<DOC>
[DOCID: f:dust.wais]

 
KEYSTONE COAL MINING CORPORATION
November 29, 1995
PENN 91-451-R


           FEDERAL MINE SAFETY AND HEALTH REVIEW COMMISSION

                    1730 K STREET N.W., 6TH FLOOR

                       WASHINGTON,  D.C.  20006


                          November 29, 1995


IN RE: CONTESTS OF RESPIRABLE        :  Master Docket No. 91-1
  DUST SAMPLE ALTERATION             :
  CITATIONS                          :
                                     :
KEYSTONE COAL MINING CORPORATION     :  Docket Nos. PENN 91-451-R
                                     :      through PENN 91-503-R
        v.                           :
                                     :  Docket Nos. PENN 91-1176-R 
SECRETARY OF LABOR,                  :      through PENN 91-1197-R
  MINE SAFETY AND HEALTH             :
  ADMINISTRATION (MSHA)              :
                                     :
SECRETARY OF LABOR,                  :  Docket Nos. PENN 91-1264
  MINE SAFETY AND HEALTH             :      through PENN 91-1266
  ADMINISTRATION (MSHA)              :
                                     :  and
        v.                           :
                                     :  Docket No. PENN 92-182
KEYSTONE COAL MINING CORPORATION     :  Docket No. PENN 92-183
                                     :
JIM WALTER RESOURCES,                :
  INC., et al.,                      :
           Intervenors               :
                                     :
UNITED MINE WORKERS                  :
  OF AMERICA (UMWA),                 :
           Representative of Miners  :


BEFORE: Doyle, Holen and Marks, Commissioners[1] 

                                  DECISION

BY:  Doyle and Holen, Commissioners

     This proceeding arises under the Federal Mine Safety and
Health Act of 1977, 30 U.S.C.  801 et seq. (1988) ("Mine Act"
or "Act").  Section 202(a) of the Mine Act requires coal mine
operators to take accurate samples of the respirable dust
in the mine atmosphere to which each miner is
exposed.[2]  30 U.S.C.  842(a).  This proceeding
involves 3,460 citations[3] issued by the Department
of Labor's Mine Safety and Health Administration
("MSHA") to coal mine operators across the country,
each of which alleges a violation of 30 C.F.R. 
70.209(b), 71.209(b), or 90.209(b) (collectively,
"section 209(b)"), for tampering with and altering
the weight of respirable dust samples ("Dust Cases").
[4]

     The Dust Cases were assigned to Administrative Law
Judge James A. Broderick, who consolidated them for a 
trial of the issue common to all citations, i.e., whether
the appearance of an abnormal white center ("AWC") on
a respirable dust sample filter establishes that the
mine operator had intentionally altered it.  The
judge found that the Secretary had failed to prove by
a preponderance of the evidence that an AWC on a
filter establishes that the operator had altered the
weight or that deliberate conduct was the only
reasonable cause of an AWC.  In re: Contests of
Respirable Dust Sample Alteration Citations, 15
FMSHRC 1456, 1521-22 (July 1993) (ALJ) ("Common
Issues Decision").  The judge then ordered a trial on
the citations issued to a single mine, the Urling No.
1 Mine ("Urling"), operated by Keystone Coal Mining
Corporation ("Keystone").  In that case, the judge
held that the Secretary of Labor had failed to carry
his burden of proving by a preponderance of the
evidence that the weight of the 75 cited filters had
been intentionally altered by the operator.  Keystone
Coal Mining Corp., 16 FMSHRC 857, 903 (April 1994)
(ALJ) ("Keystone Decision").[5]

     The Secretary filed with the Commission a petition
for discretionary review ("PDR") seeking review of the
decisions and asserting 14 points of error by the
judge.  Among the Secretary's assignments of error
was his challenge to the judge's articulation and
application of the standard of proof in both the
Common Issues Decision and in the Keystone Decision
and his claim that, if the proper standard had been
used, the Secretary would have prevailed in both
cases.

     The Commission granted the Secretary's PDR and granted
intervenor status to a number of mine operators (the
"Intervenors").  The parties and Intervenors submitted 
briefs and the Commission heard oral argument.[6]  After
careful review of the record, and for the reasons that 
follow, we affirm the judge's decisions.

                                I.

                 Background and Judge's Decisions

     A.  Factual and Procedural History in Common Issues

     Coal mine operators are required to submit accurate dust
samples on filter cassettes to MSHA for measurement of the
quantity of respirable coal dust in the mine atmosphere.  15
FMSHRC at 1457; 30 C.F.R.  70.201-220, 71.201-220, and
90.201-220.  These samples are taken in a sampling unit,
consisting of a pump, hose, cyclone assembly, and plastic
cassette, manufactured by the Mine Safety Appliance
Corporation ("MSA").  15 FMSHRC at 1457.  The pump draws air
into the cyclone assembly, which separates out larger dust
particles.  Air containing respirable dust particles is
directed into the plastic cassette, which contains a capsule
consisting of an aluminum foil cone, a filter, and a backing
pad.  Id.  Airborne particles are deposited on the filter
face.  Id.  The cassette is removed from the sampling unit
and sent to MSHA's weighing laboratory along with a card
providing information on the sample ("dust data card").  Id.
At the weighing laboratory, MSHA technicians open the sealed
cassette, remove and desiccate the capsule, and then weigh
it to determine whether the respirable dust concentration is
in compliance with the levels required by 30 C.F.R. 
70.100, 71.100, and 90.100.  See id.

     In 1983, Mr. Robert Thaxton, then an industrial hygienist
at MSHA's District Office in Mt. Hope, West Virginia, subjected
25 to 50 dust filter cassettes to reverse air flow tests by
blowing or otherwise directing air into the outlet of the
cassette to determine the potential for removal of dust by
tampering.  Id. at 1457-58; Tr. 108-10.  The resulting
filters exhibited white circular areas in the center.  15
FMSHRC at 1458.  In February 1989, a laboratory technician
at Mt. Hope noticed a protruding filter on a cassette
submitted by Peabody Coal Company ("Peabody").  Id.; Tr.
327-28.[7]  When the foil was removed, a sharply defined
circular white center that was aligned with the aluminum
foil inlet opening of the filter capsule was visible on the
filter.  Tr. 329, 336-37.  Mr. Thaxton, the supervisory
industrial hygienist at Mt. Hope, regarded this filter
appearance as abnormal and believed that the Peabody filter
resembled some of his 1983 experimental filters.  15 FMSHRC
at 1457-58; Tr. 108-10, 330-31.  Filters with this abnormal
white center appearance were termed AWCs.  15 FMSHRC at
1458.

     The Pittsburgh Health Technology Center ("PHTC"), MSHA's
main laboratory, began to examine all filters from that same
Peabody mine and, later, from all Peabody mines.  Id.; Tr.
337-38.  In August 1989, MSHA's investigation expanded to
include all filters submitted by coal mine operators
nationwide.  15 FMSHRC at 1458; Tr. 342.  Filters were
examined for abnormalities and those with suspected AWCs
were forwarded to Thaxton at the Mt. Hope facility. 15
FMSHRC at 1458; Tr. 128-29, 339.

     On March 19, 1990, MSHA initiated an AWC "void code"[8] and
began rejecting respirable dust samples that exhibited AWCs.
15 FMSHRC at 1460; R. Ex. 1400, at 12.  On April 4 and June
7, 1991, MSHA issued approximately 4,700 citations to
approximately 847 mines and proposed civil penalty
assessments totaling about $6.5 million.[9]  See 15 FMSHRC
at 1460; Tr. 3 (Prehr'g Conf. June 19, 1991).  The citations
were issued by MSHA inspectors, but Thaxton alone determined
whether a particular filter was to be cited.   15 FMSHRC at
1460.    Each citation charged the mine operator with
violating the provisions of section 209(b) and alleged that
"the weight of the respirable dust cassette . . . has been
altered while the cassette was being submitted to fulfill
the sampling requirements . . . ."  Id.  Each citation
characterized the level of the operator's negligence as
"reckless disregard," and the Narrative Findings for a
Special Assessment ("Special Assessment Findings") attached
to the citation stated that "[t]he violations resulted from
an intentional act of altering the dust samples."  See,
e.g., Citation dated April 4, 1991, and Special Assessment
Findings dated June 12, 1991, issued to Keystone; see also
14 FMSHRC at 1512.

     The cases in this proceeding arose from citations contested
by operators and petitions for assessment of penalty filed
by MSHA.  Extensive discovery was conducted and the parties
twice sought interlocutory Commission review of pretrial
matters.  In a pretrial order issued on
August 13, 1992 ("August 1992 Order"), Judge Broderick,
citing the time and expense of trying each case separately
and relying on the Manual for Complex Litigation,[10]
consolidated the cases for trial of the issue common to all
cases and appointed a Lead Defense Counsel Committee to
participate in the trial on behalf of all operators.  14
FMSHRC 1510, 1511, 1516 (August 1992) (ALJ).  In the same
order, the judge rejected the Secretary's argument that, if
he proved that the weight of a dust sample had been altered,
he need not prove that the alteration was deliberate.  Id.
at 1515.  The judge concluded that the plain words of
section 209(b) do not give rise to a violation based on
accidental or unintentional altering of the cassette's
weight.  Id. at 1515-16.  Rather, the judge found that a
violation necessarily included an intentional action on the
part of the mine operator.  Id. at 1515.  The judge set
forth the issue to be determined as:  "[w]hether an abnormal
white center (AWC) on a cited filter cassette establishes
that the operator intentionally altered the weight of the
filter?"  Id. at 1517.  The judge stated, "the Secretary has
the burden of establishing [his] case by the preponderance
of the evidence."  Id.

     B.  Common Issues Trial

     The Common Issues trial commenced on December 1, 1992, and
concluded on February 22, 1993.  Mr. Thaxton testified for eight
days on his AWC classification and the potential causes of AWC
formation.  Thaxton had developed ten "tamper codes" to
describe the various AWC appearances.  15 FMSHRC at 1460-62;
Tr. 168-71; R. Ex. 1064.  Approximately 97% of the cited
filters were originally classified under tamper codes 1, 2
or 3.[11]  15 FMSHRC at 1462.  Filters originally suspected
of having AWCs, but which Thaxton decided should not be
cited, were termed "no-calls."  Id. at 1460; Tr. 129-31.  In
March 1992, Thaxton reexamined the cited filters and
reclassified 464 filters; 95% of the cited filters remained
as tamper code 1, 2 or 3.  15 FMSHRC at 1462.  In his
opinion, AWCs resulted from acts of intentional alteration
by mine operators, primarily by the application of reverse
air through the filters.  Tr. 183, 191, 209, 598-99.  Lewis
Raymond, Chief of the Weighing Branch, Dust Division of the
PHTC, testified on the handling and screening practices of
filters exhibiting AWCs.  The Secretary offered the
scientific testimony of Dr. Virgil Marple and his colleague,
Dr. Kenneth Rubow, who had conducted experiments involving
AWCs, including application of reverse air flow to filter
cassettes and dropping cassettes and pumps.  15 FMSHRC at
1474-83.  Dr. Marple concluded that the most probable cause
of AWC dust dislodgment was the deliberate application of
reverse air flow.  Id. at 1469-70, 1481; Gov't Ex. 280, at
4-7, 57, 103-05; Gov't Ex. 282, at App. A; Tr. 2590, 2597-
98.  The Secretary's statistical expert, Dr. John J. Miller,
testified that AWCs were not random across all coal mines.
15 FMSHRC at 1485, 1488; Tr. 3721-23.  According to Dr.
Miller, there was a marked decline in AWCs after MSHA's
initiation of the AWC void code on or about March 19, 1990.
15 FMSHRC at 1486, 1488; Tr. 3723-24.  Miller also testified
that the decrease in the rate of cited AWCs was not
explained by the dates on which filters were manufactured.
15 FMSHRC at 1486-88.

     The operators offered the scientific testimony of Dr.
Richard J. Lee, who also classified the cited filters into
groups based on appearance.  Id. at 1470-71.  Dr. Lee
performed a series of dust dislodgment tests and concluded
that AWCs can result from accidental and incidental events.
Id. at 1488-96; Tr. 6531-34.  He testified that
manufacturing variations in the sampling units, such as a
shorter filter-to-foil distance[12] in the cassette and the
pliability of the hose, increase susceptibility to AWC
formation.  15 FMSHRC at 1494-95; Tr. 6534-35.  The
operators' other scientific experts, Dr. R. Larry Grayson,
Dr. Andrew R. McFarland, and Dr. Morton Corn, similarly
testified that AWCs can result from accidental and
incidental events, such as dropping or other impacts to
sampling units and impacts to hoses of sampling units. 15
FMSHRC at 1497-99, 1505-06.  Dr. McFarland conducted a
courtroom demonstration in which he twice dropped a 31-pound
tool box on the hose of a sampling assembly, each time
producing an AWC.  Id. at 1503.  The operators' statistical
expert, Dr. H. Daniel Roth, testified that the AWC citation
rate declined continuously after September 1989 and that the
void code date of March 19, 1990, was not statistically
significant.  Tr. 3983, 3987-88, 3994, 4001; R. Ex. 1041, at
4.  Roth criticized Miller's analysis of filter
manufacturing dates.  15 FMSHRC at 1508.

     The judge observed the filters presented at the hearing.
Id. at 1467.  The cited and experimental filters are not in
the record but, during discovery, the operators' expert
witnesses were permitted to inspect the cited filters and
each expert had the opportunity to review the others'
experimental filters.  E.g., Tr. 5949, 7521; Gov't Ex. 267,
at 4-6.   Photographs of the cited filters and of many of
the experimental filters are in the record.  See, e.g.,
Gov't Exs. photograph albums entitled Cited Filters, vols.
1-7, set 2.   Evidence concerning the practices or
circumstances of any particular mine was excluded from the
Common Issues trial. 15 FMSHRC at 1464; see also id. at
1522; 16 FMSHRC at 896.

     C.  Common Issues Decision

     The parties filed post-trial and reply briefs in April and
May 1993, and the judge issued his decision on July 20,
1993.  15 FMSHRC 1456.  His findings and conclusions are as
follows:

          1.  Burden of Proof

     The judge held that the Secretary bore the burden of 
proving "by a preponderance of evidence that (1) the term `AWC'
has a coherent meaning and was consistently applied;
(2) the cited AWCs can only have resulted from
intentional acts; and (3) the AWCs resulted in weight
losses in the cited filters."  15 FMSHRC at 1463-64.

          2.  Mr. Thaxton's AWC Classifications

     The judge found that the term "AWC" has a coherent meaning
and refers to an "abnormal filter appearance in a dust
sample consisting of dust dislodgment from the central
portion of the filter."  15 FMSHRC at 1513.  He found
that the classification of AWCs by Thaxton under his
tamper codes, although not perfectly consistent, was
sufficiently consistent to require a determination of
whether the existence of an AWC establishes a
violation.  Id. at 1469, 1513.

          3.  Possible Causes of AWCs

     The judge determined that "[t]he dust dislodgment patterns
on the cited filters classified under tamper codes 1,
2, 3, and 7[13] can have resulted from intentional
acts: blowing by mouth through the cassette outlet,
otherwise directing a jet or pulse of air into the
cassette outlet, or introducing a vacuum source into
the cassette inlet."  15 FMSHRC at 1513 (emphasis
added).  He also found that the dust dislodgment
patterns on filters classified under these tamper codes
"can have resulted from:

          1.   impacts to the cassette from dropping or
               striking it;

          2.   impacts to the hose from stepping on it,
               dropping an object on it, striking it
               against a wall while the hose was
               wrapped around the sampling assembly,
               closing a door or drawer on it, or
               sitting on it;

          3.   snapping together the two halves of the
               filter cassette."

Id. (emphasis added).

     The judge explained that, although the experts differed as
to the likelihood that AWC dislodgment patterns would result from
incidental events or accidents, "the experiments all show that at
least sometimes they do occur."  Id. at 1513-14.  He observed
that dust dislodgment patterns on many of the filters subjected
to impact or snapping tests were indistinguishable from cited
AWCs.  Id. at 1514.  The judge concluded that the AWCs did not
result from handling by the United States Postal Service or from
the PHTC's handling or desiccation processes.  Id.

