Box Design

Large storage boxes for potatoes are a relatively new method of storage. During the early 1960s there was a steady move from more casual storage of large piles of potatoes in growers’ sheds to neat vertical stacking of potatoes in large pallet based boxes up to 6 or 7-high in large purpose-built stores. These boxes at the time typically varied from 500 kg to 1000 kg capacity and the buyer usually dictated the exact design and size of the boxes, often to match existing box stock.

3.1_400
1000 kg potato boxes

Almost the entire British potato crop is now stored in these boxes in purpose-built stores, whether for seed or for ware (consumption). They are block-stacked up to 8 boxes high, usually several boxes deep either side of a central fork truck aisle in a large storage building, usually cooled to low temperature. Most boxes are made from one of the European pines or spruces since these species seem to suit the crop and are able to take the very large loads in the stores. These loads have to be withstood without respite for several months of indoor storage and experience has shown this intensity can only be economically met by timber. Other materials such as recycled thermoplastic have not been successful due to lower strength and stiffness under long term load not meeting the BS requirements.

Safety and design. During the time of the change from loose piled storage to boxes from the 1960s to late 1980s there was no British Standard to guide box construction, nor any Potato Marketing Board design guide. The HSE became concerned over what they considered unsafe height stacks (they felt 4-high was a safe limit) and this was causing wasted storage space and higher costs in stores originally built for 7 or 8 high. The Potato Marketing Board (now the Potato Council) supported the technical development work PalletLink proposed and PalletLink successfully bid for a UK Government contract to produce the technical content for a BS. The aim of the BS was greater stack height with appropriate safety which would give a more commercial marketplace. The Potato Marketing Board chaired the technical committee with its members including box manufacturers and timber suppliers who guided PalletLink work throughout the 2 year project.

In 1992 after a substantial amount of testing and development BS 7611: Potato storage boxes for mechanical handling was published, it reflected industry needs and listed several plan sizes each of 1000 kg capacity. These, in the strongest well braced constructions permitted stacks up to 8-high. The BS 7611 is now considered a benchmark for the box construction industry by box manufacturers, potato growers, the storing industry and processors.

Handling and treatment. Wood can decay with innapropriate storage and a past remedy by some seed potato growers, was to  treat the timber with chemical preservative. However, this is strictly not permissible as there are as yet no preservative treatments permitted by the EU for use with timber in contact with foodstuffs and unfortunately boxes used for seed potatoes are indistinguishable from preservative-free boxes produced for ware. 1000 kg seed boxes are usually the same size and design as boxes used for potatoes for human consumption and may easily end up in the food-chain. There is an imminent EN standard aimed at food processors and supermarkets requiring packaging users to audit any chemicals in packaging, this is EN 15593: Management of hygiene in the production of packaging for foodstuffs - Requirements. In the last few years there have been several legal claims for damages in Europe where traces of wood preservatives have been found in foodstuffs so there may now be a case if a new revision of BS 7611 is pressed for by organisations such the Potato Council to require marking of seed boxes at manufacturing point if preservatives have been used.

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PDF31a Agricultural Produce Storage Box Terminology. (PDF 12kb)
PDF31g Avoiding wood decay in potato storage boxes. (PDF 30kb)
PDF52j International strength levels for pallet & box nails. (PDF 72kb)
PDF78b Natural Durability of Timber used in pallets and packaging. (PDF 26kb)
PDF79b Bending strength properties of softwoods. (PDF 32kb)
PDF81h The causes of bluestain in packaging timber. (PDF 83kb)
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