UNITED STATES ENVIRONMENTAL PROTECTION AGENCY 

WASHINGTON, D.C. 20460 

September 20, 1999

MEMORANDUM

SUBJECT: State Implementation Plans: Policy Regarding Excess

Emissions During Malfunctions, Startup, and Shutdown

FROM: Steven A. Herman 

Assistant Administrator for Enforcement and Compliance

Assurance

Robert Perciasepe

Assistant Administrator for Air and Radiation

TO: Regional Administrators, Regions I - X 

EPA’s policy for state implementation plans (SIPs) regarding

excess emissions during malfunctions, startup, shutdown, and

maintenance is contained in memoranda from Kathleen Bennett,

formerly Assistant Administrator for Air, Noise and Radiation

dated September 28, 1982 and February 15, 1983. A recent review

of SIPs suggests that several contain provisions that appear to

be inconsistent with this policy, either because they were

inadvertently approved after EPA issued the 1982-1983 guidance or

because they were part of the SIP at that time and have never

been removed. In order to address these provisions in a

consistent manner, today we are reaffirming and supplementing the

1982-83 policy. In so doing, we are taking this opportunity to

clarify several issues of interpretation that have arisen since

that time. The updated policy will clarify the types of excess

emissions provisions states may incorporate into SIPs so that

they can in turn provide greater certainty to the regulated

community. 

As EPA stated in its 1982 memorandum, because excess

emissions might aggravate air quality so as to prevent attainment

or interfere with maintenance of the ambient air quality

standards, EPA views all excess emissions as violations of the

applicable emission limitation. Nevertheless, EPA recognizes

that imposition of a penalty for sudden and unavoidable
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malfunctions caused by circumstances entirely beyond the control

of the owner or operator may not be appropriate. Accordingly, a

state or EPA can exercise its “enforcement discretion” to refrain

from taking an enforcement action in these circumstances. 

The main question of interpretation that has arisen

regarding the old policy is whether a state may go beyond this

“enforcement discretion” approach and include in its SIP a

provision that would, in the context of an enforcement action for

excess emissions, excuse a source from penalties if the source

can demonstrate that it meets certain objective criteria (an

“affirmative defense”). This policy clarifies that states have

the discretion to provide such a defense to actions for penalties

brought for excess emissions that arise during certain

malfunction, startup, and shutdown episodes.

In the context of malfunctions, EPA recognizes that even

equipment that is properly designed and maintained can sometimes

fail. At the same time, EPA has a fundamental responsibility

under the Clean Air Act to ensure that SIPs provide for

attainment and maintenance of the national ambient air quality

standards (“NAAQS”)and protection of PSD increments. Thus, EPA

cannot approve an affirmative defense provision that would

undermine the fundamental requirement of attainment and

maintenance of the NAAQS, or any other requirement of the Clean

Air Act. See sections 110(a) and (l) of the Clean Air Act, 42

U.S.C. § 7410(a) and (l).1 Accordingly, an acceptable

affirmative defense provision may only apply to actions for

penalties, but not to actions for injunctive relief. This

restriction insures that both state and federal authorities

remain able to protect air quality standards and PSD increments. 

Furthermore, this approach is appropriate only when the

respective contributions of individual sources to pollutant

concentrations in ambient air are such that no single source or

small group of sources has the potential to cause an exceedance

of the NAAQS or PSD increments.2 Where a single source or small

1Pursuant to Section 110(l), EPA may not approve a SIP

revision if “the revision would interfere with any applicable

requirement concerning attainment and reasonable further

progress, or any other applicable requirement of this chapter.” 

See also CAA § 193, 42 U.S.C. § 7515, and the definitions of

“emission limitation” and “emission standard” contained in CAA

§ 302(k), 42 U.S.C. § 7602(k).

2 In the case of lead and sulfur dioxide, attainment

problems usually are caused by one or a few sources and an

affirmative defense is not appropriate. This situation can be
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group of sources has the potential to cause an exceedance of the

NAAQS or PSD increments, EPA believes an affirmative defense

approach will not be adequate to protect public health and the

environment, and the only appropriate means of dealing with

excess emissions during malfunction, startup, and shutdown

episodes is through an enforcement discretion approach.3

EPA is also taking this opportunity to clarify that it does

not intend to approve SIP revisions that would allow a state

director’s decision to bar EPA’s or citizens' ability to enforce

applicable requirements. Such an approach would be inconsistent

with the regulatory scheme established in Title I of the Clean

Air Act. EPA is also adding contemporaneous record keeping and

notification criteria to make its policy regarding these types of

events consistent with its enforcement approach. 