     The judge determined that the manufacturing characteristics
of filter-to-foil distance and filter floppiness varied from
filter to filter and mine to mine.  Id. at 1515, 1521.  The judge
found that a filter cassette with a smaller filter-to-foil
distance was more susceptible to an AWC dislodgment pattern than
one with a larger distance; that a floppy filter was more
susceptible than a taut one; and that AWC susceptibility also
depended on the pliability of the sampling hose.  Id. at 1515-17.
He determined that the cited filters came from a population of
cassettes with shorter filter-to-foil distances than those
manufactured subsequently.  Id. at 1515-16.  The judge also
identified mine and dust variables that would affect dislodgment,
such as type of coal, humidity in the mine environment, weight of
dust on the filter, size and shape of dust particles, and
quantity of rock dust or diesel dust on the filter.  Id. at 1516-
17, 1521.

          4.  Statistical Evidence

     The judge found Miller's conclusion that the AWC rate
was not random across the mining industry was not
"persuasive evidence of intentional tampering" because
of the existence of many other potential causes.  15
FMSHRC at 1519, 1522.  The judge also rejected the
Secretary's claim that the sharp decline in cited AWCs
beginning about March 19, 1990, "can only be construed
as showing intentional misconduct" that ceased when the
operators became aware of the void code.   Id. at 1519.
He reasoned that AWC citations continued, at a reduced
rate, long after the void code was instituted and after
significant publicity about the criminal investigation.
Id. at 1519-20.[14]  The judge stated that the
statistical evidence showed cassettes manufactured
before January 1, 1990, had a much higher citation rate
than those manufactured later, suggesting manufacturing
variables as a cause of AWC formation.  Id. at 1520.
The judge discounted Miller's opinion that there were
no statistically significant relationships between dust
dislodgment and filter-to-foil distance or floppiness
of filters, concluding that the weight of the
scientific evidence showed that such factors did, in
fact, affect susceptibility to AWC formation.  Id.


**FOOTNOTES**

     [1]:   Chairman  Jordan  has recused herself in this matter.
Pursuant to section 113(c) of the  Federal Mine Safety and Health
Act of 1977, 30 U.S.C.  823(c), we  have  designated ourselves a
panel  of  three  Commissioners  to exercise the  powers  of  the
Commission in this matter.

     [2]:   The  Mine Act and mandatory  standards  require  each
operator to maintain  an average concentration of respirable dust
in the mine atmosphere  at  or below 2.0 milligrams of respirable
dust per cubic meter of air.   30  U.S.C.   842(b); 30 C.F.R. 
70.100,  71.100.   Under  certain  circumstances,   it   must  be
maintained  at  or below 1.0 milligrams.  See, e.g., 30 C.F.R.  
90.100.

     [3]:  An additional  110  contested  citations  are  on stay
pending  resolution  of  the  Common  Issues case.  Approximately
5,000 citations were issued in total.   Not  all,  however,  were
contested and some were settled.

     [4]:   Section  209(b)  of  30  C.F.R.  Parts 70, 71, and 90
provides:

               The  operator  shall not open or  tamper
          with the seal of any filter cassette or alter
          the weight of any filter  cassette  before or
          after  it is used to fulfill the requirements
          of this part.

     [5]:  The United  Mine Workers of America ("UMWA") participated
in  both  proceedings as representative of miners but did not submit
briefs to the judge.

     [6]:   The  UMWA  filed  an appearance but did not submit briefs 
to the  Commission  or participate in oral argument.

     [7]:   "Tr."  refers to transcript of the Common Issues trial. 
"K.  Tr." refers to the  transcript  of  the trial in  Keystone. "R.
Ex." refers to Respondent Exhibits and "Gov't Ex." to Government 
Exhibits introduced at the Common  Issues trial.  "K. Ex." refers
to Keystone  Exhibits  and  "K.  Gov't Ex." to Government Exhibits 
introduced  at the Keystone  trial.   "Oral  Arg. Tr." refers to
the transcript of oral argument  held  before the Commission on 
March 29, 1995.

     [8]:    A   void   code  is  a  three-letter  code indicating
that  MSHA  will  not  accept  the respirable dust sample for use 
in determining compliance    with    the   respirable   dust
standards.  Tr. 848.

     [9]:  MSHA continued to cite operators  for AWCs. By the time
of the Common Issues trial, approximately 370 additional citations
had been  issued.  The last  contested  citation, now on stay, was
issued on April 6, 1993.

     [10]:   "Actions   pending   in   the  same  court involving
common questions of law or fact may be consolidated under Fed. R. 
Civ.  P. 42(a) for  trial  or  pretrial  if  it  will  avoid
unnecessary   cost  or  delay."   Manual  for Complex   Litigation
 21.631 (1995) (supplement to James W. Moore et al.; Moore's
Federal Practice (2d ed.)).

     [11]:   Filters  classified  under  tamper code 1, termed by
Thaxton as "light cleaned,"  were described as  containing  a white
ring in the center   of   the  filter,  approximately  6 millimeters
("mm") in  diameter, directly aligned   with  the  cassette  inlet.
The appearance  of the center portion of the ring was not markedly 
lighter.   In  Thaxton's opinion,  tamper code 1  AWCs  resulted 
from reverse air  flow.   15  FMSHRC  at 1461; Tr. 179-181, 183; 
R. Ex. 1064. Filters classified  under  tamper  code 2, "cleaned,"
were  described  as  exhibiting   a  markedly lighter dust deposit
within  the  circular area.   Thaxton  believed that tamper code 2
AWCs also resulted from reverse air flow.  15 FMSHRC at 1461; Tr. 
184-85, 191, 193-98, 767-68,  776; R. Ex. 1064. Filters  classified
under tamper  code  3,  "cleaned  and coned," were described as 
similar to those classified under tamper code 2, but exhibiting a
slight rise or cone in the center.  Thaxton believed that tamper
code  3  AWCs  resulted  from "forceful" reverse  air  flow.  
15 FMSHRC at 1461; Tr. 198-201, 208-09, 1258; R. Ex. 1064.

     [12]: Filter-to-foil distance is the distance in the cassette
between the filter surface and the opening of the  aluminum  foil
cone.  Tr. 2279; R. Ex. 1001, at ii, B-8.7.

     [13]:   The  judge  noted  that  Thaxton  came  to believe
that filters classified  under tamper code  7, known as "clean 
tool" and  which  he originally  believed  were created by a tool,
were created by reverse  air flow.  15 FMSHRC at 1461-62, 1513;
Tr. 259.

     [14]:   At  the  time  of MSHA's investigation  of operator
samples,   a   large   number   of respirable  dust  samples 
taken   by   MSHA inspectors  were  also found to exhibit AWCs.
15 FMSHRC at 1462.   Thaxton classified these samples under his 
tamper  codes and most, but not  all, were classified under one
of  the reverse  air  flow  tamper codes.  Id. The judge noted
evidence  indicating  that  the number  of  inspector samples
exhibiting AWCs declined at about  the  same  rate during the
relevant periods as operator samples.  Id. at 1519.  The Office
of Inspector General of the Labor  Department  investigated  
whether  the inspectors  who submitted these samples  were
guilty of misconduct.   The investigation was closed   with 
no  finding  of   misconduct, apparently based on the finding
that AWCs can result from the two parts of a cassette being
snapped together.  Id. at 1462


5.   Judge's Conclusions

     Based on these findings, the judge concluded that (1) the
Secretary "failed to carry his burden of proving by a
preponderance of the evidence that an AWC on a cited
filter establishes that the mine operator intentionally
altered the weight of the filter," and (2) the
Secretary "failed to carry his burden of proving by a
preponderance of the evidence that deliberate conduct
on the part of the cited mine operators is the only
reasonable explanation for the cited AWCs."  15 FMSHRC
at 1521.  The judge emphasized that filter variables
(filter-to-foil distance and floppiness), pliability of
the hose, and dust variables (type of coal, humidity,
weight of dust on the filter, size and shape of dust
particles, and quantity of rock or diesel dust) affect
susceptibility to AWC formation and that Miller's
statistical analysis failed to adequately account for
these variables.  Id. at 1521-22.  The judge concluded
that Miller's analysis also failed to establish that
the cited AWCs were not the result of accidental
occurrences or manufacturing variables.  Id.  Noting
that the expert testimony as to causes of AWCs was
conflicting, the judge, in summary, concluded that the
record showed too many other potential causes "to
accept the Secretary's circumstantial evidence as
sufficient to carry his burden of proof that the mine
operators intentionally altered the weight [of] the
cited filters."  Id.

     The judge ordered a mine specific hearing to address the
75 AWC citations issued to Keystone's Urling mine.  Id. at
1522.  He set forth the main issue as "whether the
weight of the filters cited as AWCs from . . . Urling .
. . was intentionally altered by the mine operator" and
stated that the burden of proof remained with the
Secretary.  Id.  The judge stayed all other Dust Cases.
Id. at 1523.

     D.  Factual and Procedural History in Keystone

     The Urling mine, in Indiana County, Pennsylvania, is
operated by Keystone, a wholly owned subsidiary of Rochester
and Pittsburgh Coal Company ("R&P").  The dust sampling
program for all 13 R&P mines, including Urling, was
conducted by R&P's Environmental Safety Department ("ESD"),
also in Indiana, Pennsylvania.  16 FMSHRC at 858-59;
Stipulations by Secretary and Keystone, No. 14, filed
November 30, 1993 ("Stip.").  From 1970 until his retirement
in 1991, Donald Eget, who was trained as an engineer, was
the supervisor of ESD.  16 FMSHRC at 861; K. Tr. 2231-33.
During 1989 and 1990, Shawn Houck worked with Eget in the
ESD laboratory as a maintenance and calibration technician.
16 FMSHRC at 861-62.  Douglas Snyder was the dust technician
responsible for Urling sampling; three other dust
technicians handled sampling for R&P's other mines.  Id. at
862.

     Pursuant to normal operating procedures at ESD during 1989
to 1991, the dust technicians picked up pumps and sampling
assemblies in the morning and delivered them to R&P's mines
for use on that day's three shifts.   Id.  Each morning,
Eget drove to all 13 R&P mines to retrieve pumps and samples
from the previous afternoon and midnight shifts.  Id.  The
dust technicians returned to the ESD after 4:00 p.m.,
delivering pumps used during the day shift.  Id. at 863.

     While Eget collected pumps, Houck processed those from the
previous day shift.  Id. at 862.  Houck removed the sampling
head[15] and the hose from each pump, filled out the dust
data cards, cleaned the sampling units, calibrated the
pumps, reassembled the units, and inserted a new filter
cassette in each one for use the next day.  Id. at 862-63;
K. Tr. 2103-04.  When Eget returned to the laboratory, Houck
took the cassettes into Eget's office.  16 FMSHRC at 862.
Eget inspected the used cassettes, recorded their
identification numbers, checked the dust data cards against
the cassette numbers, and looked into the cassette inlets
and recorded the filter appearances in a logbook he kept for
each mine.  Id. at 862-63, 889.  The cassettes were then
packaged for mailing to MSHA and taken to the R&P mailroom.
Id. at 863; K. Tr. 2102-03, 2174.

     Dust technician Snyder delivered pumps to Urling and
distributed them to the miners or section foremen on the day
and afternoon shifts.  16 FMSHRC at 864.  He left pumps for
the midnight shift.  Id.

     On April 4, 1991, the Secretary issued 53 citations to
Urling, and on June 7, 1991, issued 22 additional citations,
alleging violations of section 70.209(b).  Id. at 858.
Three filters forwarded to Thaxton were determined to be no-
calls.  Id. at 868, 870.

     E.  Keystone Trial

     The trial in Keystone commenced on November 30, 1993, and
concluded on January 6, 1994.  16 FMSHRC at 859.  Robert
Thaxton testified with respect to the appearance of the
75 cited and three no-call filters.  Mr. Thaxton was of the
opinion that the dust dislodgment patterns of the cited
filters resulted from deliberate acts, in most cases from
air blown through the filter cassette in a reverse
direction.  Id. at 868-72; K. Tr. 864-66, 911-15; see K.
Gov't Ex. 505.  Dr. Marple, the Secretary's scientific
witness, also examined and classified the 78 filters.  16
FMSHRC at 872-74.  Marple concluded that 71 or 72 resulted
from reverse air flow, two or three resulted from a vacuum
source introduced into the cassette inlet, and one resulted
from water introduced into the filter (Marple was originally
unable to ascribe a cause to that filter's appearance).  Id.
at 873, 898-99.  Marple further concluded that none of the
dislodgment patterns on the Urling filters resulted from
impacts to the cassettes.  Id. at 873-74, 899.

     Dr. Miller, the Secretary's statistical expert, testified
that, before March 26, 1990, the date that MSHA alleges
Urling learned of the void code, Urling had a much higher
citation rate than other mines.[16]   Id. at 878-79.  He
testified that Urling had a citation rate of 42.77% (74
cited samples out of 173) in the period August 1989 through
March 26, 1990.  After March 26, the rate fell to 0.18% (one
cited out of 552).  In contrast, other mines had an average
citation rate of 5.96% for the earlier period.  Id. at 878.
Miller also testified that the date of cassette manufacture
failed to explain the differences in citation rates between
Urling and other mines because Urling's citation rate was
eight times higher than that of other mines using cassettes
manufactured on the same dates.  Id. at 879.

     Dr. Lee, Keystone's scientific expert, concluded that most
of the cited filters showed comparatively slight dust
dislodgments from the central area, slightly larger
diameters, no cones, and only a slight indication of
dimpling, all of which indicated lesser forces than would
have occurred with deliberate reverse air flow.  Id. at 876,
899.   Lee testified that the appearance and dimensions of
the dislodgment patterns on the Urling filters were
consistent with a mixed mechanical pulse/reverse air pulse
mode of occurrence ("mixed-mode" theory).  Id. at 876-
77.[17]  He also testified that humidity in the mine
atmosphere reduced the susceptibility to dislodgment of dust
on filters and that the introduction of water sprays and
scrubbers at Urling beginning in 1989 and 1990 contributed
to the decline in AWCs.  K. Tr. 3891-97, 4042-44, 4087-89;
see also 16 FMSHRC at 877; K. Ex. 2001, at 14.

     Dr. Roth, the operators' statistical expert, testified that
he examined the citation rates of Urling and all R&P mines
on a bimonthly basis and that the data showed a strong trend
of declining rates over the entire period from August 1989
to March 1992.  16 FMSHRC at 880.  Roth also testified that
manufacturing variables may have been a factor in AWC
formation because the rate of cited AWCs was greater for
cassettes manufactured on earlier dates compared to later
dates.  Id.  He concluded that R&P's high incidence rates
"may be attributable to cassettes manufactured on four
consecutive dates, May 26, May 31, June 1, and June 2,
1989."  Id.  The AWC citation rate of R&P mines, including
Urling, for cassettes manufactured on those dates was 49.6%
compared to 5.8% for other dates.  Id.

     ESD personnel testified as to their involvement in the
respirable dust sampling program at Urling.  Id. at 888-
93.[18]  Eget, Houck, and Snyder denied tampering with the
dust cassettes or observing anyone else tamper with the
cassettes.  Id. at 890-91.

     F.  Keystone Decision

     The parties filed post-hearing briefs in March 1994 and the
judge issued his decision on April 20, 1994.  His findings
and conclusions are as follows:

          1.  Burden of Proof

     The judge held that the Secretary bore the burden of
proving "by a preponderance of the evidence that the 75 cited
Urling filters resulted from intentional tampering."
16 FMSHRC at 895.  The judge noted that Keystone "d[id]
not have the burden of establishing that the
appearances on the samples resulted from some other
cause."  Id. at 896.  The judge reasoned that the
Secretary, as the party bearing the burden, must
convince the trier of fact "that the existence of a
fact is more probable than its nonexistence . . . ."
Id. at 895, quoting Concrete Pipe and Products of Cal.,
Inc. v. Construction Laborers Pension Trust for S.
Cal., 508 U.S. ___, 113 S. Ct. ___, 124 L. Ed. 2d 539,
563 (1993).   He explained that "[t]o preponderate, the
evidence must be sufficient to convince the trier of
fact that the proposition asserted is more likely true
than not true."  16 FMSHRC at 895-96 (citations
omitted).  The judge also noted that "[a]ll of the
evidence must be given appropriate weight, whether it
be direct or circumstantial" and that "[c]ircumstantial
evidence may prove an ultimate fact."  Id. at 896.

