- Jerry Schultz, P.E.
Solid Shelving (part 3)
I am back. Sorry for the delay in getting this blog post out, but now let’s talk about what we have to do when we have solid shelving. Up to this point, we have discussed what solid shelving is and spent time talking about how the load can determine if a shelf is a solid shelf. Now we are ready to ask, “So What?” Once we determine that we have solid shelving, what needs to be done?
In the 2016 edition of NFPA 13, Standard for the Installation of Sprinkler Systems, the following Sections apply:
Section 22.214.171.124 Where solid shelving in single-, double-, and multiple-row racks exceeds 20 sq ft (1.9 sq m) in area, but does not exceed 64 sq ft (5.9 sq m), sprinklers shall not be required below every shelf but shall be installed at the ceiling and below shelves at intermediate levels not more than 6 ft. (1.8 m) apart vertically.
Section 126.96.36.199 Where solid shelving in single-, double- and multiple-row racks exceeds 64 sq ft (5.9 sq m) in area or where the levels of storage exceed 6 ft. (1.8 m), sprinklers shall be installed at the ceiling and below each level of shelving.
Let’s take some time to understand this and tie it back to the first two blog posts on solid shelving:
1) If the load exceeds 20 sq ft (1.9 sq m) but is less than 64 sq ft (5.9 sq m), the sprinklers are to be installed at a maximum of 6 foot (1.8 m) vertical spacing. Assume that one is storing doors in boxes laying on the shelf (or the arms of a cantilever rack). The box is 4 feet (1.2 m) by 8 feet (2.4 m) or 32 sq ft (3 sq m). Sprinklers are to be on 6 foot (1.8 m) vertical centers or below every shelf, if the shelves are more than 6 feet (1.8 m) apart.
2) If the load exceeds 64 sq ft (5.9 sq m), then sprinklers are to be below every shelf. Looking back at the earlier example in blog post 1.5 where I discussed cantilever racking and stacked racks, the load is 4 feet (1.2 m) wide by 20 feet (6.1 m) long, or 80 sq ft (7.4 sq m), so sprinklers would be required under each shelf.
The solid shelving requirement has evolved since its first appearance in the standard. In 1999, NFPA 13 incorporated the requirements found in NFPA 231C (Standard for the Protection of Racking) for the first time. At that time the document defined solid shelving as “Solid, slatted, and other types of shelving located with racks that obstruct sprinkler water penetration down through the racks.” The section (7-188.8.131.52) that outlined what had to be done when solid shelving was present was very basic and stated that sprinklers shall be provided at the ceiling and below every shelf when both the longitudinal and transverse flue were obstructed. Later, the committee felt that this was not specific enough since there was no reference to a minimum distance between flues. AHJ’s were left arguing where flues were required.
In 2002, the requirements were revised to address the issue of flues. The solid shelving definition added requirements that referred to flue spaces. The definition at that time stated:
Solid shelving is fixed in place, slatted, wire mesh, or other type of shelves located within racks. The area of a solid shelf is defined by perimeter aisle or flue space on all four sides. Solid shelves having an area equal to or less than 20 sq ft (1.9 sq m) are defined as open racks. Shelves of wire mesh, slats, or other materials more than 50 percent open and where the flue spaces are maintained are defined as open racks.
There was no reference to the placement of loads in 2002. The reference to the placement of loads that block openings appeared for the first time in the 2010 edition but it did not appear in the definition for Solid Shelving. Instead, a new definition was developed for the Rack Shelf Area which stated:
184.108.40.206.6 Rack Shelf Area. The area of the horizontal surface of a shelf in a rack defined by perimeter aisle(s) or nominal 6 in. (152 mm) flue spaces on all four sides, or by the placement of loads that block openings that would otherwise serve as the required flue spaces.
Although it seemed evident, even back in 2010, the committee intended to include the loads when determining the rack shelf area, there were issues raised because there was not a clear connection between the definitions and requirements for “Solid Shelving” and the calculation of “Rack Shelf Area”. There was no use of the phrase “rack shelf area” in the solid shelving requirements section. The committee finally added the same requirements within the definition of Solid Shelving in the 2016 edition of the standard. At that time, the committee added the red underlined words below within the Solid Shelving definition.
