Rosebud Mining Co. v. Mine Safety & Health Administration ( 2016 )


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  •  United States Court of Appeals
    FOR THE DISTRICT OF COLUMBIA CIRCUIT
    Argued November 16, 2015             Decided July 5, 2016
    No. 14-1285
    ROSEBUD MINING COMPANY AND PARKWOOD RESOURCES,
    INC.,
    PETITIONERS
    v.
    MINE SAFETY AND HEALTH ADMINISTRATION AND
    JOSEPH A. MAIN, ASSISTANT SECRETARY OF LABOR FOR
    MINE SAFETY AND HEALTH,
    RESPONDENTS
    No. 14-1286
    CANYON FUEL COMPANY, LLC, ET AL.,
    PETITIONERS
    v.
    MINE SAFETY AND HEALTH ADMINISTRATION AND
    JOSEPH A. MAIN, ASSISTANT SECRETARY OF LABOR
    FOR MINE SAFETY AND HEALTH,
    RESPONDENTS
    On Petitions for Review of Decisions of the
    Assistant Secretary of Labor for Mine Safety and Health
    Ralph Henry Moore II argued the cause for the
    petitioners. Patrick W. Dennison was with him on brief.
    2
    Lynne B. Dunbar, Attorney, United States Department
    of Labor, argued the cause for the respondents. W. Christian
    Schumann, Counsel, was with her on brief.
    Before: HENDERSON, ROGERS and KAVANAUGH,
    Circuit Judges.
    Opinion for the Court filed by Circuit Judge
    HENDERSON.
    KAREN LECRAFT HENDERSON, Circuit Judge: Several
    coal mine operators—Rosebud Mining Company, Parkwood
    Resources, Inc., Canyon Fuel Company, LLC, Mountain Coal
    Company, LLC, Bowie Resources, LLC and Peabody Sage
    Creek Mining, LLC (collectively, petitioners)—seek review
    of two orders of the United States Department of Labor
    (Labor)—per its Mine Safety and Health Administration
    (MSHA)—modifying the application of mandatory mine
    safety standards to their respective mines. The petitioners
    contend that the orders contain three conditions unnecessary
    to ensure adequate mine safety, thus making them arbitrary
    and capricious. For the reasons set forth below, we deny the
    petitions for review.
    I. BACKGROUND
    Under section 101(a) of the Federal Mine Safety and
    Health Act of 1977 (Mine Act), 30 U.S.C. §§ 801 et seq., the
    Labor Secretary must promulgate “mandatory health or safety
    standards for the protection of life and prevention of injuries
    in coal or other mines.” 30 U.S.C. § 811(a). The Assistant
    Secretary of Labor for Mine Safety and Health (Assistant
    Secretary)1 may grant mine-specific modifications of the
    1
    For MSHA matters, the Labor Secretary acts through the
    Assistant Secretary. 29 U.S.C. § 557a.
    3
    standards if he finds that “an alternative method of achieving
    the result of such standard exists which will at all times
    guarantee no less than the same measure of protection
    afforded the miners of such mine by such standard, or that the
    application of such standard to such mine will result in a
    diminution of safety to the miners in such mine.” 
    Id. § 811(c).
    Thus, the statute permits modification if an equally
    effective alternative exists or if the standard itself negatively
    affects mine safety.2 To satisfy either option, MSHA
    conducts a two-step inquiry which asks, first, whether the
    proposed alternative “promote[s] the same safety goals as the
    original standard with no less than the same degree of
    success” and, second, whether the “modification would
    achieve a net gain, or at least equivalence, in overall mine
    safety.” United Mine Workers of Am., Int’l Union v. MSHA,
    
    928 F.2d 1200
    , 1202 (D.C. Cir. 1991) (S. Ohio Coal Co.)
    (emphasis added).3 At the second step, “both advantages and
    2
    The latter scenario seems counter-intuitive—MSHA plainly
    does not intend to harm miners—but can be conceptualized as
    follows: assume arguendo that MSHA requires all elevator shafts
    to be manually operated, reasoning that elevators with electrical
    components could spark and start a mine fire. An operator with an
    especially deep shaft might argue that the requirement nonetheless
    results in a diminution in mine safety because a manual elevator is
    relatively slow and, in a mine disaster, could prevent miners from
    surfacing quickly. For another example, see Int’l Union, United
    Mine Workers of Am. v. Fed. Mine Safety & Health Admin., 
    924 F.2d 340
    (D.C. Cir. 1991) (Quarto Mining).
    3
    We have concluded that the “diminution of safety” clause
    requires only that the Assistant Secretary determine “whether
    application of a particular mandatory safety regulation would be
    unsafe” and that “the Assistant Secretary need not balance the
    efficacy of the existing rule against the net benefits produced by the
    proposed modification,” Quarto 
    Mining, 924 F.2d at 343
    , basing
    our interpretation on the Assistant Secretary’s practice at the time.
    4
    disadvantages of the alternative method” are weighed,
    including those that are unrelated to the original standard. 
    Id. The party
    seeking modification has the burden of proof to
    establish that the proposed modification complies with
    section 811(c). 30 C.F.R. § 44.30(b).
    The modification process begins with an operator’s filing
    a petition for modification with MSHA. See 
    id. § 44.10.
    After an investigation, the MSHA Administrator issues a
    proposed order. 
    Id. § 44.13.
    The operator may request a
    hearing before an administrative law judge (ALJ), 
    id. §§ 44.14,
    44.15, 44.20, who, after investigation/hearing,
    issues his decision, 
    id. § 44.32.
    Any party—including
    MSHA—may then appeal to the Assistant Secretary. 
    Id. § 44.33.
    The Assistant Secretary’s order may contain “special
    terms and conditions” which “shall have the same effect as a
    mandatory safety standard.” 
    Id. § 44.4(c).
    “Only a decision
    by the Assistant Secretary [is] final agency action for
    purposes of judicial review.” 
    Id. § 44.51.
    These six petitions for review involve MSHA’s
    “permissibility” requirements, which, in general, mandate that
    certain equipment located in certain mine areas be approved
    by MSHA (i.e., that they be permissible). The focus of the
    permissibility requirements is to “assure that [electrically
    operated] equipment will not cause a mine explosion or mine
    See 
    id. at 344.
    The record reveals some confusion, however, about
    whether MSHA now applies the Southern Ohio Coal Co. test to
    both statutory options or to the first only. Compare ALJ’s Decision
    and Order at 14, Rosebud Mining Co., Case Nos. 2010-MSA-1,
    2011-MSA-2, -11, -12 (Dep’t of Labor Apr. 11, 2013) (Rosebud
    ALJ Order I) with Assistant Secretary’s Decision and Order at 13,
    Case Nos. 2010-MSA-1, 2011-MSA-2, -11, -12 (Dep’t of Labor
    Nov. 14, 2013) (Rosebud Order I). Because the petitioners do not
    raise this issue, we do not reach it.
    5
    fire . . . . ” 30 C.F.R. § 75.2; see also Administrator’s
    Proposed Decision and Order at 5, Canyon Fuel Co., Docket
    No. M-2009-025-C (Dep’t of Labor May 6, 2011) (“MSHA
    requirements for permissible . . . equipment are intended to
    prevent mine explosions from unpredicted methane
    accumulations, methane outbursts, or float coal dust in
    suspension by removing a possible ignition source.”). MSHA
    does not define “non-permissible” but its definition of
    “permissible” substantially illuminates the former.
