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Research Paper FPL–RP–707 8 Brindley 2006). The selected, most typical, designs were 48 by 40 in. (19 by 16 cm) retail- or distribution-style stringer LD, stringer HD, block LD, and block HD pallets (see Appendix B for technical specifications). The design specifications and RSL data for the four different pallet types and FUs are provided in Table 2. Load carrying capacity and RSL of the pallets were used to calculate the amount of pallets required to satisfy the selected FU (Table 2). As noted, the load carrying capacity is vitally important in determining the FU of a pallet. The load carrying capacity of a pallet can vary greatly depending on the intended usage and should therefore be clearly stipulated. For this study, the RAL basis was used for loading capacity values, because it is typically the most aggressive support condition a pallet may encounter. As expected, HD pallets lasted longer and were heavier than LD pallets for both stringer and block. The design specifications and FU for the industry-average pallet used for the analysis are provided in Table 3. 1.4 Allocation Rules Allocation is required for multi-output systems where two or more functions are delivered (ISO 2006b). For the life- cycle phases including multifunctional processes, economic allocation can be used depending on the value of product and coproducts. However, for this study, mass allocation was used (UL Environment 2019a). Mass allocation has become the preferred approach for wood products given the uncertainty and poor availability of pricing data especially for coproducts (Taylor and others 2017, UL Environment 2019b). The system process was divided into unit processes, and allocation occurred at the wood preparation and board shaping unit processes. Producing pallet boards from cants and lumber coming in produces wood coproducts. The energy and material inputs of the downstream unit processes, including assembly–nailing, heat treatment, and stamping–painting, were not allocated to coproducts because they were consumed after the coproducts were produced. Table 2—Specifications, predicted reference service life (RSL), and functional units of wooden pallet designs Pallet type Overall predicted service life (trips) Load capacity a (racked "across the length") (lb) b Average board feet per pallet Average weight (lb) Number of pallets required to transport 100,000 lb of product Stringer light duty 10 1,000 (454) 10.9 31 10 Stringer heavy duty 38 1,500 (680) 14.4 41 1.75 Block light duty 16 1,500 (680) 14.2 44 4.07 Block heavy duty 66 2,500 (1,134) 22.1 67 0.61 a The Pallet Design System (National Wooden Pallet and Container Association, Alexandria, Virginia, USA) incorporates a safety factor of 2 to 2.5 in all loading capacity estimations. b Equivalent values in kilograms are given in parentheses. Table 3—Specifications and functional units of the industry-average wooden pallet Specification Value Average weight (kg) at 12% moisture content 18.57 Average weight (oven-dry kg) at 12% moisture content 16.58 Average actual board feet per pallet 14.069 Load supported during the life of the pallet (racked "across the length") (lb) 46,986 Number of pallets required to transport 100,000 lb (45.4 metric tons) pallet loads of product 2.13 1.5 Life-Cycle Impact Assessment Methodology and Types of Impacts The impact categories examined in this study included GW (kg CO 2 -eq), acidification (kg SO 2 -eq), eutrophication (kg N-eq), ozone depletion (OD) (kg chlorofluorocarbons- 11-eq), smog formation (kg O 3 -eq), and fossil fuel depletion (FD) (MJ surplus). Among the available methods for the LCIA, TRACI v2.1 was used in this study (Bare 2011). TRACI is a midpoint level impact assessment model developed by the U.S. Environmental Protection Agency and is specifically representative for the United States using input parameters consistent with U.S. conditions. The LCIA phase establishes links between the LCI results and potential environmental impacts. The LCIA calculates impact indicators, such as GW and smog. These impact indicators provide general, but quantifiable, indications of potential environmental impacts. The target impact indicator, the impact category, and means of characterizing the impacts are summarized in Table 4. The six impact categories reported were consistent with the requirement of the wood pallet PCR (UL Environment 2019a). 1.6 Biogenic Carbon Calculations The carbon accounting was performed by taking into account the biogenic carbon content of wood, which is a biobased material. The calculations were performed in line with the wooden pallet PCR and conform to ISO 21930

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