          2.  Possible Causes of Urling AWCs

     Preliminarily, the judge reviewed the evidence pertaining
to the handling of dust pumps and cassettes at the Urling
mine and ESD laboratory.  He found that dust
dislodgment patterns on the cited filters could have
resulted in whole or in part from the handling of the
sampling equipment by Urling miners or ESD personnel.
16 FMSHRC at 864, 868.  The judge found that AWCs
"could have resulted wholly or partly" from incidental
and accidental events occurring in the mine, such as
pumps falling to the mine floor and hoses being pinched
by mantrips, snagged on other objects, or wrapped
around pumps, and from other contacts to hoses.[19]
Id. at 868.  The judge also found that AWCs "could have
resulted wholly or partly" from incidental and
accidental events occurring in the ESD laboratory or
during transportation of the pumps, including multiple
pumps being carried by their hoses and boxes containing
pumps being dropped to the floor of a vehicle or onto a
table.  Id. at 861-64.

     The judge made findings regarding factors that could
have contributed to the decline of AWCs at Urling.  Id. at
882-87.  He found that changes in handling practices of
ESD personnel during the spring of 1990 could have been
a factor in the reduced incidence of AWCs.  Id. at 884.
He found that Eget, whose handling of the sampling
equipment was rougher than that of the others, did not
handle samples from April 9 to May 10, 1990, and that
Snyder and the other technicians exercised more care in
their handling of the equipment, avoiding impacts to
the hoses because of MSHA's investigation.  Id.  The
judge concluded that, because dust deposits were damper
and less susceptible to dislodgment when scrubbers were
in use, the installation of scrubber systems on the
continuous miners at Urling beginning in 1989 could
have been a factor in the decline of AWCs.  Id. at 882-
83.  With respect to sampling equipment, the judge
found that the Urling cassettes more probably than not
had shorter filter-to-foil distances and this could
have been a factor in the decline of AWCs.  Id. at 885-
86.[20]

     On the basis of his Common Issues Decision, the judge
determined that the dislodgment patterns on the Urling
filters could also have resulted from intentional
tampering. Id. at 898.  The judge concluded that, if
tampering occurred, it must have occurred at the ESD
laboratory.  Id.  In resolving whether the AWCs
resulted from intentional acts at ESD, the judge
analyzed the scientific and statistical evidence and
evaluated the testimony and credibility of ESD
employees.  Id.

          3.  Scientific Evidence

     Based on Mr. Thaxton's testimony, the judge concluded
that the appearances of the cited filters "did not result
from normal sampling."  16 FMSHRC at 897 (emphasis
added).  The judge was not persuaded, however, by
Thaxton's reports and testimony asserting that the
Urling AWCs had been caused by intentional tampering.
Id.  The judge discounted Thaxton's analysis as to
causation because Thaxton's conclusions were "to a
considerable extent subjective."  Id.  His tests were
not conducted according to a written protocol based on
systematic testing that related specific dislodgment
patterns to types of tampering.  Id.  Additionally, the
judge found that the distinction Thaxton made between
cited and no-call filters was "difficult to discern"
and "tenuous at best."  Id. at 870-71, 897.

     The judge concluded, on the basis of the testimony of
Dr. Marple and Dr. Lee, that 73 of the cited Urling filters
"resulted in whole or in part from reverse air flow
through the filter."  Id. at 898-900.  The judge
credited Lee's testimony that those filters showed
comparatively slight dislodgments from the central
area, had no cones at the time the citations were
issued, and had slightly larger areas of dust
dislodgment.  Id. at 899.  On that basis, he reasoned
that the forces responsible for the Urling AWCs were
"relatively slight" and concluded that the reverse air
forces involved in the creation of those filters were
"generally less" than the force associated with
deliberate blowing through the filter cassette.  Id. at
899-900.  The judge also concluded that the dust
dislodgment patterns of the Urling filters "may have
been influenced" by accidental and incidental events
involving impacts to the cassette and sampling
assembly, as set forth in Dr. Lee's mixed-mode theory.
Id. at 900; see id. at 876-77.

     As to the other two cited filters, the water stain filter
No. 324842 and filter No. 325300, the judge held that
the Secretary's evidence was inconsistent and
unconvincing and failed to establish deliberate
tampering.  Id. at 900.

          4.  Statistical Evidence

     The judge noted that the statistical experts, Dr. Miller
and Dr. Roth, reached different conclusions using the same
data.  16 FMSHRC at 900.  The judge agreed with Miller
that there was a sharp decline in Urling's citation
rate on or about March 26, 1990, the date used by
Miller in his analysis.  Id.  He concluded, however,
that March 26, 1990, was not a logical cutoff date for
examining changes in behavior at Urling because the
evidence showed that ESD personnel and Keystone
management had become aware much earlier, in February
1990, of MSHA's investigation of AWCs.  Id.  He also
found that there was an overall decline in Urling's
citation rate from September 1989 to April 1990.  Id.
The judge agreed with Miller that dates of manufacture
of the cassettes "do not seem overall to explain all
the differences" in the AWC rate.  Id. at 900.  On the
other hand, he agreed with Roth that manufacturing
anomalies may have affected AWC formation because, as
Roth showed, 60% of the cited Urling cassettes were
manufactured on four consecutive work days in May and
June 1989.  Id. at 900-01.

     The judge was unable to conclude on the basis of the
statistical evidence that the reduction in the rate of
cited filters at Urling was related to MSHA's
investigation.  Id. at 901.

          5.  Testimony of ESD Personnel

     Preliminarily, the judge recognized that a large number
of mine operators and their agents had pled guilty to
criminal charges of tampering.  16 FMSHRC at 901.  The
judge summarized the testimony of employees of the ESD
laboratory during 1989 and 1990, all of whom were
witnesses.  Id. at 888-893.  He determined that only
Eget and Houck had any substantial opportunity to
tamper with the samples.  Id. at 901.  The judge was
impressed by the backgrounds of Eget and Houck and by
their forthrightness on the witness stand.  Id. at 902.
He credited their statements that they had not tampered
with the dust samples submitted to MSHA.  Id. at 902-
03.  The judge found the Secretary's proffered motives
for tampering by Eget and Houck (to avoid penalties and
resampling and the enormous cost of non-compliance) to
be very weak.  Neither employee paid the R&P penalties,
resampling would not have been a substantial burden on
ESD, and neither was involved in coal production or
reported to a production supervisor.  Id. at 902.  He
noted that they knew that tampering was illegal and
that Eget, at least, was aware that criminal sanctions
could result from tampering.  Id.  For the same
reasons, he also accepted as true the statements of the
other dust technicians that they did not tamper with
the dust cassettes and further noted that they had
little opportunity to tamper.  Id. at 901, 903.

     Overall, the judge credited the testimony of ESD
personnel, expressly taking into consideration the evidence
concerning handling of dust samples at the mine and the
testimony of Thaxton, the scientists, and the
statisticians.  Id. at 903.  He considered credibility
determinations with respect to ESD personnel to be of
primary importance in his decision.  Id.

          6.  Judge's Conclusions

     Based on the records in the Common Issues and Keystone
trials, the judge concluded that the Secretary "failed
to carry his burden of proving by a preponderance of
the evidence that the weight of the 75 cited Urling
filters was intentionally altered by Keystone."  16
FMSHRC at 903.  Accordingly, he vacated the Urling
citations, denied the Secretary's petitions for civil
penalties, and dismissed the proceedings.  Id.  The
judge stayed all other Dust Cases until further order
of the Commission.  Id.

                                    II.

                                Disposition

     A.  Introduction

     In his PDR, the Secretary sets forth 14 points of error.
He asserts that, in the Common Issues trial, the judge imposed
an improper burden of proof, which he also applied in
Keystone.  In addition, he contends that the judge made
incorrect scientific, statistical, and credibility
determinations as well as erroneous procedural rulings.  The
Secretary places the following issues in contention and
numbers them in the PDR as follows:

     1.  The judge misstated and misapplied the burden of proof
     in both proceedings.  His use of the wrong burden in the
     Common Issues Decision fatally tainted his analysis in
     Keystone.  PDR at 10-12 (addressed in section B., slip op.
     at 17).

     2.  The judge erred in failing to credit the opinions of Mr.
     Thaxton and Dr. Marple that AWCs were more consistent with
     deliberate application of reverse air flow through filters
     than with accidental events.  PDR at 12 (addressed in
     section C. 2., slip op. at 26).

     3.  The judge erred in crediting Dr. Lee's opinion that AWCs
     were more consistent with  accidental impact forces than
     with tampering.  PDR at 12-14 (addressed in section C. 3.,
     slip op. at 29).

     4.  The judge erred in admitting the testimony of Dr. Corn
     because his testimony was improperly withheld from the
     Secretary during discovery.  PDR at 14 (addressed in section
     C. 4., slip op. at 34).

     5.  The judge erred in relying upon the conclusions of Dr.
     Corn as to accidental causation of AWCs because they lacked
     scientific foundation.  PDR at 14 (addressed in section C.
     4., slip op. at 34).

     6.  The judge erred in Keystone in failing to give weight to
     evidence regarding the optional quartz sampling program.
     PDR at 14 (addressed in section F. 2., slip op. at 59).

     7.  The judge erred in failing to appreciate that the
     statistical evidence supported intentional tampering as the
     likely cause of AWC formation.  PDR at 15-16 (addressed in
     section D., slip op. at 47).

     8.  The judge erred in his analysis of the statistical
     evidence in Keystone in focusing on bimonthly sampling
     periods instead of on March 26, 1990, as the pertinent date
     for evaluating the rates of AWCs.  PDR at 16 (addressed in
     section D. 2. b., slip op. at 55).

     9.  The judge erred in finding that "filter-to-foil"
     distance and other manufacturing variables affected the
     likelihood of AWC formation.  PDR at 16 (addressed in
     section C. 5., slip op. at 37).

     10.  The judge erred in Keystone in admitting the testimony
     of Dr. Lee regarding water sprays and scrubber systems
     because it was improperly withheld from the Secretary during
     discovery.  PDR at 17 (addressed in section C. 6., slip op.
     at 44).

     11.  The judge erred in Keystone in crediting the opinion of
     Dr. Lee over that of Dr. Marple concerning the effects of
     water sprays and scrubber systems.  PDR at 17 (addressed in
     section C. 6., slip op. at 44).

     12.  The judge erred in concluding in Keystone that handling
     changes by the ESD personnel explained a decline in AWCs on
     or about March 26, 1990.  PDR at 18 (addressed in section F.
     1., slip op. at 58).

     13.  The judge erred in Keystone in his analysis of the
     credibility of the ESD witnesses.  PDR at 18-20  (addressed
     in section F. 3., slip op. at 60).

     14.  The judge erred in excluding evidence of criminal
     tampering with dust samples by other individuals and
     entities.  PDR at 20-21 (addressed in section E., slip op.
     at 55).

     B.   Burden of Proof[21]

          1.  Judge's Conclusions

     The judge, in the Common Issues Decision, set forth his
conclusion that the Secretary had failed to carry his
burden of proving, by a preponderance of the evidence,
that an AWC established that the operator "had
intentionally altered the weight of the filter" or that
"deliberate conduct on the part of the cited mine
operators is the only reasonable explanation for the
cited AWCs."  15 FMSHRC at 1521.

     In the Keystone Decision, the judge, noting that the burden
of proof was the same as in the Common Issues Decision,
set forth his conclusion that the Secretary had the
burden of proving, by a preponderance of the evidence,
that the Urling filters resulted from intentional
tampering.  16 FMSHRC at 895.

          2.   Parties' Contentions

     The Secretary contends that the judge imposed an improper
burden of proof in both proceedings.  PDR at 10-12.  He
argues that the judge erred in the Common Issues
Decision in requiring him to prove that "deliberate
conduct on the part of the cited mine operators is the
only reasonable explanation for the cited AWCs."  15
FMSHRC at 1521 (emphasis added); PDR at 7.  The
Secretary asserts that this is a burden of proof
greater than the preponderance of evidence standard and
that the judge required the Secretary to prove that
there was no contradictory evidence or explanation
regarding the basic propositions the Secretary sought
to establish.  S. Br. at 30-35.[22]  The Secretary
asserts that, by using the "only reasonable cause"
formulation, the judge imposed a burden of proof that
was greater than the burden in criminal cases.  Id. at
31-32; Oral Arg. Tr. 208-09.  The Secretary argues
that, under the preponderance standard, he should have
been required to show only that the propositions sought
to be established were more likely true than not.  S.
Br. at 32; S. Reply Br. at 2-3.


**FOOTNOTES**

     [15]:   The sampling head  includes  the  cyclone  unit  and
filter cassette.  Tr. 91-94.

     [16]:  Data  from other mines consisted of data for all dust
samples processed by  MSHA from August 8, 1989, through March 31,
1992, except data from  R&P  mines,  mines  whose  operators pled
guilty to tampering, and mines whose cassettes may not  have been
examined for AWCs.  16 FMSHRC at 878.

     [17]:  Under Lee's mixed-mode theory, two impacts may  occur
almost simultaneously: an impact to the cyclone that results in a
mechanical  pulse  to the cassette and an impact to the hose that
results in a reverse  air  pulse  to  the cassette.  According to
this theory, the mechanical pulse tends  to  dislodge dust on the
filter  outside  of  the 6 mm ring, while the reverse  air  pulse
tends to dislodge dust inside the ring.  See 16 FMSHRC at 876-77.

     [18]:  Thirty-three  current  and  former  Keystone  and R&P
employees,   including   miners,  section  foremen,  technicians,
managers,  and  safety department  personnel,  testified  at  the
trial.  All employees  who  worked  at  the ESD laboratory during
1989 and 1990 testified.  16 FMSHRC at 888.

     [19]:   Some  miners attached the pumps  to  their  clothing
during sampling, while  others  attached  them  to the continuous
miners.  16 FMSHRC at 866.  Urling used two types  of  continuous
miners,  Lee-Norse  and Joy.  Id.  The judge found that the  dust
dislodgment patterns  could have been caused or contributed to by
attachment of the sampling  head  to  the Lee-Norse miners, which
vibrated while cutting coal.  Id. at 882.   However, he concluded
that changes in the dust deposition patterns  on  Urling  filters
after  the void code date were not due to changes in handling  by
section  foremen or miner operators or helpers, although he noted
that some  Urling  foremen  kept a closer eye on dust pumps after
learning of the MSHA investigation.  Id. at 882, 898.

     [20]:  The judge determined  that a number of other factors,
such as changes in MSHA's AWC selection  criteria  and other mine
conditions  at  Urling,  including height of the coal seam,  roof
stability, presence of a layer  of  rock  in  the  coal seam, and
changes  in mantrips did not explain the decline in Urling's  AWC
rate.  16  FMSHRC  at  882-87.  The judge was unable to determine
whether the section in the  mine  from  which  dust  samples were
taken  affected  the  decline of AWCs.  Id. at 883.  Although  he
found in the Common Issues  Decision that pliability of dust pump
hoses may be related to AWC formation,  the  judge  was unable to
conclude  whether  this  was a factor in the decline in  AWCs  at
Urling.  Id. at 886.  He also noted that equipment changes at ESD
were of questionable significance.  Id. at 884.

     [21]:  This section addresses Issue No. 1 in the PDR.

     [22]:   "S. Br." refers  to  the  Secretary's  Brief,  filed
September   26,   1994.    "S.  Reply  Br."  refers  to  the
Secretary's Reply Brief, filed  December 23, 1994.  "K. Br."
refers to Keystone's Brief, filed  November  14,  1994.  "I.
Br." refers to Respondent Intervenors' Brief, filed November
23,  1994.   "S.  P.H. Br. (C.I.)" refers to the Secretary's
Posthearing Brief,  filed  April  30, 1993, after the Common
Issues trial.


     Keystone and the Intervenors respond that the judge
explicitly adopted the preponderance standard in his
decisions and properly applied that standard.  They
argue that the Secretary has confused the burden of
proof with the issue to be decided in the Common Issues
trial, i.e., whether AWCs could only have resulted from
deliberate acts.  They assert that the judge properly
found that the evidence did not support a finding that
intentional tampering was the only reasonable
explanation.  K. Br. at 12-19; I. Br. at 20-25.

