American Federation of Labor and Congress of Industrial Organizations, Interstate Natural Gas Association of America, Intervenors v. Occupational Safety and Health Administration, United States Department of Labor, Texas Laundry and Drycleaning Association, National Grain and Feed Association, National Industrial Sand Association, National Stone Association, Polyurethane Manufacturers Association, the Society of the Plastics Industry, Scientific Apparatus Makers Association, Thermal Insulation Manufacturers Association, Inc., United States Gypsum Company, Usg Interiors, Inc., Dap, Inc., American Petroleum Institute, Chemical Manufacturers Association, American Gas Association, American Iron & Steel Institute, American Mining Congress, American Paper Institute, Inc., National Forest Products Association, Inc., Brush Wellman, Inc., Ngk Metals Corporation, the Chlorine Institute, Inc., Corn Refiners Association, Inc., Courtaulds Fibers, Inc., Halogenated Solvents Industry Alliance, Inco United States, Inc., Inco Ltd., Inter-Industry Committee on Carbon Disulfide, Inter-Industry Wood Dust Coordinating Committee, International Fabricare Institute, Furniture Workers Division, I.U.E., Local 800 Intervenors. American Iron and Steel Institute, Corn Refiners Association, Inc., Archer Daniels' Midland Company, A.E. Staley Manufacturing Company, National Grain & Feed Association, Inc., International Fabricare Institute, Texas Laundry and Drycleaning Association, United States Gypsum Company, Usg Interiors, Inc., Dap, Inc., Intervenors v. Occupational Safety and Health Administration, United States Department of Labor, American Petroleum Institute, Chemical Manufacturers Association, American Federation of Labor and Congress of Industrial Organizations, Intervenors. Corn Refiners Association, Incorporated, Archer Daniels' Midland Company, and A.E. Staley Manufacturing Company, American Iron and Steel Institute, National Grain & Feed Association, Inc., International Fabricare Institute, Texas Laundry and Drycleaning Association, the Fertilizer Institute, Intervenors v. Occupational Safety and Health Administration, United States Department of Labor, American Petroleum Institute, Chemical Manufacturers Association, American Federation of Labor and Congress of Industrial Organizations, Intervenors. Interstate Natural Gas Association of America, American Iron and Steel Institute, Corn Refiners Association, Inc., Archer Daniels' Midland Company, A.E. Staley Manufacturing Company, National Grain & Feed Association, Inc., International Fabricare Institute, Texas Laundry and Drycleaning Association, American Gas Association, Intervenors v. Elizabeth Hanford Dole, Secretary of Labor, and United States Department of Labor, Occupational Safety and Health Administration, American Petroleum Institute, Chemical Manufacturers Association, American Federation of Labor and Congress of Industrial Organizations, Intervenors. The Society of the Plastics Industry, Inc., American Iron and Steel Institute, Corn Refiners Association, Inc., Archer Daniels' Midland Company, A.E. Staley Manufacturing Company, National Grain & Feed Association, Inc., International Fabricare Institute, Texas Laundry and Drycleaning Association, Intervenors v. Occupational Safety and Health Administration, United States Department of Labor, American Petroleum Institute, Chemical Manufacturers Association, American Federation of Labor and Congress of Industrial Organizations, Intervenors. American Mining Congress and the Coastal Corporation, American Iron and Steel Institute, Corn Refiners Association, Inc., Archer Daniels' Midland Company, A.E. Staley Manufacturing Company, National Grain & Feed Association, Inc., International Fabricare Institute, Texas Laundry and Drycleaning Association, Interstate Natural Gas Association of America, American Gas Association, Intervenors v. Occupational Safety and Health Administration, United States Department of Labor, American Petroleum Institute, Chemical Manufacturers Association, American Federation of Labor and Congress of Industrial Organizations, Intervenors. American Gas Association, American Iron and Steel Institute, National Grain & Feed Association, Inc., International Fabricare Institute, Texas Laundry and Drycleaning Association, International Natural Gas Association of America, Intervenors v. Secretary of Labor, United States Department of Labor, and Occupational Safety and Health Administration, United States Department of Labor, American Petroleum Institute, Chemical Manufacturers Association, Intervenors. Inco United States, Inc. And Inco Ltd., American Iron and Steel Institute, Corn Refiners Association, Inc., Archer Daniels' Midland Company, A.E. Staley Manufacturing Company, National Grain & Feed Association, Inc., International Fabricare Institute, Texas Laundry and Drycleaning Association, Intervenors v. Occupational Safety and Health Administration, United States Department of Labor, American Petroleum Institute, Chemical Manufacturers Association, American Federation of Labor and Congress of Industrial Organizations, Intervenors. International Fabricare Institute, for Itself and on Behalf of Its Members, American Iron and Steel Institute, Corn Refiners Association, Inc., Archer Daniels' Midland Company, A.E. Staley Manufacturing Company, National Grain & Feed Association, Inc., Intervenors v. Occupational Safety and Health Administration, United States Department of Labor, Halogenated Solvents Industry Alliance, American Petroleum Institute, Chemical Manufacturers Association, American Federation of Labor and Congress of Industrial Organizations, Intervenors. Caterpillar, Inc., American Iron and Steel Institute, Corn Refiners Association, Inc., Archer Daniels' Midland Company, A.E. Staley Manufacturing Company, National Grain & Feed Association, Inc., International Fabricare Institute, Texas Laundry and Drycleaning Association, Intervenors v. Occupational Safety and Health Administration, United States Department of Labor, American Petroleum Institute, Chemical Manufacturers Association, American Federation of Labor and Congress of Industrial Organizations, Intervenors