    Permissible equipment includes, as relevant here, “completely
    assembled electrical machine[ry]” for which MSHA has
    issued “a formal approval.” 30 C.F.R. § 18.2. Thus,
    electrical equipment without this approval is non-permissible
    and, accordingly, unauthorized in certain mine areas.4 Not all
    mine equipment is subject to the permissibility scheme—for
    example, “[m]echanical surveying equipment,” which “poses
    no risk of ignition,” requires no modification order for use.
    Rosebud ALJ Order I at 5.5 For our review, the permissibility
    scheme breaks down into three categories:           (1) non-
    permissible equipment to which the non-use in certain mine
    areas restriction applies; (2) non-permissible equipment with
    a MSHA modification which removes the non-use restriction
    and (3) equipment (like mechanical surveying equipment) for
    4
    The parties stipulated that “[t]he concern with any electrical
    equipment is that if used in an explosive atmosphere it will produce
    a spark, fire or heating with enough energy that an ignition of
    methane and/or coal dust may result, possibly leading to a fire or
    explosion.” Stipulations ¶ 19, In re Rosebud Mining Co., Docket
    Nos. 2010 MSA-1, 2011 MSA-2, 2011-MSA-12, 2011 MSA-11
    (Dep’t of Labor Mar. 28, 2013) (hereinafter Stipulations).
    5
    Relatedly—although not relevant for our review—MSHA
    deems permissible “intrinsically safe” equipment, that is,
    equipment “incapable of releasing enough electrical or thermal
    energy . . . to cause ignition.” 30 C.F.R. § 18.2.
    6
    which no modification order is needed to authorize its use in
    certain mine areas.6
    The petitioners sought to use non-permissible equipment
    and petitioned for modification of the following MSHA safety
    standards: (1) 30 C.F.R. § 75.500, the standard requiring,
    inter alia, that electrical equipment used in or inby the last
    crosscut7 constitute permissible equipment, (2) 
    Id. § 75.507-1,
    the standard requiring that electrical equipment used in return
    6
    As the parties stipulated, there is a difference between
    category two equipment and “permissible” equipment. The parties
    refer to category two equipment as “permitted” equipment—
    meaning it is “non-permissible equipment allowed to be used at a
    particular mine pursuant to the granting of a petition for
    modification.” Stipulations ¶ 29. By contrast, permissible
    equipment has “a formal approval [without conditions] . . . issued
    by MSHA[].” 
    Id. 7 Throughout
    the record, this area of the mine is referred to as
    “in or inby the last open crosscut.” See, e.g., Rosebud Order I at 17
    (emphasis added); see also FMC Wyoming Corp., v. MSHA, 16
    FMSHRC 1787, 
    1994 WL 445344
    , at *4 (Aug. 16, 1994) (“the
    term ‘last open crosscut’ is interchangeable with ‘last crosscut’ ”).
    MSHA defines “[t]he area of a coal mine inby the last open
    crosscut” as the “working place.” 30 C.F.R. § 75.2. The parties
    stipulated that the “the ‘last open crosscut’ is the last crosscut
    without a permanent stopping in a line of pillars containing the
    permanent stoppings that separate the intake air courses and the
    return air courses. This area includes the most advanced mining
    area in the mine, where the ventilating air reaches the areas of
    active coal removal and deepest penetration and starts its course
    back out of the coal mine.” Stipulations ¶ 10. “ ‘Inby’ refers to
    something facing the direction of the coal face. Conversely,
    ‘outby’ refers to the direction facing the mine entrance (the
    surface).” Andalex Res., Inc. v. MSHA, 
    792 F.3d 1252
    , 1254 n.2
    (10th Cir. 2015).
    7
    airways8 constitute permissible equipment and (3) 
    Id. § 75.1002,
    the standard requiring that electrical equipment
    used within 150 feet of pillar workings or longwall faces9
    constitute permissible equipment. In short, the modification
    petitions sought authorization to use non-permissible
    equipment in three mine locations where use of the equipment
    was otherwise off-limits. Each of the three described
    locations is “more likely to have an explosive environment”
    than other mine areas, thus triggering the applicable standard.
    Assistant Secretary’s Decision and Order at 27, Canyon Fuel
    Co., Case Nos. 2011-MSA-00006 to 00009, 2011-MSA-
    00014 to 00021, 2013-MSA-00012, -00024, -00025, -00037
    (Dep’t of Labor Nov. 24, 2014) (Canyon Fuel Order).
    A. MSHA PROCEEDINGS REGARDING ROSEBUD AND
    PARKWOOD
    Petitioners Parkwood Resources and Rosebud Mining
    filed identical modification petitions in December 2008 and
    January 2009.10 Each operator sought to use non-permissible
    8
    Return air is “[a]ir that has ventilated the last working place
    on any split of any working section or any worked-out area whether
    pillared or nonpillared. If air mixes with air that has ventilated the
    last working place on any split of any working section or any
    worked-out area, whether pillared or nonpillared, it is considered
    return air. For purposes of § 75.507–1, air that has been used to
    ventilate any working place in a coal producing section or pillared
    area, or air that has been used to ventilate any working face if such
    air is directed away from the immediate return is return air.” 30
    C.F.R. § 75.301.
    9
    Pillar workings and longwall faces are simply “areas in
    which miners extract coal.” Andalex 
    Res., 792 F.3d at 1254
    .
    10
    The Parkwood and Rosebud petitions were subsequently
    consolidated at the administrative level and we follow suit,
    hereinafter referring to them as the Rosebud petitioners.
    8
    equipment—specifically, battery-powered (i.e., electrical)
    surveying instruments—11in or inby the last open crosscut and
    in return airways. See 30 C.F.R. §§ 75.500; 75.507-1. They
    maintained that the two applicable safety standards hampered
    both their ability to accurately and quickly map the mines—
    resulting in a “diminution of safety” to miners, see 30 U.S.C.
    § 811(c)—12as well as their compliance with other MSHA
    regulations, see 30 C.F.R. § 75.372 (requiring “up-to-date
    map of the mine drawn to a scale of not less than 100 nor
    more than 500 feet to the inch”), 
    id. § 75.1200
    (requiring
    mine operator to maintain “accurate and up-to-date map” of
    mine “in a fireproof repository located in an area on the
    surface of the mine”), and state law, see 52 PA. STAT. ANN.
    § 690-224 (requiring “professional quality map of the mine on
    a scale of not less than 200 feet to the inch”), that require
    current and accurate mine maps. To obtain the modification,
    the Rosebud petitioners proposed seven conditions on their
    use of the NPESE, see generally S. Ohio Coal 
    Co., 928 F.2d at 1202
    (alternative must “promote the same safety goals as
    the original standard with no less than the same degree of
    11
    This equipment is hereinafter referred to as non-permissible
    electronic surveying equipment (NPESE).
    12
    According to all six petitioners, accurate surveying is critical
    because it “prevents intersection of the mine with abandoned
    working of other mines which may contain water in large
    quantities, explosive gas or the absence of oxygen.” Pet’rs’ Br. at
    12. Surveying is also necessary to avoid “sealed areas,” 
    id. at 13,
    which areas MSHA subjects to regular “monitoring.” See 30
    C.F.R. § 75.336.
    9
    success”), one of which—no use when float coal dust13 is in
    suspension14—is of particular relevance to our review.15
    1. ADMINISTRATOR’S DECISION
    The Rosebud petitioners’ “diminution of safety”
    argument pressed that the NPESE was needed in order to
    accurately map mines because of its ability to obtain
    measurements superior to non-electric (mechanical) surveying
    equipment.       The Administrator rejected the Rosebud
    petitioners’ arguments for two reasons. First, he determined
    that “when using [NPESE] the equipment need not be taken
    into return air or inby the last open crosscut if the surveying is
    carefully coordinated with the mining activity.”
