Safe Working Loads

With some types of packaging the safe working load (SWL) is clearly stated on it by the packer or a licensing authority. An example is with ISO Series 1 freight containers where a 20' container has a SWL of 28 tons. With BS 7611 Potato boxes the SWL marked on all boxes is 1000 kg. Certain rental pallet pool operators will advise users on loading but not mark the pallet, but with white pallets there is often much more difficulty when manufacturers or users need to know SWL. Quite frequently manufacturers and users feel they are 'left in the dark' by a BS, EN or ISO standard.

Compression failure in pallet bearer and
deckboards with consequent damage to
the upper payload

Part of the problem is that every pallet has several safe working loads depending on the customer’s type of load and the support variations (eg. goods comprised of interlocked cartons on pallets racked across beams or the same pallet and load never racked) as explained in Datasheet 21f. Vague guidance is published by some exchange-pool operators such as the CP range where a specific test load applied to a given CP pallet results in a given deflection, but how safe is a user or manufacturer in working that out when every pallet has several safe working loads? How much should a manufacturer add (or take away) for safety factor? All pallet users have a duty to address this issue.

When pallet failures occur, not all are common bending failures in deckboards or stringers. The photo above shows an unusual mode of pallet timber failure (compression damage) resulting from too great a superimposed load in stack and/or too small a timber section to resist the load. Apart from the pallet damage, the damage to the sheet material even before delivery to the customer can be clearly seen (compression damage is actually a problem easily solved).

Britain has greater difficulty than most countries with defining SWL. A contributory factor is that we have the largest range of proprietary pallet designs for end users of any European country and even though this range is constrained by an increasingly common overall size of 1200 x 1000, industry still has many different pallet designs without a clearly stated safe working load.

There are methods of working this out, such as using pallet design software, but design software is only as good as the software and the user inputting the data and like any design software it takes no chances with safety and the user might end up with heavier sections and a less commercial specification than preferred. Some of our members use such software and some come to PalletLink when things do not seem quite right. In helping out we sometimes see a rather casual approach to data entered, such as species and moisture condition but we then help out by accessing our database of ISO load test results. Data from a wide range of European designs tested means our recommendation to the Member might be lower, or to increase the SWL.

PalletLink’s service to Members on SWLs divides into these areas –

          Making available published figures for SWL for a well known design
          Providing our estimate of SWL for a well known design
          Providing our estimate of SWL for a proprietary design
          Providing our estimate of SWL for a skid-based packing case

If you doubt a loading figure you have arrived at, contact us with full specification details plus payload and handling method expected and we can usually work it out for you. This is an inclusive member service. The exact input we need to do this for pallets is listed below in Datasheet 25b, for skids and export cases look on the CONTAINERS/EXPORT CASES pages.

If you are looking for a small increase in strength (and SWL) of an existing pallet consider moving to a stronger timber species, see Datasheet 79b on the SPECIES STRENGTH page (due shortly), or increasing thickness see Excel sheet 64b on EXCEL TOOLS page. If fastenings seem to be the cause of failure look at Datasheet 52b to check you are using the recommended size for the payload you are using. If still in doubt we suggest you contact PalletLink.

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PDF21f Every pallet has more than one safe working load (PDF 152kb)
PDF25a Stacking heights for loaded pallets. (PDF 64kb)
PDF25b Data we need to estimate SWL on a pallet. (PDF 200kb)
PDF52b Block pallets - safe nail loads. (PDF 129kb)
PDF92a Safety factors in wood pallets and packaging. (PDF 84kb)
PDF92b Dynamic and nominal pallet rating (PDF 116kb)
PDF92c Pallet distortion and creep deflection under load. (PDF 30kb)
PDF94b Marking of pallets with safe load is not recommended. (PDF 64kb)
Word Doc.96a Hand-arm vibration syndrome. (Word Doc. 30kb)
PDF96b MHSWR, PUWER and LOLER - UK workplace regulations. (PDF 126kb)
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