Shelving that is fixed in place, slatted, wire mesh, or other type of shelves located within racks. The area of a solid shelf is defined by perimeter aisle or flue space on all four sides or by the placement of loads that block openings that would otherwise serve as the required flue spaces. Solid shelves having an area equal to or less than 20 sq ft (1.9 sq m) are defined as open racks. Shelves of wire mesh, slats, or other materials more than 50 percent open and where the flue spaces are maintained are defined as open racks.
In 2002, the committee felt that they had clarified the issue sufficiently but the field interpreted things a bit differently. In the first place, there were officials’ going out and applying the solid shelving requirements to grocery store shelving and requiring sprinklers underneath shelves. The committee dealt with this by adding terms to the definitions for light and ordinary hazard and by running tests on shelving and introducing back to back shelving. The bigger issue is that this new requirement in 2002 did not take into account long standing design criteria. As an example, a longitudinal flue is not required in double row rack up to 25 feet (7.6 m) and is never required in a multiple row rack. Using the load criteria and recognizing that there would be no flue in the double row rack up to 25 feet (7.6 m) and in a multiple row rack of any height, in-rack sprinklers were being mandated in areas that never required sprinklers previously. It took two cycles (2007 and 2010 editions) before the issue was addressed. In the 2013 edition of NFPA 13, the committee added the following in Section 220.127.116.11 (my editorial comments are in italics):
Where multiple-row racks of any height have no longitudinal flue (remember they are not required to have one) or where double-row racks with storage up to and including 25 ft. (7.6 m) in height have no longitudinal flue (again they are not required to have one), the situation shall not be considered solid shelves where transverse flues exist at maximum 5 ft. (1.5 m) intervals and additional in-rack sprinklers shall not be required in accordance with 18.104.22.168 and 22.214.171.124.
By providing a transverse flue on 5 foot (1.5 m) centers, a double row rack up to 25 feet (7.6 m) without a longitudinal flue and a multiple row rack of any depth does not need to be treated as a solid shelf and does not require additional sprinklers.
I do find it interesting that I could have a multiple-row rack that is 100 feet (30.5 m) deep with no longitudinal flue, and as long as I have a transverse flue every 5 feet (1.5 m), this does not constitute a 500 sq ft (46.5 sq m) solid shelf (5x100) and sprinklers are not required by the solid shelving rules. However, if I install a double row rack over 25 feet (7.6 m) tall that is 8 feet (2.4 m), deep without a longitudinal flue, even though I still have a transverse flue every 5 feet (1.5 m), this constitutes a solid shelf of 40 sq ft (3.7 sq m) and sprinklers are to be provided every 6 feet (1.8 m) vertically.
Photo 1: Plan View of Double Row Rack
Photo 2: Plan View of Multiple Row Rack
One other item that occurred in 2016 is that the committee applied the solid shelving requirements to Chapter 13 for the first time. Chapter 13 addresses Miscellaneous and Low Piled Storage. Low piled was defined as storage in 2016 as storage up to 12 feet (3.7 m). The same requirements, including the flue space requirements, apply to storage below 12 feet (3.7 m) when on a rack. In-rack sprinklers are required when solid shelving is present in storage below 12 feet (3.7 m).
In summary, here is where we are as of today:
In addition to the shelving material, the load may define the area of the shelf.
If the area exceeds 20 sq ft (1.9 sq m), sprinklers shall be provided on 6 foot (1.8 m) vertical centers.
If the area exceeds 64 sq ft (5.9 sq m), sprinklers shall be provided below every shelf.
If a longitudinal flue is not required, then the solid shelving requirements do not apply if a transverse flue is present every 5 feet (1.5 m).
These solid shelving requirements also apply to racks less than 12 feet (3.7 m) high.
The requirements have evolved and if under an earlier edition of the standard (pre 2016), bullet points 4 and 5 were not in the document. It is probably necessary to discuss this with the AHJ.
I plan to consolidate the blogs on Solid Shelving into one concise document and offer it as a white paper to those who want it. As I stated back in blog post 1 on solid shelving, this is one of the most misunderstood code requirements out there and requires discussion and review by all impacted.
Next month I plan to talk about shelving and clearly identify the differences between shelving and racking as identified by NFPA 13.
As always, I welcome your comments: email@example.com