concurring in part and dissenting in part:
I concur in the majority’s opinion except for Part III — 2 relating to the complicating effects of an earthquake on emergency planning and Part IV relating to the Petitioners’ Motion to Supplement the Record. While I too am mindful of the Supreme Court’s “unequivocal proscriptions against judicial overreaching” in Nuclear Regulatory Commission (“NRC” or “Commission”) actions, see Maj.Op. at 1296,1 do not find in those proscriptions a directive for this court to abandon, or even to weaken, its statutory duty to provide thorough and meaningful judicial review of the Commission’s actions in this important area of nuclear safety. Indeed, it is difficult to iden*111tify any area where effective judicial review of agency action is more crucial than in the area of nuclear power regulation; even a small lapse in rational decisionmaking may have the most profoundly devastating effects on public health and safety. In my view, the Commission’s decision not to include consideration of earthquakes in emergency planning for Diablo Canyon exhibits a substantial lapse in rational decisionmaking.
The fundamental issue is whether the Commission acted arbitrarily and capriciously in excluding consideration of the complicating effects of an earthquake on nuclear emergency response plans1 for Diablo Canyon. The Commission concluded that the failure to plan specifically for an earthquake occurring simultaneously with a nuclear emergency is not a material issue upon which affected parties have a right to a hearing under section 189(a) of the Atomic Energy Act (the “Act”), 42 U.S.C. § 2239(a). See Maj.Op. at 1307. It is true, of course, that the Commission has broad authority to decide what matters are relevant to its licensing decision. See Siegel v. Atomic Energy Comm’n, 400 F.2d 778, 783 (D.C.Cir.1968); see also Bellotti v. NRC, 725 F.2d 1380, 1383 (D.C.Cir.1983) (NRC may define scope of § 189(a) hearing except that “[p]ublic participation is automatic with respect to all [§ 189(a) ] Commission actions that are potentially harmful to the public health and welfare.”). But, at the same time, this court has stressed the acutely serious nature of the Commission’s duty to account to Congress and the public for its handling of “one of the most sensitive and difficult issues of our time: the safety of nuclear power.” Philadelphia Newspapers, Inc. v. NRC, 727 F.2d 1195, 1203 (D.C.Cir.1984). As a reviewing court, we cannot blink the immense gravity of the stakes in this case — the safety of a nuclear power plant persistently beleaguered by unforeseen calamities since its very inception more than ten years ago.2 The extraordinary combination of calamitous circumstances displayed by the record of this plant not only invites — it compels — extreme hesitation in upholding the Commission’s decision not to consider the complicating effects of earthquakes on emergency response plans for Diablo Canyon, even if a similar decision would not be considered arbitary or capricious with respect to a less plagued facility.
Initially, I believe that the denial of Petitioners’ Motion to Supplement the Record with the transcripts of Commission meetings directly relating to the August 10, 1984, issuance of the full power license, see *112Maj.Op. at 1323, without first conducting an in camera examination of the transcripts, is an abdication of this court’s responsibility to provide meaningful judicial review of the Commission’s actions. The petitioners have not presented this court with mere speculative allegations of possible error on the part of the Commission. On the contrary, the petitioners have submitted a letter from Congressman Richard Ottinger, the Chairman of the House Subcommittee on Energy Conservation and Power, one of the NRC’s oversight committees, stating that the transcripts and related documents, which he has read, reveal improper and possibly illegal actions by the Commission. Specifically, Chairman Ottinger states that the transcripts and related documents show that the Commission acted despite knowledge that there was insufficient evidence in the record to support its decision, that it relied on material outside the record to support its decision, and that it seriously misrepresented its actions in its brief to this court.3 Chairman Ottinger’s allegations were repeated by Commissioner Asselstine, a member — albeit a dissenting one — of the NRC itself.4 I, for one, do not take such serious accusations by responsible officials so lightly that I can justify refusing even to look at the transcripts of the Commission proceedings to see if there is in fact a basis for the accusations.