          3.  Development of the Common Issue

     On July 1, 1992, a group of operators moved for
consolidation of all Dust Cases for purposes of a
separate trial on the issue of causation of AWCs.  They
asserted that the basic issue common to all the
citations was whether "the existence of an AWC
dispositively prove[d] that an operator intentionally
altered the weight of a respirable dust sample."
Contestants' Mot. for Cons. and Separate Trial at 2.
The Secretary opposed the consolidation as well as the
operators' statement of the issue.  S. Statement in
Opp'n to Contestants' Mot. for Cons. filed July 15,
1992 ("S. Opp'n"), at 1-2.

     At a pretrial conference on July 17, 1992, the Secretary's
counsel requested a "bellwether"  trial involving a
large company with a number of citations.  Tr. 6, 11-12
(Prehr'g Conf. July 17, 1992).  The Secretary contended
that it was imperative to resolve the standard of proof
and how "the issue is to be framed within that standard
of proof."  Id. at 33.  The Secretary argued that the
major issue in the proceedings was whether the weight
of a cited filter had been altered while in the custody
or control of the operator and maintained that the
issue of whether a deliberate or accidental act caused
the alteration was relevant only to the penalty.  Id.
at 27-28.  The operators responded that, in order to
establish a violation under the cited regulatory
provisions, the Secretary had to establish a deliberate
act by the operator.  Id. at 40.

     The Secretary subsequently withdrew his opposition 
to a common issues trial.  S. Statement of the Issues and
Trial Proposal filed Aug. 7, 1992 ("S. Statement") at
1.  The Secretary urged that, in order to be useful,
the common issues trial must include all operators and
be binding on all parties.  Id. at 13.  As before, the
Secretary argued that, to prove a violation, he was not
required to prove that intentional tampering occurred
but only that a weight alteration occurred while the
filter was within the operator's control.[23]  Id. at
3-10.  The operators again asserted that the issue to
be determined was whether an AWC proved that an
operator intentionally altered the weight of a
respirable dust filter.  Contestants' Br. in Resp. to
Judge's Prehr'g Conf. filed Aug. 7, 1992, at 28.

     In the August 1992 Order, the judge noted the sharp
disagreement that had emerged recently between the
parties as to the basic issue presented for resolution.
14 FMSHRC at 1511.   He also stated that "whatever [the
Secretary's] position on what is necessary to prove a
violation of the standard in the abstract, [he] has
clearly taken the position . . . that the violations
resulted from deliberate acts."[24]  Id. at 1513.
Rejecting the Secretary's assertion that he should not
be required to prove intentional conduct, the judge
found that, by the plain meaning of section 209(b), a
violation was established by proving that an operator
intentionally altered the dust on a filter.  Id. at
1513-16.  He held that, "as a matter of law the
accidental, unintentional altering (changing, reducing)
the weight of a filter cassette while the cassette is
in the custody of the mine operator is not a violation
. . . ."  Id. at 1515-16.  Citing the burden of trying
each case separately, the judge consolidated the Dust
Cases for the purpose of trying the issue common to
all.  Id. at 1511.  The judge delineated the issue to
be determined as "[w]hether an abnormal white center
(AWC) on a cited filter cassette establishes that the
operator intentionally altered the weight of the
filter," and further specified that "the Secretary has
the burden of establishing [his] case by the
preponderance of the evidence."  Id. at 1517.

     On August 24, 1992, the Secretary filed a Motion for
Reconsideration and Clarification of the August 1992
Order ("S. Mot. for Recons."), in which he challenged
the judge's interpretation of the Secretary's
regulations to require proof of intentional conduct.
S. Mot. for Recons. at 2-3, 6.

     In a September 8, 1992, order ("September 1992 Order"), the
judge denied the motion for reconsideration and
repeated his conclusion that "the accidental,
unintentional altering (changing, reducing) the weight
of a filter cassette while the cassette is in the
custody of the mine operator is not a violation . . .
."  14 FMSHRC 1675, 1676 (September 1992) (ALJ).  The
judge stated:

          The purpose of  the common issues trial is to
          receive evidence concerning this allegation
          [so] that I may determine whether or not the
          AWCs on the cited filters can only have
          resulted from such deliberate acts.
          (emphasis added).

Id. at 1677.  At the outset of the Common Issues trial, the judge
again stated that, to prevail, the Secretary must prove, by a
preponderance of the evidence, that an AWC establishes that the
mine operator intentionally altered the weight of the filter.
Tr. 7.

     The Secretary did not appeal, either in a petition for
interlocutory review (29 C.F.R.  2700.76) or in his PDR giving
rise to this proceeding, the judge's ruling that, in order to
prove a violation, the Secretary was required to prove 
deliberate acts.  Section 113(d)(2)(A)(iii) provides: "If 
[petitions for review are] granted, review shall be
limited to the questions raised by the petition."  30 U.S.C. 
 823(d)(2)(A)(iii).  Consequently, that determination is not
in issue in this proceeding.

          4.  Judge's Formulation and Application of the Burden
of Proof

               a.  Applicable Legal Principles

     The Mine Act imposes on the Secretary the burden of proving
each alleged violation by a preponderance of the
credible evidence.  Garden Creek Pocahontas Co.,
11 FMSHRC 2148, 2152 (November 1989).  The
preponderance standard, in general, means proof
that something is more likely so than not so.  See
3 Edward J. Devitt et al., Federal Jury Practice
and Instructions  72.01 (1987); 2 Kenneth S.
Brown et al., McCormick On Evidence  339, at 439
(4th ed. 1992); Hopkins v. Price Waterhouse, 737
F. Supp. 1202, 1206 (D.D.C. 1990).  The Supreme
Court, in Concrete Pipe, 124 L. Ed. 2d at 563,
relied on by the judge, 16 FMSHRC at 895,
explained that "[t]he burden of showing something
by a `preponderance of the evidence,' the most
common standard in the civil law, simply requires
the trier of fact `to believe that the existence
of a fact is more probable than its nonexistence
before [he] may find in favor of the party who has
the burden to persuade the [judge] of the fact's
existence.'"  See also 2 McCormick  339, at 439
n.12, citing Model Code of Evidence, Rules 1(3) &
(5).

               b.  Burden of Proof in Common Issues Decision

     The Common Issues Decision fully supports the judge's
application of the proper burden of proof.  We
find that, in his rulings prior to and during the
trial as well as in his decision, the judge
appropriately articulated the appropriate burden.
Based on our review of the record, we
conclude that the judge also properly applied the
burden.  Further, the judge's use of the phrase
"only reasonable explanation" addressed the
Secretary's argument, not the burden of proof.


**FOOTNOTES**

     [23]:  The Secretary asserted that  three  issues  should be
determined: (1) whether it was established, by a preponderance of
the  evidence,  that the weight of the cited filters was altered;
(2)  whether  it was  established,  by  a  preponderance  of  the
evidence, that  the  weight alteration occurred while the samples
were in the control of the operator; and (3) whether the proposed
penalty was appropriate  in  light  of  the  level  of negligence
exhibited.  S. Statement at 2.

     [24]:   As support for this statement, the judge  referenced
the citations,  in  which  the  Secretary  uniformly  alleged the
operators'  negligence  level  as  "reckless disregard," and  his
proposed   penalties,  which ranged from  $1,000  to  $1,800  for
violations of sections 70.209(b)  and  71.209(b)  and $10,000 for
each violation of section 90.209(b).  14 FMSHRC at 1512.  (In his
closing arguments in Keystone, the Secretary argued for a fine of
$5,000 for each violation of section 70.209 (b).  K.  Tr.  4321.)
The  judge  also noted that, in his Response to the First Set  of
Interrogatories, dated January 10, 1992, propounded by Utah Power
and Light Co.  ("Resp.  to  Interrog."),  the Secretary responded
affirmatively  to  the  question:   "State  whether   it  is  the
Secretary's  contention that the alleged AWC on the cited  sample
could not occur  in  any manner other than by the intentional act
of an individual."  14  FMSHRC at 1513, citing Resp. to Interrog.
No. 17(h) at 12.  In addition,  the  judge  relied  on  Thaxton's
deposition testimony:

          Q.   Okay.  So that you believe that the
               phenomenon   described   in   those
               citations  resulted from deliberate
               dust removal; correct?

          A.   It resulted  from a deliberate act,
               yes.

14 FMSHRC at 1513-14, quoting  Thaxton Deposition (July 25, 1991)
at 310-12.


     In the September 1992 Order, the judge ordered the
Common Issues trial to receive evidence on which to base
a determination of whether AWCs can only have
resulted from deliberate conduct.  14 FMSHRC at
1677.  At the commencement of the trial, the judge
stated that, in order to prevail, the Secretary
must prove by a preponderance of the evidence that
dust cassettes with AWCs were caused by mine
operators intentionally altering their weight.
Tr. 7.  The Secretary, in his Posthearing Brief
and Proposed Findings of Fact, argued that he had
established that the "only reasonable explanation"
for the AWCs was intentional tampering.  S.P.H.
Br. (C.I.) at 1-2, 224.

     In his decision, the judge reiterated that the
"Secretary has the burden of proof" and that this
burden requires that the Secretary prove by a
"preponderance of the evidence that (1) the term
`AWC' has a coherent meaning and was consistently
applied; (2) the cited AWCs can only have resulted
from intentional acts; and (3) the AWCs resulted
in weight losses in the cited filters."  15 FMSHRC
at 1463-64.  The judge addressed both the issue
and the Secretary's "only reasonable explanation"
language in his decision:

     1.  The Secretary . . . failed to carry his burden of
     proving by a preponderance of the evidence that an AWC on a
     cited filter establish[ed] that the mine operator
     intentionally altered the weight of the filter.

     2.  The Secretary . . . failed to carry his burden of
     proving by a preponderance of the evidence that deliberate
     conduct on the part of the cited mine operators [was] the
     only reasonable explanation for the cited AWCs.

Id. at 1521.  The two-part holding reveals that, first, the judge
addressed the issue being tried in the Common Issues trial, i.e.,
whether the existence of an AWC established deliberate conduct,
and generally concluded that the Secretary had not shown that it
was more likely than not that an AWC established that a mine
operator intentionally tampered with the filter.  Second, the
judge addressed the Secretary's argument that he had proven
deliberate conduct was the only reasonable explanation for AWCs
and found that the Secretary had failed to prove such assertion
by a preponderance of the evidence. The Secretary now argues that
we should reverse the judge for addressing the issue being tried
and for responding to the Secretary's argument as set forth in
his posthearing brief.

     In arguing that the judge's reference to the "only
reasonable explanation" for AWCs was reversible error, the
Secretary has confused the burden of proof articulated by the
judge with his statement of the central issue to be determined in
the Common Issues trial.  The issue, as set forth in the
September 1992 Order, was whether the presence of an AWC, by
itself, indicated that tampering had occurred.  14 FMSHRC at
1677.  As the judge explained: "[t]he basic issue to be
determined in the common issues trial is whether an AWC on a
cited filter establishes per se that the mine operator
intentionally altered the weight of the filter."  15 FMSHRC at
1464 (emphasis added).  We believe the judge appropriately
exercised his discretion in setting forth that issue for
determination in the Common Issues trial.  Had per se violations
been established, mine specific trials could have been avoided,
except as to issues other than the violation, e.g., negligence
and penalty.  The determination sought by the Secretary in this
review proceeding (that he had shown by a preponderance of the
evidence that it was more likely than not AWCs were the result of
deliberate conduct) would not have obviated the need for mine
specific trials on the issue of whether each particular operator
had intentionally altered the weight of a filter and, thus,
violated section 209(b).[25]  When he determined the issue to be
decided in the Common Issues trial, in the August 1992 Order, the
judge was endeavoring to avoid such protracted litigation.  See
14 FMSHRC at 1511.

     Contrary to the Secretary's assertion, S. Br. at 31-33, the
judge did not require that the Secretary eliminate all other
causes of AWCs.  Application of the preponderance standard
necessarily required an examination of the evidence as to other
possible causes of AWCs.  The judge weighed the evidence and
concluded that the Secretary simply had not shown that it was
more likely than not that an AWC established that a mine operator
had engaged in tampering.  He stated: "Weighing the conflicting
opinions and considering all the evidence of record, especially
the systematic studies of the experts, I conclude that the
evidence does not establish that the AWCs resulted from
deliberate mishandling."  15 FMSHRC at 1521.[26]  The judge found
that the Secretary failed to carry his burden of proof, which he
correctly characterized as the preponderance of the evidence
standard, because "too many other potential causes for the dust
dislodgment patterns on the cited AWCs" existed.  Id. at 1521-22.
The judge thus determined that the Secretary's evidence did not
have such "convincing force" that what he was required to prove
(that AWCs were the result of deliberate tampering) was "more
likely true than not true."  See, e.g., Merzon v. County of
Suffolk, 767 F. Supp. 432, 444-45 (E.D.N.Y. 1991); St. Paul Fire
& Marine Ins. Co. v. United States, 6 F.3d 763,769 (Fed. Cir.
1993); 16 FMSHRC at 896.

     The Secretary also argues that, contrary to the judge's
statement, his position early in the case was that intentional
tampering was the most likely, but not necessarily the only,
cause of AWCs.  S. Reply Br. at 3 n.3; S. Letter to Comm'n dated
April 4, 1995, at 2.  Although the judge referenced the
Secretary's earlier allegations of deliberate conduct as
evidenced by the allegations set forth in the citations, the size
of his penalty proposals, his responses to interrogatories, and
Mr. Thaxton's deposition testimony,[27] the judge did not rely on
those allegations in determining that deliberate conduct must be
shown in order to prove a violation.  Rather, he relied on the
plain language of the regulation.  14 FMSHRC at 1513-16.  Thus,
irrespective of the Secretary's position on whether deliberate
conduct need be proven, the judge concluded, based on the plain
language of the regulation, that deliberate conduct was a
necessary element in proving a violation of section 209(b).  In
view of that determination, the judge appropriately exercised his
discretion in seeking to determine, by way of the Common Issues
trial, whether the existence of an AWC, in itself, established
deliberate conduct.

     The Secretary did not appeal the judge's determination that
deliberate conduct must be proven to establish a violation of
section 209(b) and, consequently, that determination is not in
issue in this proceeding.  30 U.S.C.  823(d)(2)(A)(iii).  As
noted, he did not seek interlocutory review, pursuant to the
Commission's Procedural Rules (29 C.F.R.  2700.76), of the
August 1992 Order or the September 1992 Order, which set forth
the central issue and the burden of proof for the Common Issues
trial.

               c.  Burden of Proof in Keystone Decision

     We disagree with the Secretary's assertion that 
the judge erred as to the burden of proof in the Common
Issues trial and that this error "fatally tainted
his entire evaluation of the evidence" in
Keystone.  S. Br. at 34.  The judge used the
phrase, "only reasonable explanation," in the
Keystone Decision solely in recounting his
holdings in the Common Issues Decision.  16 FMSHRC
at 861.[28]  The judge did not require the
Secretary to prove that the cited AWCs could only
have resulted from deliberate tampering.  Rather,
he expressly recognized that the Secretary bore
the burden of  proving by a "preponderance of the
evidence that Keystone tampered with the cited
samples."  Id. at 896.  Relying on Concrete Pipe,
the judge specifically discussed the meaning of
that term:

          The burden of proving by a preponderance of
          the evidence requires the party bearing the
          burden to convince the trier of fact "that
          the existence of a fact is more probable than
          its nonexistence . . . ."

Id. at 895, quoting 124 L. Ed. 2d at 563.  As noted, he also
correctly explained that, in order to preponderate, the evidence
must be sufficient to convince a trier of fact that the
proposition asserted is more likely true than not true and that,
where the evidence is equally balanced, the plaintiff has failed
to meet his burden.  16 FMSHRC at 895-96, citing Hopkins, 737 F.
Supp. 1202; Merzon, 767 F. Supp. 432; Smith v. United States, 557
F. Supp. 42 (W.D. Ark. 1982), aff'd, 726 F. 2d 428 (8th Cir.
1984).  Thus, in Keystone, the judge clearly indicated that he
understood the preponderance standard and correctly construed
that standard to mean nothing more than proof that a proposition
is more probable than not.  See 16 FMSHRC at 895-96.[29]

     According to the Secretary, the judge's statement that the
"same evidentiary burden" applied in both the Keystone and Common
Issues trial implies that a standard of proof higher than
preponderance was applied in Keystone.  S. Br. at 34-35.  In our
opinion, the judge's language merely indicates that in both cases
he applied the preponderance of the evidence standard in
determining whether the Secretary had proven that the AWCs
resulted from intentional tampering.  Except where he repeated
his conclusions from the Common Issues Decision, the judge did
not incorporate into Keystone the language articulating the issue
disposed of in the Common Issues Decision, i.e., whether an AWC
establishes that an operator intentionally altered the weight of
the filter.  See 16 FMSHRC at 861; 15 FMSHRC at 1464, 1521.
References by the judge in the Common Issues Decision to "only
reasonable explanation" addressed the issue before him and the
Secretary's argument, and were not a departure from the
preponderance of evidence standard.  We conclude that the judge
correctly applied the preponderance standard in Keystone.

