Enviro Tech Chemical Services v. Safe Foods Corp. — Federal Circuit Affirms Patent Invalidity for Indefinite Use of “About” in Claim Ranges

Background

Enviro Tech Chemical Services holds U.S. Patent 10,912,321, which covers methods for treating poultry during processing to increase yield weight using peracetic acid. The key claim limitation requires altering the pH of a peracetic acid-containing water solution to “a pH of about 7.6 to about 10 by adding an alkaline source.”

Enviro Tech sued Safe Foods Corp. for infringement in the Eastern District of Arkansas. During claim construction, Safe Foods argued that the terms “an antimicrobial amount” and “about” were indefinite under 35 U.S.C. § 112(b). The district court agreed on both counts and invalidated all asserted claims. Enviro Tech appealed to the Federal Circuit.

The Court’s Holding

The Federal Circuit affirmed, finding the term “about” indefinite. Writing for the panel, Judge Lourie acknowledged that approximation words like “about” and “approximately” are not inherently indefinite — they can legitimately “avoid a strict numerical boundary.” But a patent must still provide enough guidance that a skilled artisan can determine the scope of the claim with reasonable certainty.

The court examined three sources of intrinsic evidence and found all of them wanting. First, the claim language itself provided no guidance on how far above or below the stated pH range (7.6 to 10) would still satisfy the limitation. Second, the specification’s experimental examples were contradictory: most experiments proceeded only when the pH deviated by 0.3 or less from the target, but several key experiments — including the largest-scale trial involving 5.8 million chickens at a commercial processing plant — tolerated deviations of 0.35 to 0.5 pH. This “conflicting guidance” meant a skilled artisan could not determine the scope of “about” with reasonable certainty.

Third, the prosecution history compounded the uncertainty. In office action responses, Enviro Tech inconsistently treated “about” — sometimes omitting it when arguing that “pH 7.6” distinguished the prior art, but including it in adjacent arguments about other claims. The court was also unpersuaded by Enviro Tech’s argument that amending the lower boundary from “about 7.3” to “about 7.6” implicitly defined “about” as within 0.3 pH, noting that Enviro Tech never explained this meaning to the examiner. Crucially, because the prior art extended to pH 7.0 and the amendment was made to avoid that art, the court found the definiteness requirement “necessitates much more clarity than using the vague term ‘about.'”

Key Takeaways

• Approximation terms are not free passes. Patent drafters who use words like “about” or “approximately” must ensure the specification provides consistent, clear guidance on the permissible range of deviation — or risk indefiniteness.
• Inconsistent specification examples create indefiniteness risk. Where different experiments in the specification tolerate different deviations from a target value, a court may conclude the patent fails to define the approximation term with reasonable certainty.
• Prosecution history consistency matters. If a patentee treats a claim term as material in some arguments to the examiner but immaterial in others, this inconsistency weighs toward indefiniteness.
• Proximity to prior art heightens scrutiny. When claim boundaries are close to the prior art — here, pH 7.0 in the prior art versus “about 7.6” in the claim — courts demand greater precision in approximation terms, since vagueness could improperly recapture disclaimed scope.

Why It Matters

This decision reinforces that the word “about” in patent claims is not a magic bullet for adding flexibility to numerical limitations. Companies that rely on range-based claims — common in chemical, pharmaceutical, and manufacturing patents — should take note: the specification must provide a consistent baseline for what “about” means. When different examples in the patent suggest different tolerances, and the prosecution history fails to clarify the term, courts will not guess at the inventor’s intent.

For accused infringers, the case offers a roadmap for challenging approximation-based claims. Look for inconsistencies between the specification’s examples, arguments made to the patent examiner, and the proximity of the claimed range to the prior art. Where all three point in different directions, indefiniteness may be fatal to the patent.