    Administrator’s Proposed Decision and Order at 5, Parkwood
    Res. Inc., Docket No. M-2008-054-C (Dep’t of Labor Jan.
    29, 2010). In other words, he found that the Rosebud
    petitioners could use their preferred surveying tools—the
    NPESE—without violating the permissibility regulations
    because they did not need to use the equipment in the areas to
    which the permissibility regulations apply.             Thus the
    regulations restricting the areas into which the operators could
    13
    “Float coal dust” is defined as “coal dust consisting of
    particles of coal that can pass a No. 200 sieve.” 30 C.F.R.
    § 75.400–1(b).
    14
    MSHA regulations do not define the term “in suspension”
    but the parties stipulated that it means dust “suspended in the air
    during mining.” Stipulations ¶ 33.
    15
    The other conditions included: (1) regular examination of
    the NPESE, (2) continuous monitoring for methane during use of
    NPESE, (3) mandatory shutdown if methane concentration reaches
    a certain level, (4) changing and charging of batteries in fresh air,
    (5) proper training of personnel using NPESE and (6) use of
    NPESE after MSHA inspection only.
    10
    use NPESE did not impair the miners’ ability to map the
    mines to the desired accuracy level and likewise did not
    (because of inaccurate mapping) result in a diminution of
    safety. Second, the Administrator determined that “levels of
    accuracy fully capable of protecting miners can be achieved
    using optical non-electric surveying equipment”—i.e.,
    mechanical equipment—and “can achieve even higher levels
    of accuracy . . . through repetition of measurements and
    statistical applications.” 
    Id. Thus, to
    him, use of NPESE was
    not necessary.
    In addition, the Administrator found the proposed
    conditions duplicative because many of them simply tracked
    MSHA regulations; those that did not were found insufficient
    because they failed to ensure an adequate level of safety.
    Thus, the Rosebud petitioners’ proposed conditions did not
    “promote the same safety goals as the original standard with
    no less than the same degree of success.” See S. Ohio Coal
    
    Co., 928 F.2d at 1202
    . Regarding the proposed float coal dust
    ban, the Administrator found that its implementation was
    impossible unless mining were to cease during surveying.
    2. ALJ’S DECISION
    The Rosebud petitioners sought ALJ review. The ALJ
    held two separate hearings on the consolidated petitions,
    made findings of fact and issued his decision on April 11,
    2013.
    The ALJ first explained how methane and coal dust can
    result in a mine fire. First, he observed that methane is
    explosive at an aerial concentration between five and fifteen
    per cent. According to him, coal dust can also result in a
    mine fire but that, in order to ignite, the dust must be “in
    suspension . . . [and] sufficiently thick that you couldn’t see a
    light bulb that was turned on about four feet in front of you.”
    11
    Rosebud ALJ Order I at 6 (alterations and quotations
    omitted). He next recognized that mechanical surveying
    equipment “poses no risk of ignition” and that, although
    NPESE does present such a risk, nonetheless “it has a low
    potential for ignition.” 
    Id. at 5.
    For support on the latter
    point, the ALJ relied on the testimony of MSHA electrical
    engineer Chad Huntley and fire-and-explosion expert Noah
    Ryder. Huntley estimated “the possibility that both the
    methane detector would fail and the electronic surveying
    equipment would ignite at the same time is one in ten
    thousand.” 
    Id. at 4.
    Ryder testified that the potential for a
    coal dust ignition “inside one of the[] [NPESE]” was
    “nonexistent” because, through water immersion and dust
    swab tests, he found that dust would “settle
    on . . . component[s]” in the devices and, “if it settled there,
    it’s not in suspension and won’t ignite.” 
    Id. at 6
    & n.9
    (emphasis added). Ryder also testified that NPESE was less
    dangerous than other equipment MSHA has approved via
    modification petitions.
    Some findings were in apparent tension with others. For
    example, Rosebud surveying manager Michael Groff testified
    that NPESE “does not get hot when it’s running” and that he
    had “never seen a spark or arc when removing the battery.”
    
    Id. at 5
    n.6. But Huntley and Ryder both testified that
    sparking could occur when “the battery was physically
    disconnected” or if “an inside component broke.” 
    Id. at 6
    .
    Huntley testified that NPESE could “overheat . . . and ignite
    methane” but also noted that it had “a thermal breaker for de-
    energizing the battery pack at a temperature below the
    ignition temperature for methane.” 
    Id. at 5
    n.6 (emphasis
    added).    Some NPESE equipment also came with a
    manufacturer safety warning indicating that it should not be
    used in an underground coal mine and that an explosion could
    12
    result if so used.16 Because the manufacturer was unable to
    testify as to the basis of the warning, however, the ALJ gave it
    no weight. The ALJ also recognized that Rosebud had been
    using NPESE “in all areas of [its] mine[s]” for over 20 years
    and that MSHA, by not issuing any citation during that time,
    had “tacitly approved [its] use.” 
    Id. at 13.
    The ALJ, concluding that mechanical surveying
    equipment was “obsolete, far less accurate than electronic
    surveying equipment, and above all, not realistically available
    on the commercial market except in used condition,” 
    id. at 2,
    approved the petitions. He anticipated that the conditions he
    set out in his order “promote[d] the same safety goals as the
    original standard with no less than the same degree of
    success.” 
    Id. at 14
    (quoting S. Ohio Coal 
    Co., 928 F.2d at 1202
    ). The ALJ’s conditions were substantially similar to
    those contained in the petitions, including the prohibition on
    surveying in the presence of float coal dust. He added a
    requirement that the Rosebud petitioners gradually phase out
    old equipment so that, within five years, the NPESE in use
    would be no more than five years old. The ALJ thought this
    condition would “prevent the degradation of [NPESE] seals”
    through which float coal dust could enter and cause ignition.
    
    Id. at 17.
    He observed that his conditions closely replicated
    those included in an earlier MSHA consent decree allowing
    NPESE. 
    Id. at 4
    n.5; see Initial Decision Approving
    Settlement and Order of Dismissal at 2–4, Twentymile Coal
    Co., Case No. 2007-MSA-00002 (Dep’t of Labor Dec. 5,
    2007) (Twenty Mile Consent Order).
    16
    Specifically, the warning stated: “Safety Cautions; Warning;
    May ignite explosively. Never use an instrument near flammable
    gas, liquid matter, and do not use in a coal mine.” Rosebud ALJ
    Order I at 3.
    13
    The ALJ also concluded that “granting [the] petitions for
    modification would engender a net gain in miner safety.”
    Rosebud ALJ Order I at 15 (emphasis in original); see also S.
    Ohio Coal 
    Co., 928 F.2d at 1202
    (asking whether
    “modification would achieve a net gain, or at least
    equivalence, in overall mine safety”), because, although
    “mechanical surveying equipment can meet . . . accuracy
    requirement[s],” “the use of mechanical equipment may
    require multiple set ups, increasing the length of surveyors’
    exposure to hazardous conditions.” Rosebud ALJ Order at
    15. Moreover, “mechanical parts cannot be reliably calibrated
    or repaired . . . [and] surveyors are not currently trained in
    their use. . . . Therefore, application of the [permissibility]
    standard[s] is less safe than application of the modification, as
    it is unsafe to use equipment that is not calibrated or repaired
    properly, or that surveyors have not been trained to use.” 
