Also included in the contract requirements were the doors and covers protecting the machine operators the requirements of which included E-stop button placement, fault switches, and door and cover kill switches. 
Additional requirements included a complete analysis of ergonomics and gas spring placement and alignment to provide lifting assistance and holding the covers open during maintenance or other functional activities such as clearing a jam.

             

Learn more about the FSS from Northrup Grumman here and here

Google the USPS Flat Sequence Sorter here