     In sum, we conclude that the judge correctly applied the
preponderance of the evidence standard in both the Common Issues
and Keystone Decisions.

     C.  Scientific Issues

          1.  Introduction

     The judge considered the entire record before him in
making factual findings and in reaching conclusions in his
Common Issues Decision and in his Keystone Decision. 15
FMSHRC at 1456, 1521; 16 FMSHRC at 903.  Many of his
findings were drawn from the reports and testimony of
credited experts.  On review the Secretary raises a
number of issues concerning the judge's admission and
crediting of the scientific evidence presented by the
expert witnesses to explain the causes of AWCs.
Specifically, the Secretary contends that the judge
erred in failing to credit Mr. Thaxton's and Dr.
Marple's opinions that the appearances of AWCs were
consistent with blowing air into the filters; in
crediting Dr. Lee's opinion that AWCs were consistent
with accidental impacts; in admitting and relying on
Dr. Corn's opinion that accidental events were the
likely cause of AWCs; in analyzing evidence of filter
manufacturing variables; and in admitting and crediting
Dr. Lee's testimony on the effect of water sprays and
scrubber systems on the susceptibility of AWC
formation.  PDR Issues 2, 3, 4, 5, 9, 10, and 11.

     In considering the issues raised by the Secretary's
petition, we are guided by principles established under
Rule 702 of the Federal Rules of Evidence:  "If
scientific, technical, or other specialized knowledge
will assist the trier of fact to understand the
evidence or to determine a fact in issue, a witness
qualified as an expert by knowledge, skill, experience,
training, or education, may testify thereto in the form
of an opinion or otherwise."  Fed. R. Evid.  702.
"Expert witnesses testify to offer their scientific
opinions on technical matters to the trier of fact."
Cyprus Tonopah Mining Corp., 15 FMSHRC 367, 372 (March
1993), quoting Asarco, Inc., 14 FMSHRC 941, 949 (June
1992).  "Unlike an ordinary witness, . . .  an expert
is permitted wide latitude to offer opinions, including
those that are not based on first-hand knowledge or
observation."  Daubert v. Merrell Dow Pharmaceuticals,
Inc., 509 U.S. __ , 113 S. Ct. 2786, 125 L. Ed. 2d 469,
482 (1993).

     All the witnesses who testified in technical or scientific
areas were accepted by the judge as experts in their
respective fields. The qualification of experts and the
admission of their testimony are matters within the
discretion of the trial judge.  Coleman v. Parkline
Corp., 844 F.2d 863, 866 (D.C. Cir. 1988); Polk v. Ford
Motor Co., 529 F.2d 259, 271 (8th Cir. 1976), cert.
denied, 426 U.S. 907 (1976).  "In the absence of clear
error, as a matter of law, the trial judge's decision
[as to a witness's qualification to express an opinion]
will not be reversed." Payton v. Abbott Labs, 780 F.2d
147, 155 (1st Cir. 1985), quoting A. Belanger & Sons,
Inc. v. United States, 275 F.2d 372, 376 (1st Cir.
1960).  Under an abuse of discretion standard, "a trial
court's decision [to admit expert witness testimony]
will not be disturbed unless the appellate court has a
definite and firm conviction that the lower court made
a clear error of judgment or exceeded the bounds of
permissible choice in the circumstances."  Post Office
v. Portec, Inc., 913 F.2d 802, 807 (10th Cir. 1990),
quoting United States v. Ortiz, 804 F.2d 1161, 1164 n.2
(10th Cir. 1986).

     "[T]he resolution of conflicting testimony, including
that of expert witnesses, is for the trier of fact."
Jackson v. Hartford Accident and Indemnity Co., 422
F.2d 1272, 1275 (8th Cir. 1970) (citation omitted).  If
the opinions of expert witnesses in a proceeding
conflict, the judge must determine which opinion to
credit, based on such factors as the credentials of the
expert and the scientific bases for the expert's
opinion. Cyprus Tonopah, 15 FMSHRC at 372 (citation
omitted).  "[A] trial judge must ensure that . . .
scientific testimony or evidence admitted is not only
relevant, but reliable."  Daubert, 125 L. Ed. 2d at
480.  Further, the bias of an expert witness is a
proper matter for the judge to consider in determining
the weight to be given the expert's opinion.  See
United States v. Cutler, 58 F.3d 825, 836 (2d Cir.
1995).  "[A]n ALJ has substantial latitude in choosing
between conflicting expert testimony."  L & J Energy
Co. v. Secretary of Labor, 57 F.3d 1086, 1088 (D.C.
Cir. 1995); accord Cyprus Tonopah, 15 FMSHRC at 373.
The judge's decision to credit the opinion of one
expert over the opinion of another expert is reviewable
under an abuse of discretion standard.  Chapman v.
United States, 169 F.2d 641, 645 (9th Cir. 1948), cert.
denied, 335 U.S. 860 (1948) (citations omitted); see
also Autoskill, Inc. v. National Educ. Support Sys.,
994 F.2d 1476, 1493 (10th Cir. 1993); An-Son Corp. v.
Holland-America Ins. Co., 767 F.2d 700, 702-03 (10th
Cir. 1985) (when "evidence consisted primarily of a
`battle of experts,'" resolution was the appropriate
province of the trial court and appellate court was
"loath to disturb" a finding based on such a
resolution).  Accord Cyprus Tonopah, 15 FMSHRC at 373.

     In reviewing a judge's factual determinations drawn
from credited testimony, including expert testimony, the
Commission is bound by the terms of the Mine Act to
apply the substantial evidence test.  See 30 U.S.C. 
823(d)(2)(A)(ii)(I).  The term "substantial evidence"
means "such relevant evidence as a reasonable mind
might accept as adequate to support [the judge's]
conclusion."  Rochester & Pittsburgh Coal Co., 11
FMSHRC 2159, 2163 (November 1989), quoting Consolidated
Edison Co. v. NLRB, 305 U.S. 197, 229 (1938).  "[If an]
ALJ provide[s] an explanation . . . for disregarding
[other evidence], the expert testimony alone could have
constituted substantial evidence in support of the
conclusion."  L & J Energy, 57 F.3d at 1088.

          2.  Judge's Rejection of Mr. Thaxton's Opinion on AWC
          Causation[30]

     The judge concluded that Urling's AWCs did not result
from normal sampling; something happened in the mine or
thereafter to cause the abnormal appearances.  16
FMSHRC at 897.  He found Thaxton's conclusions that the
cause was intentional tampering "to a considerable
extent subjective."  He noted that Thaxton's testing
was unscientific and that his distinction between cited
and no-call filters was "tenuous at best."  The judge
was "not able to conclude on the basis of Thaxton's
reports and testimony that the abnormal appearances on
the Urling filters were caused by intentional
tampering."  Id.

     In his PDR, the Secretary asserts that the judge erred
in failing to credit the findings of Mr. Thaxton and Dr.
Marple[31] that "the appearances of cited AWC filters
at Urling were more consistent with appearances
generated . . . by deliberately blowing reverse air . .
. than by appearances generated by simulated accidental
events."  PDR at 12.  In support, the Secretary argues
that the judge's rejection of Thaxton's opinion as to
the cause of AWCs was based, in critical part, on his
no-call findings.  Id.; S. Br. at 55.  He takes issue
with the judge's determination that Thaxton's reasons
for citing no-call filters were "tenuous at best" and
not "an appropriate exercise of agency discretion." S.
Br. at 55-56.  The Secretary contends that the no-call
designation was a reasonable way of handling a few
questionable filters and that a decision not to cite
those filters was a reasonable exercise of MSHA's
discretion.  Id. at 59.  Keystone counters that the
judge rejected Thaxton's testimony in large part
because of his failure to provide a scientific basis
for his conclusions and because of his bias.  K. Br. at
64-69.  According to Keystone, the judge's rejection of
Thaxton's opinion was justified by the record.  Id. at
64, 69, 112-18.

     The judge did not err in declining to conclude, based
on Thaxton's opinion, that intentional tampering caused
AWCs.  He found Thaxton's testing to be subjective and
non-systematic, and not conducted with any scientific
rigor.  16 FMSHRC at 897; 15 FMSHRC at 1473.  The judge
noted, in comparing Thaxton's background to the
"impressive credentials" of Lee and Marple, that
Thaxton "is not a scientist . . . ."  16 FMSHRC at 898.
Thaxton did not use written criteria to distinguish
normal filters from those he considered abnormal, Tr.
133, nor did he prepare a "comprehensive written
protocol based on scientific testing relating specific
appearances to different kinds of tampering."  16
FMSHRC at 897.  None of his tests were based on a
written protocol.  Tr. 123.  No written report of his
1983 or 1989 tests was introduced into evidence.[32]
He did not recall the number of filter cassettes he had
tested in 1983, but estimated that "between 25 to 50
filters . . . were played with to see how they would
behave."  Tr. 110.  Nor did Thaxton subject the 1983
test filters to impact forces in an attempt to
determine the potential for dust dislodgment patterns
as a result of accidental events.  Tr. 119, 123.
Thaxton kept no records as to the particulars of his
examinations, such as whether he reviewed the filters
from the reverse side or with a magnifying glass.  Tr.
619-21.  He failed to note the characteristics that
initially caused him to cite a particular filter.  Tr.
611, 628; see also Tr. 619-21.  We conclude that the
judge did not abuse his discretion in determining, on
the basis of this evidence, that Thaxton's opinion on
the causes of AWCs was not sufficiently grounded in
reliable scientific evidence to support a conclusion of
deliberate tampering.  "[A] trial judge must ensure
that . . . scientific testimony or evidence admitted is
not only relevant, but reliable."  Daubert, 125 L. Ed.
2d at 480; Cyprus Tonopah, 15 FMSHRC at 372 (in
evaluating an expert's opinion, a judge may properly
focus on the scientific basis for that opinion).

     The Secretary asserts that the judge erred in 
discounting Thaxton's testimony based on a lack of 
distinction between cited and no-call filters.[33]  Denying
that the similarity between cited and no-call filters was
the result of inconsistency on MSHA's part, the
Secretary claims prosecutorial discretion and points to
evidence of other factors that sometimes determined
Thaxton's decision on whether filters should be cited.
S. Br. at 56-60.  The Secretary states that Thaxton
considered whether the same operator had submitted
other filters with AWCs and whether those filters were
submitted at or near the time of other AWC submissions.
K. Tr. 1174-76.  Thus, if a questionable filter was the
only unusual filter submitted by an operator, Thaxton
was not likely to cite it.  K. Tr. 1172-73.  On the
other hand, a questionable filter was cited if similar
filters had been submitted by that operator within a
short time period.  K. Tr. 1174-76.  If a questionable
filter was submitted by an operator who had submitted a
number of filters with AWCs, Thaxton considered that
filter to demonstrate tampering.  K. Tr. 917-18.  Thus,
it appears that, in evaluating marginal patterns of
dust dislodgment, Thaxton's reliance on an operator's
other filters exaggerated differences in citation rates
between operators and differences in citation rates
over time.  Thaxton's procedure provides further
evidence that the judge was well within his discretion
in finding Thaxton's determinations to be non-
systematic and lacking in scientific rigor and in
discounting Thaxton's opinion as to the causes of AWCs.

     The judge, in determining that Thaxton's testimony was
not sufficiently objective to support a determination to
cite an operator with deliberate conduct, also referenced
Thaxton's own testimony that: "[t]he no-call filters do
not exhibit th[e] degree of dust removal that I would
feel comfortable . . . saying that there is a citation
to be issued."  Tr. 139; 15 FMSHRC at 1466; 16 FMSHRC
at 897.  This testimony reveals both the imprecision
and subjectivity in Thaxton's determinations and
provides support for the judge's decision to give
diminished weight to his opinion testimony as to the
causes of AWCs.  As noted by the judge, decisions to
charge operators with deliberate tampering must be
based on "more objective standards."  16 FMSHRC at 897.

     The judge also gave diminished weight to Thaxton's
determination as to causation of AWCs because "he was
not a disinterested witness."  Id. at 872; 15 FMSHRC at
1473.  He had been employed by MSHA for 16 years as an
industrial hygienist.  15 FMSHRC at 1473; Gov't Ex.
344.  Thaxton determined the issuance of each citation.
16 FMSHRC at 859.  We conclude that, in evaluating
Thaxton's testimony, the judge properly considered the
fact that Thaxton was not disinterested.   The bias of
an expert witness is a proper matter for a court to
consider in weighing the expert's opinion.  See Cutler,
58 F.3d at 836.


**FOOTNOTES**

     [25]:  In his Motion for Reconsideration  of the August 1992
Order,  the  Secretary  acknowledged  as much.  He noted  that  a
decision  in  the  Common  Issues  trial  establishing   only   a
presumption  that  AWCs  are  more  likely than not the result of
deliberate conduct would do little to advance the litigation.  S.
Mot. for Recons. at 12.

     [26]:   The  Secretary complains that  the  judge  erred  by
failing to assign probability  factors  to the possible causes of
AWCs.  See Oral Arg. Tr. 43-44, 48-49.  It  was not necessary for
the judge to determine the level of probability for each possible
cause.  Rather, the Secretary had responsibility for proving that
AWCs resulted from intentional tampering; the  judge  had only to
decide  whether  the  Secretary  succeeded in proving that  by  a
preponderance  of  the  evidence.   The   judge   determined  the
Secretary had not.

     [27]:  We also note the Secretary's allegation of deliberate
tampering set forth in the Special Assessment Findings  issued to
all   respondents  when  the  penalties  were  proposed  for  the
contested violations.  See 14 FMSHRC at 1512.

     [28]:  In Keystone, the judge stated:

               On   the   basis  of  all  the  evidence
          introduced  in the  common  issues  trial,  I
          concluded that  the Secretary failed to carry
          his burden of proving  by  a preponderance of
          the evidence . . . that deliberate conduct on
          the part of the cited mine operators  is  the
          only  reasonable  explanation  for  the cited
          AWCs.

16 FMSHRC at 861.

     [29]:  We note that the Secretary was in the  same  position
at  the commencement of the Keystone trial as he would have  been
had the judge not consolidated the Dust Cases and held the Common
Issues  trial.   He  was required to prove, by a preponderance of
the evidence, that Keystone's  AWCs  were  caused  by  deliberate
tampering.

     [30]:  This section addresses Issue No. 2 in the PDR.

     [31]:   The  Secretary has offered no support in his  briefs
for his assertion  that the judge erred in failing to credit
Dr. Marple's opinion.   Consequently,  we do not address it.
ASARCO Mining Co., 15 FMSHRC 1303, 1304 n.3 (July 1993).

     [32]:   Thaxton kept inadequate records of his tests. He
maintained  no  data on the 1983 testing other than one  page
containing eight  to  ten  of  the  actual  filters with the
weight recorded before and after application  of reverse air
flow.   Tr.  110, 118-19.  At trial, Thaxton was  questioned
regarding photographs  of  some  test  filters he created in
1991, but he was unable to identify the  specific  mechanism
that  caused  the  filter  appearances  in  the  photographs
because  he  kept  no  records of that testing.  Tr. 109-10,
120-22.

     [33]:  Dr. Lee testified that many of the Urling filters
were indistinguishable from no-calls.  16 FMSHRC  at 876; K.
Ex. 2001, at 3.  The judge himself observed filters at issue
in both the Common Issues and Keystone trials.  15 FMSHRC at
1468; 16 FMSHRC at 869.


     We conclude that the judge did not abuse his discretion
in determining that Thaxton's opinion was not sufficiently
grounded in reliable scientific evidence nor sufficiently 
objective and disinterested to support a determination of 
deliberate tampering.

