190 F.3d 545 (D.C. Cir. 1999)
In re United Mine Workers of America International Union, Petitioner
No. 97-1109
United States Court of AppealsFOR THE DISTRICT OF COLUMBIA CIRCUIT
Argued December 8, 1998Decided September 3, 1999

Petition for Writ of Mandamus
Judith Rivlin argued the cause for petitioner.  With her on  the briefs was Grant Crandall.
Robin A. Rosenbluth, Attorney, U.S. Department of Labor,  argued the cause for respondent.  With her on the brief was  W. Christian Schumann, Counsel.
Michael F. Duffy and Harold P. Quinn, Jr., were on the  brief for intervenor National Mining Association.
Before:  Wald, Tatel and Garland, Circuit Judges.
Opinion for the Court by Circuit Judge Garland.
Garland, Circuit Judge:


1
The United Mine Workers of  America (UMWA) petitions for a writ of mandamus to compel  the Mine Safety and Health Administration (MSHA) of the  Department of Labor to issue final regulations controlling  gaseous emissions in the exhaust of diesel engines used in  underground coal mines.  In 1989, MSHA issued a Notice of  Proposed Rulemaking (NPRM) to update air quality standards for hazardous substances in underground mines, including such gaseous emissions.  Although the comment period  closed in 1991, to date MSHA has not issued a final rule.


2
We find that the agency's failure to conclude its rulemaking  violates the express timetable set forth by Congress in the  Mine Safety and Health Act of 1977, 30 U.S.C. § 811(a)(4)  ("Mine Act").  However, because all parties agree that  MSHA is currently working on two other rulemakings with  greater significance for miners' health, we decline to issue a  writ that would move diesel exhaust gases to the top of the  agency's regulatory agenda.  During the course of this litigation, we issued an order requiring MSHA to file a definite  schedule for completing rulemaking with respect to these  gases.  Because the agency's response was not definite, we  grant the UMWA's alternative request that we retain jurisdiction, and we direct MSHA to file a series of status reports  until it takes final agency action.


3
* MSHA regulations require operators of underground coal  mines to test mine air for the presence of harmful gases.  30  C.F.R. § 75.322 (1998).  Concentrations in excess of permissible exposure limits (PELs) set by the agency are forbidden.Id.1  Since the early 1970s, those regulations have incorporated PELs established in 1972 by the American Conference of  Governmental Industrial Hygienists.  Id.  MSHA recognizes  that those levels are "outdated," 54 Fed. Reg. 35,760, 35,762 (Aug. 29, 1989), and concedes that its air quality standards,  overall, "do not fully protect today's miners" in their present  form.  63 Fed. Reg. 22,250, 22,250 (Apr. 27, 1998).


4
In 1983, MSHA published an Advance NPRM for an omnibus rulemaking involving a wide variety of air quality standards for underground mines, including PELs, respirator  protection rules, and abrasive blasting and drill dust controls.See 48 Fed. Reg. 31,171 (July 6, 1983).  In 1989, MSHA  issued an NPRM that included over 600 PELs and was  intended to "eliminate outdated incorporations by reference  in the existing standards."  54 Fed. Reg. at 35,762.  Among  the 600 were PELs for diesel exhaust gases.  See id. at  35,807.  The record for the omnibus air quality rulemaking  closed in August 1991.  See 56 Fed. Reg. 29,201 (June 26,  1991).  In the eight years since, the agency has neither  promulgated nor rescinded the proposed PELs, and has  concluded only one portion of the air quality rulemaking  (relating to abrasive blasting and drill dust control).  See 59  Fed. Reg. 8318 (Feb. 18, 1994).


5
MSHA has, however, taken other steps to protect coal  miners from exposure to diesel exhaust.  The most significant  is the regulation of the use and maintenance of diesel equipment.  In 1987, MSHA convened an advisory committee "to  provide advice on the complex issues concerning the use of  diesel-powered equipment in underground coal mines."  Report of MSHA Advisory Comm. on Standards & Regs. for  Diesel-Powered Equipment in Underground Coal Mines 1  (July 1988) [hereinafter Advisory Comm. Report].  MSHA  accepted the committee's recommendation to develop regulations to govern the approval and use of diesel-powered equipment.  Id. at 7-9.  In 1989 the agency issued an NPRM, and  in 1996 it promulgated final rules.  See 61 Fed. Reg. 55,412  (Oct. 25, 1996).  Among other things, the new rules require  agency approval of most diesel engines;  mandate that engines use low-sulfur fuel and be clean-burning;  limit their  gaseous emissions;  and establish monitoring and ventilation  requirements when they are in use.  See id. at 55,412-14.Upon promulgating the rules, MSHA stated that its "[e]xperience confirms that compliance with these regulations ... produces engines that operate without excessive gaseous  emissions that can be harmful to miners."  Id. at 55,419.  The  effective dates for the rules were staggered;  final compliance  is scheduled for November of this year.  See 30 C.F.R.  § 75.1907(b), (c).


