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On October 16, 2009, the United States Court of Appeals for the District of Columbia Circuit (DC Circuit) mandated the vacatur of the “Startup, Shutdown, and Malfunction (SSM) exemption” allowed under General Provisions in Subpart A of the National Emission Standards for Hazardous Air Pollutants (NESHAP).1   Under the SSM exemption, NESHAP Subpart A previously stipulated that an affected source must minimize emissions during SSM events, but it did not require the affected source to comply with the emission limits specified in the relevant NESHAP Subpart.2  As a result of the vacatur, facilities subject to a NESHAP Subpart that directly references the SSM exemption under Subpart A are required to be in compliance with emission limits at all times, even during SSM events. If a particular NESHAP Subpart explicitly exempts applicable sources from meeting emission limits during SSM events, then the specific SSM exemption continues to apply.3  The U.S. Environmental Protection Agency (EPA) issued a memorandum dated July 22, 2009 discussing impacts of court rulings on listed NESHAP Subparts that have no specific SSM exemptions and rely upon Subpart A requirements.4

Since the Subpart A SSM exemption vacatur, a number of NESHAPs have been promulgated, updated, or proposed by EPA. In all cases, EPA addressed SSM events as factory flarepart of the rulemaking process. Depending on the NESHAP, EPA provided different scenarios that apply during SSM events, as follows:

  • Affected sources may be required to comply with emission limits at all times including during startup (SU) and shutdown (SD) events,
  • Affected sources may be required to comply with separate emission limits and/or work practices specifically set for SU and SD events, and/or
  • Affected sources may be required to provide an “affirmative defense” of why an emission limit was exceeded during a malfunction event in order to avoid civil penalties.

Each NESHAP Subpart includes a table that outlines what parts of NESHAP Subpart A are applicable to the subject source category; this table is known as the “General Provisions Table.” Since the SSM exemption vacatur, the General Provisions Table in each promulgated, updated, or proposed NESHAP Subpart specifically states that the Subpart A SSM exemption citations (e.g. 40 CFR 63.6(e)(1)(i), (f)(1), and (h)(1)) do not apply.

EPA’s Strategy to Set Emission Limits for SU and SD Events

Consistent with the SSM exemption vacatur, EPA has set emission limits for recently proposed and final NESHAP Subparts that apply at all times (i.e., there is no exclusion from the emission limits for periods of SSM). EPA reviewed available data from each relevant source category in order to determine if it is appropriate to establish emission limits or work practices during SU and/or SD events that are different from steady-state emission limits. In some cases, EPA determined it was justifiable to require the source category to comply with the previously set “normal operating” emission standards at all times, even during SU and SD events. EPA concluded that this was appropriate because of the length of the averaging period to demonstrate compliance with the emission limitation, or because higher levels of emissions were not expected during SU or SD events.

Additionally, EPA eliminated the SSM Plan requirement in updated and proposed NESHAP Subparts, but affected sources must continue to operate, including operation of associated air pollution control equipment and monitoring equipment, in a manner consistent with safety and good air pollution control practices for minimizing emissions at all times including SSM events.

Malfunction Events and the Affirmative Defense

Under 40 CFR 63.2, a malfunction is defined as a “sudden, infrequent, and not reasonably preventable failure of air pollution control and monitoring equipment, process equipment or a process to operate in a normal or usual manner.”  EPA believes “that a malfunction should not be viewed as a distinct operating mode, and therefore, any emissions that occur during malfunctions do not need to be factored into development of… standards, which, once promulgated, apply at all times.”5  As such, EPA sets NESHAP emission limits by analyzing emissions data that occurs during SU, SD, and/or normal operations.

EPA has included the concept known as the “affirmative defense,” that can be used if an affected source exceeds an emission standard during a malfunction event, in a number of updated NESHAP Subparts.  Affirmative defense is defined as “in the context of an enforcement proceeding, a response or defense put forward by a defendant, regarding which the defendant has the burden of proof, and the merits of which are independently and objectively evaluated in a judicial or administrative proceeding.”6 The concept of “affirmative defense” is meant to offer the source some possible protection from civil penalties for emission limit exceedances during malfunction events. If a malfunction occurs that causes emission limits to be exceeded, the source can use the affirmative defense if the following criteria are met:

  1. Notify the Administrator by telephone or fax as soon as possible, but no later than two business days after the initial occurrence of the malfunction, with an additional written report due to the Administrator within 30 days of the initial occurrence of the exceedance of the standard;
  2. Demonstrate that the excess emissions were caused by a sudden, short, infrequent, and unavoidable failure of air pollution control and monitoring equipment, process equipment, or a process to operate in a normal or usual manner;
  3. Prove that excess emissions could not have been prevented through careful planning, proper design or better operation and maintenance practices and did not stem from any activity or event that could have been foreseen and avoided, or planned for;
  4. Show that the malfunction(s) were not part of a recurring pattern indicative of inadequate design, operation, or maintenance;
  5. Repair the equipment as expeditiously as possible when the applicable emission limitations are exceeded;
  6. Minimize the frequency, amount, and duration of the excess emissions (including any bypass) to the maximum extent practicable;
  7. If the excess emissions resulted from a bypass of control equipment or a process, show that the bypass was unavoidable to prevent loss of life, severe personal injury, or severe property damage;
  8. Take all possible steps to minimize the impact of the excess emissions on ambient air quality, the environment, and human health;
  9. Keep all emissions monitoring and control systems in operation if at all possible;
  10. Document that all actions in response to the excess emissions were properly signed in contemporaneous operating logs;
  11. Demonstrate that at all times, the affected source operated in a manner consistent with good practices for minimizing emissions; and
  12. Prepare a written root cause analysis to determine, correct, and eliminate the primary causes of the malfunction and the excess emissions resulting from the malfunction event at issue. The analysis shall also specify, using best monitoring methods and engineering judgment, the amount of excess emissions that were the result of the malfunction.

