Dear Tapan Kumar Panda,
not much to add to the above references. As a general rule, after DEHT look for actives and degradation product, focusing on sticky, hygroscopic products, and equipment for wet or humid processing where caking is to be expected. CEHT is of microbiological concern.
One issue, which came up during a recent inspection, is the storage of the equipment. Although we have validated a DEHT of seven days, the inspectors did not accept that time. Their concern was that equipment stored dirty (in the dirty equipment storage area), even covered with stretch film, poses a cross contamination risk between stored dirty equipment, potentially passing the cleaning validation looking for one active but potentially contaminated with another active from neighbouring equipment, not considered in the cleaning validation. Although the risk seems low and the whole issue an “inspectional overshoot”, we are now forced to clean the equipment immediately after use, and a DEHT of more than 24 hours is to be treated as a deviation and includes extensive sampling after cleaning, and equipment quarantine until approval.