    Id. Finally, he
    reasoned that NPESE “is 8-10 times more accurate
    than mechanical equipment” and “greater accuracy leads to
    increased safety in the mines.” Id.17
    3. ASSISTANT SECRETARY’S DECISION
    The Administrator appealed the ALJ’s order to the
    Assistant Secretary who, applying a de novo standard of
    review, conducted an independent analysis of the evidence
    and rejected many of the ALJ’s factual findings. For
    17
    The ALJ made no finding regarding diminution of safety,
    treating the case as one arising under the first prong of 30 U.S.C.
    § 811(c) (asking whether “an alternative method of achieving the
    result of such standard exists which will at all times guarantee no
    less than the same measure of protection afforded the miners of
    such mine by such standard”). But, as noted, 
    see supra
    n.3, the
    Rosebud petitioners do not challenge MSHA’s application of both
    section 101(c)’s “alternative method” option and its “diminution of
    safety” option to their petitions.
    14
    example, although MSHA never sanctioned Rosebud for its
    20-year use of NPESE, the Assistant Secretary declined to
    conclude that MSHA had thus tacitly approved thereof in
    view of the fact that Rosebud produced no evidence that
    MSHA knew of the use; moreover, MSHA had sanctioned
    other operators for similar use. The Assistant Secretary also
    disputed Ryder’s opinion that the Rosebud petitioners’
    NPESE was “well-sealed against [methane] gas and [coal]
    dust” ingress because Ryder had tested “none of . . . the
    specific instruments that [the Rosebud petitioners] identified
    in [the] petitions.” Rosebud Order I at 28–29. Moreover, the
    Assistant Secretary found Ryder’s assertion that he tested
    substantially similar equipment “suspect” given Ryder’s
    failure to “take apart any of the specific instruments identified
    in the petitions” to determine their similarity vel non. 
    Id. at 29.
    In addition, the Assistant Secretary credited Huntley’s
    testimony that tended to discredit Ryder’s tests—specifically,
    that, according to International Electrotechnical Commission
    standards, “ingress protection tests” using “dust and moisture”
    were not proper surrogates for gas. 
    Id. at 30.
    And, even
    assuming Ryder’s tests were fair proxies, “moisture was
    detected inside all of the pieces of used equipment that Ryder
    tested.” 
    Id. The Assistant
    Secretary also rejected the ALJ’s
    characterization of some of Huntley’s testimony.             For
    instance, the “one-in-ten-thousand probability” of both the
    “methane detector failing and the electronic surveying
    equipment igniting” was based on a premise with which
    Huntley explicitly disagreed. 
    Id. at 28–29
    n.12. The
    Assistant Secretary also rejected the ALJ’s Ryder-supported
    conclusion that coal dust did not present an ignition concern.
    Although “Ryder testified that coal dust . . . would settle on a
    component and not remain in suspension”—thus, not
    igniting—Huntley testified that coal dust can “enter non-
    15
    permissible electronic equipment, layer itself on internal
    components, and cause the equipment to overheat and ignite
    methane.” 
    Id. at 32.
    The Assistant Secretary also disagreed
    with the ALJ’s conclusion that, “because the equipment has
    internal thermal breakers that are designed to de-energize the
    battery pack at a temperature below the ignition temperature
    of methane, coal dust layering on the internal
    components . . . is not a concern,” 
    id. at 32–33,
    because, the
    Assistant Secretary opined, “thermal breakers can fail, and
    there [wa]s no evidence concerning their reliability,” 
    id. at 33.
    Moreover, he noted the likelihood of a coal dust-based
    explosion even in the absence of the required aerial
    concentration because coal dust can “be rapidly placed in
    suspension, [and] even a vigilant surveyor may not have the
    time to de-energize his instrument before it encounters an
    explosive concentration of coal dust.” 
    Id. Finally, the
    Assistant Secretary disagreed with the ALJ
    on the importance of the NPESE warning. Although the
    manufacturer was unable to explain the reason for the
    warning, “[the Rosebud petitioners], not the Administrator,
    ha[d] the burden of proof in th[e] proceeding.” 
    Id. at 34
    (citing 30 C.F.R. § 44.30(b)).
    On November 14, 2013, the Assistant Secretary issued
    his decision upholding the ALJ’s modification grant but
    substantially modifying and tightening the conditions. In
    addition to prohibiting NPESE use when float coal dust was
    in suspension, the Assistant Secretary required that coal
    production shut down while the equipment was used in or
    inby the last open crosscut and in return air and that, if
    “viable” mechanical equipment became available, use of
    NPESE must cease. Rosebud Order I at 50. With these
    conditions in place, the Assistant Secretary concluded that the
    modification “promotes the same safety goals as [the
    16
    standards] with no less than the same degree of
    safety. . . . [and] that the overall effect of the proposed
    alternative method, including the modifications . . . will
    achieve at least a net least [sic] equivalence in overall mine
    safety.” 
    Id. at 14
    (applying S. Ohio Coal Co. 
    test, 928 F.2d at 1202
    ).
    The Assistant Secretary remanded to the ALJ to consider
    two conditions for which the record contained insufficient
    support (and which are not before us on appeal). The ALJ
    subsequently approved a consent agreement applying four
    new conditions (in lieu of the remanded pair) and the Rosebud
    petitioners then appealed to the Assistant Secretary to renew
    their objections to the originally disputed conditions and to
    facilitate judicial review therefrom.18 See 30 C.F.R. § 44.51
    (“Only a decision by the Assistant Secretary [is] final agency
    action for purposes of judicial review.”). On November 24,
    2014, the Assistant Secretary issued Rosebud Order II, once
    again rejecting the Rosebud petitioners’ arguments.
    The Rosebud petitioners argued in the second round
    before the Assistant Secretary that three of the unchanged
    requirements “[we]re unnecessary to meet [the modification]
    standard.” Rosebud Order II at 3. It was undisputed that,
    with the Assistant Secretary’s conditions, the modification
    grant “guarantee[d] no less than the same measure of
    protection afforded the miners of such mine by” the
    permissibility standards, see S. Ohio Coal 
    Co., 928 F.2d at 18
             The Administrator asserted that the Rosebud petitioners’
    objections “essentially reargue[d] matters already unsuccessfully
    litigated” and the Assistant Secretary accordingly treated them “in
    the nature of a motion for reconsideration.” Assistant Secretary’s
    Decision and Order at 3–4, Rosebud Mining Co., Case Nos. 2010-
    MSA-1, 2011-MSA-2, -11, -12 (Dep’t of Labor Nov. 24, 2014)
    (Rosebud Order II).
    17
    1202. The Rosebud petitioners argued that cessation of coal
    production while surveying took place was unnecessary
    because (1) “surveying will not be conducted in an entry
    where production is occurring,” Rosebud Order II at 4; (2)
    “surveying will not be set up close to the face” of the mine,
    id.; (3) “surveying generally will be upwind of the . . . mining
    machine, and, even when it is downwind, methane and [coal]
    dust will be removed by the ventilation system” and other
    safeguards, 
    id. at 4–5;
    (4) “surveyors spend minimal time in
    or inby the last open crosscut or in the return,” 
    id. at 7;
    (5)
    “surveying equipment . . . does not [cut into or] liberate
    methane or generate coal dust,” id.; and (6) the ALJ-imposed
    condition that, “if one percent methane is detected,” use of
    NPESE was to cease, was sufficient to protect against
    methane explosions, 
    id. at 8.
    The Assistant Secretary was not persuaded.              He
    concluded that the first, second and fourth objections relied on
    factual assertions rebutted by the record.19 He found the third
    objection “d[id] not offset the decrease in safety from using”
    NPESE because the ventilation system and other safety
    features were “present whether surveyors use mechanical,
    permissible, or non-permissible surveying equipment.” 
