D.C. Circuit Reaffirms The Affirmative Defense For Emergency Events

Key Takeaways

• What Happened? The U.S. Court of Appeals for the District of Columbia Circuit (D.C. Circuit) recently overturned the U.S. Environmental Protection Agency's (EPA's) 2023 final rule rescinding the affirmative defense for exceedances of emissions limitations under the Clean Air Act (CAA) caused by emergency events. Read the case here.
• Who is Impacted? The ruling should lead to the reinstatement of the affirmative defense for companies subject to emissions limitations in their Title V permits.
• What Should Industry Do? The regulated community should (1) record and preserve the evidence from emergency events needed to support the defense, (2) urge EPA to reinstate the affirmative defense in its regulations, consistent with the D.C. Circuit opinion, (3) urge states to reinstate the affirmative defense in their Title V regulations, (4) examine existing enforcement cases to raise the affirmative defense if appropriate, and (5) consider and monitor changes to the applicability of the affirmative defense to CAA actions under New Source Performance Standards (NSPS), National Emission Standards for Hazardous Air Pollutants (NESHAP), and Prevention of Significant Deterioration (PSD) regulations.

Overview

EPA must now reinstate its decades-old, recently rescinded, affirmative defense under the CAA for excess emissions caused by emergency events. With the reinstatement of this defense, industry regains its ability to defend unavoidable exceedances of emission limits. Companies have the burden of demonstrating the affirmative defense, and doing so can be fact-intensive and challenging because the narrative criteria of sudden, unforeseeable, and unavoidable are undefined. Companies should employ best practices in recording and preserving evidence they may need to support their defense.

Background

For 30 years, federal CAA Title V operating permit regulations and the vast majority of SIP-approved state and tribal rules included so-called "affirmative defense" provisions to account for emergency situations akin to the "force majeure" defense at common law and codified in most statutes. Emergency events are "sudden and reasonably unforeseeable events beyond the control of the source" that unavoidably cause emissions to exceed technology-based limits in the permit. With a successful demonstration of the affirmative defense, a source can avert or mitigate civil enforcement.

The affirmative defense has a colorful history. Title V of the CAA was enacted in 1990, and in 1992, EPA promulgated the affirmative defense among its Title V implementing regulations. It was in place until its rescission by EPA in 2023.

In 2008, the D.C. Circuit shut down a related EPA exemption for emissions exceedances during startup, shutdown, and malfunction events (SSM) on the basis that the exemption rendered Section 112 air toxics emissions limitations non-continuous, in violation of the CAA, 42 U.S.C. § 7602(k). Sierra Club v. EPA, 551 F.3d 1019, 1027–28 (D.C. Cir. 2008).

EPA originally proposed to repeal the longstanding emergency event affirmative defense provisions in 2016 during the Obama administration, but the first Trump administration withdrew the proposal. On April 1, 2022, the Biden EPA re-proposed the Obama-era rulemaking, 87 Fed. Reg. 19042 (Apr. 1, 2022). See B&D alerts here. On July 21, 2023, the Biden EPA issued a final rule rescinding the emergency event affirmative defense for state and federal operating permit programs under 40 C.F.R. §§ 70.6(g) and 71.6(g), respectively. 88 Fed. Reg. 47029.

If both the SSM exemption and emergency event affirmative defense are unavailable, EPA and state regulators have often approached CAA enforcement actions as if industry must achieve 100% compliance 100% of the time. Although companies could eventually argue that unavoidable emergency events should not be construed as per se violations, this would prolong enforcement litigation, which the enforcing agency would likely view poorly.

The D.C. Circuit's Decision

A coalition of trade associations challenged the 2023 final rule in the D.C. Circuit, and on September 5, 2025, the Court issued its opinion striking down the final rule's rescission of the emergency event affirmative defense (contained in 40 C.F.R. § 70.6(g) (2022)). The case is SSM Litigation Group v. EPA, No. 23-1267, 2025 WL 2552531 (D.C. Cir. Sept. 5, 2025) (https://media.cadc.uscourts.gov/opinions/docs/2025/09/23-1267-2133591.pdf).

In SSM, the EPA offered two arguments in defense of the final rule:

• First, EPA argued the affirmative defense unlawfully "encroached on the judiciary's role under the Clean Air Act to assess penalties for violations of emission limitations." SSM Litig. Grp. at 10 (citing 88 Fed. Reg. at 47030–34). The panel disagreed, characterizing the emergency affirmative defense as a complete affirmative defense to liability and determining that such an affirmative defense does not tie the hands of courts to fashion remedies, as it limits legal liability itself. Id. at 11.
• Second, EPA argued that the D.C. Circuit's reasoning in Sierra Club v. EPA that the SSM exemption violates requirement that emissions limitations be "continuous" under 42 U.S.C. § 7602(k) should be extended to the emergency event affirmative defense as well because it also effectively renders applicable emission limitations non-continuous. SSM Litig. Grp. at 11. The panel rejected this second argument, distinguishing its rulings in both Sierra Club v. EPA and Environmental Committee of Florida Electric Power Coordinating Group, Inc. v. EPA, 94 F.4th 77 (D.C. Cir. 2024) (Florida Electric). The panel clarified that it was not bound by Sierra Club because that case addressed an ex ante exemption, whereas an affirmative defense is a distinct legal concept. The court also explained that Florida Electric did not reach the question of whether a complete affirmative defense would render an emission limitation non-continuous under § 7602(k). On this basis, the panel then held that a complete affirmative defense to liability does not render an emission limitation non-continuous under 42 U.S.C. § 7602(k) because an affirmative defense to violation of an emissions standard leaves that emissions standard in place, even though it relieves the successful party from liability for violating the standard. SSM Litig. Grp. at 12–13.

Because EPA had offered only these two legal arguments to justify its final rule, and not any independent policy rationale for the rescission of the emergency conditions affirmative defense rule, the panel granted the petition and reversed EPA's 2023 rescission of the affirmative defense.

What's Next

The D.C. Circuit's decision does not take effect until the mandate issues in the case, so it is not yet legally in force. In addition, EPA had removed the affirmative defense from its regulations pursuant to the 2023 final rule, so EPA will need to add the affirmative defense back into its regulations under the D.C. Circuit decision. States may also have updated their own Title V regulations to remove the affirmative defense. The regulated community should monitor whether these steps are occurring and advocate for the reinstatement of the affirmative defense where appropriate.

With the reinstatement of the affirmative defense for emergency emissions exceedances under the CAA, industry will regain a necessary opportunity to defend its liability for unforeseeable emissions exceedances.