Related: How do I quickly open or close a jammed zipper?:
In an emergency situation, what would be the fastest way to open a zipper, provided that the use of the pull tab is disabled, and access to the top stop and box pin are inaccessible?
Neglecting issues of damage to what lies behind the zipper, is there a specific method by which to easily separate the teeth with an instrument such as a knife from the middle? Where easily is defined as factor of minimal applied force and accessibility of said tool.