    Id. at 5
    –6. Further, he reasoned that “ventilation systems do not
    always work effectively and [that] operators do not always
    comply with ventilation requirements.” 
    Id. at 6
    . He rejected
    the fifth objection because, although it “might mean that the
    risk of using non-permissible surveying equipment is less than
    19
    See 
    id. at 4
    n.2 (Rosebud surveyors testified only that
    “usually we coordinate ourselves in different entries”) (emphasis in
    original); 
    id. n.3 (“Rosebud
    Surveying Manager Groff testified that
    he has taken shots as close as 50 feet from the face.”); 
    id. at 7
    n.4
    (“Groff . . . acknowledged that he does not always set up in the
    middle of the entry.”).
    18
    the risk of using other types of non-permissible equipment,” it
    did not mean that NPESE was safe. 
    Id. at 7–8.
    Finally, the
    Assistant Secretary criticized the methane monitoring
    condition because the “detectors may fail” and because there
    “is a lag time in methane detectors and that if there were a
    sudden inundation of methane, by the time the methane
    detector registered one percent methane, and by the time the
    surveyor reacted to shut the surveying equipment off, there
    might already be an explosive amount of methane
    surrounding the equipment.” 
    Id. at 8.
    The Rosebud petitioners also argued that the prohibition
    on surveying when float coal dust existed was both unclear
    and unnecessary and that the requirement to switch to
    “viable” mechanical surveying equipment if it became
    available was unreasonable. Regarding the first claim, the
    Rosebud petitioners asserted that float coal dust in suspension
    always exists. But, as the Assistant Secretary observed, the
    condition could be implemented if production ceased.
    Moreover, he clarified and interpreted the condition to allow
    for a “visual determination of whether there is float coal dust
    in suspension.” 
    Id. at 11
    n.7. As to the latter objection, the
    Assistant Secretary explained that mechanical equipment
    would be viable if “sufficiently accurate for use in
    underground mines” and that MSHA’s resources should not
    be spent on ensuring the NPESE’s compliance with
    conditions if viable mechanical equipment—i.e., equipment
    that can be used without conditions—exists. 
    Id. at 15.
    B. MSHA PROCEEDINGS REGARDING CANYON FUEL AND
    MOUNTAIN COAL (CANYON FUEL PETITIONERS)
    On July 15, 2009 petitioners Canyon Fuel and Mountain
    Coal filed nearly identical petitions for modification, seeking
    to use NPESE in or inby the last crosscut, in return airways
    19
    and within 150 feet of pillar workings and longwall faces.
    See 30 C.F.R. §§ 75.500, 75.507-1, 75.1002. As did the
    Rosebud petitioners, Canyon Fuel and Mountain Coal claimed
    that the mandatory standards resulted in diminution in miner
    safety and inability to meet mapping requirements and they
    proposed comparable conditions, with one exception (the float
    coal dust condition was omitted). The Administrator denied
    the petitions for reasons substantially similar to his denial of
    the Rosebud petitioners’ petitions.
    The MSHA ALJ held a hearing on the consolidated
    Canyon Fuel and Mountain Coal petitions and released a
    decision on April 3, 2014.20 In light of the intervening
    Rosebud Order I, MSHA agreed that the petitions should be
    granted if the Assistant Secretary’s conditions set forth in
    Rosebud Order I were imposed. See ALJ’s Decision and
    Order at 7, Canyon Fuel Co., Docket Nos. 2011-MSA-00006
    to 00009, 00014 to 00021, 2013-MSA-00024, -00025, -00037
    (Dep’t of Labor April 3, 2014) (“The issues have evolved
    since the petitions were first filed. No longer is the issue . . .
    whether       the    proposed      modification   should      be
    granted . . . . The question now is simply what conditions are
    necessary.”). The ALJ subsequently revised the Rosebud
    Order I conditions—as applied to Canyon Fuel—in three
    significant respects.
    First, he found that it was “not appropriate” to disallow
    NPESE if and when “viable new mechanical surveying
    equipment” became available. 
    Id. at 13–14.
    To him, the
    20
    Petitioners Peabody Sage Creek and Bowie Resources had
    similar petitions pending and filed a letter with the ALJ agreeing to
    be bound by his decision in the Canyon Fuel case. Canyon Fuel
    references hereinafter include not only Canyon Fuel and Mountain
    Coal but also Peabody Sage Creek and Bowie Resources.
    20
    accuracy of mechanical surveying equipment—even,
    apparently, “viable” mechanical surveying equipment—was
    inferior and reduced miner safety. He also found the ban on
    surveying when float coal dust was in suspension “vague and
    ambiguous” because the condition did not include a
    measurement of float coal dust and because surveying would
    be “impossible”—due to “visibility restrictions”— long
    before an explosive quantity was in suspension. 
    Id. at 20.
    Finally, he narrowed the restriction on surveying during coal
    production, requiring only that surveying not occur at “the
    longwall or a working face during production.” 
    Id. at 23.
    The Administrator appealed once more to the Assistant
    Secretary who issued a final order simultaneously with the
    Rosebud II Order with identical conditions based on
    materially similar reasoning.
    Both sets of operators timely filed petitions for review.21
    Our jurisdiction arises under section 101(d) of the Mine Act.
    30 U.S.C. § 811(d).22
    II.     ANALYSIS
    Our review of the Assistant Secretary’s two final orders
    is pursuant to the Administrative Procedure Act, that is, we
    21
    The Rosebud petitioners, however, did not petition for
    modification of 30 C.F.R. § 75.1002 (permissibility requirement for
    “equipment . . . located within 150 feet of pillar workings or
    longwall faces”). With this exception, both sets of petitioners
    challenge the same conditions and are therefore hereinafter referred
    to as the petitioners. Because Canyon Fuel made no discrete
    argument regarding 30 C.F.R. § 75.1002, we reject its challenge
    thereto without more.
    22
    Both sets of petitioners filed a consolidated brief and we
    likewise consolidate the petitions for disposition.
    21
    determine “whether the granting of the petition for
    modification was arbitrary, capricious, an abuse of discretion
    or otherwise not in accordance with the law.” Int’l Union,
    United Mine Workers of Am. v. MSHA, 
    830 F.2d 289
    , 292
    (D.C. Cir. 1987) (Emerald Mine Corp.) (citing 5 U.S.C.
    § 706(2)(A)). This “[h]ighly deferential” standard, AT&T
    Corp. v. FCC, 
    349 F.3d 692
    , 698 (D.C. Cir. 2003), is
    especially applicable when we review “technical
    determinations on matters to which the agency lays claim to
    special expertise.” Bldg. and Const. Trades Dep’t v. Brock,
    
    838 F.2d 1258
    , 1266 (D.C. Cir. 1988); see also Int’l Union,
    United Mine Workers of Am. v. MSHA, 
    407 F.3d 1250
    , 1258
    (D.C. Cir. 2005) (Jim Walter Res., Inc.) (equivalent safety
    determination is within Assistant Secretary’s expertise). We
    uphold the agency if it “considered the relevant factors and
    articulated a rational connection between the facts found and
    the choice made.” Nat’l Ass’n of Clean Air Agencies v. EPA,
    
    489 F.3d 1221
    , 1228 (D.C. Cir. 2007) (internal quotation
    marks omitted). Because the challenged orders involve “an
    area within the [Assistant] Secretary’s expertise,” Jim Walter
    Res., 
    Inc., 407 F.3d at 1258
    , and because they are supported
    by “substantial evidence and . . . a reasoned explanation,”
    Bldg. and Const. Trades 
    Dep’t., 838 F.2d at 1266
    , we deny
    the petitions for review.