While I do agree that a court should not routinely grant motions to supplement the record based on discontented parties' general allegations of misconduct, the' unprecedented nature of the specific allegations of misconduct lodged by the chairman of one of the NRC oversight committees and one of the commissioners of the NRC, viewed against the disturbing background of the plant’s troubled safety history, seem to me clearly sufficient to meet the special exceptions criteria allowing further inquiry by this court. Courts have recognized that supplementation of an administrative record may be justified, in the interest of effective judicial review, where there are credible accusations that an agency has *113relied on material outside the record or has acted improperly or in bad faith. See Public Power Council v. Johnson, 674 F.2d 791 (9th Cir.1982) (citing cases); see also Citizens to Preserve Overton Park, Inc. v. Volpe, 401 U.S. 402, 420, 91 S.Ct. 814, 825, 28 L.Ed.2d 136 (1971) (bad faith or improper behavior exception); Natural Resources Defense Council, Inc. v. Train, 519 F.2d 287, 291-92 (D.C.Cir.1975) (exception for material relied on by agency but not submitted as part of the record). Even if the Commission’s position that supplementation of the record is not warranted here were to prove ultimately correct, I see no reason not to take the middle course, i.e., an in camera examination by the court of the transcripts and related documents before making the ultimate determination to deny Petitioners’ Motion to Supplement the Record. I simply believe the stakes are so high and the nature and source of the accusations sufficiently credible as to make a “business as usual” — “see no evil, hear no evil, confront no evil” — attitude on our part untenable, if we are to provide meaningful judicial review.
My view that it is incumbent upon this court to conduct an in camera examination of the transcripts is reinforced by what I consider to be the very thin support in the record for the Commission’s decision not to consider the complicating effects of earthquakes on emergency response plans for Diablo Canyon. The Commission’s reliance on largely unsupported conclusions and undocumented support in the record renders its decision a precarious exercise of discretion, at best. Even under the most deferential standard of review used by the majority, the Commission’s decision teeters on the line between reasoned decisionmaking and arbitrary and capricious agency action. Indeed, under any verbal formulation of review, our task of making a meaningful assessment of why the Commission refused to explicitly consider earthquakes in emergency response planning is greatly impeded on a practical level here by the Commission’s failure to specify the particular evidence in the record supporting the inferences it drew and the conclusions it reached. This court has previously stated:
For a reviewing court to perform [its] task, it is imperative that the Commission articulate the critical facts upon which it relies____ Similarly, when the Commission finds it necessary to make predictions or extrapolations from the record, it must fully explain the assumptions it relied on to resolve unknowns and the public policies behind those assumptions ____ Only if the Commission observes these minimum standards can we be confident that missing facts, gross flaws in agency reasoning, and statutorily irrelevant or prohibited policy judgments will come to a reviewing court’s attention.
Columbia Gas Transmission Corp. v. Federal Energy Regulatory Comm’n, 628 F.2d 578, 593 (D.C.Cir.1979) (footnote omitted). In my view, the NRC has not met “these minimum standards.”
The Commission cites three justifications for its decision not to include consideration of the complicating effects of earthquakes on response to a radiological emergency at Diablo Canyon: the low probability that an earthquake will initiate a radiological release; the low probability that an earthquake will occur contemporaneously with an unrelated radiological release; and the flexibility of the general emergency plans developed for other natural phenomena to handle any disruptions caused by an earthquake. See CLI-84-12, 20 N.R.C. - (1984), reprinted in Joint Appendix (Supplement) (“J.A.S.”) at 251. In my opinion, only the first of these conclusions is adequately supported by findings in the record.
A . critical issue throughout the licensing proceedings, and recognized as such by the Commission, has been the adequacy of the seismic design of Diablo Canyon to withstand an earthquake, a matter to which the Commission has given considerable attention. See LBP-79-26,10 N.R.C. 453 (1979); ALAB-644, 13 N.R.C. 903 (1981), petition for review denied, CLI-82-12A, 16 N.R.C. 7 (1982); see also CLI-84-12, J.A.S. at 257 *114(“The resources, time, and attention devoted to seismic design in this case have been unprecedented ____”) Consequently, the Commission has adequate support on the record for its conclusion that it is unlikely that an earthquake will cause a radiological release.5 The Commission’s second and third conclusions, however, appear to be based — in the main — on unexplained extrapolations from a massive and, for practical purposes, an incomprehensible mound of data, as well as what appear to be purely intuitive assumptions with no evident basis in the record.
The Commission cites no specific record support for its conclusion that it is very unlikely that an earthquake will occur contemporaneously with an unrelated radiological accident. See CLI-84-12, J.A.S. at 255 (vaguely alluding to information supplied by the parties); id. at 258 (citing ALAB644 for the conclusion that Diablo Canyon is an area of moderate rather than high seismicity). The Commission, in its reply to Petitioners’ Motion to Supplement the Record, additionally cites to decisions pertaining to the likelihood that an earthquake might initiate a radiological release to support its quite different conclusion that there is little chance the two events might occur contemporaneously. See Respondents’ Opposition to Petitioners’ Motion to Supplement the Record at 5 (citing LBP-79-26, 10 N.R.C. 453 (1979); ALAB-644, 13 N.R.C. 903 (1981)). Although it is possible that the record in these decisions contains sufficient data on earthquakes and radiological release accidents for the Commission to determine the mathematical probability of a contemporaneous occurrence of the two events, that was not the issue before the Commission or decided by the Commission in these cases. Consequently, the Commission has not, in any of the cited decisions, elucidated the path of reasoned decisionmaking it followed in arriving at its conclusion in this case that the probability of a contemporaneous occurrence of an earthquake and a radiological accident is very low. We are asked, and the majority agrees, to take it on faith alone that the data is there. In addition, however, a conclusion as to the low probability of the coincidence of the two events is only the first step in any rational analysis required of the Commission before it can conclude that no consideration of earthquakes'is necessary.