In 1989, the Occupational Safety and Health Administration ("OSHA"),1 a division of the Department of Labor, issued its Air Contaminants Standard, a set of permissible exposure limits for 428 toxic substances. Air Contaminants Standard, 54 Fed.Reg. 2332 (1989) (codified at 29 C.F.R. § 1910.1000). In these consolidated appeals, petitioners representing various affected industries and the American Federation of Labor and Congress of Industrial Organizations ("AFL-CIO" or "the union") challenge both the procedure used by OSHA to generate this multi-substance standard and OSHA's findings on numerous specific substances included in the new standard. For the reasons that follow, we VACATE the Air Contaminants Standard and REMAND to the agency.

The Occupational Safety and Health Act of 1970 ("OSH Act" or "the Act"), 29 U.S.C. §§ 651-71, was adopted "to assure so far as possible every working man and woman in the Nation safe and healthful working conditions." Id. § 651(b). To this end, the Act authorizes the Secretary to issue occupational health and safety standards, id. § 655, with which each employer2 must comply. Id. § 654. Section 6(a) of the Act provided that in its first two years, OSHA should promulgate "start-up" standards, on an expedited basis and without public hearing or comment, based on "national consensus" or "established Federal standard[s]" that improve employee safety or health. Id. § 655(a).3 Pursuant to that authority, OSHA in 1971 promulgated approximately 425 permissible exposure limits ("PELs") for air contaminants,4 29 C.F.R. § 1910.1000 (1971), derived principally from federal standards applicable to government contractors under the Walsh-Healey Act, 41 U.S.C. § 35.5 Air Contaminants Proposed Rule, 53 Fed.Reg. 20960, 20962 (1988).6

The Act then provides two mechanisms to update these standards. Most new standards or revised existing standards must be promulgated under the requirements of section 6(b) of the OSH Act. 29 U.S.C. § 655(b). This section sets forth both procedural requirements and substantive criteria which the standards must meet. In promulgating these standards, OSHA must follow a procedure that is even more stringent than that in the federal Administrative Procedure Act, 5 U.S.C. § 553. United Steelworkers v. Marshall, 647 F.2d 1189, 1207 (D.C.Cir.1980), cert. denied, 453 U.S. 913, 101 S.Ct. 3149, 69 L.Ed.2d 997 (1981). OSHA must provide notice of proposed rulemaking, give interested parties an opportunity to comment, and hold a public hearing if requested. 29 U.S.C. § 655(b)(2)-(4). As of 1988, OSHA had issued only twenty-four substance-specific and three "generic" health standards under section 6(b).7

