02 May The challenges of Commodity Classification
We all see them every day as we travel along various highways; the massive concrete structures that so neatly keep all our online purchases organised and ready for delivery. On the outside, these mammoth buildings all appear quite similar and each stand proud with their box-like appearance. However, on the inside, these facilities can be quite different in the type and scope of the thousands of products and their packaging stored in multi-level automated storage and retrieval systems. In his article, Len Swantek, Director – Global Regulatory Compliance, Victaulic, takes a closer look at warehouse storage protection from the perspective of Commodity Classification and the critical characteristics that impact the type of sprinklers to be used.
For the fire protection engineer, designing a system to protect a wide range of products and materials is certainly a challenging task. Warehouse facilities can often store just about anything from clothing, household items and automotive products to a multitude of electrical and lithium-ion battery-powered devices. Additionally, the massive cardboard and packaging inventory alone poses a serious fire risk. In fact, according to NFPA statistics in the U.S. fire departments have responded to approximately 1,450 warehouse fires resulting in an average of $283 million in property damage each year. We know that automatic sprinkler systems in warehouses provides some of the best protection, so let’s begin with some basic questions.
What is being stored?
When determining what will be stored in a warehouse, the classification of the various commodities needs to be determined. While the commodity is the physical products placed in the racks, the Commodity Classification and the resulting demand on the fire system will also include an evaluation of the packaging and the pallets. There are five basic Commodity Classifications defined in NFPA 13 arranged from the least severe to the most severe: Class I, II, III, IV, and Group A Plastics. The testing and certification agencies have benchmark commodities that are used in fire tests that replicate the burn characteristics of the various Commodity Classifications.
Class I Commodities are typically non-combustible products stored on pallets or in cardboard boxes stacked on pallets or on the floor/shelf. The storage of commodities can also be shrink wrapped. Examples of Class I Commodities include empty glass bottles, gypsum board, or metal products. The benchmark commodity for a Class I product is a steel box placed inside of a corrugated cardboard box stacked on a wooden pallet. The steel box represents a noncombustible product. This arrangement will represent the heat release rate of a noncombustible Class I Commodity during a fire test.
Class II Commodities are also non-combustible products, however in this case, the packaging is more substantial than Class I packaging and includes slatted wood crates, solid wood boxes, multiple-layered corrugated boxes with or without pallets. An example of a Class II Commodity would be empty glass bottles stored in wooden crates. The benchmark commodity for a Class II product is a steel box placed inside of a tri-wall corrugated cardboard box which is then placed inside of another tri-wall corrugated cardboard box stacked on a wooden pallet. The two tri-wall corrugated boxes represent substantial packaging. This arrangement will represent the heat release rate of a Class II Commodity during a fire test. Fires involving Class I and Class II non-combustible commodities typically are a result of the burning of the cardboard packaging and the wooden pallets.
Class III Commodities are combustible products stored on pallets or in cardboard boxes stacked on pallets or on the floor/shelf. The product may be constructed of wood, paper, natural fibers, or Group C plastics with or without pallets. Class III Commodities are allowed to contain a limited amount of plastic (5% or less by weight of non-expanded plastic or 5% or less by volume of expanded plastic). Examples of Class III Commodities include furniture, paper, or wood products.
The benchmark commodity for a Class III product includes all paper cups with single layer cardboard dividers placed inside of a corrugated cardboard box stacked on a wooden pallet. The paper cups represent a combustible product. This arrangement will represent the heat release rate of the combustible Class III Commodity during a fire test.
Class IV Commodities are also combustible products with an appreciable amount of plastic (5-15% by weight or 5-25% by volume) and meets one of the following criteria:
- Consists entirely of Group A plastics or is entirely or partially made of Group B plastics.
- Boxed or in a wood container that contains 5-15% by weight of Group A non-expanded plastics
- Boxed or in a wood container that contains 5-25% by volume of expanded Group A plastics
- Boxed or in a wood container that contains a combination of Group A expanded and non-expanded plastics.
- Exposed and contains 5-15% by weight of Group A non-expanded plastics
- Exposed and contains a combination of Group A expanded and non-expanded plastics.
The benchmark commodity for a Class IV product includes a combination of 75% paper cups and 25% plastic cups with single layer cardboard dividers placed inside of a corrugated cardboard box stacked on a wooden pallet. The paper cups represent a combustible product, and the plastic cups represent an appreciable amount of plastic. This arrangement will represent the heat release rate of a combustible Class IV Commodity during a fire test.
Plastic Commodities are classified as Group A, B, or C Plastics. Group A plastics (i.e., Acrylic, Butyl Rubber, EPDM Rubber, Natural expanded Rubber, Polyethylene and Polystyrene) are in a Commodity Classification by themselves. Group A plastics are also either expanded (i.e., Styrofoam) or nonexpanded (i.e., solid plastic parts). Fires involving Group A expanded plastics are some of the most challenging to control. Group B plastics (i.e., Cellulosic, Natural nonexpanded Rubber, Nylon and Silicone Rubber) are considered Class IV Commodities. Group C plastics (i.e., PTFE, PVC, PVDC, PVDF, melamine, phenolic and urea formaldehyde) are considered Class III Commodities.