Finally, EPA is clarifying how excess emissions that occur

during periods of startup and shutdown should be addressed. In

general, because excess emissions that occur during these periods

are reasonably foreseeable, they should not be excused. However,

EPA recognizes that, for some source categories, even the best

available emissions control systems might not be consistently

effective during startup or shutdown periods. In areas where the

respective contributions of individual sources to pollutant

concentrations in ambient air are such that no single source or

small group of sources has the potential to cause an exceedance

of the NAAQS or PSD increments, these technological limitations

may be addressed in the underlying standards themselves through

narrowly-tailored SIP revisions that take into account the

potential impacts on ambient air quality caused by the inclusion

of these allowances. In these instances, as part of its

justification of the SIP revision, the state should analyze the

particularly aggravated where a short-term standard (e.g., where

exceedances or violations are based on a few hour period) is also

in place. Although this policy is generally applicable for other

NAAQS, enforcement discretion is the only appropriate approach

for dealing with excess emissions during startup, shutdown, and

malfunction in a specific area where a single source or a small

group of sources has the potential to cause nonattainment of a

short-term NAAQS.

3 In American Trucking Association v. EPA, 175 F. 3d 1027

(D.C. Circ., 1999), the court remanded the PM2.5 NAAQS to the

EPA. The Agency has not determined whether this policy is

appropriate for PM2.5 NAAQS.
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impact of the potential worst-case emissions that could occur

during startup and shutdown.4

In addition to this approach, states may address this problem

through the use of enforcement discretion or they may include a

general affirmative defense provision in their SIPs for short and

infrequent startup and shutdown periods along the lines outlined

in the attachment. As mentioned above, however, in those areas

where a single source or small group of sources has the potential

to cause an exceedance of the NAAQS or PSD increments, issues

relating to excess emissions arising during startup and shutdown

may only be addressed through an enforcement discretion approach.

All Regions should review the SIPs for their states in light

of this clarification and take steps to insure that excess

emissions provisions in these SIPs are consistent with the

attached guidance.

Attachment

4States may account for such emissions by including them in

their routine rule effectiveness estimates. Rule effectiveness

estimates may be prepared in accordance with an EPA policy

document entitled “Guidelines for Estimating and Applying Rule

Effectiveness for Ozone/Carbon Monoxide State Implementation Plan

Base Year Inventories.” (EPA-452/R-92-010) November 1992.
Attachment

POLICY ON EXCESS EMISSIONS DURING MALFUNCTIONS, STARTUP, AND

SHUTDOWN

Introduction

This policy specifies when and in what manner state

implementation plans (SIPs) may provide for defenses to

violations caused by periods of excess emissions due to

malfunctions,1 startup, or shutdown. Generally, since SIPs must

provide for attainment and maintenance of the national ambient

air quality standards and the achievement of PSD increments, all

periods of excess emissions must be considered violations. 

Accordingly, any provision that allows for an automatic

exemption2 for excess emissions is prohibited. 

However, the imposition of a penalty for excess emissions

during malfunctions caused by circumstances entirely beyond the

control of the owner or operator may not be appropriate. States

may, therefore, as an exercise of their inherent enforcement

discretion, choose not to penalize a source that has produced

excess emissions under such circumstances. 

This policy provides an alternative approach to enforcement

discretion for areas and pollutants where the respective

contributions of individual sources to pollutant concentrations

in ambient air are such that no single source or small group of

sources has the potential to cause an exceedance of the NAAQS or

PSD increments. Where a single source or small group of sources

has the potential to cause an exceedance of the NAAQS or PSD

increments, as is often the case for sulfur dioxide and lead,3

EPA believes approaches other than enforcement discretion are not

appropriate. In such cases, any excess emissions may have a

significant chance of causing an exceedance or violation of the

applicable standard or PSD increment. 

1The term excess emission means an air emission level which

exceeds any applicable emission limitation. Malfunction means a

sudden and unavoidable breakdown of process or control equipment.

2The term automatic exemption means a generally applicable

provision in a SIP that would provide that if certain conditions

existed during a period of excess emissions, then those

exceedances would not be considered violations. 