6
Several of the diesel equipment rules contain requirements  that depend upon PELs for diesel exhaust gases.2  At the  time MSHA issued its NPRM for the equipment rules in  1989, the agency anticipated that the omnibus air quality  rulemaking would be completed before the final equipment  rules were promulgated.  54 Fed. Reg. 40,950, 40,958 (Oct. 4,  1989).  At the recommendation of its advisory committee,  MSHA said it would await the conclusion of the omnibus air  quality rulemaking, rather than update the PELs for the  diesel exhaust gases through the equipment rulemaking.  See  id. ("[E]xposure limits for the gaseous contaminants in diesel  exhaust should not be unique from the exposure limits set for  the same contaminants generated by other mining sources  such as blasting.");  Advisory Comm. Report at 67 (same).  By  the time MSHA promulgated the final equipment rules in  1996, however, the omnibus air quality rulemaking still had  not been completed.  The agency nonetheless decided "not  [to] adopt updated exposure standards at this time because  this issue remains in the rulemaking process for Air Quality  standards."  61 Fed. Reg. at 55,420.  The UMWA did not  challenge this or any other aspect of the equipment rules.


7
On March 3, 1997, the UMWA filed a petition for a writ of  mandamus directing the agency to issue regulations governing emissions in diesel exhaust.  UMWA Pet. at 1, 4.  Specifically, it sought controls over two components of exhaust: gases and particulate matter.  UMWA Reply Br. at 1-2, 1920 (June 30, 1997).  Shortly before the case was scheduled fororal argument, the parties commenced settlement negotiations and requested that the case be removed from the court's  argument calendar.  These discussions eventually led to  MSHA's publication of an NPRM for the regulation of diesel  particulate matter.  See 63 Fed. Reg. 17,492 (Apr. 9, 1998).That rulemaking is currently ongoing.


8
Citing the proposed diesel particulate regulations, as well  as the final diesel equipment rules, MSHA then moved to  dismiss the UMWA's petition as moot.  A special panel of this  court granted the motion in part, dismissing the diesel particulate portion of the petition.  The panel restored the balance  of the petition to the court's active docket, and directed  MSHA to address the issue of gaseous emissions.  In re  United Mine Workers of America, Int'l Union, No. 97-1109  (D.C. Cir. June 28, 1998).  The UMWA does not dispute the  partial dismissal of its petition, noting that the proposed  particulate rule "addresses part of what [it] seek[s]."  UMWA  Reply Br. at 1 (Aug. 5, 1998).  Accordingly, the only matter  before us is the issue of diesel exhaust gases.  The two gases  in question are carbon monoxide (CO) and nitrogen dioxide  (NO2).3

II

9
We consider first the contention of the National Mining  Association, intervenor in this case, that the UMWA's petition  is tantamount to an untimely challenge to MSHA's 1996 diesel  equipment rules.  As the Association correctly observes, the  Mine Act requires that petitions for review of MSHA safety  or health standards must be filed within sixty days of promulgation.  See 30 U.S.C. § 811(d).  The UMWA did not file a  challenge to MSHA's diesel equipment regulations, and its  petition for a writ of mandamus was filed over two months  after the sixty-day deadline for doing so had passed.  Accordingly, the Association suggests that we dismiss the UMWA's  petition as untimely.


10
But the union's petition for a writ of mandamus to compel  action on the diesel exhaust PELs does not constitute a  challenge to the agency's diesel equipment rules.  From the  outset, the agency disavowed any intention to consider new  PELs for the diesel exhaust gases during its diesel equipment  rulemaking, stating that the PELs would be reexamined as  part of its omnibus air quality rulemaking.  See 54 Fed. Reg.  at 40,958.  The UMWA does not take issue with that decision,  or any other aspect of the diesel equipment rules.  Although  the PELs are plainly related to the equipment rules, since the  latter incorporate them for certain equipment standards, the  UMWA's challenge is to the content of the PELs and not to  the agency's decision to incorporate them into the equipment  rules.  Indeed, had the UMWA challenged the diesel equipment rules on the ground that MSHA had failed to include  revised PELs for diesel exhaust gases, we might well have  denied its petition as premature.  See National Mining Ass'n  v. MSHA, 116 F.3d 520, 549 (D.C. Cir. 1997) ("An agency  does not have to 'make progress on every front before it can  make progress on any front.' ") (quoting Personal Water craft  Indus. Ass'n v. Department of Commerce, 48 F.3d 540, 544  (D.C. Cir. 1995)).


11
Because the UMWA does not complain about what the  agency has done but rather about what the agency has yet to  do, we reject the suggestion that its petition is untimely and  move to a consideration of the merits.