The Commission claims that the probability of a coincidental occurrence is too low to warrant its inclusion among the other natural events for which emergency planning is required. To make this determination the Commission would need to engage in a comparative analysis of the respective probabilities of the coincidental occurrence of a radiological accident and those natural phenomena required to be considered versus the probability of the coincidental occurrence of an earthquake and a radiological accident.6 The Commission cites to *115nothing in the record which indicates that it took this essential second step.
The Commission’s third conclusion that the emergency planning for other natural phenomena retain enough flexibility to handle any disruptions which might be caused by an earthquake appears to be based on pure conjecture. While it might be that emergency plans designed to deal with the disruption of evacuation routes or communication lines are equally effective regardless of whether the disruption is caused by a hurricane or by an earthquake, it is equally plausible that an earthquake may cause some unique problems not encompassed by the emergency plans for other natural phenomena. The Commission cites nothing in the record to suggest that the Commission , considered the possibility that an earthquake might produce unique complicating effects requiring special emergency planning. This issue should have been explicitly addressed in any rational decisionmaking process.
Finally, I must confess, on a common sense level, I am completely baffled by the Commission’s paradoxical stance with respect to the materiality of earthquakes. The Commission has considered earthquake associated risks of paramount importance with respect to the design of the Diablo Canyon plant, yet with respect to emergency planning the Commission asserts that earthquake associated risks are too unlikely to warrant consideration. Compounding the illogic of the Commission’s position is the fact that the nature of emergency planning is to develop plans to respond to unlikely but possible emergencies.7 Certainly if earthquake associated risks are significant enough to require redesigning the plant to meet seismic design criteria twice that of most other plants, see supra at 1332-33 & n. 5, they are significant enough to require emergency planning.8
In sum, the Commission’s decision not to include consideration of the complicating effects of an earthquake on emergency *116planning for Diablo Canyon rests in substantial part on predictions or extrapolations purportedly derived from the record. Yet the Commission’s decision asserts only the Commission’s ultimate conclusions with no systematic articulation of the factual data and assumptions relied upon or the path of analysis followed. This state of the record, together with the serious charges levelled by Commissioner Asselstine and Chairman Ottinger, who based on their personal familiarity with the transcripts of the proceedings concluded that the Commission acted in knowing disregard of the insufficiency of the record to support its decision, leads me to seriously question the ability of this court to provide meaningful judicial review of the Commission’s action regarding earthquakes and emergency planning. In my view, the answer is ineluctable: There is no way that this court can be confident that the Commission’s decision is not based upon “missing facts, gross flaws in ... reasoning, and statutorily irrelevant or prohibited policy judgments.” Columbia Gas Transmission, 628 F.2d at 593.
As the majority correctly points out, if effective judicial review is frustrated by an agency’s failure to provide adequate explanation of its action or if its action lacks a sufficient basis in the record, the proper course for the court is to remand to the agency for further proceedings. See Maj.Op. at 1326. This is the course that I would follow here.9 I would vacate the Commission’s decision not to include consideration of earthquakes in emergency planning for Diablo Canyon and remand to the Commission for further proceedings. Since, based on the foregoing analysis, I do not believe that the Commission can set forth a rational basis for excluding consideration of the complicating effects of an earthquake on emergency response at Diablo Canyon, the Commission on remand should be required to include consideration of earthquake complications in emergency planning not merely re-address the question of whether earthquake complications warrant consideration. In my view, as long as the Commission instituted such proceedings immediately and completed them in an expedited manner, a stay of the operating license pending completion of the proceedings would not be required. But I believe the strong public interest at stake here — ensuring the safety of those working at or living in the vicinity of the Diablo Canyon nuclear power plant — compels the Commission to address forthrightly how the emergency plans for a radiological accident at Diablo Canyon will take account of any simultaneous seismic activity. Any thoughtful inhabitant of this planet during the past century has surely learned to expect the unexpected, to anticipate the unthinkable, and to recognize the imperative need to plan for saving human life in the event of a mass disaster. I believe that the Commission’s outright refusal to make explicit provision in emergency response plans for an earthquake in a nuclear plant within three miles of a major, active fault in California is by definition an arbitrary and capricious act. I therefore dissent from the majority’s affirmance of the Commission’s decision in this respect.