3This policy also does not apply for purposes of PM2.5

NAAQS. In American Trucking Association v. EPA, 175 F. 3d 1027

(D.C. Circ., 1999), the court remanded the PM2.5 NAAQS to the

EPA. The Agency has not determined whether this policy is

appropriate for PM2.5 NAAQS.
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Except where a single source or small group of sources has

the potential to cause an exceedance of the NAAQS or PSD

increments, states may include in their SIPs affirmative

defenses4 for excess emissions, as long as the SIP establishes

limitations consistent with those set out below. If approved

into a SIP, an affirmative defense would be available to sources

in an enforcement action seeking penalties brought by the state,

EPA, or citizens. However, a determination by the state not to

take an enforcement action would not bar EPA or citizen action.5

In addition, in certain limited circumstances, it may be

appropriate for the state to build into a source-specific or

source-category-specific emission standard a provision stating

that the otherwise applicable emission limitations do not apply

during narrowly defined startup and shutdown periods.

I. AUTOMATIC EXEMPTIONS AND ENFORCEMENT DISCRETION

If a SIP contains a provision addressing excess emissions,

it cannot be the type that provides for automatic exemptions. 

Automatic exemptions might aggravate ambient air quality by

excusing excess emissions that cause or contribute to a violation

of an ambient air quality standard. Additional grounds for

disapproving a SIP that includes the automatic exemption approach

are discussed in more detail at 42 Fed. Reg. 58171 (November 8,

1977) and 42 Fed. Reg. 21372 (April 27, 1977). As a result, EPA

will not approve any SIP revisions that provide automatic

exemptions for periods of excess emissions.

The best assurance that excess emissions will not interfere

with NAAQS attainment, maintenance, or increments is to address

excess emissions through enforcement discretion. This policy

provides alternative means for addressing excess emissions of

criteria pollutants. However, this policy does not apply where a

single source or small group of sources has the potential to

cause an exceedance of the NAAQS or PSD increments. Moreover,

4The term affirmative defense means, 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.

5Because all periods of excess emissions are violations and

because affirmative defense provisions may not apply in actions

for injunctive relief, under no circumstances would EPA consider

periods of excess emissions, even if covered by an affirmative

defense, to be “federally permitted releases” under EPCRA or

CERCLA.
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nothing in this guidance should be construed as requiring states

to include affirmative defense provisions in their SIPs.

II. AFFIRMATIVE DEFENSES FOR MALFUNCTIONS

EPA can approve a SIP revision that creates an affirmative

defense to claims for penalties in enforcement actions regarding

excess emissions caused by malfunctions as long as the defense

does not apply to SIP provisions that derive from federally

promulgated performance standards or emission limits, such as new

source performance standards (NSPS) and national emissions

standards for hazardous air pollutants (NESHAPS).6 In addition,

affirmative defenses are not appropriate for areas and pollutants

where a single source or small group of sources has the potential

to cause an exceedance of the NAAQS or PSD increments.

Furthermore, affirmative defenses to claims for injunctive relief

are not allowed. To be approved, an affirmative defense

provision must provide that the defendant has the burden of proof

of demonstrating that: 

1. The excess emissions were caused by a sudden,

unavoidable breakdown of technology, beyond the control of the

owner or operator;

2. The excess emissions (a) did not stem from any activity

or event that could have been foreseen and avoided, or planned

for, and (b) could not have been avoided by better operation and

maintenance practices; 

3. To the maximum extent practicable the air pollution

control equipment or processes were maintained and operated in a

manner consistent with good practice for minimizing emissions;

4. Repairs were made in an expeditious fashion when the

operator knew or should have known that applicable emission

limitations were being exceeded. Off-shift labor and overtime

must have been utilized, to the extent practicable, to ensure

that such repairs were made as expeditiously as practicable;

5. The amount and duration of the excess emissions

(including any bypass) were minimized to the maximum extent

practicable during periods of such emissions;

6To the extent a state includes NSPS or NESHAPS in its SIP,

the standards should not deviate from those that were federally

promulgated. Because EPA set these standards taking into account

technological limitations, additional exemptions would be

inappropriate.
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6. All possible steps were taken to minimize the impact of

the excess emissions on ambient air quality; 

7. All emission monitoring systems were kept in operation

if at all possible;

8. The owner or operator’s actions in response to the

excess emissions were documented by properly signed,

contemporaneous operating logs, or other relevant evidence; 

9. The excess emissions were not part of a recurring

pattern indicative of inadequate design, operation, or

maintenance; and

10. The owner or operator properly and promptly notified

the appropriate regulatory authority.