OSHA may also issue Emergency Temporary Standards under section 6(c) of the OSH Act, 29 U.S.C. § 655(c), when it determines "that employees are exposed to grave danger from exposure" to toxic substances. Id. § 655(c)(1). However, once OSHA has published an emergency standard, proceedings must commence for issuance of a regular standard under section 6(b). Id. § 655(c)(3).

On June 7, 1988, OSHA published a Notice of Proposed Rulemaking for its Air Contaminants Standard. 53 Fed.Reg. 20960-21393. In this single rulemaking, OSHA proposed to issue new or revised PELs for over 400 substances. OSHA limited the scope of this rulemaking to those substances for which the ACGIH recommended limits that were either new or more protective than the existing PELs. Id. at 20967. There was an initial comment period of forty-seven days, followed by a thirteen-day public hearing. Interested parties then had until October 7, 1988 to submit post-hearing evidence and until October 31, 1988 to submit post-hearing briefs.8

OSHA then issued its revised Air Contaminants Standard for 428 toxic substances on January 19, 1989. 54 Fed.Reg. 2332-2983. This standard, which differs from the proposal in several respects, lowered the PELs for 212 substances, set new PELs for 164 previously unregulated substances, and left unchanged PELs for 52 substances for which lower limits had originally been proposed. Id. at 2334. The standard established an approximately four-year period for employers to come into compliance with the new standard using engineering and work practice controls. Id. at 2916. Until that time, employers may use respirators or any other reasonable methods to comply with the standards. Id. at 2915-16.

Various industry groups, the AFL-CIO, and specific individual companies filed challenges to the final standard in numerous United States Courts of Appeals. Pursuant to 28 U.S.C. § 2112(a), all petitions for review of the Air Contaminants Standard were transferred to this court, where they have been consolidated for disposition.9

Section 6(f) provides in relevant part that "the determinations of the Secretary shall be conclusive if supported by substantial evidence in the record considered as a whole." 29 U.S.C. § 655(f) (emphasis added). "Substantial evidence" is " 'such relevant evidence as a reasonable mind might accept as adequate to support a conclusion.' " American Textile Mfrs. Inst., Inc. v. Donovan, 452 U.S. 490, 522, 101 S.Ct. 2478, 2497, 69 L.Ed.2d 185 (1981) (hereinafter "ATMI") (quoting Universal Camera Corp. v. NLRB, 340 U.S. 474, 477, 71 S.Ct. 456, 459, 95 L.Ed. 456 (1951)). Under this test, "we must take a 'harder look' at OSHA's action than we would if we were reviewing the action under the more deferential arbitrary and capricious standard applicable to agencies governed by the Administrative Procedure Act." Asbestos Info. Ass'n v. OSHA, 727 F.2d 415, 421 (5th Cir.1984) (footnote omitted); see also National Grain & Feed Ass'n v. OSHA, 866 F.2d 717, 728 (5th Cir.1988). Considering the record "as a whole" further requires that reviewing courts "take into account not just evidence that supports the agency's decision, but also countervailing evidence.... Yet this requirement does not alter the court's fundamental duty to uphold the agency's 'choice between two fairly conflicting views, even though the court would justifiably have made a different choice had the matter been before it de novo.' " AFL-CIO v. Marshall, 617 F.2d 636, 649 n. 44 (D.C.Cir.1979) (quoting Universal Camera Corp., 340 U.S. at 488, 71 S.Ct. at 464-65), aff'd in relevant part, ATMI, 452 U.S. 490, 101 S.Ct. 2478, 69 L.Ed.2d 185 (1981).

