The Case in One Sentence
In Enviro Tech Chemical Services, Inc. v. Safe Foods Corp., decided on May 4, 2026, the Federal Circuit affirmed that asserted claims of U.S. Patent No. 10,912,321 were invalid as indefinite because the phrase "a pH of about 7.6 to about 10" failed to tell a skilled artisan, with reasonable certainty, where the claimed pH range began.
The technology was practical rather than exotic: Enviro Tech claimed methods of treating poultry carcasses with peracetic acid during processing. The pH range mattered because the claimed process required adjusting the peracetic-acid-containing water into a defined alkaline window. Enviro Tech sued Safe Foods for infringement. Safe Foods responded by attacking the claim language itself.
"About" Was Not the Problem
The Federal Circuit was careful on this point: terms like about, approximately, and substantially are not automatically indefinite. Patent claims often need approximation language because real-world measurements have tolerances, equipment noise, and process variation. A claim that recites a chemical concentration, temperature, pH value, particle size, or geometric relationship may need a little flexibility to map the invention onto industrial reality.
The legal problem begins when the record gives no principled way to translate the approximation into claim scope. "About 7.6" is acceptable only if a skilled artisan can understand, from the claims, specification, prosecution history, and relevant technical context, whether a value such as 7.3, 7.2, or 7.1 falls inside or outside the claim.
Approximation language is useful when it accounts for known variation. It becomes dangerous when it quietly moves the very boundary that separates the invention from the prior art.
The Specification Pointed in Different Directions
Enviro Tech's specification did not supply a stable answer. Some laboratory examples suggested that deviations within 0.3 pH units were acceptable. That would place the lower edge of "about 7.6" near 7.3.
But the specification also described a large-scale field test involving millions of poultry carcasses where the actual pH deviation was larger, roughly 0.35 to 0.5 pH units. That data implied that "about 7.6" might extend to 7.25, 7.1, or lower. The patent did not explain which dataset controlled, why the tolerances differed, or how a skilled artisan should reconcile the laboratory and field examples.
This is the drafting failure that often hides in plain sight. Examples are not just technical support; they are interpretive evidence. When examples suggest inconsistent tolerances for the same claim term, the specification can become the accused infringer's best invalidity exhibit.
The Prosecution History Made the Boundary Critical
The prosecution history turned a drafting weakness into a claim-ending problem. During examination, Enviro Tech amended the lower pH boundary from "about 7.3" to "about 7.6" to move away from prior art that disclosed pH 7.0.
That amendment made the lower boundary strategically central. If "about 7.6" could reach down by 0.5 pH units, it might cover approximately 7.1 and sit uncomfortably close to the very prior art the amendment was meant to avoid. If it could reach down only 0.3 units, the applicant had a cleaner separation. But Enviro Tech never told the examiner what "about" meant in this amended range.
On appeal, Enviro Tech argued that changing 7.3 to 7.6 implicitly showed that "about" could not exceed a 0.3 pH deviation. The Federal Circuit rejected that after-the-fact theory. Prosecution history works through what the applicant actually puts into the record, not what litigation counsel later says the amendment must have meant.
When a claim is amended to avoid prior art, any approximation word at the new boundary becomes high-risk. The response should explain why the approximation does not reclaim what was surrendered or overlap the reference being distinguished.
Drafting Lessons for Cross-Border Applicants
For Chinese applicants entering U.S. prosecution, this decision is a useful reminder that familiar words such as "about," "approximately," and "substantially" cannot be treated as harmless translation choices. They are claim-scope tools. Used well, they preserve commercially important flexibility. Used casually, they can make the claim boundary unknowable.
The decision also shows why U.S. prosecution responses should not simply state that amended claims are distinguishable. They should explain how the amended numerical boundary works, especially where the amendment was made to clear a close prior-art value. Silence may feel tactically convenient during examination, but it leaves the patent exposed in litigation.
A Practical Response Template
When amending a numerical range with approximation language, a prosecution response can often protect the record with a short, precise explanation:
The amended lower boundary of about X should be understood in view of Examples A-C, which show acceptable process variation of no more than Y under the relevant operating conditions. Thus, the amended range does not encompass the prior-art value Z relied upon by the Examiner.
That kind of statement will not solve every definiteness problem. It must be true, technically supportable, and aligned with the specification. But it gives the record a bridge between the numerical amendment, the approximation word, and the prior-art distinction. Enviro Tech's record lacked that bridge.
The Bottom Line
"About" did not destroy the patent by itself. What destroyed the asserted claims was a combination of three things: inconsistent specification data, an amendment that made the lower boundary decisive, and a prosecution history that never explained the amended approximation. For patent drafters, translators, and prosecution counsel, the lesson is simple: when a soft word sits on a hard boundary, the record must do the hard work.