III

12
The UMWA seeks a writ of mandamus under the All Writs  Act, 28 U.S.C. § 1651(a), to "compel agency action unlawfully  withheld or unreasonably delayed," 5 U.S.C. § 706(1) (Administrative Procedure Act).  Although we plainly have jurisdiction over such requests,4 "[m]andamus is an extraordinary remedy [and] we require similarly extraordinary circumstances to be present before we will interfere with an ongoing  agency process."  Community Nutrition Instit. v. Young, 773  F.2d 1356, 1361 (D.C. Cir. 1985).  In exercising our equitable  powers under the All Writs Act, we are guided by the factors  outlined in Telecommunications Research & Action Center v.  FCC (TRAC) for assessing claims of agency delay:


13
(1) the time agencies take to make decisions must be governed by a "rule of reason";  (2) where Congress has provided a timetable or other indication of the speed with which it expects the agency to proceed in the enabling statute, that statutory scheme may supply content for this rule of reason;  (3) delays that might be reasonable in the sphere of economic regulation are less to lerable when human health and welfare are at stake;  (4) the court should consider the effect of expediting delayed action on agency activities of a higher or competing priority;  (5) the court should also take into account the nature and extent of the interests prejudiced by delay; and (6) the court need not "find any impropriety lurking behind agency lassitude in order to hold that agency action is 'unreasonably delayed.' "


14
750 F.2d 70, 80 (D.C. Cir. 1984) (citations omitted).


15
* Central to the UMWA's petition is the second TRAC factor  (which, as TRAC notes, gives content to the first).  The union  contends that MSHA is in violation of the regulatory timetables imposed by Congress in the Mine Act.  It relies on two  provisions of the Act as setting those timetables.  The first  requires the Secretary of Labor to act on an advisory committee's recommendation within sixty days of its submission.  30  U.S.C. § 811(a)(2).  We agree with MSHA, however, that the  sixty-day advisory committee deadline is inapplicable here. MSHA's advisory committee on diesel equipment recommended that the agency adopt new equipment regulations, see  Advisory Comm. Report at 7-9, and "set in motion a mechanism whereby a diesel particulate standard can be set," id. at  9.  MSHA has acted on those recommendations by promulgating the diesel equipment rules and issuing an NPRM for  diesel particulate.  But the advisory committee recommended  against using the equipment rules to set new PELs for  gaseous emissions in diesel exhaust, deferring instead to the  ongoing omnibus air quality rulemaking (as to which there  was no advisory committee).  See id. at 67.  Hence, the sixty day deadline is inapplicable to the regulations at issue here.


16
The second timetable provision on which the UMWA relies  requires the Secretary of Labor to promulgate final regulations, or to explain her decision not to promulgate them,  within ninety days of the certification of the record of a  hearing if one is held, or of the close of the public comment  period if a hearing is not held.  See 30 U.S.C. § 811(a)(4).  At  oral argument, MSHA conceded that the ninety-day rule does  apply to the omnibus air quality rulemaking.  The last of the  hearings in connection with that rulemaking was held on  March 27, 1991, and the record closed in August of that year. See 56 Fed. Reg. at 29,201.  Eight years later, the agency has  taken no action on any portion of the proposed regulations,  other than that relating to abrasive blasting and drill dust  control.


17
MSHA nonetheless contends that it is not in violation of the  ninety-day deadline because Congress intended it to have  discretion to defer action despite that deadline.  In support of  this proposition, MSHA relies on National Congress of Hispanic American Citizens v. Usery, 554 F.2d 1196 (D.C. Cir.  1977), in which the plaintiffs sued to compel the Occupational  Safety and Health Administration (OSHA) to comply with the  rulemaking timetables of section 6(b) of the Occupational  Safety and Health Act ("OSH Act").  See 29 U.S.C. § 655(b).Rejecting the plaintiffs' claim, we found that "traditional  agency discretion to alter priorities and defer action" permitted OSHA to deviate from the statutory deadlines.  554 F.2d  at 1200.  Although the government contends that the timetable provision in the Mine Act is similar to that in the OSH  Act, critical to our holding in National Congress was section  6(g) of the latter, which explicitly authorizes OSHA to "determin[e] the priority for establishing standards" with "due  regard to the urgency of the need for mandatory safety and  health standards for particular industries, trades, crafts, occupations, businesses, workplaces or work environments."  29  U.S.C. § 655(g);  see 554 F.2d at 1199-1200.  As we subsequently observed in Action on Smoking & Health v. Department of Labor, 100 F.3d 991, 994 (D.C. Cir. 1996), this  provision was "the main reason we gave for treating [the  OSH Act's deadlines] as non-mandatory."  But as MSHA  concedes, the Mine Act contains no counterpart to section  6(g) giving it similar flexibility to set aside statutory deadlines.  See MSHA Br. at 16.5