          3.  Judge's Crediting of Dr. Lee's Opinion on AWC
          Causation[34]

     In his Common Issues Decision, the judge found that 
AWCs could have resulted from intentional acts.  15 FMSHRC
at 1513.  Crediting the opinion testimony of Dr. Lee
and other operator experts, he also found that AWCs
could have resulted from accidental and incidental
impacts to the cassette and hose.  Id. at 1513-14.  He
found that many of the filters subjected to impact
tests exhibited dust dislodgment patterns
indistinguishable from cited filters.  Id. at 1514.

     In his Keystone Decision, the judge concluded that 73
of the 75 cited filters resulted in whole or in part from
reverse air flow, but that the forces involved were
"generally less than those created by deliberate
blowing through the filter cassette."  16 FMSHRC at
900.  He found that none of the Urling filters
exhibited cones and that this indicated only slight
impact forces had created the dislodgments.  Id. at
899-900.  The judge further concluded that the "dust
dislodgment patterns may have been influenced by
impacts to the cassettes or sampling assemblies as well
as reverse air though the cassettes," as described in
Dr. Lee's mixed-mode theory.  Id. at 900.

     In his PDR, the Secretary contends that the judge erred
in crediting and relying on Lee's opinion that AWCs were
consistent with accidental impacts rather than
intentional blowing through filter cassettes.  PDR at
12-13.  In support, he argues that the relative degrees
of force involved in intentional blowing and accidental
impacts had not been measured, that Lee's opinion on
his "coning theory" in the Keystone trial was
inconsistent with his opinion in the Common Issues
trial, that his classification system was unreliable,
and that the judge erred in crediting Lee's opinion on
causation of AWCs while rejecting his opinion on MSHA
handling.  Id. at 13-14.  The Secretary further argues
that Lee's mixed-mode theory, advanced in Keystone, was
unreliable and that the judge erred in failing to
provide adequate reason for crediting Lee's opinions.
S. Br. at 64-75.

     In support of his position that the judge erred in 
crediting Lee's opinion that AWCs were consistent with
accidentally caused impacts, the Secretary argues that
Dr. Marple's testimony provided clear evidence that the
cited AWCs were consistent with intentional tampering
and inconsistent with accidental forces.  S. Br. at 60.
He points to Dr. Marple's testimony that his
experiments simulating accidental events produced few
AWCs.  Id. at 60 n.22.

     Keystone counters that the record fully supports the
judge's conclusions that the dislodgment patterns on Urling
filters may have been caused by impacts to the hoses,
causing  reverse air pulses, as well as impacts to the
cyclones, causing mechanical pulses, as set forth in
Lee's mixed-mode theory, and that these forces, which
were weaker than those caused by deliberate blowing,
resulted in the absence of cones on Urling filters and
in dislodgment patterns that were often larger and more
diffuse than those caused by deliberate blowing.  K.
Br. at 74-79, 82-86.

      Dr. Lee has a doctorate in solid state physics
and is president and chief scientist of the
R. J. Lee Group, which had performed testing and
research studies for numerous government agencies and
for private industry.  15 FMSHRC at 1470; Tr. 5923-48,
5935; R. Ex. 1001A.  He was accepted as an expert
witness in physics, materials characterization and
analysis, and environmental monitoring.  15 FMSHRC at
1488.  His opinion that AWCs could be caused by
accidental means was based on his Common Issues
experiments, in which he generated more than 3,100 dust
samples in the R. J. Lee Group dust tunnel, using coal
from various seams and particles of similar size,
shape, and aerodynamic diameter as found in coal mines.
Id. at 1489.  His samples were collected under
controlled temperature and humidity.  Id.  He also
obtained more than 650 samples from mines across the
country.  Id.  He then conducted a series of tests
involving impacts to the cyclones and hoses of dust
sampling units, which produced filters with AWCs.  Id.;
R. Ex. 1001, at 11-13, R. Ex. 1002; see Tr. 6315-51.
In addition to his reports and testimony, Lee showed a
videotape recording of three incidents of a pump being
dropped on a hose, two of which resulted in AWCs on the
cassette filter.  R. Ex. 1006.  In the Keystone
proceeding, Lee refined his experiments and performed
55 tests in which carrying boxes were dropped on
sampling unit hoses; 40 AWC appearances, similar to
those of the Urling filters, resulted.  K. Ex. 2002.

     Lee's opinion as to accidental causation of AWCs was
also corroborated by other experts, Dr. McFarland and Dr.
Grayson, who testified that they had produced AWCs
through impacts.  (McFarland) Tr. 4759-60, 4915, 5199-
5200; (Grayson) R. Ex. 1014, at 16; Tr. 5551.
McFarland conducted a courtroom demonstration in which
a 31-pound tool box was twice dropped on the hose of a
sampling assembly and twice resulted in AWCs.  15
FMSHRC at 1503; Tr. 4877-80, 4887-88, 4891, 5187-90.

     Moreover, the record shows that Dr. Marple, the 
Secretary's expert, came to realize that impacts to hoses 
could result in AWCs.  His first report, Gov't Ex. 280,
failed to address the effects of hose impacts or the
effect of filter-to-foil distance on susceptibility to
AWCs and he performed further studies only after he
learned of these phenomena from the operators' experts.
Tr. 2277, 2282.  After performing hose impact tests,
Marple retracted the conclusion set forth in his first
report that AWCs "could only occur by an intentional
act."  Gov't Ex. 280, at 7.  In his supplemental
report, Marple concluded that "extreme mishandling"
could cause AWCs.[35]  Gov't Ex. 282, at 14.  Compare
Gov't Ex. 280 with Gov't Ex. 282.  Marple was able to
replicate AWCs by forcefully stepping on hoses.  Tr.
2354-56; Gov't Ex. 282, at 6-7; see also Gov't Ex. 311.
The Secretary, in his Reply Brief to the Commission,
concedes: "[A]s evidence was developed during the
course of discovery, the Secretary's understanding of
AWC formation also developed."  S. Reply Br. at 3 n.3.

     Similarly, Mr. Thaxton reviewed Lee's experimental 
filters and determined that 105 had AWCs.[36]  Tr. 439, 
445. Of those 105 filters, 40 had been formed by cassette
drop, cyclone drop, hose impact, hose tread, or hose
wrap -- each a type of forceful contact.  See Gov't Ex.
267, Attach. 2; Tr. 7062-63.  See also Tr. 577-78.
Thaxton's testimony that 40 impact-caused AWCs were
citable also corroborates the evidence that accidental
events could have caused the AWCs.

     Thus, we conclude that the judge did not err in choosing to
credit Lee's opinion over Marple's to the contrary.

     The Secretary also contends that Lee's testimony on 
coning in Keystone was inconsistent with his testimony in
the Common Issues trial.  S. Br. at 61.[37]   In the 
Common Issues proceeding, Lee stated that coning is not
necessarily associated with AWCs, R. Ex. 1003, at 2;
Tr. 6418-37, and that deliberate reverse air flow is
not necessary for the creation of cones.  R. Ex. 1003,
at 5.  Lee noted that cones were present on the MSHA
inspectors' sample filters.  Id.  In Keystone, he
stated that "air blowing through filters using reverse
air has a tendency to generate cones," K. Tr. 3879; K.
Ex. 2001, at 7, and that, as a general proposition,
deliberate reverse air flow involves more force than
accidental events.  K. Tr. 3988.  Lee concluded that
the slight dust dislodgment on many of the Urling
filters indicated causation by a much smaller force
than that generated by deliberate reverse air.  K. Ex.
2001, at 5; see also 16 FMSHRC at 899.  We find no
discrepancy between Lee's testimony in the Common
Issues trial and his testimony in Keystone.  In fact,
Lee's report in Keystone expressly harmonizes his
conclusions with respect to the Urling filters with his
general observations in the Common Issues trial:
"Results by all experts indicate that physically
blowing through the outlet creates a high percentage of
cones although some dimples and cones are observed
under other conditions."  K. Ex. 2001, at 7.  Moreover,
Thaxton corroborated Lee's view by acknowledging in
both trials that cones indicated very forceful
application of reverse air to the filters.  Tr. 209,
1258; K. Tr. 908, 1072.  Thaxton testified that R&P
filters had only slight cones or dimples as compared to
those of some other mines, in which 50 to 60% of the
cited filters had cones.[38]  K. Tr. 1072-73.

     Consequently, we reject the Secretary's contention that
Lee's testimony on coning was inconsistent.

     The Secretary further contends that the judge erred 
in accepting Lee's opinion as to accidental AWC causation
while rejecting his opinion that MSHA's handling of
sample filters was one cause of AWCs.  PDR at 13-14; S.
Br. at 74, citing Ona Corp. v. NLRB, 729 F.2d 713, 719
(11th Cir. 1984) ("ALJ's credibility finding will be
disregarded if . . . inherently unreasonable or self-
contradictory").  We conclude that it was not
unreasonable or contradictory for the judge to accept
Lee's opinion as to AWC formation in general, which was
based on scientific experiments, while rejecting other,
less compelling, aspects of his opinion.  See DeSarno
v. Department of Commerce, 761 F.2d 657, 661 (Fed. Cir.
1985); Hathaway v. Merit Systems Protection Bd., 981
F.2d 1237, 1241 (Fed. Cir. 1992).  In our view, the
judge closely examined Lee's opinion, including its
underlying basis, and properly chose to credit those
aspects that he found persuasive.  The judge similarly
credited certain aspects of Thaxton's opinion,
concerning the classification of filters, 15 FMSHRC at
1469, while rejecting other aspects, concerning
causation.  Id. at 1473-74, 1513, 1518, 1521.

     The Secretary also asserts that the judge erred in
accepting Lee's opinion as to causation because his AWC
classification system was unreliable.  PDR at 13; S.
Br. at 61-64.  The judge recognized that Lee's
classification system was not applied without error.
15 FMSHRC at 1489.  Lee's inconsistency, however, in
categorizing filter appearances does not substantially
detract from his conclusion, drawn from his
experiments, that accidental impacts to sampling
equipment can cause AWCs.

     The Secretary also challenges, on the basis that the
theory lacks scientific support, S. Br. at 69, the judge's
crediting of Lee's mixed-mode theory, in which he
attributed the appearance of the Urling filters, which
differed from those blown through deliberately, to a
combination of events involving both impacts to the
hose (causing reverse air pulses) and impacts to the
cyclone (causing mechanical pulses).  K. Ex. 2001, at
18; K. Tr. 3849-50, 3864-65, 3867-68.[39]  That theory
is supported by Lee's experiments, involving mixed-mode
events, by Marple's testimony and videotape, Gov't. Ex.
286, and by Marple and Rubow's dust dislodgment
studies.  As noted, Lee performed 55 tests of box drops
that resulted in 40 filters with AWCs similar to those
on the Urling filters.  K. Tr. 3846; K. Ex. 2002, at 3.
(Of the remaining 15 filters, Lee opined that eleven
had no dust dislodgment pattern and four had
dislodgment patterns that were dissimilar to the Urling
filters.  K. Ex. 2002, at 3.)  For his tests, Lee
employed the actual carrying boxes used by R&P and
dropped them or firmly placed them down on hoses.  K.
Tr. 3833-36, 3843; K. Ex. 2002.  Lee's theory was also
based in part on his Common Issues experimental filters
and on Marple's videotape of AWC formation, Gov't Ex.
286, shown at the Common Issues trial.  K. Tr. 3817,
3871, 3915-16.

     Dr. Lee concluded that most of the cited filters 
showed comparatively little dust dislodgment and had
slightly larger dislodgment areas than AWCs created by
deliberate blowing.  16 FMSHRC at 899.  The Secretary
criticizes Lee's mixed-mode theory in part by arguing
that the Urling filters do not have large and diffuse
patterns of dislodgment.  S. Br. at 71.  The Secretary
recognizes, however, that the diameters of the
dislodgment area of the Urling filters were somewhat
larger than those of experimental filters subjected to
deliberate blowing.  S. Br. at 68.  Marple acknowledged
that the dislodgment areas of the Urling filters were,
in fact, larger than those of his experimental filters
created by deliberate blowing.  K. Tr. 1468; K. Gov't
Ex. 508, at 13, 16.  Marple as well as Lee found that
the Urling filters had dislodgments with diameters
larger than 6 mm.  K. Tr. 1468, 3849; K. Ex. 2002A; K.
Gov't Ex. 508.  Marple stated his belief that the
larger diameters resulted from deterioration as the
filters aged, but he presented no scientific research
to support that view.  K. Tr. 1468-69.  Lee concluded
that the larger diameters showed that the filters were
subjected to mechanical pulses due to impacts because,
in his experiments, such impacts caused larger
dislodgment areas.  K. Tr. 3849-50, 3856-58, 3863-65,
3911-18; K. Ex. 2002A.  Marple acknowledged and his
videotape showed that impacts to cassettes result in
dislodgments with a "wider, more diffuse ring," whereas
reverse air flow caused sharply defined 6 mm circular
dislodgments.  Tr. 2111-16, referencing Gov't Ex. 280,
at 35; see also Gov't Ex. 280, at 36.  Lee relied on
this videotape to explain his theory that the Urling
filters, which had dislodgment both inside and outside
the 6 mm central area, exhibited characteristics of
both reverse air and mechanical pulses.  K. Tr. 3817,
3870-71.  Lee's theory is further supported by Marple
and Rubow's systematic dust dislodgment studies, in
which 210 filter cassettes subjected to three to six-
foot drops resulted in a dislodgment pattern different
from that resulting from reverse air, "it was larger in
diameter and less sharply defined."  15 FMSHRC at 1476-
77.

     Consequently, we reject the Secretary's assertion that
the mixed-mode theory lacks scientific support.

     The Secretary also complains that Lee's mixed-mode 
theory was not developed until after the Common Issues trial.
S. Br. at 71-72.  We do not find it inappropriate that
Lee conducted further research and produced a second
report to address more specifically the particular
characteristics of the filters cited in the Keystone
case.

     We also reject the Secretary's assertion that the 
judge failed to discuss the comparable strengths and
weaknesses of the opinions of Lee, Marple, and Thaxton
or explain his reasons for crediting Lee.  In the
Common Issues Decision, as well as in the Keystone
Decision, the judge described the scientific testimony
in detail and carefully explained the basis for
crediting Lee's testimony.  See 15 FMSHRC at 1473-84,
1488-96, 1513-18, 1521-22; 16 FMSHRC at 872-878, 898-
900.

     "[A]n [administrative law judge] has substantial latitude
in choosing between conflicting expert testimony."  L&J
Energy, 57 F.3d at 1088.  Lee's opinions had a
scientific basis and the judge was within his
discretion in crediting it.  We emphasize that, in
evaluating Lee's testimony, the judge himself observed
Urling filters.  16 FMSHRC at 869.  We conclude that
the judge did not abuse his discretion in crediting
Lee's testimony that AWCs were consistent with
accidental impacts over Marple's testimony that they
were not.

          4.  Judge's Admission of and Reliance on Dr. Corn's
          Opinions[40]

     The judge credited the opinion of Dr. Corn, along with
that of Dr. Lee, Dr. Grayson, and Dr. McFarland, in
determining that a filter cassette with a shorter
filter-to-foil distance is more prone to dust
dislodgment than one with a greater distance.  15
FMSHRC at 1515.  The judge also credited Dr. Corn's
opinion that size and shape of the dust particles could
be a factor in dust dislodgment patterns.  Id. at 1517.

     In his PDR, the Secretary asserts that the judge 
erred in admitting and relying on Corn's testimony to
corroborate Lee's opinion that accidental impacts cause
AWCs.[41]  PDR at 14.  The Secretary argues that the
judge erred in admitting portions of Corn's opinion at
trial[42] and that the testimony lacked a scientific
foundation.  S. Br. at 75-78.  The Secretary relies on
Rule 26(b)(4)(A), (e)(1), & (e)(2) of the Federal Rules
of Civil Procedure, which provides that discovery may
be obtained of facts known and opinions held by experts
and that a party has a duty to supplement its
disclosure of information provided by experts.[43]
Intervenors counter that the judge's admission of and
reliance on Corn's testimony was within his discretion,
was reasonable given Corn's background and credentials,
and was justified because Corn's opinions were
supported by the evidence.  I. Br. at 72-77.