    The thrust of the petitioners’ argument is that the three
    above-discussed conditions—the requirement that coal
    production cease while surveying with NPESE occurs in or
    inby the last open crosscut, in return air or within 150 feet of
    longwall faces or pillar workings (high risk areas), the bar on
    surveying with NPESE when float coal dust is in suspension
    and the instruction to use viable mechanical surveying
    equipment if it becomes available—are unnecessary and
    22
    therefore arbitrary and capricious.23 But the Assistant
    Secretary weighed the relevant factors—whether the
    alternative “promote[s] the same safety goals as the original
    standard with no less than the same degree of success” and
    whether it improves “overall mine safety,” S. Ohio Coal 
    Co., 928 F.2d at 1202
    —and “articulated a rational connection
    between the facts found and the choice made,” Nat’l Ass’n of
    Clean Air 
    Agencies, 489 F.3d at 1228
    (internal quotation
    marks omitted). In so concluding, we note that “the Mine Act
    and its standards require redundant safety measures.”
    Rosebud Order II at 6 (emphasis added).
    A. CESSATION OF PRODUCTION
    It is uncontested that the condition requiring coal
    production to stop while the NPESE is used in high risk areas
    enhances mine safety. What is at issue is whether this
    23
    The petitioners also contend that the Assistant Secretary’s de
    novo review of the ALJ orders and factual findings is ultra vires.
    Section 101(c) of the Mine Act provides that a petition for a
    modification hearing is subject to section 554 of the Administrative
    Procedure Act (APA). 30 U.S.C. § 811(c). Section 554 of the
    APA in turn cross-references section 557 which provides that “[o]n
    appeal from or review of [an] initial decision, the agency has all the
    powers which it would have in making the initial decision.” 5
    U.S.C. § 557(b) (emphasis added); see also Kay v. FCC, 
    396 F.3d 1184
    , 1189 (D.C. Cir. 2005) (“The law is settled that an agency is
    not required to adopt the credibility determinations of an
    administrative law judge.”); 
    id. (agency not
    in position analogous to
    appellate court reviewing trial court). We have suggested that
    findings dependent on “demeanor of witnesses” must be “given
    special weight,” Mathew Enter., Inc. v. NLRB, 498 F. App’x. 45, 46
    (D.C. Cir. 2012) (quoting 2 Richard J. Pierce, Jr., Administrative
    Law Treatise § 11.2 (5th ed. 2010)) (emphasis added), but
    demeanor is not at issue here.
    23
    condition is unnecessary and, indeed, whether it is so
    unnecessary as to fail arbitrary and capricious review. The
    objections of the petitioners break down into the following
    groups: (1) surveying equipment is not used to mine coal, (2)
    use of the NPESE must stop if the methane level approaches a
    level well below its explosive threshold, (3) even while
    production is ongoing, the NPESE will not come in contact
    with methane and coal dust, (4) the NPESE has a slight
    potential for ignition, (5) it is unlikely methane or coal dust
    will enter the NPESE compartments that contain electrical
    components, (6) previously approved modification petitions
    manifest that this condition is unnecessary and (7) the
    manufacturer’s warning about use of NPESE in coal mines
    was “not probative,” Pet’rs’ Br. at 61. We address the
    objections in seriatim.
    1. Surveying equipment is not used to mine coal
    The petitioners argue that the Assistant Secretary failed
    to appreciate the differences between NPESE and other—
    riskier—mine equipment. For example, they claim that he
    failed to account for the fact that the NPESE does not cut
    coal, that it is peripheral in the mining process and that it does
    not cause methane to disperse or coal dust to be in suspension.
    But the Assistant Secretary addressed this argument. He
    reasoned that “[a]lthough these circumstances . . . might mean
    that the risk of using non-permissible surveying equipment is
    less than the risk of using other types of non-permissible
    equipment, nothing in the record convinces me that the
    circumstances would sufficiently offset the dangers of using”
    NPESE in high risk areas. Rosebud Order II at 7–8 (emphasis
    added). Moreover, MSHA has, by regulation, applied its
    permissibility requirements to equipment other than that
    which “cuts into coal.” Canyon Fuel Order at 41. See, e.g.,
    30 C.F.R. § 75.500(d) (“All . . . electric face equipment which
    24
    is taken into or used inby the last crosscut of any coal mine”
    must be permissible) (emphasis added). The petitioners’
    contention that the NPESE—although non-permissible—is
    relatively safe suggests only that this condition is less
    necessary than others, not that it is arbitrary. In addition, the
    Assistant Secretary noted that the petitioners used the Twenty
    Mile consent order, Case No. 2007-MSA-00002 (Dep’t of
    Labor Dec. 5, 2007), as a template for their petition and
    Twenty Mile included the same condition.
    2. Methane detection and shutdown requirement guards
    against explosions
    The petitioners next contend that, because the ALJ
    imposed a condition that operators cease using NPESE if the
    methane level reaches a 1% concentration and, because a 5%
    concentration is the minimum concentration necessary for
    ignition, the requirement that production cease during NPESE
    use is arbitrary. The Assistant Secretary amply rebutted this
    argument.      He noted that although the 1% methane
    concentration condition “provide[s] some protection from the
    increased risk of a methane ignition posed by using non-
    permissible equipment . . . [it is] not enough.” Rosebud Order
    I at 35–36. As he explained, the record indicated that
    methane detectors are not always properly calibrated and also
    may fail. Moreover, he cited testimony that a “lag time”
    exists between an increase in methane concentration and its
    detection. Rosebud Order II at 8. Thus, if there were a
    “sudden inundation of methane,” the methane detector might
    not register it before an explosive quantity accumulated near
    the NPESE. 
    Id. 3. NPESE
    will not encounter methane or float coal dust
    The petitioners next contend that, as a matter of practice,
    surveying generally does not occur in areas where methane
    25
    and coal dust are present and that, even when it does, the
    ventilation systems will prevent an explosion. First, we note
    that much of this argument is equivocal.24 To second-guess
    the Assistant Secretary on this ground would require us to
    weigh the evidence de novo and usurp MSHA’s statutorily
    conferred authority to determine whether a specific mine
    hazard—once its existence is conceded—is substantial
    enough to impose restrictions. See, e.g., Partington v. Houck,
    
    723 F.3d 280
    , 291 (D.C. Cir. 2013) (“we do not substitute our
    judgment for that of the agency or evaluate de novo” its
    factual findings).
    In any event, the Assistant Secretary adequately
    addressed the objection with a reasoned explanation. First, he
    observed that the record was ambiguous about whether
    surveying sometimes occurred in the areas the petitioners
    claimed to avoid.25 Moreover, he observed that nothing in the
    24
    See, e.g., Pet’rs’ Br. at 44 (there is “little or no exposure to
    either” dust or methane) (emphasis added); 
    id. at 4
    5 (in “most
    instances, the surveying equipment will be positioned upwind of
    the continuous miner and thus not exposed in any way to methane
    or dust”) (emphasis added); 
    id. (“surveyors are
    generally upwind of
    the entry where production is occurring”) (emphasis added); 
    id. at 4
    6 (“it is clear that the instrument will not often be in close
    proximity downwind of the continuous miner”) (emphasis added).
