft rule apply vertically? I've been looking, but I can't find anything.

And one other thing. The existing upright heads by the ceiling are standard response, but the existing pendants beneath obstructions are all quick response. They are similar temperature ratings (200-F). It almost looks like they added QR pendants after a ductwork project. Our agency's design policy is to generally require all QR sprinklers unless unavailable in the temperature range.

Thank you,

RE: Vertical separation between standard sidewall sprinklers

I would say NFPA 13 would disqualify the lower sprinkler installation.
Unless the requirements of are met, sidewall sprinkler deflectors shall be located not more than 6 in. (152 mm) or less than 4 in. (102 mm) from ceilings.
Horizontal sidewall sprinklers shall be permitted to be located in a zone 6 in. to 12 in. (152 mm to 305 mm) or 12 in. to 18 in. (305 mm to 457 mm) below noncombustible and limited-combustible ceilings where listed for such use.

RE: Vertical separation between standard sidewall sprinklers

If I understand the question, you have

1. Sprinklers near the ceiling.

2. A sprinkler UNDER neath duct work.

If that is the set up

No Problem

RE: Vertical separation between standard sidewall sprinklers

Agreed. I would see this as uprights at the ceiling and below ductwork, both are legal; so I would think using sidewall sprinklers achieve the same intent and will operate comparably.

RE: Vertical separation between standard sidewall sprinklers

I'm confused. Is the duct an obstruction, as described in NFPA 13 Section

RE: Vertical separation between standard sidewall sprinklers

Exactly how big is the room including the ceiling height?

RE: Vertical separation between standard sidewall sprinklers

NFPA 13 2013 section 8.4.2: Sidewall Spray Sprinklers

Sidewall sprinklers shall only be installed as follows:
1. Light hazard occupancies with smooth, horizontal or sloped, flat ceilings
2. Ordinary hazard occupancies with smooth, flat ceilings where specifically listed for such use
3. To protect areas below overhead doors

Commentary from the Handbook
The discharge characteristics of sidewall sprinklers are not as effective as those of upright and pendent sprinklers for all applications. Accordingly, sidewall sprinklers are limited to light hazard occupancies, unless the sprinkler is specifically listed for use in ordinary hazard occupancies. Several horizontal sidewall sprinklers are now listed for use in ordinary hazard occupancies.
In addition to being limited by the occupancy hazard classification, sidewall sprinklers are also limited to the ceiling configurations listed in 8.4.2.
Sidewall sprinklers are often used in retrofit situations where access to ceilings can be limited. System piping can be installed along the intersection of a wall and ceiling and covered with a built-up soffit, with the sidewall sprinkler protruding through the soffit.

Based on this I have been of the understanding that sidewall sprinklers are not suitable for using under obstructions. Perhaps I'm wrong?

RE: Vertical separation between standard sidewall sprinklers

Reference #3 of the section you provided.

HSW's have been used under ducts for a long time, as it would seem obstructions were in mind when overhead doors were listed as an example.

RE: Vertical separation between standard sidewall sprinklers

I have taken the specific reference to overhead doors as being a very specific situation for which they are permitted by NFPA. I would not have taken that as a go ahead for using under obstructions in general.

RE: Vertical separation between standard sidewall sprinklers

Point granted.

However, the sprinklers under an obstruction seem to be activated from impingement and not heat flow from the jet. Or maybe they do.

An interesting item for consideration.

RE: Vertical separation between standard sidewall sprinklers

It would be nice if NFPA did state it more definitively (if it is in fact the intent), however there are a few sections that lead me to this conclusion.

Commentary under section in the NFPA 13 2013 Handbook says:
"Does NFPA 13 consider overhead doors an obstruction?

It is important to stress that overhead doors are considered an obstruction (see Although the overhead door is not considered an obstruction when in the closed position, as shown in Exhibit 8.12, the discharge from the sprinkler over the door will be obstructed when the door is in the open position. Sprinklers need to be positioned so that their discharge can adequately reach under the overhead door. The 1999 edition of NFPA 13 was revised to specifically allow the use of sidewall sprinklers for these applications. [See 8.4.2(3).]"

Also, section provides specific criteria for sidewall sprinklers in ordinary hazard occupancies to use light hazard spacing for under overhead doors. Which would seem to give weight that the allowance for using sidewall sprinklers under overhead doors only. As in I would think one would have a hard time justifying using light hazard spacing of sidewalls under runs of ducts/other obstruction types so I would likewise think it a stretch to take the allowance for SWs to be used for under obstructions that are not overhead doors. The provisions for use of SWs under overhead doors seems to be very specific to overhead doors and not necessarily to be used as a go ahead for using under obstructions in general.

Commentary in the Handbook to section states 'Sprinkler protection is required under overhead doors so that protection is provided when the doors are open and the ceiling sprinklers are obstructed. In ordinary hazard areas, this provision permits larger doors to be protected by a single sidewall sprinkler, reducing the installation costs while not significantly impacting the protection of the space.

Again, that seems to be providing very specific to overhead doors.

In looking at the handbook it states in regards to 'Obstructions to Sprinkler Discharge Pattern Development.' (8.7 being for sidewalls...)

"Sidewall sprinklers, like upright and pendent sprinklers, must be located to avoid obstructions that affect the discharge pattern development or prevent the discharge from reaching the protected hazard. Paragraphs through on obstructions are similar in content to those for upright and pendent sprinklers in through Rather than assume that these types of obstructions do not exist, these requirements are included in NFPA 13 to address what to do when these obstructions are encountered. Other types of sprinklers, such as upright or pendent sprinklers, should be used if the obstruction cannot be relocated, or if the sidewall sprinkler cannot be repositioned along the wall to avoid the obstruction."

I have seen others installations where they have installed ECHSW at 24’ spacing under runs of ducts. It would seem that there would have to be a huge fire before those sprinklers activate. I know FM have drastically revised their criteria for under obstruction protection (with the criteria in FM 2-0) where they have reduced the allowable spacing under obstructions so that the sprinkler will be close enough to the plume of the fire to activate.

Also in regards to CKCECB’s post, it would seem that the mixing of Standard Response and Quick Response would be a violation of NFPA 13 2013 section

CKCECB, is the project NFPA? What hazard classification is the room being considered?

RE: Vertical separation between standard sidewall sprinklers

Well, I cleared things up quite a bit with a site visit. The submittal I was working off of made it appear that the duct run would be parallel with the wall on which the sidewall heads are going, with a stand-off, so that's why I was worried about vertical spacing/stacking and cold soldering, etc. The duct is actually penetrating the wall on which the sidewall heads are going, so one sidewall will be on top of the duct penetration, and one below, so no problem like cdafd said. But I still wonder about the vertical spacing if the duct was parallel to the wall and, say 5-ft off the wall, thought it won't bear on this project.

And I found another thing related to the mixing of standard response and quick response heads. The standard response upright heads by the ceiling are ordinary temperature 155-F (red bulbs), and the quick response heads beneath the duct penetrations are high temperature 286-F (blue bulbs). This is for an air conditioned room with three oil-cooled electrical transformers. The sprinklers beneath the ducts are newish (2006 on frame) that were probably put during an HVAC upgrade. This makes no sense to me to have 286-F beneath the ducts, and 155-F at the ceiling. I cannot find anything in 8.3.2 that requires high-temp sprinklers for this application, so wouldn't all sprinklers in this room need to have the same temperature rating (either all ordinary or all high)? That is my biggest concern now.

Thank you all for participating in this thread!

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