The substantial evidence test applies to review of policy decisions as well as factual determinations, see Texas Indep. Ginners Ass'n v. Marshall, 630 F.2d 398, 404 (5th Cir.1980),10 even though policy decisions are " 'not so susceptible to verification or refutation by the record.' " Id. (quoting American Petroleum Inst. v. OSHA, 581 F.2d 493, 497 (5th Cir.1978), aff'd sub nom., Industrial Union Dept., AFL-CIO v. American Petroleum Inst., 448 U.S. 607, 100 S.Ct. 2844, 65 L.Ed.2d 1010 (1980). "[I]n setting an element of the standard OSHA must demonstrate substantial evidence for all matters of determinable fact and, on matters having no possible basis in determinable fact, must explain the relevant considerations on which it relied and its reasons for rejecting alternate views." United Steelworkers, 647 F.2d at 1253. OSHA's policy decisions must be: (1) consistent with the language and purpose of the OSH Act, and (2) reasonable under the rulemaking record. Texas Indep. Ginners, 630 F.2d at 404; see also National Grain & Feed, 866 F.2d at 729.

Furthermore, "the validity of an agency's determination must be judged on the basis of the agency's stated reasons for making that determination." Industrial Union Dept., AFL-CIO v. American Petroleum Inst., 448 U.S. 607, 631 n. 31, 100 S.Ct. 2844, 2858 n. 31, 65 L.Ed.2d 1010 (1980) (plurality opinion) (hereinafter "Benzene "). Section 6(e) of the OSH Act provides that "[w]henever the Secretary promulgates any standard ... he shall include a statement of the reasons for such action, which shall be published in the Federal Register." 29 U.S.C. § 655(e). In that statement of reasons,

the agency must pinpoint the factual evidence and the policy considerations upon which it relied. This requires explication of the assumptions underlying predictions or extrapolations, and of the basis for its resolution of conflicts and ambiguities. In enforcing these requirements, the court does not reach out to resolve controversies over technical data. Instead it seeks to ensure public accountability.

AFL-CIO v. Marshall, 617 F.2d at 651 (footnotes omitted). "[T]he courts will not be expected to scrutinize the record to uncover and formulate a rationale explaining an action, when the agency in the first instance has failed to articulate such rationale." ATMI, 452 U.S. at 539 n. 73, 101 S.Ct. at 2506.

In challenging the procedure by which OSHA promulgated the Air Contaminants Standard,11 a group of industry petitioners complain that OSHA's use of generic findings, the lumping together of so many substances in one rulemaking, and the short time provided for comment by interested parties, combine to create a record inadequate to support this massive new set of PELs. The union also challenges the rulemaking procedure utilized by OSHA for the Air Contaminants Standard. Not surprisingly, however, the union claims that this procedure resulted in standards that are systematically underprotective of employee health. The union further challenges OSHA's decision to limit the scope of the rulemaking to substances for which the ACGIH recommendation was more protective than the current PEL, and thereby to ignore both other air contaminant substances in need of regulation and standards for exposure monitoring and medical surveillance. Moreover, the union argues that there is no record support for a four-year compliance period for these standards, given that OSHA itself found that the standards can be met by existing technology.

Unlike most of the OSHA standards previously reviewed by the courts, the Air Contaminants Standard regulates not a single toxic substance, but 428 different substances. The agency explained its decision to issue such an omnibus standard in its Notice of Proposed Rulemaking:

OSHA has issued only 24 substance-specific health regulations since its creation. It has not been able to review the many thousands of currently unregulated chemicals in the workplace nor to keep up with reviewing the several thousand new chemicals introduced since its creation. It has not been able to fully review the literature to determine if lower limits are needed for many of the approximately 400 substances it now regulates.

Using past approaches and practices, OSHA could continue to regulate a small number of the high priority substances and those of greatest public interest. However, it would take decades to review currently used chemicals and OSHA would never be able to keep up with the many chemicals which will be newly introduced in the future.

53 Fed.Reg. at 20963. For this reason, "OSHA determined that it was necessary to modify this approach through the use of generic rulemaking, which would simultaneously cover many substances." 54 Fed.Reg. at 2333 (emphasis added).