The benchmark commodity for a nonexpanded Group A plastic commodity includes all plastic cups with single layer cardboard dividers placed inside of a corrugated cardboard box stacked on a wooden pallet. The benchmark commodity for an expanded Group A plastic includes Styrofoam with plastic shrink wrap. These arrangements will represent the heat release rate of the various Group A plastic commodities during a fire test. For reference, NFPA 13 provides a complete list of the Group A, B, and C plastics.
Plastic pallets are often used in lieu of wooden pallets. If plastic pallets are used, the Commodity Classification is increased to represent the higher heat release rate from the fire. Plastic pallets can also have steel reinforcing rods placed inside for rigidity. If a plastic pallet is reinforced, then the Commodity Classification is increased by two classifications (i.e., a Class II Commodity will increase to a Class IV Commodity). If a plastic pallet is not reinforced, then the Commodity Classification is only increased by one classification (i.e., a Class II Commodity will increase to a Class III Commodity). Since the benchmark commodities are all tested by the regulatory agencies using wooden pallets, then the plastic pallet Commodity Classification increases will represent the heat release rate of these commodities on plastic pallets during a fire. In some warehouses, plastic pallets are special ordered with a fire-retardant chemical formulated into the plastic. In this case, these fire-retardant plastic pallets burn like wooden pallets and there is no increase in the Commodity Classification. Reinforced and fire-retardant pallets must be provided with markings indicating as such. NFPA 13 also provides requirements for idle pallets. Idle pallet is the term used for pallets that are stored when not in use. These stored idle pallets represent an additional fire load in the warehouse, therefore NFPA 13 requires that they be stored external to the building. If they must be stored inside the warehouse, the size of the idle pallet pile is limited.
What if a commodity is not classified?
If a product is not classified, it can be evaluated by a nationally recognised testing agency to determine the Commodity Classification. This includes three separate fire tests of eight pallet loads of the commodity (24 pallet loads in total). The burn characteristics of the unknown commodity is then compared to the heat release rate of the benchmark commodities to determine the specific Commodity Classification.
How is it being stored?
NFPA 13 recognises two basic storage arrangements: rack storage and all other types of storage arrangements. Rack storage arrangements are common in automated warehouses today. Products are placed on pallets and then placed on the rack supports. Racks can be single row racks up to 1.8 metres (6 feet) in width, double row racks up to 3.7 metres (12 feet) in width, or multi row racks over 3.7 metres (12 feet) in width. If the aisle width between the racks is less than 1 metre (3.5 feet), then a single row rack is considered a double row rack and a double row rack is considered a multi row rack.
The sprinkler installation rules for rack storage are typically organised for racks under 7.6 meters (25 feet) or over 7.6 meters in height. When the racks get very tall or will hold a more combustible commodity, it is common to install in-rack sprinklers to control the fire. In-rack sprinklers are typically installed in the intersecting gaps (flue spaces) between the rack rows and the pallet loads.
Storage arrangements other than rack storage includes solid piles, palletised, shelves, or bin boxes. These types of storage arrangements typically do not have large gaps between the boxes or pallets. Because they are typically stacked on top of each other, their storage height is limited. Solid piles include boxes stacked on top of each other directly on the floor and palletized storage is often stacked on the floor with additional pallet loads stacked on top. Shelf storage arrangements are 0.76 metre (30 inches) wide and can also include back-to-back shelf storage up to 1.5 metres (5 feet) wide.
How tall is the storage and the building?
The storage height is measured to the top of the storage rack frame or to the top of the solid pile or shelves. The height of the building is measured from the floor to the underside of the roof deck/ceiling. These measurements will determine the appropriate installations rules to be followed in NFPA 13.
The greater the ceiling and rack storage height, the more challenging it is for the sprinkler system to deliver the needed water to all levels of the storage system. Densely packed shelves can also create a barrier that prevents water from reaching the fire inboard and at lower-level shelving. Large K-factor sprinklers are utilised to force extinguishing water down through the flue spaces while wetting the surrounding commodity to prevent fire spread.
Full-scale fire simulations are routinely conducted by UL LLC and FM Approvals for the qualification of each sprinkler model and type to ensure there is sufficient water delivery to control the fire. Once the building design and storage arrangement is known, the designer can then begin to select from various types of sprinklers to be considered: Early Suppression Fast Response (ESFR), Control Mode Density Area (CMDA), or Control Mode Specific Application (CMSA), to ensure the appropriate level of protection.
As warehouses and the ever-increasing number of products and storage arrangements continue to evolve, so will the standards that govern these applications. With the help of industry expertise like NFPA and the certifying agencies, sprinkler manufacturers will also continue to develop new products that will meet the growing challenges of warehouse storage protection.