EPA interprets these criteria narrowly. Only those

malfunctions that are sudden, unavoidable, and unpredictable in

nature qualify for the defense. For example, a single instance

of a burst pipe that meets the above criteria may qualify under

an affirmative defense. The defense would not be available,

however, if the facility had a history of similar failures

because of improper design, improper maintenance, or poor

operating practices. Furthermore, a source must have taken all

available measures to compensate for and resolve the malfunction.

If a facility has a baghouse fire that leads to excess emissions,

the affirmative defense would be appropriate only for the period

of time necessary to modify or curtail operations to come into

compliance. The fire should not be used to excuse excess

emissions generated during an extended period of time while the

operator orders and installs new bags, and relevant SIP language

must limit applicability of the affirmative defense accordingly. 

III. EXCESS EMISSIONS DURING STARTUP AND SHUTDOWN

In general, startup and shutdown of process equipment are

part of the normal operation of a source and should be accounted

for in the planning, design, and implementation of operating

procedures for the process and control equipment. Accordingly,

it is reasonable to expect that careful and prudent planning and

design will eliminate violations of emission limitations during

such periods. 

A. SOURCE CATEGORY SPECIFIC RULES FOR STARTUP AND SHUTDOWN

For some source categories, given the types of control

technologies available, there may exist short periods of

emissions during startup and shutdown when, despite best efforts

regarding planning, design, and operating procedures, the
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otherwise applicable emission limitation cannot be met. 

Accordingly, except in the case where a single source or small

group of sources has the potential to cause an exceedance of the

NAAQS or PSD increments, it may be appropriate, in consultation

with EPA, to create narrowly-tailored SIP revisions that take

these technological limitations into account and state that the

otherwise applicable emissions limitations do not apply during

narrowly defined startup and shutdown periods. To be approved,

these revisions should meet the following requirements: 

1. The revision must be limited to specific, narrowlydefined source categories using specific control strategies

(e.g., cogeneration facilities burning natural gas and using

selective catalytic reduction);

2. Use of the control strategy for this source category

must be technically infeasible during startup or shutdown

periods;

3. The frequency and duration of operation in startup or

shutdown mode must be minimized to the maximum extent

practicable;

4. As part of its justification of the SIP revision, the

state should analyze the potential worst-case emissions that

could occur during startup and shutdown; 

5. All possible steps must be taken to minimize the impact

of emissions during startup and shutdown on ambient air quality;

6. At all times, the facility must be operated in a manner

consistent with good practice for minimizing emissions, and the

source must have used best efforts regarding planning, design,

and operating procedures to meet the otherwise applicable

emission limitation; and 

7. The owner or operator's actions during startup and

shutdown periods must be documented by properly signed,

contemporaneous operating logs, or other relevant evidence. 

B. GENERAL AFFIRMATIVE DEFENSE PROVISIONS RELATING TO

STARTUP AND SHUTDOWN

In addition to the approach outlined in Section II(A) above,

states may address the problem of excess emissions occurring

during startup and shutdown periods through an enforcement

discretion approach. Further, except in the case where a single

source or small group of sources has the potential to cause an

exceedance of the NAAQS or PSD increments, states may also adopt

for their SIPs an affirmative defense approach. Using this
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approach, all periods of excess emissions arising during startup

and shutdown must be treated as violations, and the affirmative

defense provision must not be available for claims for injunctive

relief. Furthermore, to be approved, such a provision must

provide that the defendant has the burden of proof of

demonstrating that: 

1. The periods of excess emissions that occurred during

startup and shutdown were short and infrequent and could not have

been prevented through careful planning and design;

2. The excess emissions were not part of a recurring

pattern indicative of inadequate design, operation, or

maintenance;

3. If the excess emissions were caused by a bypass (an

intentional diversion of control equipment), then the bypass was

unavoidable to prevent loss of life, personal injury, or severe

property damage;

4. At all times, the facility was operated in a manner

consistent with good practice for minimizing emissions;

5. The frequency and duration of operation in startup or

shutdown mode was minimized to the maximum extent practicable; 

6. All possible steps were taken to minimize the impact of

the excess emissions on ambient air quality;

7. All emission monitoring systems were kept in operation

if at all possible; 

8. The owner or operator’s actions during the period of

excess emissions were documented by properly signed,

contemporaneous operating logs, or other relevant evidence; and

9. The owner or operator properly and promptly notified the

appropriate regulatory authority.

If excess emissions occur during routine startup or shutdown

periods due to a malfunction, then those instances should be

treated as other malfunctions that are subject to the malfunction

provisions of this policy. (Reference Part I above).

bennett899a.wpd/August 11, 1999