"Generic" means something "common to or characteristic of a whole group or class; typifying or subsuming; not specific or individual." Webster's Third New International Dictionary 945 (1966). Previous "generic" rulemakings by OSHA have all dealt with requirements that, once promulgated, could be applied to numerous different situations. For example, OSHA's Hazard Communication Standard, 29 C.F.R. § 1910.1200, mandates that employers inform employees of potentially hazardous materials. The regulation includes a basic list of substances which employers must treat as hazardous, but requires that the employers themselves also evaluate substances produced in their workplaces to determine if they are potentially hazardous based on available scientific evidence. United Steelworkers v. Auchter, 763 F.2d 728, 732 (3d Cir.1985). Similarly, OSHA has issued standards regulating employee access to medical and toxic substance exposure records, 29 C.F.R. § 1910.20, and setting forth uniform criteria for application in future regulation of exposure to carcinogens, 29 C.F.R. Part 1990.

By contrast, the new Air Contaminants Standard is an amalgamation of 428 unrelated substance exposure limits. There is little common to this group of diverse substances except the fact that OSHA considers them toxic and in need of regulation. In fact, this rulemaking is the antithesis of a "generic" rulemaking; it is a set of 428 specific and individual substance exposure limits. Therefore, OSHA's characterization of this as a "generic" rulemaking is somewhat misleading.

Nonetheless, we find nothing in the OSH Act that would prevent OSHA from addressing multiple substances in a single rulemaking.12 Moreover, because the statute leaves this point open and because OSHA's interpretation of the statute is reasonable, it is appropriate for us to defer to OSHA's interpretation. See Chevron U.S.A., Inc. v. Natural Resources Defense Council, Inc., 467 U.S. 837, 842-45, 864-66, 104 S.Ct. 2778, 2781-83, 2792-93, 81 L.Ed.2d 694 (1984); see also Vermont Yankee Nuclear Power Corp. v. Natural Resources Defense Council, Inc., 435 U.S. 519, 524-25, 543-49, 98 S.Ct. 1197, 1211-15, 55 L.Ed.2d 460 (1978) (Courts should not impose procedural requirements on agencies if not statutorily required.). However, we believe the PEL for each substance must be able to stand independently, i.e., that each PEL must be supported by substantial evidence in the record considered as a whole and accompanied by adequate explanation. OSHA may not, by using such multi-substance rulemaking, ignore the requirements of the OSH Act. Both the industry petitioners and the union argue that such disregard was what in essence occurred. Regretfully, we agree.

B. SIGNIFICANT RISK OF MATERIAL HEALTH IMPAIRMENT

Section 3(8) of the OSH Act defines "occupational health and safety standard" as "a standard which requires conditions, or the adoption or use of one or more practices, means, methods, operations, or processes, reasonably necessary or appropriate to provide safe or healthful employment and places of employment." 29 U.S.C. § 652(8) (emphasis added). The Supreme Court has interpreted this provision to require that, before the promulgation of any permanent health standard, OSHA make a threshold finding that a significant risk of material health impairment exists at the current levels of exposure to the toxic substance in question, Benzene, 448 U.S. at 614-15, 642, 100 S.Ct. at 2850-51, 2864; ATMI, 452 U.S. at 505-06, 101 S.Ct. at 2488-89,13 "and that a new, lower standard is therefore 'reasonably necessary or appropriate to provide safe or healthful employment and places of employment.' " Benzene, 448 U.S. at 615, 100 S.Ct. at 2850. OSHA is not entitled to regulate any risk, only those which present a "significant" risk of "material" health impairment. Id. at 641-42, 100 S.Ct. at 2863-64. OSHA must therefore determine: (1) what health impairments are "material," Texas Independent Ginners, 630 F.2d at 407, and (2) what constitutes a "significant" risk of such impairment, Benzene, 448 U.S. at 641-42, 655, 100 S.Ct. at 2863-64, 2870-71. Moreover, OSHA ultimately bears the burden of proving by substantial evidence that such a risk exists and that the proposed standard is necessary. Id. at 653, 100 S.Ct. at 2869-70. The agency "has no duty to calculate the exact probability of harm," id. at 655, 100 S.Ct. at 2870-71, or "to support its finding that a significant risk exists with anything approaching scientific certainty," id. at 656, 100 S.Ct. at 2871. However, OSHA must provide at least an estimate of the actual risk associated with a particular toxic substance, see Public Citizen Health Research Group v. Tyson, 796 F.2d 1479, 1502-03 (D.C.Cir.1986), and explain in an understandable way why that risk is significant. Benzene, 448 U.S. at 646, 100 S.Ct. at 2866.14 In past rulemakings, OSHA has satisfied this requirement by estimating either the number of workers likely to suffer the effects of exposure or the percentage of risk to any particular worker.15 See ATMI, 452 U.S. at 503, 505 n. 25, 101 S.Ct. at 2487-88, 2870-71 n. 25; Building & Constr. Trades Dept., AFL-CIO v. Brock, 838 F.2d 1258, 1263 (D.C.Cir.1988); Public Citizen, 796 F.2d at 1502; ASARCO, Inc. v. OSHA, 746 F.2d 483, 488 (9th Cir.1984).