    25
    See Rosebud Order II at 4 n.2 (“Although initially stating
    that he did not survey in the entry where the continuous miner is
    mining, . . . Groff then testified that ‘usually we coordinate
    ourselves in different entries.’ ” (emphasis in original)); 
    id. at n.3
    (“The evidence does not support Rosebud’s assertion that surveying
    is not conducted close to the face. . . . Groff testified that he has
    taken shots as close as 50 feet from the face.”); 
    id. at 7
    n.4 (“The
    evidence does not support Rosebud’s assertion that surveying
    equipment is always used in the middle of the entry. . . . [Groff]
    26
    ALJ orders “require[d] that the equipment be used” only in
    the areas identified by the petitioners—i.e., in different mine
    entries, a sufficient distance from the face or in the middle of
    mine entries. Canyon Fuel Order at 41–42. Regarding
    whether surveying often or always occurred upwind of
    production, the Assistant Secretary noted the same ambiguity,
    i.e., that the petitioners occasionally surveyed downwind. See
    
    id. at 4
    2–43 n.18 (Canyon Fuel expert “testified that when one
    surveys in the longwall tailgate return production is ‘most
    always’ upstream.”) Moreover, the conditions of use did not
    require that surveying equipment be used only outside the
    designated areas—that the Assistant Secretary was unmoved
    by the assertion that this would almost always be the case was
    not arbitrary.26
    Regarding ventilation, the Assistant Secretary noted that
    MSHA regulations already require ventilation so that it does
    not “offset the decrease in safety from using” NPESE.
    Rosebud Order II at 6. In addition, “ventilation systems do
    not always work effectively and operators do not always
    comply with ventilation requirements.” 
    Id. Ventilation is
    but
    one of many “redundant safety measures . . . the Mine Act
    and its standards require” to guard “against ignitions and
    explosions.” 
    Id. at 5
    –6; see also Canyon Fuel Order at 40
    acknowledged that he does not always set up in the middle of the
    entry.”).
    26
    It is unclear from the record whether the risk of NPESE use
    is mitigated entirely if its use is limited to, inter alia, areas upwind
    of production or in entries where production is not occurring. The
    Assistant Secretary did not reach this issue and thus we need not
    reach it. The petitioners do not argue that it was arbitrary to impose
    the cessation of production condition in lieu of a condition
    requiring, for example, that surveyors always remain upwind of
    production.
    27
    (“One of the most frequently cited violations is the failure to
    comply with ventilation requirements.”). In addition, even if
    the ventilation system functioned properly, the Assistant
    Secretary concluded that it captured only “significant
    amount[s] of dust and methane”—not all of it. 
    Id. Record evidence
    supports his conclusion. See id.at 40 n.14 (citing
    ALJ hearing transcript).
    4. NPESE has low ignition potential
    The petitioners also argue that NPESE is unlikely to
    cause an explosion. See, e.g., Pet’rs’ Br. at 52 (although
    NPESE is not “permissible,” it nonetheless “has a very low
    potential for ignition of methane or coal dust”); 
    id. at 53
    (NPESE “does not generate heat”). Substantial evidence
    supports the Assistant Secretary’s rejection of this argument.
    The Assistant Secretary considered—and rejected—
    expert testimony on the relative ignition potential of the
    equipment. For example, he noted that as part of the test for
    determining whether equipment is permissible, “MSHA
    layers dust onto components to see if dust will smolder.”
    Canyon Fuel Order at 35. Smoldering corresponds to
    overheating, which can result in ignition. Granted, record
    evidence suggested that if there is significant overheating,
    “components inside the devices would ‘likely’ fail, the
    equipment would not function, and there would be no safety
    hazard.” 
    Id. But the
    Assistant Secretary observed that the
    evidence was equivocal and not supported with test results.
    There was also testimony indicating that “if there were
    internal sparking or overheating it would not be detected.” 
    Id. at 36.
    The Assistant Secretary further observed that the safety
    warning contained in the manual indicated that certain
    equipment “[m]ay ignite explosively.” 
    Id. 28 The
    petitioners supplement their argument about the
    equipment’s relative safety with the observation that it cannot
    create sparks. See Pet’rs’ Br. at 63 (“[U]nlike a continuous
    miner or roofbolter, [NPESE] creates no sparks.”). But see 
    id. at 53
    (“[T]he changing of batteries has a potential for creating
    sparks.”). They argue, therefore, that “dust or methane would
    necessarily have to enter the instrument” in order for an
    explosion to occur. 
    Id. at 6
    3. But the Assistant Secretary
    disagreed and record evidence supports his skepticism. For
    example, Ryder “acknowledged that non-permissible
    electronic surveying equipment can spark if there is
    something wrong with the device such as a loose connection.”
    Canyon Fuel Order at 28 n.8. And a MSHA witness “testified
    that batteries in the equipment can short out and cause an
    arc.” 
    Id. 5. Methane
    and dust will not enter NPESE electrical
    compartments
    Based on their dubious contention that sparking cannot
    occur, the petitioners argue that ignition can result only if dust
    or methane gets into the NPESE. See Pet’rs’ Br. at 63 (“dust
    or methane would necessarily have to enter the instrument”
    for ignition to occur). And the petitioners contend that the
    devices were adequately sealed and that the ALJ-imposed
    condition requiring updating of equipment sufficiently
    guarded against degradation of seals. The Assistant Secretary
    concluded that the record rebutted this claim.
    The premise that the devices were well-sealed was based
    on Ryder’s faulty water immersion and dust swab tests. As
    the Assistant Secretary explained, the test results were
    performed on equipment different from that the petitioners
    sought to use. Ryder claimed that the equipment he inspected
    was substantially similar to the petitioners’ but he “did not
    29
    take apart” the latter; and Huntley testified that, absent such
    an examination, it would be difficult to conclude that it was
    similar. Rosebud Order I at 29. Moreover, even assuming
    Ryder tested sufficiently similar devices, Huntley testified
    that it was “suspect” to use water as a surrogate for gas and, in
    any event, moisture was found in all of the equipment Ryder
    tested. Rosebud Order I at 30. Although Ryder testified that
    the water entered only because the seals were degraded, the
    Assistant Secretary observed that there was no record
    evidence documenting how long it took a seal to degrade.
    And, again, the petitioners had the burden of proof. 30 C.F.R.
    § 44.30(b).
    The petitioners argue that, even if dust or methane can
    enter the electrical compartments, the openings “are
    sufficiently small in most cases to prevent the escape of flame
    outside the compartment.” Pet’rs’ Br. at 58. We once again
    note the petitioners’ equivocal language and also observe that
    the Assistant Secretary referenced testimony rebutting this
    contention.       See Rosebud Order I at 31 (“I credit
    Huntley’s . . . testimony that internal pressures from an
    ignition could create larger openings.”).
    6. Other petitions
    The petitioners next contend that the Assistant Secretary
    improperly analogized to other petitions in imposing the
    condition that coal production cease when surveying occurs in
    high-risk areas. We need make only two brief observations.
    First, we question the relevance of this claim. The petitioners
    contend, for example, that MSHA “permits photography [in
    high-risk areas] with less extensive requirements than the
    [NPESE] petitions and permits cutting and welding under less
    extensive conditions which do not involve cessation of
    production.” Pet’rs’ Br. at 60 n.23. But we have no basis on
    30
    this record to conclude either that that equipment poses the
    same (or greater) risk as the NPESE or that the conditions
    imposed on the use of that equipment, even if not identical,
    are not nonetheless more stringent. Even if we could reach
    those conclusions, they do not establish, on their own, that the
    condition MSHA placed on NPESE is arbitrary. Second, the
    petitioners apparently encouraged the Assistant Secretary to
    rely on other petitions such as Twenty Mile. See Canyon Fuel
    Order at 40 (“Canyon Fuel expert witness Hartsog
    acknowledged . . . reli[ance] on other granted-petitions [sic]
    for modification of permissibility standards that allow the use
    of diagnostic and testing equipment in high risk areas as well
    as the modification in In re Twentymile Coal Co.”); Rosebud
    Order I at 39 (“Rosebud mining engineer Cobaugh
    acknowledged that the Twentymile consent agreement was a
    template for Rosebud’s petitions for modification in this
    case.”). And the Twenty Mile petition did involve NPESE.
