Atmospheric conditioning in ISTA 3E requires a minimum chamber time of 72 hours. If controlled temperature and humidity conditions are required or are to be used in any test procedure, the best approach is to perform all tests directly in the conditioned atmosphere. If this is not possible, then tests should be performed quickly after removal of test items from the conditioned atmosphere, and test items should be returned periodically to conditioning as necessary to maintain the required control.
The temperature and humidity conditioning times specified in the procedures are dwell times at the specified conditions, and do not include any time which may be required to transition from one condition to another. Some Procedures specify the transition times (ramp times), and those should be followed.
In certain situations longer temperature and humidity conditioning dwell times may be required. There are packaged-product configurations which may equilibrate extremely slowly with their surrounding atmospheres. For example, hot-filled containers in the interior of dense unitized loads may require a week or more to reach room temperature. If necessary, make measurements or calculations and extend the conditioning times accordingly.
The strength of corrugated board is affected by its moisture content, not directly by the surrounding atmospheric humidity. It may be helpful to measure levels and changes in board moisture content during atmospheric conditioning.