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Status:Closed    Asked:Dec 04, 2012 - 08:31 AM

Will the compensating factor for Compression be different when Atmospheric Conditioning be done or not be done?

The Compensating Factor is used toaccount for effects which may not be simulated in the laboratory tests, such astemperature/humidity conditions, misalignments, long-duration loading,etc. ISTA suggests a factor, but other values may be used in certainsituations including reduced factors. Then if the Atmospheric Conditioning is performed at the first of the test , should we reduce the Compensating Factor? If we should reduced,then what the Compensating Factor might be?

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Compression test compensating factors are meant to account for things which affect stacking strength in the real world but which are not being tested for in the lab like temperature/humidity, storage time under load, pallet stacking patterns, overhang, pallet deck board gap and excessive handling. Corrugated containers are usually tested in the lab at around 50% relative humidity, yet under high humidity conditions in the field can lose more than half their strength. If you are conditioning and testing your packaged-product at an elevated relative humidity/temperature level then you do not need to compensate for those factors when calculating your test force or test load. How much to reduce your compensating factor will depend on the extent and level of your conditioning. If you do not use the ISTA recommended compensating factor, sufficient justification must be provided in the test report for the change. Please see the “Package Engineering” section of the Fibre Box Handbook (available from for a more detailed discussion on compensating factors and how to reduce them if you are already conditioning your packaged product to elevated RH levels.

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Source: A.J. Gruber - ISTA


Dec 04, 2012 - 08:31 AM

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To add to AJ's comments, I have worked up a justification before. See the example below:

When preconditioning to elevated humidity levels, it is important to consider that the ISTA 3E compensation factor of 3 already accounts for some level of increased humidity. Based on the multipliers defined in the Fibre Box Handbook, the factor of 3 could be based on 30 day stack life multiplier of 0.6, 80%RH multiplier of 0.68 and misalignment of column stack multiplier of 0.85 (resulting in a calculated multiplier of 1/[0.60*0.68*0.85] = 2.88; rounded up to 3). So, based on the same formula, if the sample was conditioned to 80% prior to testing, a safety factor of 2 could justifiably be used (1/[0.60*1.0*0.85] = 1.96; rounded up to 2).


Dec 04, 2012 - 09:19 AM

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