. Following the 1979 accident at Three Mile Island, the NRC began requiring offsite, as well as onsite, emergency plans as a licensing condition. See infra note 8. 10 C.F.R. § 50.47(a)(1) (1984) states:
[N]o operating license for a nuclear power reactor will be issued unless a finding is made by NRC that there is reasonable assurance that adequate protective measures can and will be taken in the event of a radiological emergency.
See also Union of Concerned Scientists v. NRC, 735 F.2d 1437 (D.C.Cir.1984) (§ 189(a) of the Atomic Energy Act guarantees right to a hearing on issues material to emergency planning).
. Confirmation of this statement requires only a cursory look at the major mishaps at Diablo Canyon. The plant was originally missited adjacent to a major, active earthquake fault — the Hosgri Fault — which was not discovered until four years after construction permits had issued and construction begun. The plant was then reanalyzed and redesigned. The NRC issued a low power license to the plant on September 22, 1981. See LBP-81-21, 14 N.R.C. 107 (1981); CLI-81-22, 14 N.R.C. 598 (1981). Due to subsequently discovered errors in the plant’s design, the low power license was suspended on November 9, 1981. See CLI-81-30, 14 N.R.C. 950 (1981). The mistaken reversal of blueprints in the design of the licensed reactor was one of the belatedly discovered errors leading to this suspension. Design and construction deficiencies requiring modifications have since been continually discovered at the plant. In fact, the plant has shut down numerous times due to malfunctions just since beginning operation in early November. See Wash.Post, Dec. 9, 1984, at A8, col. 1 (“Thursday's shutdown, the fourth in less than two weeks and the second in 24 hours, was caused by a pressure sensor that was set ‘too conservatively.’”); N.Y.Times, Nov. 30, 1984, at Bll, col. 1 (generator of Unit 1 "automatically shut down Wednesday for the second time in less than a week because of malfunction.”); Wash.Post, Nov. 14, 1984, at A15, col. 2 (unplanned shutdown of Diablo Canyon plant due to water pump malfunction).
. See Letter from Richard L. Ottinger, Chairman of the House Subcommittee on Energy Conservation and Power to Nunzio J. Palladino, Chairman of the NRC (Oct. 26, 1984), reprinted in Petitioners' Motion to Supplement the Record, Exhibit 2. Chairman Ottinger explained his allegation further stating:
For example, there appears to be no documentation for the Commission’s assertion that "when the relevant probabilities are considered, the Commission’s decision not to look at the effects of earthquakes on emergency planning at Diablo Canyon is well supported.” (Brief for Respondents, page 41.) Whether or not this decision is correct, I can find nothing in the record to support this statement. Indeed, my review of the transcripts of the Commission's discussion of this issue, and the supporting staff documents, leads me to agree with the Commission's General Counsel, ... that there is "no convincing rational basis for the Commission’s view that the complicating effects of earthquakes on emergency response deserves no consideration."
Id. at 2.
. See Letter from Nunzio J. Palladino, Chairman of the NRC to Edward Markey, Chairman of the House Subcommittee on Oversight and Investigations (Oct. 29, 1984) (containing the comments of Commissioner Asselstine), reprinted in Petitioners’ Motion to Supplement the Record, Exhibit 1, at 3. Specifically, Commissioner Asselstine states:
... I agree entirely with the descriptions of the Commission’s deliberations in the Diablo Canyon case which were contained in Chairman Ottinger's October 26, 1984 letter to the Commission.
The Commission ignored the possibility of the simultaneous occurrence of an emergency at the plant (e.g. a fire) which could require emergency response and an unrelated earthquake which could affect emergency response features such as communication and emergency response to the site even though the Commission’s legal and technical advisors told the Commission that this approach was fundamentally different than the Commission’s approach for considering the complicating effects of all other natural phenomena on emergency planning and there was no factual basis in the Diablo Canyon record for adopting this different approach for earthquakes. The Commission relied on material not in the record of the Diablo Canyon proceeding to conclude that the Diablo Canyon emergency plan is sufficiently flexible to accommodate the complicating effects of earthquakes on emergency planning despite repeated warnings that such reliance on extra-record material was inappropriate and legally impermissible.
Id.
. Indeed, it is noteworthy that the Diablo Canyon plant has been designed to withstand an earthquake with ground motions almost twice those of other plants in the country. See CLI-84-12, J.A.S. at 274 (Asselstine, Comm’r, dissenting). Thus, the Commission impliedly concedes that the earthquake risk for Diablo Canyon is considerably higher than for other sites outside California.
