Senate Report stated that Exemption 2 “relates only to the internal personnel rules and practices of an agency. Examples of these may be rules as to personnel’s use of parking facilities or regulation of lunch hours, statements of policy as to sick leave, and the like.” S.Rep. No. 89-813, at 8 (1965). Taking a different view, the House Report described the exemption as encompassing “[ojperating rules, guidelines, and manuals of procedure for Government investigators or examiners.” H.R. Rep. No. 89-1497, at 10 (1966). Even given these differences, however, the House and Senate committees both saw Exemption 2 as narrowing the public disclosure exemption under former section 3 of the Administrative Procedure Act (APA), which protected from disclosure “any matter relating solely to the internal management of an agency.” Rose, 425 U.S. at 362, 96 S.Ct. 1592 (citing Congress’s dissatisfaction with the broad sweep of the APA’s exemption, 5 U.S.C. § 1002 (1964 ed.)).
Confronting the dueling House and Senate Reports for the first time in Department of the Air Force v. Rose, 425 U.S. 352, 96 S.Ct. 1592, 48 L.Ed.2d 11 (1976), the Supreme Court declined to pick sides. On the one hand, the Court accepted the Senate’s interpretation of Exemption 2 as covering minor employment-related matters in which the public lacked a significant interest. Id. at 369-70, 96 S.Ct. 1592. On the other hand, the Court acknowledged, but did not decide, that the exemption might protect the more important materials contemplated by the House Report “where necessary to prevent the circumvention of agency regulations that might result from disclosure to the subjects of regulation of ... procedural manuals and guidelines used by the agency.” Id. at 364, 96 S.Ct. 1592.
With the question thus left open by the Supreme Court, and facing what we believed to be mutually exclusive views of Exemption 2, we initially adopted the Senate Report as the authoritative expression of Congress’s intent. In Jordan v. United States Department of Justice, 591 F.2d 753, 763 (D.C.Cir.1978) (en banc), we stated that “personnel” refers only to “matters relating to pay, pensions, vacations, hours of work, lunch hours, parking, etc.” Applying this construction, we ordered the release of prosecutorial guidelines used by U.S. Attorneys on the ground that, as envisioned by the Senate Report, the guidelines fell outside Exemption 2’s scope. Id.
Three years later and sitting en banc, we reversed course and expressly repudiated Jordan’s “limited” interpretation of Exemption 2 in Crooker v. Bureau of Alcohol, Tobacco & Firearms, 670 F.2d 1051, 1073 (D.C.Cir.1981). There, the FOIA requester sought a copy of a Bureau of Alcohol, Tobacco & Firearms (ATF) manual used to train new agents in surveillance techniques. Picking up where the Supreme Court left off in Rose, we held that Exemption 2 protects nontrivial matters “where disclosure might risk circumvention of the law.” Id. at 1066. Accordingly, “the words ‘personnel rules and practices’ encompass not merely minor employment matters,” as we held in Jordan, “but may cover other rules and practices governing agency personnel, including significant matters like job training for law enforcement personnel.” Id. at 1056.
Despite Exemption 2’s reference to documents related “solely” to internal rules and practices, we further explained in Crooker that the exemption covers documents that are “predominantly” internal. Id. at 1056-57. This modification stemmed from our recognition that, if interpreted literally, the term “ ‘relating’ is potentially all-encompassing while ‘solely’ is potentially all-excluding.” Id. at 1056 (quoting Vaughn v. Rosen, 523 F.2d 1136,