The US Court of Appeals for the Federal Circuit affirmed a judgment of indefiniteness, concluding that the use of the term “about” to define a critical pH limitation failed to inform skilled artisans of claim scope with reasonable certainty under 35 U.S.C. § 112. Enviro Tech Chemical Services, Inc. v. Safe Foods Corp., Case No. 24-2106 (Fed. Cir. May 4, 2026) (Lourie, Prost, Burroughs, JJ.)

Enviro Tech owns a patent that claims a method for treating poultry during processing to increase the weight of the poultry by using peracetic acid. Each claim in the patent requires the 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.

During claim construction, the district court concluded that the term “about” was indefinite, finding that the intrinsic evidence did not inform a skilled artisan as to the scope of the term “about” with reasonable certainty. Enviro Tech appealed.

The Federal Circuit has long held that words such as “about” and “approximately” may be appropriately used to avoid a strict numerical boundary to the specified parameter. However, when a word of approximation is used, the parameter’s range must be reasonably certain based on the “technological facts of the particular case” and considering the claims, specification, prosecution history, and extrinsic evidence.

Starting with the claims, the Federal Circuit found that they failed to provide meaningful guidance on how far below a pH of 7.6 or above a pH of 10 the peracetic-acid-containing water could fall and still satisfy the limitation. Although the parties agreed that “about” ordinarily means “approximately,” the Court concluded that substituting one term for the other does not clarify the permissible deviation from the claimed range or otherwise inform a skilled artisan of the scope of the claims.

The Federal Circuit next turned to the specification, finding that it also failed to define the scope of “about” with reasonable certainty because it provided inconsistent guidance on acceptable pH deviations. Although the specification disclosed experiments where Enviro Tech only proceeded when the measured pH was within 0.3 of the target, the specification also described instances where Enviro Tech continued experiments despite larger deviations, including a large scale poultry processing test with pH variances of up to 0.5. Given these unexplained exceptions (particularly in a commercially significant real world setting) the Court found that the 0.3 threshold could not be treated as a reliable boundary for “about.” Thus, the Court found that the specification’s conflicting examples left skilled artisans without clear notice of the claimed scope.

Turning to the prosecution history, the Federal Circuit found that Enviro Tech treated the term “about” inconsistently. For instance, 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 word “about.” Yet on the very next page, Enviro Tech asserted that “a step of adjusting the pH to the range [...]

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