Federal Circuit Holds ‘About’ Indefinite Where Specification Is Internally Contradictory — Enviro Tech v. Safe Foods

The U.S. Court of Appeals for the Federal Circuit issued a precedential opinion on May 4, 2026, affirming that the claim term “about” in a poultry treatment patent is indefinite under 35 U.S.C. § 112(b) where the specification provides internally contradictory guidance on its numerical scope. The decision in Enviro Tech Chemical Services, Inc. v. Safe Foods Corp., No. 24-2160 (Fed. Cir. May 4, 2026), authored by Judge Lourie, provides important guidance on the risks of using terms of approximation without consistent definitional support.

Facts of the Case

Enviro Tech Chemical Services, Inc. owns U.S. Patent No. 10,912,321, titled “Methods of Using Peracetic Acid to Treat Poultry in a Chill Tank During Processing.” Claim 1 requires treating poultry with “an antimicrobial amount of a solution of peracetic acid” at “a pH of about 7.6 to about 10.” Enviro Tech sued Safe Foods Corp. for infringement. Safe Foods challenged the claims as indefinite at the claim construction stage, and the district court agreed.

The Federal Circuit’s Analysis

The Federal Circuit reaffirmed that terms of approximation such as “about” and “approximately” are not inherently indefinite and can be used appropriately in patent claims. However, the definiteness requirement under § 112(b) demands that the scope of a claim be reasonably certain to a person of ordinary skill in the art, in light of the specification and prosecution history.

The problem in this case was not a silent specification — rather, the specification said too much. Laboratory experiments in the specification treated a pH deviation of 0.3 as the working tolerance for “about.” A separate commercial-scale trial, however, documented deviations ranging from 0.35 to 0.5. The court found that these internally conflicting disclosures compounded the uncertainty rather than resolving it: either value could represent the intended meaning of “about 7.6,” but no principled basis existed to choose between them.

Enviro Tech’s prosecution history provided no additional clarity. At no point did Enviro Tech explain what “about” meant in quantitative terms. The term was treated as material and significant in some claims, yet as immaterial in others — an inconsistency that further undermined confidence in the claim scope.

The Federal Circuit thus concluded that the specification “said too much rather than too little” — an unusual circumstance in which affirmative disclosure itself generated indefiniteness by introducing competing numerical ranges without resolving which controlled.

Practical Implications

The Enviro Tech decision carries important lessons for patent prosecutors and litigators. First, terms of approximation in numerical claim limitations require consistent definitional support throughout the specification. If multiple embodiments or examples suggest different tolerances, the patent owner risks having the approximation term declared indefinite under § 112(b). Second, prosecution history must provide consistent treatment of approximation terms across all claims — varying treatment weakens the position in an indefiniteness challenge. Third, as a precedential Federal Circuit opinion, Enviro Tech will serve as a reference point in future claim construction disputes involving “about,” “approximately,” “substantially,” and similar terms of degree.