     Corn's report, disclosed during discovery, states:
"[W]e reviewed data generated by the R.J. Lee Group as a
result of their experiments.  We agree with their
conclusions regarding filter cassette susceptibility to
[AWC] formation . . . (e.g., `filters-to-foil'
distance) . . . ."  R. Ex. 1037, at 7.  At the Common
Issues trial, the Secretary objected to the questioning
of Corn about Lee's work, on the grounds that portions
of his opinion had not been disclosed during discovery.
Tr. 7551-52.  The judge overruled the objection
because, at the pretrial conference, he had ruled that,
at trial, "expert witnesses . . . should be able to
respond to criticism by other experts" and he
considered Corn's testimony to be a response to Dr.
Marple's criticism of Dr. Lee.  Tr. 7573; Tr. 23-24
(Prehr'g Conf. Nov. 17, 1992).  We conclude that, under
Rule 26(a)(2)(B),[44] the judge properly admitted
Corn's expert report because he had "otherwise . . .
directed" in a pretrial ruling that experts would be
allowed at trial to respond to other experts' opinions.

     Further, a judge's determination of a duty to supplement
discovery under Rule 26(e) and the exclusion of trial
testimony are committed to his sound discretion.  Phil
Crowley Steel Corp. v. Macomber, Inc., 601 F.2d 342,
344 (8th Cir. 1979).[45]  A judge's decision to allow
such evidence will usually not be disturbed unless it
results in undue prejudice or fundamental unfairness.
Id.  The Secretary was not prejudiced by Corn's
testimony.  Corn had been deposed by the Secretary
concerning his work with Lee.  Tr. 7552.  Further,
Corn's report, disclosed during discovery, stated that
he had reviewed the experimental data of the R. J. Lee
Group and that he agreed with their conclusions
regarding filter susceptibility to AWC formation.   We
find no abuse of the judge's discretion in his
admission of Corn's testimony.

     The Secretary specifically disputes the scientific
foundation for Corn's opinions that: (1) a filter
cassette with a smaller filter-to-foil distance was
more prone to dust dislodgment than a filter with a
larger filter-to-foil distance; and (2) the size and
shape of dust particles could be a factor in
dislodgment patterns.  S. Br. at 75.  We conclude that
these two opinions were within Corn's area of
expertise.[46]  Corn has a doctorate in industrial
hygiene and sanitary engineering and is professor in,
and division director of, the Department of
Environmental Health Services, School of Hygiene and
Public Health at Johns Hopkins University.  15 FMSHRC
at 1496.  He was accepted as an expert witness in the
fields of aerosol and particle physics, including the
adhesion and dislodgment of particles, coal mine dust
sampling technology, and federal occupational safety
and health regulation and enforcement systems.  Tr.
7490; see also 15 FMSHRC at 1496-97.  Corn studied the
adhesion forces of particles and concluded, based on
his review of the scientific literature and information
received from Lee, that Lee's dust particles were
representative of dust in mines.  Tr. 7553-55, 7570-71,
8025-26.  Thus, Corn's testimony had a proper
scientific foundation.  In addition, Corn was directly
involved with the measurements and tests on which he
based his opinion.  Corn visited Lee's research
facility on a number of occasions and reviewed Lee's
equipment, protocols, and procedures.  Tr. 7560, 7581-
83, 7585, 8009, 8085-86.  Corn himself measured filter-
to-foil distances of cassettes and also examined 1,248
of the cited filters.[47]  Tr. 7562, 7591; R. Ex. 1037,
at 2.  Corn requested that Lee examine the size of the
airborne dust particles used in his dust tunnel
experiments.  Tr. 7570-71.  We conclude that the
Secretary has not demonstrated that the judge abused
his discretion in crediting Dr. Corn's testimony.

          5.  Filter-to-foil Distance and Other Manufacturing
          Variables[48]

     The judge determined that the distance between the
filter and the aluminum foil cone of dust sampling cassettes
was variable and that casettes with shorter filter-to-
foil distances were more susceptible to AWC dust
dislodgment patterns than those with greater distances.
15 FMSHRC at 1515, 1521.  In the Common Issues
Decision, the judge concluded that the cited filters
had "shorter filter-to-foil distances than those
manufactured subsequently."  Id. at 1515-16.  In the
Keystone Decision, he concluded that the cited filters
"more probably than not had shorter filter-to-foil
distances than those manufactured subsequently" and
that this "could have been a factor in the decline of
cited AWCs [at Urling] in the Spring of 1990."  16
FMSHRC at 885-86 (emphasis added).

     The Secretary asserts that the judge erred in several
respects in his analysis of filter-to-foil distances
and other manufacturing variables of dust sampling
cassettes in reaching his conclusion that accidental
and incidental impacts could have caused Urling's AWCs.
PDR at 16-17; S. Br. at 78-88.  First, the Secretary
argues that the judge's findings that filter-to-foil
distance affects the likelihood of AWCs and that the
cited filters had shorter filter-to-foil distances are
not supported by substantial evidence.  PDR at 16; S.
Br. at 78-81.  Second, he argues that, in Keystone, the
evidence does not show that filter-to-foil distances or
other variables associated with the manufacturing
process changed over time.  PDR at 16-17; S. Br. at 82-
83.  He also contends that the statistical evidence in
Keystone does not support a finding that manufacturing
variables caused Urling's AWCs or a sudden decline in
their rate of occurrence.  PDR at 17; S. Br. at 87.  In
response, Keystone and Intervenors contend that there
was ample evidence that manufacturing variables
influenced the frequency of AWCs.  I. Br. at 26; K. Br.
at 80-81.  Keystone further asserts that there is
record support for the judge's crediting of Lee's
testimony that its cited filters had shorter filter-to-
foil distances and were more susceptible to accidental
or incidental AWC formation than filters manufactured
later.  K. Br. at 79.  After reviewing these
contentions and the record evidence, we affirm the
judge.

               a.  Filter-to-foil Distance and Susceptibility to
          AWCs

     In the Common Issues Decision, the judge found that 
shorter filter-to-foil distance makes a filter more prone 
to AWC formation.  15 FMSHRC at 1515.  He credited the
testimony of the operators' experts,  Drs. Lee,
Grayson, McFarland and Corn, that filter-to-foil
distance was an important characteristic of filter
cassettes that varied with date of manufacture and that
a shorter filter-to-foil distance made a filter more
susceptible to AWC formation.  (Lee) R. Ex. 1001, at
ii; Tr. 6225, 6238-41; (Grayson) Tr. 5551, 5648;
(McFarland) Tr. 5183-85, 5196, 5321; (Corn) Tr. 7567,
7697-98.

     As noted, Dr. Lee was accepted as an expert witness
in physics, materials characterization and analysis, and
environmental monitoring.  15 FMSHRC at 1488.  Using a
stereo optical microscope, Dr. Lee measured the filter-
to-foil distance of the 3,100 samples generated in his
dust tunnel as well as 650 samples taken from coal
mines across the country.  Id. at 1489; R. Ex. 1001, at
1, 11.  Based on his tests of subjecting cassettes to
drops and hoses to impacts, Dr. Lee concluded that
filter-to-foil distance was the strongest factor
influencing susceptibility to AWC formation.  15 FMSHRC
at 1491; Tr. 6238-39; R. Ex. 1001, at 11, 15.  In tests
of dropping cassettes a distance of 4 feet, 33% of 30
filters with filter-to-foil distance of 1 mm or less
had potentially citable AWCs; 27% of 129 filters with a
distance of 1 to 2 mm had potentially citable AWCs;
none of 43 filters with a distance of 2 to 3 mm had
potentially citable AWCs; 4% of 52 filters with a
distance of 3 to 4 mm and none of 5 filters with a
distance of 4 to 5 mm had potentially citable AWCs.  15
FMSHRC at 1491; R. Ex. 1001, at 11; App. B-4.3, B-4.7,
B-8.  In tests of hose impacts using a one pound
weight, 66% of 30 filters with a distance of 0 to 1 mm,
12% of 8 filters with a distance of 1 to 2 mm, none of
3 filters with a distance of 2 to 3 mm, 12% of 30
filters with a distance of 3 to 4 mm, and none of 9
filters with a distance of 4 to 5 mm had potentially
citable AWCs.  15 FMSHRC at 1491; R. Ex. 1001, at B-
5.2-5.3, B-5.6.  Dr. Lee also produced a video, R. Ex.
1006, which illustrated that, under the same
conditions, it is easier to produce an AWC with a short
filter-to-foil distance than with a larger distance.
Tr. 6241-53.  Dr. Lee explained that, as a matter of
basic physics, it is easier to dislodge dust on a
filter that is closer to the foil.  Tr. 6241; See 15
FMSHRC at 1515.

     Dr. Grayson is dean of the College of Mineral and
Energy Resources at West Virginia University and has a
doctorate in mining engineering.  15 FMSHRC at 1497;
Tr. 5518-20; R. Ex. 1014C.  He was accepted as an
expert witness in aerosol mechanics, fluid mechanics,
thermodynamics, aerosol filtration, and engineering
statistics.  15 FMSHRC at 1499.  In his research on
filter-to-foil distance, Dr. Grayson measured the
distances of 178 samples from various mines by
inserting a millimeter scale into the cassette inlet.
Id. at 1498.  Of those filters, 94 were drop tested and
the remaining filters were examined for existing AWCs.
Id.; Tr. 5644-45; R. Ex. 1014, at 14-16.  Dr. Grayson
concluded that there was a strong relationship between
filter-to-foil distance and creation of AWCs.  15
FMSHRC at 1499; R. Ex. 1014, at 18.

     Dr. McFarland is a professor of mechanical engineering
and was accepted as an expert in the fields of aerosol
mechanics, fluid mechanics, thermodynamics, aerosol
filtration, and engineering statistics.  15 FMSHRC at
1499; Tr. 4480, 4548.  Dr. McFarland measured the
filter-to-foil distances of several hundred cassettes.
15 FMSHRC at 1502; Tr. 4730-38, 4752.  Based on his tests
of applying varying degrees of pressure to cassettes
with varying distances between the filter and the foil,
Dr. McFarland concluded that it was more difficult to
form AWCs on filters with larger filter-to-foil
distances.  15 FMSHRC at 1502, 1505, 1515-16; Tr. 5004-
05 ; R. Ex. 1018, at 37.


**FOOTNOTES**

     [34]:  This section addresses Issue No. 3 in the PDR.

     [35]:   The  changing nature of Marple's opinions diminishes
their weight.  See, e.g., Kenbrooke Fabrics, Inc. v. Holland
Fabrics, Inc., 602 F. Supp. 151, 154 (S.D. N.Y. 1984).

     [36]:  Thaxton  did  not  review  Lee's  3,877 filters under
scientific,  double-blind  conditions  and, therefore,  knew
that  he  was  reviewing  filters of the operators'  expert.
Gov't Ex. 267, at 4-6; Oral Arg. Tr. 46.

     [37]:  The Secretary's Brief  refers  to Lee's Coning Report
as R. Ex. "1002"; that report was admitted as R. Ex. "1003."
Tr. 5996.

     [38]:   Although, in 1992, Thaxton had classified seven
Urling filters as having cones, a year later  he  determined
that none of the filters had cones and only one or  two  had
dimples.   K.  Gov't  Ex.  505.  Thaxton believed that cones
relaxed with time.  His belief  was  based not on systematic
experimentation  but  on  his  knowledge  that  filters  are
composed of a plastic material and plastics flatten out with
time, as well as on his observation of one coned filter.  K.
Tr.   888-891.    Lee,   in  his  observations  of  numerous
experimental filters, found  no  evidence that cones relaxed
or flattened over time.  K. Tr. 3883.

     [39]:  We note that Marple testified to the contrary, that
mixed-mode events failed to cause filter  appearances  similar
to  those  on the cited filters.  K. Tr. 1472-81.   Although
Marple's  tests   of  40  mixed-mode  events,  performed  by
subjecting dust sampling  units  to  rough transportation in
trucks and tractors, resulted in only  one AWC, K. Gov't Ex.
509;  K.  Tr.  1509, Marple's tests were criticized  by  Lee
because he failed to adequately compress the hoses under the
carrying box.  K. Tr. 3848-49; K. Gov't Ex. 509, at 3-4.

     [40]:  This section addresses Issues No. 4 and 5 in the PDR.

     [41]: The Secretary, in his brief, asserts generally that
"[t]he judge used Dr. Corn's  testimony  to  corroborate  Dr.
Lee's  opinion  that  accidental  causes  account  for   AWC
patterns,"  but  he provides no supporting citation.  S. Br.
at 75.  In our opinion,  the  judge  did  not credit Corn in
areas other than the effect of filter-to-foil  distance  and
dust  particle  size  and  shape.  See 15 FMSHRC at 1512-13,
1515, 1517.

     [42]:   Apparently, the Secretary's  objection  to  the
admission  of  Corn's  testimony  does  not  extend  to  his
testimony on filter-to-foil distances.  At trial, in support
of  his  objection,  the  Secretary acknowledged that Corn's
report, disclosed during discovery,  contained the statement
 that "he agreed with Dr. Lee on filter-to-foil  distance 
. .  . ."  Tr. 7551-52.

     [43]:    Commission Procedural  Rule  1(b),  29  C.F.R.
 2700.1(b),  incorporates  the   Federal   Rules  of  Civil
Procedure, so far as practicable, on any procedural question
not  regulated by the Mine Act, the Commission's  Procedural
Rules, or the Administrative Procedure Act, 5 U.S.C.
 500 et seq.

     [44]:  Rule 26(a)(2)(B) provides:

               Except  as  otherwise stipulated or
               directed by the  court, . . . [t]he
               [expert]  report  shall  contain  a
               complete statement  of all opinions
               to be expressed and the  basis  and
               reasons therefor; the data or other
               information   considered   by   the
               witness in forming the opinions . .
               . .

Fed. R. Civ. P. 26(a)(2)(B) (emphasis added).

     [45]:   In support of the proposition that Corn's  testimony
should have been  excluded,  the  Secretary  relies  on Freund v.
Fleetwood  Enterprises,  Inc.,  956  F.2d  354, 356-59 (1st  Cir.
1992); Jenkins v. Whittaker Corp., 785 F.2d  720,  728  (9th Cir.
1986), cert. denied, 479 U.S. 918 (1986); and Jefferson v. Davis,
131 F.R.D. 522, 528 (N.D. Ill. 1990).  S. Br. at 77.  These cases
emphasize  the  trial  judge's  discretion  in  discovery-related
matters.   For example, Freund, which involved the  exclusion  of
expert testimony  at trial, states that the judge's discretion is
not to be disturbed absent manifest error.  956 F.2d at 356-59.

     [46]:  The judge  did  not  accept Corn as an expert in, nor
rely  on his conclusions as to, image  analysis.   15  FMSHRC  at
1509-13.   There  is  no  inherent  contradiction  in  a  judge's
accepting  an  expert's  testimony  in  areas in which he is well
qualified and rejecting his testimony in  areas  in  which  he is
less  qualified.   Cf. Wilkinson v. Rosenthal & Co., 712 F. Supp.
474, 478 (E.D. Pa. 1989) (expert qualified to testify in areas in
which he had appropriate  education  and  experience  but was not
qualified  to  testify  in areas in which he lacked education  or
experience); Bass v. Spitz,  522  F.  Supp.  1343,  1352-53 (E.D.
Mich.  1981)  (economist  could  not testify in areas beyond  his
knowledge and expertise).

     [47]:  Corn's opinion that a shorter filter-to-foil distance
makes a filter more prone to dust  dislodgment was one of several
expert opinions to that effect.  See  15  FMSHRC  at 1515.  Thus,
even  if  Corn's  opinion had not been properly credited  by  the
judge, other record  evidence  supports  the  judge's findings on
filter-to-foil distance.

     [48]:  This section addresses Issue No. 9  in  the PDR.  The
Secretary's  briefs fail to provide support for the argument  set
forth in section  (c)  of  that  issue,  dealing  with changes in
floppiness of filters over time, and we do not address  it.   The
judge  found  in  his  Common  Issues Decision that floppiness or
tautness of the filters varied and  that a floppy filter was more
prone to AWC formation than a taut one.   15  FMSHRC at 1515.  In
his  Keystone  Decision,  the  judge,  referencing  Dr.  Marple's
testimony that floppiness was "associated with smaller  filter to
foil  distances,"  stated  that  the  "evidence  related  to  the
question  whether  the  more  recently  manufactured filters were
floppier  than  the older ones is not sufficiently  clear,"  thus
precluding his making  a finding on this issue.  16 FMSHRC at 885
n.3.


