## Facts

- The Clean Air Act § 112 directed EPA to set hazardous air pollutant standards “at the level” that provides an “ample margin of safety” to protect public health.
- EPA regulated vinyl chloride, which it treated as a potent carcinogen and an apparent nonthreshold pollutant for which science could not identify a completely safe exposure level.
- EPA adopted a technology-based standard reflecting the lowest emissions achievable with best available control technology, producing large reductions but not zero emissions.
- In selecting the standard, EPA relied heavily on technological feasibility and the high cost of additional reductions relative to expected added health benefits.
- NRDC petitioned for review, arguing that because no safe exposure level could be identified, § 112 required emissions limits at or near zero without regard to cost or feasibility.
- The challenged agency action included EPA’s standard for vinyl chloride and EPA’s withdrawal of proposed amendments developed during an earlier regulatory dispute.

## Issues

1. Under Clean Air Act § 112, may EPA consider cost and technological feasibility when setting emission standards for carcinogenic hazardous air pollutants?
2. Must EPA first determine a health-based “safe” (acceptable-risk) emissions level before considering cost and feasibility to set an “ample margin of safety,” or may EPA use feasibility as the primary method for defining the standard?

## Decision

- The D.C. Circuit, sitting en banc, held that § 112 does not bar consideration of cost and technological feasibility.
- The court required a two-step decision process: (1) a health-based determination of a “safe” or acceptable-risk level, and (2) a margin-of-safety determination that may consider cost, feasibility, and related implementation factors.
- The court concluded EPA’s vinyl chloride standard was unlawful because EPA did not adequately make the initial health-based acceptable-risk finding and instead treated feasibility as the primary driver.
- The court vacated the challenged EPA action and remanded for reconsideration consistent with the required framework.

## Legal Principles

- Clean Air Act § 112 makes protection of public health the primary focus of hazardous air pollutant standard-setting.
- For carcinogens where a zero-risk level cannot be scientifically identified, EPA must still make an explicit health-based judgment identifying a “safe” or acceptable-risk level independent of cost.
- After identifying the health-based benchmark, EPA may consider cost, technological feasibility, and practical implementation limits in setting standards that provide an “ample margin of safety.”
- An emissions standard driven principally by technological feasibility, without a prior health-based acceptable-risk determination, violates § 112 and is subject to vacatur and remand.

## Conclusion

The court required EPA to regulate carcinogenic hazardous air pollutants under § 112 through a structured analysis that identifies an acceptable health-risk level first and only then considers cost and feasibility to set the added “ample margin of safety,” vacating and remanding EPA’s vinyl chloride action for failing to follow that sequence.


Nat. Res. Def. Council, Inc. v. EPA, 824 F.2d 1146 (D.C. Cir. 1987) (en banc)