. The Commission refers to the natural phenomena it generally considers as "frequently occurring natural phenomena [such] as snow, heavy rain, and fog____” CLI-84-12, J.A.S. at 255. However, the Commission apparently also considers more severe, less frequently occurring events such as blizzards, hurricanes, or tornados if they are endemic to a particular area. See Brief for Respondents, No. 84-1410, at 44 n. 30; see also Commissioner Bernthal’s Additional Views, CLI-84-12, J.A.S. at 265 ("It clearly makes sense to consider, in emergency response planning, hurricane-type events ... in California or blizzards in the northern half of the United States____"). In fact, the complicating effects of a hurricane were considered in Diablo Canyon’s emergency planning, yet there is apparently no evidence in the record to support the assertion that a hurricane is more likely than an earthquake to occur contemporaneously with an unrelated radiological release accident at the Diablo Canyon site. Commissioner Asselstine noted this deficiency:
The probability that a tornado will travel through a particular 10 mile area and thereby initiate or disrupt response to an emergency at a nuclear plant must be quite low; yet, the Commission requires consideration of that issue for certain plants. Similarly, the proba*115bility of a hurricane striking the San Luis Obispo coastal area and initiating or disrupting an emergency response must also be quite low; yet, the Commission considered that very issue in the Diablo Canyon case. I see no factual basis for the Commission’s assertion that earthquakes in California are so much more unlikely than either of these events that earthquakes need not be considered.
CLI-84-12, J.A.S. at 275 (Asselstine, Comm’r, dissenting).
. I do not suggest that the Commission is required to engage in "an open-ended exercise in creative speculation about possibilities,” see Brief for Respondents, No. 84-1410, at 42, regardless of how remote. I do, however, agree with Commissioner Asselstine that ”[t]o apply this argument to California, where almost 90 percent of the seismic activity in the United States occurs and where earthquakes which damage, obstruct or disrupt roads, buildings, bridges and communications networks occur with some regularity, simply ignores common sense." CLI-84-12, J.A.S. at 273 (Asselstine, Comm’r, dissenting). I am also inclined to give some credence to the argument that the NRC staffs own actions in the Diablo Canyon proceeding undercut the Commission’s position. See Brief for Petitioners, No. 84-1410, at 42-43; CLI-84-12, J.A.S. at 277 (Asselstine, Comm’r, dissenting) (“By their own actions, the agency’s technical experts have demonstrated that they consider this issue to be material to the Commission’s licensing decisions in these two cases."). In a memorandum to the Commission dated June 22, 1982, the staff is represented as holding the position that: "Planning for earthquakes ... in areas where the seismic risk of earthquakes to offsite structures is relatively high may be appropriate (e.g., California sites...).” Memorandum to Commissioners from William J. Dircks, Executive Director of Operations (June 22, 1982), Attachment I to CLI-84-4, 19 N.R.C. 937, 941 (1984). Moreover, ”[t]he complicating effects of earthquakes on emergency planning were formally considered by the staff in the San Onofre proceeding, and were informally considered by the staff for Diablo Canyon.” CLI-84-12, J.A.S. at 276 (Asselstine, Comm’r, dissenting).
. It should be noted that when the Commission issued its proposed rule on emergency response planning following the Three Mile Island accident, the Commission announced that it now "view[ed] emergency planning as equivalent to, rather than as secondary to, siting and design in public protection____” 44 Fed.Reg. 75,169 (1979). "The Commission’s perspective was severely altered by the unexpected sequence of events that occurred at Three Mile Island. The accident showed clearly that the protection provided by siting and engineered safety features must be bolstered by the ability to take protective measures during the course of an accident.” Id.
. I see no inconsistency between my view that the court should conduct an in camera examination of the transcripts to determine whether supplementation of the record is warranted here, and my ultimate conclusion that, under the circumstances of this case, the deficiencies in the Commission's articulated rationale and supporting evidence in the record, as presently constituted, require a remand to the Commission for further proceedings to consider the effects of an earthquake on emergency planning for Diablo Canyon. A reviewing court’s task is to decide whether rational decisionmaking has taken place — lack of rationality may stem from inadequate reasoning and insufficient evidence or from illegitimate outside considerations and bad faith. Certainly if the latter can be shown, it cannot help but color the lens through which the court looks at the agency’s articulated path of decisionmaking. And similarly in close cases, based on the record before the court, a showing of bad faith or illegitimate outside considerations could militate toward remand for a properly thorough and untainted reconsideration.