Lessons from Enviro Tech Chemical Services, Inc. v. Safe Foods Corp. and Beyond

Few words in patent drafting carry as much interpretive weight as the word "about." It is a term of approximation that patent practitioners routinely deploy to cushion numerical claim limitations, hoping to capture embodiments that fall near — but not precisely on — a stated value. Yet, as the Federal Circuit's decision in Enviro Tech Chemical Services, Inc. v. Safe Foods Corp. demonstrates, the scope of "about" is far from self-defining, and its interpretation can be outcome-determinative in both infringement and validity disputes.

The Enviro Tech Decision

In Enviro Tech, the patent at issue claimed a method of treating food products with a sanitizing solution containing peracetic acid at a concentration of "about 30 ppm." The central question before the Federal Circuit was straightforward in its framing but vexing in its resolution: what range of concentrations does "about 30 ppm" actually encompass?

The district court had construed "about 30 ppm" narrowly, and the Federal Circuit took the opportunity to articulate guiding principles for the construction of approximation terms. The court emphasized that "about" is a term of degree, which avoids a strict numerical boundary to a specified parameter. Its meaning must be interpreted in the context of the patent specification, the prosecution history, and the understanding of a person of ordinary skill in the art. The court cautioned against reducing "about" to a fixed mathematical tolerance — such as plus or minus ten percent — absent clear intrinsic evidence supporting that construction. In the court's view, the permissible range of "about" is technology-dependent, and what constitutes a meaningful deviation from a stated value in one field may be trivial in another.  In addition, the relevant art impacts the range for which “about” may reach.

The practical consequence is significant. By defining the scope of "about 30 ppm" more broadly than the district court had, the Federal Circuit altered the infringement calculus entirely, underscoring how a single modifier can shift the boundaries of patent protection.

A Recurring Battleground

Enviro Tech is hardly an isolated example. The word "about" has generated substantial litigation across technology sectors. In Ortho-McNeil Pharmaceutical, Inc. v. Caraco Pharmaceutical Laboratories, Ltd., the court grappled with the meaning of "about 1:5" as a weight ratio in a pharmaceutical formulation patent. There, the intrinsic record provided guidance that allowed for a reasonable construction, but the dispute itself illustrated the recurring tension: patentees want "about" to be broad enough to capture competitive products, while accused infringers argue it should be limited closely to the literal value stated.

Similarly, in Pall Corp. v. Micron Separations, Inc., the Federal Circuit addressed approximation language in the context of pore sizes for filtration membranes. The court reinforced the principle that the meaning of "about" depends on the technological context and cannot be divorced from the specification and prosecution history.

Drafting Implications

For patent practitioners, these cases collectively offer several practical lessons. First, relying on "about" without providing definitional support in the specification is a gamble. Drafters should consider including explicit statements defining the intended range of approximation terms, or at least disclosing embodiments at the outer bounds of the intended range to anchor a broader construction. Second, the prosecution history matters enormously. Amendments or remarks made during prosecution that narrow the scope of an approximation term can estop a patentee from later reclaiming the breadth it surrendered, making careful prosecution conduct essential. Third, practitioners should be mindful that "about" does not function identically to other approximation terms such as "approximately," "substantially," or "generally." Each carries its own interpretive baggage, and courts have not always treated them as interchangeable.

Conclusion

The word "about" is deceptively simple. In ordinary conversation, it signals imprecision and invites little scrutiny. In patent claiming, however, it is a term of art whose scope is determined by the intrinsic record and the expectations of those skilled in the relevant field. Enviro Tech remains a foundational decision for understanding how courts approach this term, but it also serves as a reminder that approximation language is not a substitute for careful claim drafting and thorough specification support. Patent practitioners who treat "about" as a one-size-fits-all safety net do so at their own risk — and at the risk of their clients' patent portfolios.