As promised, we return to the original discussion on Solid Shelving. In my writings I have tried hard not to just reproduce the standard by copying sections and inserting them in the blog. However, in order to truly understand the solid shelving requirements, I am going to have to do that--present sections for you, the reader, to examine. The definition for Solid Shelving, as it appears in the 2016 edition of NFPA 13 under the subcategory, Storage Definitions is:
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 ft2 (1.9 m2) 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 reviewing each line of the definition, it becomes evident that this is a game changer. "Shelving that is fixed in place, slatted, wire mesh, or other types of shelves located within racks." Right off the top, slatted or wire mesh or other types of shelves located within the rack can be classified as solid. (see Photo 1 of wire mesh shelving). Note that there is no reference to a shelving material being 50% open or 70% open. The definition applies to any shelving material. The product in Photo 1 is obviously greater than 50% open and yet by definition it can be considered as solid shelving. This is one of the main issues that we have to understand and it can be summarized by asking—wasn’t wire mesh developed to help eliminate solid shelving issues? Of course it did, but the standard has changed and now the material being stored determines if the shelf is solid or not.
Photo 1: Wire Mesh Shelving
The definition further states: "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." It is this part of the definition that starts to elaborate on how a shelf material that is obviously open can be classified as solid shelving. The area of a solid shelf is to be measured from opening to opening that surround the loads themselves. For example, take the shelf shown in Picture 1 and cover it with boxes spanning from side to side, now it has become solid shelving. The picture below shows small boxes on slatted shelves (which appear to be covered by a board) and would qualify as solid shelving whether the board was there or not. There is no defined flue being shown so one would have to measure from rack upright to rack upright.
Photo 2: Note the small boxes with no defined flue
So the next part of the definition gets even more interesting. "Solid shelves having an area equal to or less than 20 ft2 (1.9 m2) are defined as open racks." The 20 square feet is designed to represent a pallet load with openings on all four sides and this section is stating that pallet loads are not solid shelving so therefore if a shelf unit is 20 square feet, this shall not be considered solid shelving. Please understand that it is not the pallet load that is making this “not solid shelving” but the fact that there are openings on all four sides of the pallet. If we push two pallets together and do not maintain a flue around them then we measure from the opening to the opening and we are back to a solid shelf. As shown in Photo 3, the pallet loads have been pushed back to back such that a longitudinal flue is not provided therefore the area of the solid shelf would run from aisle to aisle in the one dimension and flue to flue (note there is a transverse flue shown) in the other dimension. (There is an exception to this requirement that we will discuss as we fine tune the actual definition).
Photo 3: Pallet loads eliminate the longitudinal flue leading to measuring the shelf from aisle to aisle
The final part of the definition states: "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." This is the section that I have had the most arguments about. Several individuals have taken this to mean as long as the rack component/material is 50 percent open (i.e. wire mesh deck) and a flue space is maintained somewhere then regardless of the area of the load, it is to be considered as open shelf. The argument is being made that this section reverses what is being said above and one can have a load that is over 20 square feet in area as long as flues (or aisles) are maintained around it and the shelf is not to be classified as solid shelving.
The argument above can be refuted by reviewing the Annex but there is another way to address it. In addressing it, we will complete the definition itself. The first line of the definition requires shelving material to be provided, and if there is no shelving material (i.e. cantilever racking as discussed in the first blog on solid shelving), then it does not appear to apply. NFPA 13, in Section 188.8.131.52.4 defines Open Rack as:
Racks without shelving or with shelving in racks that are fixed in place with shelves having a solid surface and a shelf area equal to or less than 20 ft2 (1.9 m2) or with shelves having a wire mesh, slatted surface or other material with openings representing at least 50 percent of the shelf area including the horizontal area of rack members and where the flue spaces are maintained.
By definition, we cannot classify cantilever shelving with product that exceeds 20 ft2, nor can we classify a rack without shelving material where the loads exceed 20 ft2, as open racking so it falls back to solid shelving.
This is perhaps better explained by reviewing the Annex material. As one is aware, the Annex is not considered enforceable (I have seen ordinances which state that the Annex is adopted and is enforceable so watch yourself) but is “included for informational purposes only. This annex contains explanatory material, numbered to correspond with the applicable text purposes.” The Annex material for the definition on Solid Shelving in A.184.108.40.206 states:
The placement of loads affects the calculated area of the shelf. It is the intent to apply this definition to loads on the rack where 6 in (150 mm) nominal flues are not provided on all four sides, regardless of whether shelving materials are present. (underscore added)
At this point, it seems unarguable that the loads define the shelf area and therefore define the classification as solid shelving not some shelving material itself.
Further support for this interpretation can be found in the NFPA 13, 2016 Automatic Sprinkler Systems Handbook which includes the response to a Frequently Asked Question:
If the shelf material is considered open but the loads on the shelf, without the required 6 in. (150 mm) flue space between loads, are greater than 20 ft2 (1.9 m2) in area, do the shelves have to be protected as solid shelf?
One of the most significant changes to rack storage in the 2010 edition was the new method to calculate the rack shelf area. The placement of loads on the shelf now affects the calculated area of the shelf. Previous editions only dealt with the shelf material alone and did not consider the loads on the shelf. With this definition, shelving material that had been classified as open, such as wire grate, which is more than 50 percent open, could be calculated as solid shelf if the loads on the shelf cover the required flue spaces to separate shelf area calculations.
The intent was to have flues surrounding the load or shelf material that will not block more than 20 ft2 (1.9 m2) in area. Even though the shelf material (if any) is considered open, the distribution is blocked if the area of load or shelf is greater than 20 ft2 (1.9 m2) in area and solid shelf rack rules would apply.
This gets us to the understanding that the load (commodity being stored) and not the shelving material, determines whether to consider the arrangement as solid shelving or not. In the next blog I will address what happens when there is solid shelving present and what sprinkler protection method is required within those racks.
As always, I welcome your comments: firstname.lastname@example.org
Jerry Schultz, P.E.