Once OSHA finds that a significant risk of material health impairment exists at current exposure levels for a given toxic substance, any standard promulgated to address that risk must comply with the requirements of section 6(b)(5) of the OSH Act. 29 U.S.C. § 655(b)(5). That section provides that the agency

in promulgating standards dealing with toxic materials or harmful physical agents under this subsection, shall set the standard which most adequately assures, to the extent feasible, on the basis of the best available evidence, that no employee will suffer material impairment of health or functional capacity even if such employee has regular exposure to the hazard dealt with by such standard for the period of his working life. Development of standards under this subsection shall be based upon research, demonstrations, experiments, and such other information as may be appropriate. In addition to the attainment of the highest degree of health and safety protection for the employee, other considerations shall be the latest available scientific data in the field, the feasibility of the standards, and experience gained under this and other health and safety laws. Whenever practicable, the standard promulgated shall be expressed in terms of objective criteria and of the performance desired.

Id. (emphasis added). In other words, section 6(b)(5) mandates that the standard adopted "prevent material impairment of health to the extent feasible." ATMI, 452 U.S. at 512, 101 S.Ct. at 2492 (emphasis omitted).

In this rulemaking, OSHA grouped the 428 substances into eighteen categories by the primary health effects of those substances, for example, neuropathic effects, sensory irritation, and cancer. See 54 Fed.Reg. at 2402-03. Industry petitioners charge that for several categories of substances OSHA failed to adequately justify its determination that the health effects caused by exposure to these substances are "material impairments." We disagree.

Petitioners cite the category of "sensory irritation" as a particularly egregious example. Id. at 2434. At the beginning of the discussion for each category, the agency summarized the types of health effects within that category, and discussed why those effects constituted "material impairments." The "Description of Health Effects" for the "sensory irritation" category includes the following discussion:

The symptoms of sensory irritation include stinging, itching, and burning of the eyes, tearing (or lacrimation), a burning sensation in the nasal passages, rhinitis (nasal inflammation), cough, sputum production, chest pain, wheezing, and dyspnea (breathing difficulty)....

These effects may cause severe discomfort and can be seriously disabling, as is the case with dyspnea or wheezing. The tearing and eye irritation associated with exposure to sensory irritants are often severe and can be as disabling as the weeping caused by exposure to tear gas. In addition to these primary effects, workers distracted by material irritant effects are more likely than nonexposed workers to have accidents and thus to endanger both themselves and others. (These adverse health effects also clearly have substantial productivity impacts.)

....

During the rulemaking, the question arose as to the level of irritation that constitutes a significant risk of material impairment.... Some commenters were of the opinion that transient irritant effects should not be considered material impairment of health....

Most commentators, however, recommended that these signs and symptoms be regarded as material health impairments....