Even if a claim of affirmative defense is prepared by a source, excess emissions resulting from malfunctions must be reported in semiannual reports. The reports must include the number, duration, and a brief description for each type of malfunction that occurred during the reporting period and that caused or may have caused any applicable emission limitation at an affected source to be exceeded. The reports must also include a description of actions taken by an owner or operator during a malfunction of an affected source to minimize emissions, including actions taken to correct a malfunction.

Recently Proposed and Final NESHAP Rules

Table 1 summarizes several NESHAP Subparts that have been proposed or finalized since October 16, 2009, following the vacature of the SSM exemption under Subpart A. EPA has taken several different approaches to align updated NESHAP Subparts with the SSM vacatur, thereby requiring an affected source to comply with emission limits or work practice standards at all times. A select number of approaches are further described below:

  • In the Portland Cement Manufacturing Industry NESHAP and the Chemical Manufacturing Area Source NESHAP, separate emissions limits and averaging periods were set for SU events, SD events, and normal operations. In these instances, EPA determined that SU and SD events were characterized by activities and/or production rates that were not typical of normal operation. Therefore, EPA defined SU and SD periods, and set separate emission limits. In the case of the Portland Cement NESHAP, the SU and SD emission limits are in different units (concentration limits) as compared to the emission limits during normal operation (limits normalized to production). EPA provided facilities with the option to claim the affirmative defense when a malfunction occurs at a Portland Cement source.
  • The RICE NESHAP does not include emission limits for SU/SD periods. However, as a work practice requirement, facilities must minimize engine idle time and minimize engine SU to a period needed for appropriate and safe loading of the engine, not to exceed 30 minutes, after which the normal operating emission limitations apply.
  • The Asphalt Processing and Asphalt Roofing Area Source NESHAP contains production-based emission limits that apply at all times. Despite requiring the same production-based emission limits at all times, the averaging period for operations that include a SU/SD event is 24 hours, rather than the 3 hour averaging period for normal operation, in order to account for the decreased production during SU/SD events. Facilities must include emissions during SU/SD events in the calculations of lb/ton emission factor rates for comparison to the emission standards.
  • In the proposed residual risk and technology review (RTR) determination for six previously promulgated NESHAP Subparts, EPA did not propose new emission limits for SU or SD events. However, EPA is accepting emissions information from SU and/or SD events to update the residual risk analysis. EPA also proposed to provide facilities with the option to claim the affirmative defense when a malfunction occurs at an affected source.
  • The proposed Boiler and Process Heater Major Source and Area Source NESHAP Subparts do not set separate emission limits for periods of SU and SD.  In the development of the proposed emission limits, EPA used daily or 30-day rolling compliance periods, which are intended to encompass periods of SU and SD. 

NESHAP Subpart chart


EPA is required to perform RTR determinations for NESHAP Subparts every eight years, depending on when the NESHAP was originally promulgated. As such, all NESHAP Subparts will be reopened in the future, and facilities should expect that EPA will address how an affected source should comply with emission limits during SSM events. Additionally, updated NESHAP Subparts will likely provide facilities with protection against civil penalties by including the affirmative defense option if an emission exceedance occurs at an affected source as a result of a malfunction event.

For facilities currently subject to a NESHAP Subpart that references the vacated SSM exemption in Subpart A, the emission limits in the relevant NESHAP Subpart apply at all times, even during SSM events. Facilities subject to these NESHAP Subparts should keep the required documentation necessary to use the affirmative defense in case an emission exceedance occurs during a malfunction event.  Following the same logic that EPA used in the recently updated NESHAP Subparts, this may protect the facility from civil penalties even if the NESHAP Subpart does not currently address the affirmative defense option. It is important to note that the affirmative defense has not been established for non-malfunction types of events such as planned SU, SD, or maintenance.

In conclusion, facilities should monitor and document emissions at all times to demonstrate that NESHAP Subpart emission limitations are not exceeded. A facility must also develop a good system for tracking excess emissions (planned vs. unplanned SU and SD, malfunction, and other events). Should an exceedance occur, facilities should clearly document all events (and causes of these events) in order to mitigate the risk of incurring a civil penalty. Affected sources complying with NESHAP Subparts that explicitly exempt SSM events should stay informed about proposed or updated NESHAPs to prepare strategies for continuous compliance with emissions limits, including periods of SSM.

1 40 Code of Federal Regulations (CFR), Part 63
2 As noted at 40 CFR 63.6(e)(1)(i), 40 CFR 63.6(f)(1); 40 CFR 63.6(h)(1).  As of the date of this article, 40 CFR 63.6 has not been updated to reflect the vacatur of the SSM exemption.
3 Note that the requirements of Subpart A apply unless superseded by a source category subpart. 
4 Memorandum from Adam M. Kushner, Director, Office of Civil Enforcement, EPA, dated July 22, 2009
5 Federal Register, Volume 75, Number 203, page 65074, dated October 21, 2010.
6 40 CFR 63.1341