18
Nor are we persuaded by MSHA's broader claim that the  Mine Act's deadlines are merely hortatory.  See In re Barr  Labs., Inc., 930 F.2d 72, 74 (D.C. Cir. 1991) (rejecting similar  claim by FDA).  Nothing about the language of those deadlines suggests they are anything other than mandatory.  See,  e.g., 30 U.S.C. § 811(a)(4)(B), (C) ("[T]he Secretary, within 90  days after the period for filing ... objections has expired,  shall by rule promulgate, modify, or revoke such mandatory  standards" or "publish his reasons" for concluding "that a  proposed mandatory health or safety standard should not be  promulgated....") (emphasis added).  Failing to find support  in the statutory language, MSHA points us to the following  sentence from the Senate Report on the Mine Act:  "[T]he  Committee realizes that despite the exercise of good faith, the  Secretary may in certain cases be unable to meet the time  limitations."  S. Rep. No. 95-181, at 20 (1977).  This sentence, however, must be read in context.  The sentence that follows  reads:  "Failure to meet the time frames in such cases should  not be grounds for challenging the validity of the standard."Id.  This bespeaks not a congressional intention to give the  agency unlimited flexibility to delay promulgation, but rather  a concern that a violation of the deadlines not serve to  invalidate a completed rule.


19
This reading is supported by consideration of the passage  that immediately precedes the sentence quoted by MSHA. The statutory timetable, the Committee said,


20
eliminates the possibility of the lengthy standard promulgating procedures, which have too often been experienced under the current Coal and Metal Acts, by putting a closure date on the several steps of the process.  Once the standard promulgation procedure begins, it is regulated within a specific statutory time frame.  This procedure should facilitate more expeditious promulgation of standards.


21
Id.  The Report thus makes clear that Congress did intend  the ninety-day rule to "put[ ] a closure date" on the rulemaking process.  Id.


22
We also reject MSHA's claim that its breach of the deadline is excused by additional rulemaking requirements that  Congress has imposed on agencies since the Mine Act was  passed in 1977, including the Regulatory Flexibility Act of  1980 (as amended by the Small Business Regulatory Enforcement Fairness Act of 1996), and the Paperwork Reduction  Act of 1980.  See 5 U.S.C. §§ 601-612;  44 U.S.C. §§ 35013520.  Despite the increased requirements this legislation  imposes on the agency, nothing in either of these general purpose statutes indicates a congressional intention to set  aside the specific timetables of the Mine Act (or any other  statute).  Nor are we persuaded by MSHA's complaint that a  1993 executive order "makes compliance with Section 101(a)'s  timetables virtually impossible," by requiring agencies to  submit their rules for up to ninety days of pre-publication  review by the Office of Management and Budget.  MSHA Br.  at 17 n.7;  see Exec. Order No. 12,866,  6(b)(2)(B), 58 Fed. Reg. 51,735, 51,742 (Sept. 30, 1993).  Needless to say, the  President is without authority to set aside congressional  legislation by executive order, and the 1993 executive order  does not purport to do so.


23
We conclude that Congress meant what it said.  In the  words of the Senate Report, "[w]ithin 90 days of the certification of the hearing record (or of the close of the comment  period if no hearing is required), the Secretary is required to  issue his final rule or to make a determination not to issue the  proposed rule."  S. Rep. No. 95-181, at 20 (emphasis added).As the Secretary concededly has done neither here, she is in  clear violation of the Mine Act.  See Barr Labs., 930 F.2d at  74.  Indeed, even if we were to read the statute not as  specifying an express "timetable" for decision, but as merely  providing an "indication of the speed with which [Congress]  expects the agency to proceed," TRAC, 750 F.2d at 80, it  would still be clear that the agency has transgressed congressional expectations.  The eight-year delay here is simply not  in the same ballpark as the ninety-day period contained in the  statute, a timetable intended to "eliminate the possibility of  ... lengthy standard promulgating procedures."  S. Rep. No.  95-181, at 20;  see also id. at 18;  H.R. Rep. No. 95-312, at 1718 (1977);  Oil, Chem. & Atomic Workers Int'l Union v.  Zegeer, 768 F.2d 1480, 1488 (D.C. Cir. 1985) (noting "indications in the legislative history of the Mine Act that Congress  did not expect MSHA to tarry for years over its health and  safety rulemakings").

B

24
Our conclusion that the Secretary has violated the deadline  set forth in the Mine Act does not end the analysis.  As we  have noted before, "[e]quitable relief, particularly mandamus,  does not necessarily follow a finding of a [statutory] violation...."  Barr Labs., 930 F.2d at 74.  Indeed, not even the  UMWA urges us to hold the agency strictly to a ninety-day  deadline.  Accordingly, we must continue our analysis of the  remaining TRAC factors to determine whether mandamus is  appropriate in this case.


