IP Law Daily, PATENT—Fed. Cir.: Patent infringement claim invalid, use of ‘about’ found indefinite, (May 4, 2026)

By Jonathan Anderson

When a word of approximation is used, the parameter’s range must be reasonably certain.

The U.S. Court of Appeals for the Federal Circuit affirmed a lower court ruling holding a patent infringement claim invalid because use of the term “about,” as a word of approximation, was indefinite. A three-judge panel of the appeals court said it agreed with the district court’s determination that the intrinsic evidence did not inform a skilled artisan as to the scope of the term “about” with reasonable certainty. The appeals court cited conflicting guidance in the specification and the plaintiff’s inconsistent treatment of the word “about” during the patent’s prosecution (Enviro Tech Chemical Services, Inc. v. Safe Foods Corp., No. 24-2160 (Fed. Cir. May 4, 2026)).

Background. Plaintiff-appellant, Enviro Tech Chemical Services, Inc., sued defendant-appellee, Safe Foods Corporation, alleging that Safe Foods infringed on a patented method of preparing poultry for distribution and sale. Specifically, Enviro Tech alleged that Safe Foods infringed various claims of Enviro Tech’s ‘321 patent directed to “[m]ethods for treating poultry” using “peracetic acid.” During claim construction, Safe Foods alleged that two terms of the representative claim, “an antimicrobial amount” and “about,” were indefinite. In 2022, the U.S. District Court for the Eastern District of Arkansas determined that both terms were indefinite and issued a judgment that the asserted claims were invalid. Enviro Tech appealed.

“About.” Affirming the district court, the Federal Circuit held that the term “about” as used in the representative claim is indefinite, thereby rendering the asserted claims of the ‘321 patent invalid. The appeals court said it agreed with the district court’s determination that the intrinsic evidence did not inform a skilled artisan as to the scope of the term “about” with reasonable certainty.

The Federal Circuit said it has long held that the word “about” may be appropriately used to “avoid[] a strict numerical boundary to a specified parameter,” citing Ortho-McNeil Pharm., Inc. v. Caraco Pharm. Lab’ys, Ltd., 476 F.3d 1321, 1326 (Fed. Cir. 2007) (quoting Pall Corp. v. Micron Separations, Inc., 66 F.3d 1211, 1217 (Fed. Cir. 1995)). Further, the appeals court said that terms of degree, like “about,” are not inherently definite or indefinite. When a word of approximation is used, the parameter’s range must be reasonably certain based on the “technological facts of the particular case.” Ortho-McNeil, 476 F.3d at 1326 (quoting Pall, 66 F.3d at 1217). To ascertain the range, the appeals court said it considers intrinsic evidence—the claims, patent specification, and prosecution history—and extrinsic evidence.

Claim language. The representative claim states that the acidity of the peracetic acid-containing water will be altered to a “pH of about 7.6 to about 10 by adding an alkaline source.” However, the appeals court found that the claims do not provide any guidance on how much below a pH of 7.6 or above a pH of 10 the peracetic acid-containing water can be to meet the limitation. The parties agreed that the ordinary meaning of “about” is “approximately,” but the appeals court said the term “approximately” provides no more guidance on the permissible deviation of the claimed range than the word “about” such that the claim language would inform a skilled artisan as to the meaning of the term.

Patent specification. The appeals court held that the ‘321 patent specification does not inform a skilled artisan of the scope of “about” with reasonable certainty. The appeals court highlighted what it described as conflicting guidance in the specification.

Prosecution history. Enviro Tech’s treatment of the word “about” during the patent’s prosecution was inconsistent and failed to inform a skilled artisan of the representative claim’s scope with reasonable certainty, the appeals court said. The panel further determined that at no point in the prosecution history did Enviro Tech explain what “about” means. Rather, Enviro Tech treated the term inconsistently, which the appeals court said suggested that the term was material to some claims and immaterial to others.

Enviro Tech argued that the district court should have considered the fact that Enviro Tech surrendered claim scope during the prosecution of the ‘321 patent. The Federal Circuit rejected this argument, concluding that Enviro Tech pointed to no remarks it made to the examiner that amount to “repeated and consistent remarks during prosecution [that] can define a claim term.” Enviro Tech, the appeals court said, did not offer an argument to the examiner indicating what “about” means.

“Antimicrobial amount.” Because the appeals court affirmed the district court that “about” is indefinite, which renders all the asserted claims invalid, the appeals court did not address the alternative ground that “antimicrobial amount” is indefinite.

The Case is No. 24-2160.

Judge: Lourie, A.

Attorneys: Seth R. Ogden (Patterson Intellectual Property Law, PC) for Enviro Tech Chemical Services, Inc. Debra Janece McComas (Haynes and Boone, LLP) for Safe Foods Corp.

Companies: Enviro Tech Chemical Services, Inc.; Safe Foods Corp.

Cases: Patent FedCirNews GCNNews