    The petitioners now contend that Twenty Mile was “never
    subjected to the test of litigation and a decision by an
    impartial ALJ.” Pet’rs’ Br. at 60. Although accurate, their
    backtracking does little to establish that the conditions are
    arbitrary or capricious. The Assistant Secretary’s conditions
    are supported by the record before him and his reference to
    Twenty Mile was little more than an aside. See Rosebud
    Order I at 39 (“I also note that the same requirement is
    contained in the Consent Agreement in [Twenty Mile].”).
    7. Reliance on device warning
    The petitioners also argue that the Assistant Secretary
    improperly relied on the manufacturer’s warning inasmuch as
    neither MSHA nor the manufacturer could explain its basis.
    The petitioners again overlook that they bear the burden of
    proof in the modification petition process. See 30 C.F.R.
    § 44.30(b). And, in any event, it was not arbitrary for the
    31
    Assistant Secretary to rely on the warning applicable to the
    very equipment the petitioners sought to use.              The
    manufacturer, after all, “is in the best position to know about
    the ignition risks of the equipment it manufactures.” Rosebud
    Order I at 34; see also Canyon Fuel Order at 37 (“[T]he
    manufacturers of the equipment are in the best position to
    evaluate its ignition potential.”).
    B. FLOAT COAL DUST CONDITION
    The petitioners separately argue that the condition
    prohibiting surveying in high-risk areas when float coal dust
    is in suspension is arbitrary. It is uncontested that this
    condition enhances mine safety. What is at issue is whether
    the Assistant Secretary reasonably concluded that it is
    necessary. We note, first, that the petitioners’ arguments
    repeat earlier contentions. See Pet’rs’ Br. at 63 (“[T]here is
    nothing about use of a surveying instrument that liberates dust
    or methane.”); 
    id. (“it creates
    no sparks”); 
    id. at 65
    (for
    explosion to occur “dust must still find its way into the insides
    of the electronic surveying instrument which is highly
    unlikely”). Only two contentions require analysis: the
    condition is unclear and impossible to implement and the
    condition is self-regulating because surveying becomes
    impossible at a dust concentration well below an explosive
    point.
    The petitioners rely on the Administrator’s statements in
    his denial of their original petitions that “it is not possible for
    the petitioner to implement this action item [because] [f]loat
    coal dust cannot be entirely eliminated during the cutting
    process of mining. . . . Unless all mining were to cease, float
    coal dust would be generated.” Administrator’s Proposed
    Decision and Order at 6, Parkwood Res. Inc., Docket No. M-
    2008-054-C (Dep’t of Labor Jan. 29, 2010). But, given that
    32
    the Assistant Secretary has required coal production to cease
    while surveying is conducted in the high-risk areas, the
    petitioners’ point is weakened. And we have found no other
    record support for this argument.27 Regarding whether the
    condition is clear enough to be implemented, the Assistant
    Secretary resolved its vagueness by noting that a “visual
    determination” suffices to determine if dust is in suspension.
    Rosebud Order II at 11 n.7.
    The petitioners also contend that this condition is
    unnecessary because it is “self-regulating.” Pet’rs’ Br. at 63.
    They claim that “far less than a sufficient amount of dust to be
    explosive would preclud[e] surveying” by reducing visibility
    below levels necessary for surveying. 
    Id. But the
    Assistant
    Secretary reasonably rejected this argument. As he explained,
    “coal dust can be rapidly placed in suspension . . . [and] even
    a vigilant surveyor may not have the time to de-energize his
    instrument before it encounters an explosive concentration of
    coal dust.” Rosebud Order I at 33.
    C. VIABLE MECHANICAL SURVEYING EQUIPMENT
    The final condition under challenge is that the petitioners
    must switch to viable mechanical surveying equipment when
    it becomes commercially available. We first note that it is
    MSHA’s position that the use of NPESE, under the conditions
    of use imposed by the Assistant Secretary’s two orders, is no
    more dangerous than the use of mechanical surveying
    27
    The petitioners argue in the alternative that the prohibition
    on surveying in high-risk areas while production is ongoing renders
    this condition redundant. But the record reflects that coal dust can
    also be placed in suspension from “methane explosions, bumps,
    fans, roof falls, brushing up against insufficiently rock-dusted float
    coal dust, and the exhaust from large pieces of equipment.”
    Canyon Fuel Order at 35.
    33
    equipment. See Rosebud Order I at 44 (“I have found that the
    [NPESE], including the modifications and additional
    conditions in the [ALJ’s] decision and order, as modified and
    supplemented by the conditions in this decision and order,
    will at all times promote the same safety goals as the original
    standards [allowing mechanical equipment] with no less than
    the same degree of success.”). If that were not so, the
    modification grant here would be improper. See S. Ohio Coal
    
    Co., 928 F.2d at 1202
    (modification must “promote the same
    safety goals as the original standard with no less than the
    same degree of success.”). And the petitioners contend that
    NPESE (with the conditions of use) is not only as safe as, but
    safer than, mechanical surveying equipment.
    The petitioners make two arguments to suggest that
    mechanical surveying equipment, even when “viable,” is less
    safe than NPESE. First, they argue that surveying with
    NPESE is faster and thus surveyors are exposed to the
    dangers of mines for less time than they would be with
    mechanical equipment. But the Assistant Secretary observed
    that this assertion was unsupported by data, see Rosebud
    Order I at 45 n.25 (“The evidence concerning the increased
    likelihood of injury from the asserted increase in exposure
    time is general and not quantified and does not establish that
    the increase in exposure time would result in anything more
    than an insubstantial decrease in safety.”), and it did not
    consider “the additional time needed to comply with the
    conditions for use” of NPESE, 
    id. The petitioners
    also assert that even “viable” mechanical
    surveying equipment will have inferior accuracy. The record
    supports this assertion, compare Rosebud Order I at 44 n.23
    (suggesting “1 foot-in-10,000 feet accuracy levels” viable)
    with Petition for Modification Stipulations ¶ 21, In re
    Rosebud Mining Co., Docket Nos. 2010-MSA-1, 2011-MSA-
    34
    2, -11, -12 (reflecting NPESE achieved 1 foot in 81,507 feet
    accuracy), but, even assuming the accuracy gap is more than
    de minimis, we have no way to measure its impact on mine
    safety. See Rosebud Order I at 44 n.23 (expert testimony
    reflecting that “there are no safety issues when surveying
    equipment achieves 1 foot-in-10,000 feet accuracy levels.”).
    Thus, whatever accuracy gain is made by using NPESE, it is
    not plain that it improves mine safety more than would viable
    mechanical equipment.
    Finally, the Assistant Secretary identified a mine safety
    risk from the use of NPESE that would not exist with viable
    mechanical surveying equipment—the use of “MSHA’s
    limited resources . . . spent ensuring compliance with the
    terms and conditions” of use. Rosebud Order I at 45.
    Because MSHA must assess what effect modifications will
    have on “overall mine safety,” S. Ohio Coal 
    Co., 928 F.2d at 1202
    , the preservation of finite resources for use in ensuring
    compliance with other standards is a reasonable basis upon
    which to include this condition.
    For the foregoing reasons, we deny the petitions for
    review.
    So ordered.