25
The UMWA contends that the third TRAC factor, which  directs us to be particularly wary of delay when human health  and welfare are at stake,6 also weighs in favor of mandamus. MSHA responds that although the rulemaking involves human health and welfare, they are not "at stake" because it has  "no scientific data that underground coal miners are currently  suffering a significant risk of material impairment from overexposure to gaseous emissions in diesel exhaust."  Thaxton  Aff. p 8.7  While the UMWA cites some (primarily anecdotal)  evidence regarding health effects from exposure to diesel  exhaust, see UMWA Response to MSHA Sched. at 4 (Jan. 11,  1999), that evidence fails to distinguish between the distinct  contributions of diesel particulate matter (which MSHA acknowledges as a health concern) and the diesel exhaust gases  at issue here.  Moreover, MSHA believes that the new diesel  equipment rules, already partially in effect and scheduled to  take full effect this November, are substantially reducing the  levels of gaseous emissions actually occurring in mines regardless of the current PELs.  See Thaxton Aff. p 12.


26
Even without fully crediting MSHA's data and predictions,  there is no question that in this case we have substantially  less evidence that delay would put human health at risk than  we had in Public Citizen Health Research Group v. Auchter,  where we ordered OSHA to issue an NPRM setting an  exposure limit for ethylene oxide (EtO) within thirty days.702 F.2d 1150, 1159 (D.C. Cir. 1983).  In that case, the  district court had found, supported by "[a]mple evidence in  the record," id. at 1157, that workers were being "subjected  to grave health dangers from exposure to ethylene oxide within the currently permissible range," id. at 1153.  See also  In re International Chem. Workers Union, 958 F.2d 1144,  1150 (D.C. Cir. 1992) (requiring OSHA to adhere to schedule  in light of "admittedly serious health risks associated with the  current permissible levels of cadmium exposure").  Not only  is there no such evidence in the record here, the UMWA has  not even suggested that a "grave danger to human life" arises  from exposure to diesel gases at current levels.  Auchter, 702  F.2d at 1159.


27
MSHA also argues that since its entire regulatory agenda  concerns health and welfare issues, the third TRAC factor  cannot carry as much weight as it otherwise might.  See  Sierra Club v. Thomas, 828 F.2d 783, 798 (D.C. Cir. 1987)  (noting that third TRAC factor "can hardly be considered  dispositive when ... virtually the entire docket of the agency  involves issues of this type").  In the circumstances of this  case, that argument is just another way of invoking the fourth  TRAC factor--the need to consider the consequences of  expediting one rulemaking on the progress of other agency  priorities--when the agency's other priorities also involve  human health and welfare.8  As MSHA points out, the two  gases of concern here represent only a small fraction of the  over 600 contaminants of mine air at issue in the omnibus air  quality rulemaking.  To single out diesel exhaust gases and  designate them for expedited treatment might well delay  rulemaking for other contaminants that are at least as dangerous to the health of the nation's miners.  See generally  Action on Smoking, 100 F.3d at 994;  Barr Labs., 930 F.2d at  73, 75.


28
Indeed, citing the fourth TRAC factor, MSHA points to two  other contaminants, not covered by the omnibus air quality  rulemaking, that it ranks as considerably more dangerous  than diesel exhaust gases, and whose control is thus of higher priority to the agency:  diesel particulate matter, the subject  of a pending rulemaking noted above, and respirable dust,  which is associated with black lung disease and silicosis.  By  contrast to diesel exhaust gases, the agency says, data shows  that exposure to these contaminants does materially impair  the health of miners.  MSHA Sched. at 7-8 (Dec. 23, 1998);see also 63 Fed. Reg. at 17,538;  63 Fed. Reg. 62,000, 62,000  (Nov. 9, 1998).


29
The UMWA does not disagree.  It is sometimes the case  with mandamus petitions that the agency's priorities are of  little concern to the petitioner, whose goal is simply to force  its matter to the front of the line.  See Kenneth Culp Davis &  Richard J. Pierce, Jr., Administrative Law Treatise § 12.3, at  225 (3d ed. 1994) (noting that judicial enforcement of statutory deadlines may "confer on the private parties who are  potential petitioners the discretion to determine the agency's  priorities and its allocation of resources among the tasks that  are subject to deadlines").  Here, however, the UMWA candidly stated at oral argument that it could not characterize  diesel exhaust gases as its highest priority among all mine  safety regulations.  It agreed it was possible that the diesel  equipment rules alone may have the desired effect of reducing exposure to those gases.  And it further agreed that  control of diesel particulate matter and respirable mine dust  rank as higher priorities.  We must, therefore, take care not  to craft a remedy for MSHA's statutory violation that could  both interfere with the agency's internal processes and damage the very interests the petitioner seeks to protect.  Compare Auchter, 702 F.2d at 1158 ("We would hesitate to  require [OSHA] to expedite the EtO rulemaking if such a  command would seriously disrupt other rulemakings of higher  or competing priority.").

