finally, OSHA cannot issue an ETS unless it determines that employees are exposed to "grave danger" and that immediate action is "necessary" to protect them. Needless to say, "the gravity and necessity requirements lie at the center of proper invocation of the ETS powers." Asbestos Information Ass'n, supra, 727 F.2d at 424.
Not surprisingly, the courts, considering the emergency and non-public character of ETS proceedings, consistently hold that the ETS power may be employed only in "limited situations." Public Citizen, supra, 702 F.2d at 1155. Section 6(c) represents "extraordinary power," and should be "delicately exercised." Florida Peach Growers, supra, 489 F.2d at 129. It may be used only as "an unusual response to exceptional circumstances." Dry Color Manufacturers, supra, 486 F.2d at 104 n.9a. It is the "most dramatic weapon in [OSHA's] enforcement arsenal," Asbestos Information Ass'n, supra, 727 F.2d at 426, and accordingly, Congress "narrowly circumscribed the Secretary's power to issue" them. API, supra, 448 U.S. at 651. The exceptional nature of the ETS power, of course, must be considered by a court in deciding whether to compel its invocation. Cf. Public Citizen, supra, 702 F.2d at 1156-57.
The ETS cases also give due regard to the subject matter of the agency's action. The determination required by § 6(c) -- whether emergency government action is "necessary" to protect workers from "toxic or physically harmful" substances -- is "essentially legislative and rooted in inferences from complex scientific and factual data." Public Citizen, supra, 702 F.2d at 1156 (quoting United Steelworkers of America v. Marshall, 208 U.S. App. D.C. 60, 647 F.2d 1189, 1206 (D.C.Cir. 1980), cert. denied sub nom. Lead Industries Ass'n v. Donovan, 453 U.S. 913, 101 S. Ct. 3148, 69 L. Ed. 2d 997 (1981)). See also Asbestos Information Ass'n, supra, 727 F.2d at 427 ("gravity of danger is a policy decision committed to OSHA, not the courts"). Such "mixed fact/policy judgments," based on incomplete or uncertain scientific evidence, are entitled to great deference, Public Citizen, supra, 702 F.2d at 1156, and OSHA has the "prerogative to choose between conflicting evidence." Asbestos Information Ass'n, supra, 727 F.2d at 425. See also API, supra, 448 U.S. at 656-57. These observations are but manifestations in the ETS setting of a general principle of administrative law: when an agency "mak[es] predictions, within its area of special expertise, at the frontiers of science, [a] reviewing court must generally be at its most deferential." Baltimore Gas & Electric Co. v. Natural Resources Defense Council, Inc., 462 U.S. 87, 103 S. Ct. 2246, 2256, 76 L. Ed. 2d 437 (1983). Cf. Chevron U.S.A. Inc. v. Natural Resources Defense Council, Inc., 467 U.S. 837, , 52 U.S.L.W. 4845, 4853, 81 L. Ed. 2d 694, 104 S. Ct. 2778 (1984).
The Public Citizen court also noted the "legislative", as well as "scientific" character of the action challenged here: an agency decision not to issue a rule. "The scope of review of such a determination must, of necessity, be very narrow." WHHT, Inc. v. FCC, 211 U.S. App. D.C. 218, 656 F.2d 807, 809, 818 (D.C.Cir. 1981). As the Court of Appeals recently observed:
"rulemaking is an inherently policy-oriented process and the agency must be accorded considerable deference in evaluating information presented and reaching decisions based upon its expertise." Professional Drivers Council v. Bureau of Motor Carrier Safety, 227 U.S. App. D.C. 312, 706 F.2d 1216, 1221 (D.C.Cir. 1983).