Approximation Terms in Claim Language
In Enviro Tech Chemical Services, Inc., v. Safe Foods Corp.,[1] the U.S. Court of Appeals for the Federal Circuit ruled that a set of patent claims reciting the term “about” was indefinite under 35 U.S.C. § 112(b) because no sufficient guidance was provided regarding the scope of this term. The Federal Circuit thus affirmed an invalidity decision of the district court.
Enviro Tech owns U.S. Patent No. 10,912,321 directed to methods for treating poultry using a peracetic acid solution to increase their weight. In particular, representative claim 1 relates to the treatment of a poultry carcass in peracetic acid-containing water, and recites the steps 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,” and “wherein the peracetic acid-containing water comprises … an antimicrobial amountof a solution of peracetic acid.”
In 2021, Enviro Tech sued Safe Foods Corp. alleging that Safe Foods infringed claims 1–3, 5–12, 14–19, 21–24, 26–29, and 31–33 of the ’321 patent. Safe Foods challenged the validity of these claims by arguing that the terms “about” and “antimicrobial amount” were indefinite under 35 U.S.C. § 112(b). The district court agreed and held that the challenged claims are invalid. Enviro Tech appealed the district court’s decision.
In its decision, the Federal Circuit first reiterated that terms of approximation such as “about” and “approximately” are not inherently definite or indefinite and may appropriately be used to avoid strict numerical boundaries for the range of a parameter. However, the court also emphasized that the use of such approximation terms requires that the claims, patent specification, prosecution history and extrinsic evidence (e.g., prior art) provide sufficient information for a person of ordinary skill in the art to ascertain the scope of that range with reasonable certainty. The Federal Circuit then proceeded to analyze indefiniteness of the term “about” in the claims of the ’321 patent.
First, the court observed that the claim language itself did not clearly define the extent to which the pH of the of the peracetic acid solution could deviate from the recited lower and upper values of 7.6 and 10 while remaining within the scope of the claims.
Next, the Federal Circuit examined the patent specification’s description of multiple examples of an experiment in which the actual pH of peracetic acid-containing water is measured and compared to a predefined target pH value before proceeding with poultry treatment. In many of these examples, treatment proceeded without altering the pH of the solution if the measured pH did not deviate from the target value by more than 0.3. Conversely, when the deviation exceeded 0.3, the pH was often altered in accordance with the ’321 patent before proceeding with treatment.
However, it was noted that the specification also included other examples that did not follow this approach, as treatment proceeded without altering the solution despite larger pH deviations, including deviations between 0.35 and 0.5. In particular, one such example involves large-scale treatment of 5.8 million chickens in a large commercial facility, emphasizing that large pH deviations should not be viewed as anecdotal. The Federal Circuit concluded that the examples presented in the specification provided conflicting guidance that failed to inform a skilled artisan of the scope of the term “about” with reasonable certainty.
Next, the court examined the prosecution history and noted that Enviro Tech’s use of the term “about” was inconsistent. For example, in a response to an Office Action, Enviro Tech stated that a pH of 7.6 was at the lower end of the claim range and argued, without using the term “about,” that the value of this boundary would not have been obvious over the prior art. In the same response, Enviro Tech also argued that “a step of adjusting the pH to the range of about 8 to about 9” would not have been obvious over the prior art. Because Enviro Tech used the term “about” inconsistently during prosecution without ever providing a clear definition of that term, the Federal Circuit concluded that the prosecution history likewise did not appear to offer further guidance regarding the scope of “about.” Enviro Tech argued that because the claimed range had been amended from a pH of “about 7.3” to a pH of “about 7.6” during prosecution, the term “about” should be interpreted as indicating any pH deviation of less than or equal to 0.3. The Federal Circuit found this argument inconclusive as the remarks accompanying the amendments did not support or suggest such an interpretation.
Finally, the Federal Circuit noted that the amendment to recite a pH of “about 7.6” was made to overcome prior art disclosing a pH of 7.0, while the specification itself describes pHs ranging from 6 to 10. The court emphasized that when a claim is amended to overcome a rejection over prior art, the definiteness requirement under 35 U.S.C. § 112(b) requires greater clarity than that provided by an approximation term such as “about.” The Federal Circuit further observed that, without additional guidance, the pH of 7.0 recited in prior art could itself reasonably interpreted as within the scope of “about” 7.6.
In conclusion, the Federal Circuit affirmed the district court's determination that the term “about,” as used in the challenged claims and in further view of the patent specification and the prosecution history, failed to inform a person of ordinary skill in the art of its intended scope with reasonable certainty. On this basis, the court affirmed the district court’s decision that the term “about” rendered those claims indefinite, and therefore invalid.
This decision illustrates that approximation terms, such as “about,” remain permissible in patent claims, and use of such terms may allow inclusion of a specified parameter range without a strict numerical boundary. However, patent drafters and prosecutors are reminded that in including such approximation terms, the claim language, specification and prosecution history must provide clear guidance regarding the interpretation of these terms for the terms to be considered definite. For example, when using an approximation term, one may consider including a specific definition of the term in the specification, providing specific deviation values, or referring to acceptable tolerances known in the art. Furthermore, particular caution should be exercised when relying on approximation terms for a numerical range recited as a distinguishable feature over prior art.