C

30
Although there is insufficient record evidence that a substantial health risk would result from some further delay in  promulgating the regulation petitioner seeks, and no dispute  that the agency's priorities are appropriate, the fact remains that the delay here has been substantial.  Congress directed  MSHA to use "the latest available scientific data in the field"  to set exposure standards that will ensure "that no miner will  suffer material impairment of health or functional capacity."30 U.S.C. § 811(a)(6)(A).  Despite that statutory mandate,  the agency's PELs are now twenty-seven years old, promulgated at a time when coal mines employed diesel engines with  far less frequency.  See 30 C.F.R. § 75.322;  61 Fed. Reg. at  55,412.  The same scientific organization that authored the  PELs originally incorporated by MSHA now advocates lower  airborne concentrations for many substances, including CO  and NO2;  indeed, it advocates reducing the current PEL for  CO by half and for NO2 by two-fifths.  See American Conference of Governmental Industrial Hygienists, TLVs and BEIs: Threshold Limit Values for Chemical Substances & Physical  Agents and Biological Exposure Indices 23, 52 (1999) (recommending that PEL for CO be lowered from 50 ppm to 25, and  that PEL for NO2 be lowered from 5 ppm to 3).  MSHA has  failed "to meet its self-declared prior deadlines" for action on  air quality standards, TRAC, 750 F.2d at 80,9 and concedes  that its existing standards are "outdated," 54 Fed. Reg. at  35,762.  However many priorities the agency may have, and  however modest its personnel and budgetary resources may  be, there is a limit to how long it may use these justifications  to excuse inaction in the face of the congressional command to  act within ninety days.  Compare Sierra Club, 828 F.2d at  797 (denying writ where "[n]o statutory deadline limits the  duration of rulemakings....  [and there is no] generalized  congressional mandate for EPA to expedite").


31
Notwithstanding the length of time by which its decision on  this issue is overdue, the agency's briefs contained no hint of a schedule for coming into compliance with the Mine Act.  To  the contrary, the agency said only that it "continues to  vigorously work on the portion of the [air quality] rulemaking  to which [it] has given priority."  MSHA Br. at 20.  Since the  portion of the rulemaking involving diesel exhaust gases is  concededly not the agency's priority, that statement suggested that MSHA was not working "vigorously" on the matter at  issue here.  At oral argument, MSHA was somewhat more,  but not much more, forthcoming about its plans for issuing  revised PELs for diesel exhaust gases.10


32
In light of the agency's vagueness, and in order to assist us  in determining whether to exercise our discretion to issue the  requested writ, on December 9, 1998 we directed MSHA to  file "a definite schedule for completing rulemaking with respect to the diesel emission gases, and an explanation justifying that schedule."  In re United Mine Workers of America  Int'l Union, No. 97-1109, at 2 (D.C. Cir. Dec. 9, 1998)  (unpublished order).11  In response to our order, the agency  submitted the following schedule "for completing rulemaking  on the gases in diesel exhaust":  (1) December 1999--complete data collection;  (2) June 2000--complete analysis of the  data, decide whether to proceed with rulemaking, and publish  decision not to proceed if that is the agency's conclusion;  (3)  December 2000--issue new NPRM if the agency decides to  proceed with rulemaking;  (4) December 2001--promulgate  final rule.  See MSHA Sched. at 2, 9 (as corrected Jan. 13,  1999).


33
This schedule and the explanations the agency offers for  each of its four phases are not facially unreasonable.  First, it  would not be unreasonable for it to take MSHA a year (until  December 1999) to collect additional data to determine whether a regulation is still necessary.  Additional data regarding  current levels of exposure to diesel exhaust gases is required,  the agency says, because it currently has no data that miners  are suffering material impairment from overexposure to such  gases, and because preliminary data suggests that the new  diesel equipment rules have significantly lowered the amount  of such gaseous emissions.  This data collection should be  accomplished when diesel emissions are greatest, the agency  continues, which happens only during "long wall moves" that  occur once or twice a year.  Finally, the agency states that  data collection cannot be completed until December 1999  because the impact of the new equipment rules will not be  fully measurable until they completely take effect in November 1999.  As the UMWA concedes that the diesel equipment  rules may reduce exposure to diesel exhaust gases even with  the current PELs in place, a plan to collect data on a one year schedule would not be unreasonable.


34
Second, it would not be unreasonable for MSHA to require  six months (until June 2000) to analyze the data, to decide  whether to proceed with rulemaking regarding diesel exhaust  gases, and to publish a decision not to proceed if that is its  conclusion.  This phase is drawn out somewhat because the  agency's resources are primarily devoted to other priorities,  particularly respirable mine dust and diesel particulate matter.  In light of these considerations, six months would not be  an unreasonable amount of time to evaluate what the agency  has collected, to determine whether exhaust gases need to be  regulated, and to determine at least preliminarily whether, as  required under the Mine Act, a lower standard is "feasib[le]."30 U.S.C. § 811(a)(6)(A).


