In a recent precedential decision from the Federal Circuit, the appellate court explained that words of approximation like “about” are not inherently definite or indefinite — but when a patentee fails to provide sufficient guidance as to the meaning of such terms, it can be fatal to the claims. More specifically, in Enviro Tech Chemical Services, Inc. v. Safe Foods Corp., the court affirmed the lower court’s determination that all asserted claims of U.S. Patent No. 10,912,321 were invalid as indefinite under 35 U.S.C. § 112(b) because the term “about” failed to inform skilled artisans about the scope of the invention with reasonable certainty.
Link to Background Background
Enviro Tech’s ’321 patent is directed to methods for treating poultry during processing to increase the weight of the poultry using peracetic acid. Representative claim 1 recites, among other things, a step of altering the pH of the peracetic acid-containing water “to a pH of about 7.6 to about 10 by adding an alkaline source.”
When Safe Foods was sued by Enviro Tech in U.S. District Court for the Eastern District of Arkansas for allegedly infringing the ’321 patent, it argued during claim construction that the term “about” was indefinite. The district court agreed, determining that both “about” and “an antimicrobial amount” were indefinite, and entered judgment that the asserted claims were invalid.
Link to The Federal Circuit’s Analysis The Federal Circuit’s Analysis
In an opinion authored by Judge Alan Lourie, the Federal Circuit reiterated that terms of degree like “about” and “approximately” are not inherently definite or indefinite. However, when such words of approximation are used, the parameter’s range must be “reasonably certain based on the technological facts of the particular case.” The appellate panel systematically examined the intrinsic evidence — the claims, specification, and prosecution history — and found that none provided adequate guidance as to the scope of the term.
Starting with the claim language, the panel noted that, while the claims recite a “pH of about 7.6 to about 10,” they provide no guidance on how much below 7.6 or above 10 the pH could deviate while still meeting the claim limitation. The parties agreed that “about” means “approximately,” but the court observed that “approximately” provides no more clarity than “about” itself.
Turning to the specification, the court found it equally unhelpful. The specification recited numerous experiments where Enviro Tech would set a target pH, measure the actual pH, and proceed based on the difference. In a majority of experiments, Enviro Tech proceeded only when the difference was less than or equal to 0.3 of the target pH. However, there were notable exceptions. In one particularly informative experiment conducted at a major U.S. poultry processing plant with 5.8 million chickens, Enviro Tech proceeded with deviations between 0.35 and 0.5 of the target pH. The court concluded that this conflicting guidance “does not allow a skilled artisan to determine the scope of ‘about’ with reasonable certainty.”
The prosecution history also failed to clarify the scope of the term. In fact, the court found that Enviro Tech’s treatment of “about” during prosecution was inconsistent. In one office action response, Enviro Tech argued that “a peracetic acid solution at the lower end of the claimed range, pH 7.6” would not have been obvious over the prior art — notably omitting the term “about.” Yet, when discussing another claim in the same response, Enviro Tech included “about” in its arguments about pH values. Enviro Tech did not explain what “about” means at any point during prosecution.
Enviro Tech attempted to argue that its amendment of the lower boundary from “about 7.3” to “about 7.6” during prosecution demonstrated that “about” should be construed to mean less than or equal to 0.3 pH. The Federal Circuit was not persuaded and noted that Enviro Tech did not cite any remarks made to or by the examiner that would define the term and never offered any argument indicating what “about” means. The panel also observed that the prior art disclosed a pH as close as 7.0, which necessitated the amendment to the claims. The court noted that the prior art is “almost ‘about’ a pH of 7.6,” highlighting the imprecision of the term.
Link to Takeaway Takeaway
This decision serves as an important reminder that words of approximation in patent claims are not a free pass to avoid strict numerical boundaries. While the Federal Circuit has long recognized that terms like “about” and “approximately” may be appropriately used, patentees bear the burden of ensuring that the intrinsic evidence — particularly the specification and prosecution history — provides skilled artisans with reasonable certainty as to the scope of such terms. When the specification provides conflicting examples of permissible deviations, and the prosecution history is inconsistent in its treatment of the approximation term, the claims will likely fall as indefinite.
In short, if a patent relies on terms like “about” to define a claim boundary, the specification should provide clear and consistent guidance as to what deviations are acceptable — ideally with explicit statements defining the term.