One of the classic canons of claim construction is that different claim terms in a patent are presumed to have different meanings.  The Board found an exception to that general rule in Air Liquide Large Indus. v. Praxair Technology, IPR2015-01075, Paper 11.  The technology involved storing hydrogen in a salt cavern. The issue involved the broadest reasonable interpretation of “substantially impermeable barrier” and “permeation barrier,” two terms used in separate independent challenged claims.  Petitioner argued, with specification and expert support, that permeation barrier meant something formed in the cavern walls to reduce the permeation of the cavern after it is formed.

“Substantially impermeable barrier” was not defined in the specification. Petitioner’s expert found it simply meant the walls of the cavern. The PTAB criticized this because it ignored the claim language required the barrier to be “formed” by maintaining a certain pressure. The PTAB thus construed found the term also meant a barrier formed in the cavern from sufficient pressure to become substantially impermeable to hydrogen.

In doing so, the PTAB recognized it was “construing two terms, used in different independent claims…, to refer essentially to the same thing.”  Mindful of the canon against this, the Board found some saving grace:  “We understand there may be a slight difference between the terms, but, on the present record, this distinction does not come into play and, as such, it is proper to construe these terms to be the same insofar as they are both directed to a formed barrier as construed above.”