35
Third, if MSHA does decide to go forward, the agency's  filing provides a justification for taking another six months  (until December 2000) to issue a new NPRM.  The agency  plans to issue a new NPRM for diesel exhaust gases, rather  than continue with the 1989 NPRM for the omnibus air quality rulemaking, in part because of the Eleventh Circuit's  decision in AFL-CIO v. OSHA, 965 F.2d 962 (11th Cir. 1992).In that case, the court invalidated omnibus OSHA regulations  that revised PELs for 428 toxic substances because the  agency failed to analyze each individual toxin with sufficient  particularity.  MSHA fears that its 1989 omnibus NPRM  could be vulnerable for the same reason.  In addition, MSHA  notes that it is now subject to statutory rulemaking requirements that were not considered in 1989, see 2 U.S.C. § 1501  et seq. (Unfunded Mandates Reform Act of 1995);  5 U.S.C.  §§ 601-612 (Small Business Regulatory Enforcement Fairness Act of 1996), and that any newly-proposed PELs would  be based on data not available when it drafted the original  NPRM.  Although it might still be possible for MSHA to go  forward on the current rulemaking record, the agency's plan  may well shorten the overall period of delay by resolving  issues that would otherwise become the subject of litigation. See Sierra Club, 828 F.2d at 798-99 ("[B]y decreasing the  risk of later judicial invalidation and remand to the agency,  additional time spent reviewing a rulemaking proposal before  it is adopted may well ensure earlier, not later, implementation of any eventual regulatory scheme.").


36
Finally, it would not be unreasonable for it to take MSHA a  year (until December 2001) to complete the fourth phase of  the schedule, running from the issuance of the NPRM  through the promulgation of a final rule.  By way of rationale, the agency states that it is required to provide a public  comment period, that it anticipates receiving comments from  a substantial number of interested parties, that it will have to  analyze those comments, and that it may then have to revise  the rule to take the comments into account.  It is difficult for  us to second-guess this projection in light of the "host of  complex scientific and technical issues" involved in the promulgation of revised PELs.  United Steelworkers, 783 F.2d at  1120;  see id. (accepting 14-month period from NPRM to final  rulemaking as not "facially unreasonable" in light of complex  technical issues and fact that "OSHA obviously cannot know at present how many comments it will receive or the nature of  those comments").12


37
In sum, a reasonably definite schedule along the above  lines would represent a good faith effort by MSHA to come  into compliance with it statutory obligations under the Mine  Act.  The problem is that we cannot fairly describe MSHA's  schedule as "reasonably definite."  The agency does not even  attempt to characterize the final promulgation date as a  reliable estimate.  See, e.g., MSHA  Sched. at 13 ("[The Secretary] will not be able to promulgate afinal rule until at least  December 2001.") (emphasis added).  And although MSHA  appears to characterize as firm the June 2000 date for  deciding whether to proceed and the December 2000 date for  issuing a new NPRM,13 it ultimately hedges even as to those  interim dates.14


38
To advise us that regulations will not issue until "at least  December 2001" is to provide no end-date at all.  It is  unresponsive to our order to provide a "definite schedule,"  and it offers no assurance that the agency will remedy its  continuing violation of the Mine Act.  Accordingly, MSHA's  response is insufficient to justify its request that we deny the  union's petition "in its entirety."  MSHA Br. at 20.  And while the considerations recounted in Parts III(A) and III(B)  persuade us that issuance of a writ of mandamus at this time  could do more harm than good, we accept the UMWA's  alternative suggestion that we retain jurisdiction of this matter.  UMWA Reply Br. at 8 (Aug. 5, 1998);  see Monroe, 840  F.2d at 947;  TRAC, 750 F.2d at 80-81;  In re Center for Auto  Safety, 703 F.2d 1346, 1354 (D.C. Cir. 1986).

IV

39
For the foregoing reasons, the court will retain jurisdiction  over this case until there is a final agency disposition that  discharges MSHA's obligations under the Mine Act.  The  agency is directed to advise the court on the date such  disposition occurs, and of the status of this matter on each of  the following dates unless final disposition has already occurred:  December 31, 1999;  June 30, 2000;  December 31,  2000;  and December 31, 2001.  Prior to final agency action,  the UMWA may petition this court to grant additional appropriate relief in the event MSHA fails to adhere substantially  to a schedule that would, as described in Part III(C), constitute a good faith effort by MSHA to come into compliance  with the Mine Act.  See Monroe, 840 F.2d at 947;  TRAC, 750  F.2d at 80-81;  see also Zegeer, 768 F.2d at 1488 ("[I]f MSHA  should fail to act with appropriate diligence in following the  estimates it has tendered to this court, petitioners may invoke  our authority to direct MSHA to complete the rulemaking  process with due dispatch.").


