It has been a few years since I worked on a medical project dealing with shipping biological samples within liquid, but there is something about including absorbing material in sufficient amount to absorb all of the liquid if the primary containment were to leak, and secondary means of containing the resulting mix of wet absorbent after it absorbed the liquid.
I have seen cheap combinations of absorbent in insufficient quantity and placement that essentially pay homage to the existence of this rule so as to get the product shipped without adding cost to the shipping by increasing weight and size, but in reality would not do the job of containing the fluid should a leak occur.
One of the things to keep in mind is that should a leak occur, the shipper may be liable for ALL the cost to clean it up. Including replacing equipment, and man-hours. And that can add up to thousands of dollars.