40
So ordered.



Notes:


1
 For the sake of simplicity, we will uniformly use the phrase  "permissible exposure limits" (PELs), although MSHA also uses  "threshold limit values" (TLVs) to refer to the same concept.  See  54 Fed. Reg. 40,950, 40,958 (Oct. 4, 1989).


2
 For example, one rule requires mine operators to "take appropriate corrective action" once the concentration of carbon monoxide  (CO) or nitrogen dioxide (NO2) exceeds half of their PELs.  30  C.F.R. § 70.1900(c);  see also id. § 75.325(j) (permitting higher  levels of CO and NO2 if air sampling demonstrates continuous  compliance with PELs).


3
 The UMWA originally identified three gases as components of  diesel exhaust:  CO, NO2, and nitric oxide (NO).  UMWA Pet. at 2.MSHA states that its 1989 air quality NPRM did not propose  lowering the existing exposure limit for NO, see MSHA Sched. at 1  n.1 (Dec. 23, 1998), a fact which the UMWA does not contest.


4
 See, e.g., Oil, Chem. & Atomic Workers Int'l Union v. Zegeer,  768 F.2d 1480, 1484-86 (D.C. Cir. 1985) (upholding judicial authority  to review claims of unreasonable delay under the Mine Act);  Telecommunications Research & Action Ctr. v. FCC, 750 F.2d 70, 7577, 79 (D.C. Cir. 1984).


5
 It is true, as MSHA notes, that the Mine Act permits the  Secretary to extend the comment period on a proposed rule, 30  U.S.C. § 811(a)(2);  but the Secretary did not extend the period past  August 1991 and it is now closed.  It is also true that the Act does  not set a time limit on the length of hearings or specify a time  within which the record must be certified, see id. § 811(a)(3);  but  MSHA has now ended the hearings and does not contend that the  record remains uncertified.


6
 As in Barr Laboratories, 930 F.2d at 75, in this case the third  TRAC factor overlaps with the fifth, which directs us to "take into  account the nature and extent of the interests prejudiced by delay."TRAC, 750 F.2d at 80.


7
 See also NCI/NIOSH Interagency Project, A Cohort Mortality Study with a Nested Case-Control Study of Lung Cancer and  Diesel Exhaust Among Non-Metal Miners 6 (1995) ("[T]he gases  and vapors in the diesel exhaust ... are not thought to be strong  mutagens or carcinogens at the levels at which they occur.").


8
 Accord Sierra Club, 828 F.2d at 798 ("[W]hether the public  health and welfare will benefit or suffer from accelerating this  particular rulemaking depends crucially upon the competing priorities that consume EPA's time, since any acceleration here may  come at the expense of delay of EPA action elsewhere.").


9
 Compare 54 Fed. Reg. at 40,958 (stating in 1989 that "[b]ecause  of the particular importance of such standards to miners exposed to  diesel exhaust, the Agency further intends that the air quality  rulemaking will be final by the time that this rulemaking on ...  diesel equipment is complete"), with 61 Fed. Reg. at 55,420 (promulgating final equipment rules in 1996 but noting that "updated  exposure standards ... remain[ ] in the rulemaking process for Air  Quality standards").


10
 Although there was some equivocating, we understood agency  counsel to state that the agency expected it would take a year to  issue an NPRM for revised PELs for diesel exhaust gases, and  another year to promulgate a final rule--and we so noted in our  December 1998 order.  MSHA's post-argument schedule lengthens  this projection by at least a year, without explaining or even  mentioning the discrepancy.


11
 See International Chem. Workers, 958 F.2d at 1147 (directing  OSHA, after oral argument, to "file a report with the court indicating the status of the proposed rule and the date by which the  agency expects to issue a final cadmium rule");  In re United  Steelworkers of America, 783 F.2d 1117, 1119 (D.C. Cir. 1986).


12
 That said, MSHA must nonetheless be mindful of its statutory  obligation to issue the final rule within ninety days of the certification of the hearing record, or of the close of the public comment  period if no hearing is held.  30 U.S.C. § 811(a)(4).


13
 See MSHA Sched. at 8-9 ("If the Secretary determines [not to  proceed], she will decide ... and will publish the reasons for that  determination ... by June 2000....  [If] the Secretary decides  that she will proceed with rulemaking on the gases in diesel  exhaust, she will issue a new notice of proposed rulemaking by  December 2000.") (emphasis added) (as corrected Jan. 13, 1999).


14
 See, e.g., MSHA Sched. at 4 ("[I]t will take at least a year to  collect a sufficient body of data....");  id. at 6 ("[I]t will take at  least six months to review and analyze the data....");  id. at 12  ("[I]t will take at least six months from the time the Secretary  decides to proceed ... to the time the Secretary issues a notice of  proposed rulemaking.") (emphasis added in all parentheticals).