     As noted, Dr. Corn was qualified as an expert in 
aerosol and particle physics, including the adhesion and
dislodgment of particles and coal mine dust sampling
technology.  Tr. 7490; See also 15 FMSHRC at 1496-97.
Corn measured filter-to-foil distances and examined
1,248 of the cited filters in reaching his opinion that
a cassette with a shorter filter-to-foil distance is
more prone to dust dislodgment than one with a greater
distance.  Tr. 7562, 7591; R. Ex. 1037, at 2.

     Thus, the operators' experts presented a scientific
basis, not merely a "common sense" view as alleged by 
the Secretary, S. Br. at 82, to support the effect of
filter-to-foil distance on susceptibility to dust
dislodgment.

     The testimony of the Secretary's experts, Drs. Marple and
Rubow, was inconsistent on the influence of filter-to-foil 
distance and filter floppiness.  The judge recognized
that, although Marple and Rubow concluded that 
manufacturing variables such as filter-to-foil
distance and floppiness were "not probably contributing
factors" to dust dislodgment, Marple had also testified
that filter floppiness and the distance between the
filter and foil influenced dust dislodgment patterns.
15 FMSHRC at 1482-83; compare Tr. 2826, 9347-48; Gov't
Ex. 282, at 13 and Tr. 2692-93, 2803-04, 2820-21, 2841-
42.  The judge reasonably discounted the inconsistent
testimony of the Secretary's experts on the effect of
filter-to-foil distance and credited the scientifically
supported, consistent, and corroborated testimony of
the operators' experts.  Thus, his finding that filter-
to-foil distance affects the likelihood of AWCs is
supported by substantial evidence and we affirm it.  In
Keystone, the judge reiterated his holding in the
Common Issues Decision, that shorter filter-to-foil
distance increases susceptibility to AWC formation.[49]
16 FMSHRC at 885.

     The Secretary also takes issue with the judge's finding
that the cited filters were from a population of filters
having short filter-to-foil distances.  15 FMSHRC at
1516; S. Br. at 78-79.   Lee testified, without
contradiction, that 80% of the cited filters were from
the series with numbers 200,000 and 300,000.[50]  See
Tr. 6271.  See also 15 FMSHRC at 1515-16.  Based on
certain graphs, the judge also found that, after the
filters were loaded with dust, the filter-to-foil
distance for 80% of the series 200,000 and 95% of the
series 300,000 filters was 2 mm or less.  15 FMSHRC at
1516; R. Exs. 1068-69.[51]

     The Secretary asserts that the judge erred in relying
on graphs that plotted filter-to-foil distances for
experimental filters in each series because the graphs
were based on a small number of filters with widely
varying measurements.  R. Exs. 1068-69; S. Br. at 79-
81.  He argues that the judge made an "inherently weak
assumption" that the very few experimental filters
manufactured before February 1990 were representative
of all such filters.  S. Br. at 80.  The Secretary also
contends that the graphs "at best showed only a slight
tendency over time toward an increase in the relative
percentages of filters with filter-to-foil distances of more
than 2 mm . . . ."  Id.  He further argues that 50% of the
filters manufactured between October 25, 1990, and
February 15, 1992, seven months to almost two years
after institution of the void code, had short filter-
to-foil distances, and that the rarity of AWCs in that
filter group refutes an association between filter-to-
foil distance and AWCs.  Id. at 80-81.

     The graphs in question were prepared by the Secretary
and set forth the filter-to-foil distances after dust
loading for experimental filters manufactured between
April 20, 1988, through the time of the Common Issues
trial; they were based on measurements by both the
Secretary's and the operators' experts.  15 FMSHRC at
1516.  In addition to showing that 80% of the series
200,000 and 95% of the series 300,000 filters had short
filter-to-foil distances (2 mm or less) the graphs
showed that a lower percentage of filters in the later
manufactured series had short filter-to-foil distances:
45% in the 400,000 series; 50% in the 500,000 series;
approximately 50% in the 600,000 series; and a little
more than 40% in the 700,000 series.  Gov't Exs. 260A,
262A; R. Exs. 1070, 1071. Thus, the graphs support the
judge's finding that the cited filters, more than 80%
of which were from the 200,000 and 300,000 series, came
from a population of filters with comparatively shorter
filter-to-foil distances.  15 FMSHRC at 1515-16.  Dr.
Rubow, Marple's colleague, acknowledged that the graphs
showed a marked increase in the percentage of filters
with filter-to-foil distances greater than 2 mm in
filters manufactured after February 1990.  Tr. 9244-47.

     Contrary to the thrust of the Secretary's argument,
the judge was mindful of the limitations of the graphs. 
15 FMSHRC at 1516.  He recognized that the number of
filters measured from each series varied considerably
and that the measurements in each series were made by
different experts who used different methods.  Id.  The
judge noted, however, that, because the cited cassettes
had been disassembled without being measured, the
graphs provided the best available evidence of the
filter-to-foil distance.  Id.

     Based on the evidence of record, we conclude that the
judge's finding in the Common Issues Decision, that the
cited filters came from a population of cassettes with
shorter filter-to-foil distance, more susceptible to
AWC formation than those manufactured subsequently, is
supported by substantial evidence.  Id. at 1515-16.

               b.  Filter-to-foil Distance and Decline of AWCs at
          Urling

     In Keystone, the judge found that the cited filters 
probably had shorter filter-to-foil distances than those
manufactured subsequently.  16 FMSHRC at 886.  He also
found that the decline in the number of cited AWCs in
the spring of 1990 could be explained, in part, by this
manufacturing variable.  Id.

     The Secretary asserts that there was no evidence
that filter-to-foil distance or other filter
characteristics, varying with date of manufacture,
changed after March 26, 1990, or provide an explanation
for the decline in AWC rates after that date.   S. Br.
at 83; S. Reply Br. at 23.

      All the cited Urling filters were series 200,000 and
300,000 filters.  16 FMSHRC at 885; see K. Ex. 2133, R.
Exs. 1068-69.  As discussed supra, the judge, in the
Common Issues Decision, found that filters from these
two series tended to have shorter filter-to-foil
distances.  15 FMSHRC at 1515-16.  The judge noted
that, according to Dr. Lee, the Urling filters
exhibited physical characteristics indicative of
shorter filter-to-foil distances.  16 FMSHRC at 885.
Lee testified that the absence of 9 mm segmented ring
standoff patterns on the Urling filters correlated with
shorter filter-to-foil distance.[52]   K. Tr. 3874-79;
R. Ex. 1001, at 15; K. Ex. 2001, at 5-6.  Dr. Marple
concluded that the absence of standoff patterns did not
indicate shorter filter-to-foil distance because his
experiments for the Common Issues trial indicated that,
even when filters were resting on the standoff, only
50% had standoff patterns.  16 FMSHRC at 885; Tr. 2528-
29.  Nonetheless, Marple agreed that the presence of
the standoff pattern was associated with greater
filter-to-foil distance; he found that standoff ring
patterns appeared only on filters with filter-to-foil
distances greater than 3.7 mm.  Tr. 2527-29, 9335-38,
9619-23; Gov't Ex. 327.  Lee also testified, without
contradiction, that the presence of crimping or
pinching on 20% of the Urling filters indicated shorter
filter-to-foil distance.  K. Tr. 3877-78; K. Ex. 2001,
at 6.  Lee noted that the incidence of crimping on
recently purchased filters was much lower, about 6%.
Id.; 16 FMSHRC at 885.

     We conclude that substantial evidence, including the
testimony of Dr. Lee, which was properly credited, as
well as the testimony of Dr. Marple, supports the
judge's conclusion in Keystone, 16 FMSHRC at 885-86,
that the cited filters more probably than not had
shorter filter-to-foil distances than filters
manufactured subsequently.

     In arguing that the judge erred in finding that
manufacturing variables provided an explanation for a
decline in AWC rates after March 26, 1990, S. Br. at
79, the Secretary mischaracterizes the Keystone
Decision.  The judge merely considered filter-to-foil
distance as one of several factors that could account
for a decline in AWCs at Urling in the spring of 1990.
16 FMSHRC at 882-86.  The failure of manufacturing
variables to explain completely a decline in AWCs in
the spring of 1990 does not substantiate the
Secretary's argument that the judge erred in finding
that such variables "could have been a factor"
contributing to the decline.  At oral argument, the
Secretary asserted that "the judge owed it to us to
analyze those data and tell us what he thought was the
most likely cause of these appearances."  Oral Arg. Tr.
48.  The judge was not required to find a complete
explanation for the downward trend in AWCs.  The
Secretary, to preponderate, was required to show that
the trend was the result of deliberate tampering.

               c.  Statistical Analysis of Manufacturing
          Variables

     In the Common Issues Decision, the judge, relying on
Dr. Roth's statistical analysis, concluded that the
evidence "does not establish . . . but may point to"
manufacturing variables as affecting the decline in AWC
formation.  15 FMSHRC at 1520.[53]  In his Keystone
Decision, the judge noted that the statistical experts
arrived at different conclusions on the effect of
cassette manufacturing date on AWC rate.  16 FMSHRC at
900.  He found that manufacturing variability may have
played some role in AWC formation.  Id. at 886, 900-01.

     The Secretary challenges the judge's analysis of
manufacturing variables in Keystone, asserting that
"the statistical evidence does not support a finding
that manufacturing variables caused AWCs or the sudden
. . . change in AWC occurrences."  PDR at 17.  The
Secretary argues, based on Miller's analysis, that,
rather than the cassette manufacturing date, the most
significant date affecting the occurrence of AWCs was
the sampling date and whether it was before or after
March 26, 1990, the date he alleges Keystone learned of
the void code.  S. Br. at 84-87.  The Secretary further
states that the judge failed to resolve conflicting
testimony of Miller and Roth on the relationship
between manufacturing dates and AWC formation.  Id. at
87-88.  In response, Keystone argues that Miller's
comparison of cassettes manufactured on certain dates
and used by R&P mines before and after March 26, 1990,
was faulty because he failed to use data for the same
mines in the two periods.  K. Br. at 109-10.  Keystone
further asserts that a valid comparison, based on
cassette manufacturing date, between R&P mines
including Urling and mines of other operators could not
be made because of handling and sampling differences.
Id. at 109.

     Dr. Roth's analysis showed that the rate of AWCs at
Urling was more than nine times higher for cassettes
manufactured on four consecutive key dates than on
other manufacturing dates, 46.9% as compared to
4.8%.[54]  K. Ex. 2004, at 6; 16 FMSHRC at 881, 900-01.
Dr. Miller's analysis showed that, for non-R&P mines
sampled before March 26, 1990, the citation rate for
cassettes manufactured on the key dates was 2.5%, lower
than that for cassettes manufactured on other dates,
6.2%.  K. Gov't Ex. 527, at 2-3, Table 1b; S. Br. at
85; 16 FMSHRC at 879.  Miller also found, however,
that, for all samples from R&P mines including Urling
that were taken before March 26, 1990, the citation
rate for cassettes manufactured on the key dates was
49.9%, higher than that for cassettes manufactured on
other dates, 38.2%.  16 FMSHRC at 879; K. Tr. 760-61;
K. Gov't Ex. 527, at Table 1a.

     Miller's analysis that manufacturing date does not
account for changes in AWC rates was countered by Roth's
analysis that the rate of AWCs tended to be higher for
cassettes manufactured earlier.  K. Ex. 2004, at 5-6;
K. Tr. 3563, 3565.  The judge explained that he saw
merit in both Miller's and Roth's analyses, i.e., that
manufacturing in general did not explain citation
rates, but that cassettes manufactured on four key
dates accounted for 60% of the AWCs at Urling,
suggesting manufacturing anomalies.  16 FMSHRC at 900-
01.  There is record evidence that the dust cassettes
were plagued by manufacturing problems.  In July 1990,
MSA, the manufacturer of the dust cassette assemblies,
recognized that filter airflow resistance exceeding the
allowed level and incompatibility of the filter and
backing pad had to be corrected.  R. Ex. 1124, at 2-4;
Tr. 9211-13.  On August 23, 1990, MSA recalled from its
district offices and destroyed all cassettes
manufactured before August 1, 1990.  R. Exs. 1134,
1144; Tr. 9221-22.  This recall included all filters in
the 200,000 and 300,000 series and part of the 400,000
series.  See note 50, supra.  Shortly thereafter, MSA
began screening all cassettes to ensure proper airflow
resistance.  Tr. 9207-08, 9221-22; R. Ex. 1180.  As the
judge noted, 15 FMSHRC at 1481, Dr. Rubow, the
Secretary's expert, conceded that a filter with a
higher airflow resistance would be more likely to flex
(and thereby be more susceptible to AWC formation) when
exposed to a constant reverse airflow.  Tr. 9147-48.
Dr. Lee similarly testified that reverse air pulses of
low magnitude would be more likely to form AWCs on
filters with higher airflow resistance.  Tr. 6214-16.
Dr. Corn also testified as to his concern that changes
associated with achieving proper airflow resistance
influenced the formation of AWCs.  Tr. 8050-51.

     We affirm the judge's refusal to infer tampering from
Miller's statistical analysis.  Miller used March 26,
1990, as the critical date in analyzing data on AWCs
submitted by Keystone.  The judge determined that March
26, 1990, is not materially significant at Urling
because R&P personnel knew of the AWC investigation
some six weeks prior to that date and Urling's AWC
citation data show a significant overall decline
beginning in September of 1989.[55]  16 FMSHRC at 900.
Accordingly, the judge could reasonably diminish the
weight accorded to Miller's statistical analysis.
Conversely, Roth's analysis of the four key dates of
cassette manufacture was not tied to March 26, 1990,
was supported by record evidence of cassette
manufacturing problems, and could reasonably be
considered more probative by the judge.  See Id. at
900-01.

     Given the conflicting analyses of the experts, the judge
was within his discretion in refusing to draw an inference
of tampering from these statistics.  We emphasize that
the judge did not hold that manufacturing variables, in
themselves, explained the decline in AWCs; rather, he
considered them as a factor, among others, that could
account for the decline in AWC rates at Urling.  Id. at
885-86.

          6.  Judge's Admission and Crediting of Dr. Lee's
          Opinion on Scrubbers[56]

     In Keystone, the judge found that, when the air was 
sampled in the vicinity of a continuous miner with a scrubber,
the dust deposits on filters were damper, had a higher
threshold velocity, and were more difficult to
dislodge.  16 FMSHRC at 883.  He noted that the experts
expressed conflicting opinions on the effect of
scrubbers and their accompanying water sprays on dust
deposits.[57]  The judge concluded that the
introduction of scrubber systems on the continuous
miners at Urling in 1989 and 1990 could have been a
factor in the decline of AWCs during that period.  Id.
at 882-83.

     The Secretary raises two issues related to the judge's
findings and conclusion.  First, citing Rule 26 of the
Federal Rules of Civil Procedure, the Secretary
contends that the judge erred in admitting Dr. Lee's
testimony on the effect of water sprays and scrubber
systems because that opinion had not been disclosed
during discovery.  PDR at 17; S. Br. at 89-90.
Further, the Secretary asserts that Lee lacked the
scientific background to offer such an opinion.  PDR at
17; S. Br. at 90-96.  Keystone responds that the judge
properly admitted Lee's opinion because the Secretary
had notice of, and opportunity to rebut, the testimony.
K. Br. at 87-88.  Additionally, Keystone argues that
Lee was qualified to give an opinion on the effects of
environmental conditions and mining equipment.  Id. at
86-87.  After review of the record, we find neither of
the Secretary's contentions well taken.

               a.  Admission of Dr. Lee's Opinion

     Under Rule 46 of the Federal Rules of Civil Procedure,
a party must make known to the court the action that
he seeks and the grounds therefor.  Fed. R. Civ.
P. 46; In Re Bildisco, 682 F.2d 72, 82 (3d Cir.
1982), aff'd on other grounds, 465 U.S. 513
(1984); accord Browzin v. Catholic Univ. of Am.,
527 F.2d 843, 850 & n.15 (D.C. Cir. 1975).  See
also section 113(d)(2)(A)(iii) of the Mine Act, 30
U.S.C.  823(d)(2)(A)(iii).  Here, the Secretary
failed to do that.  Several times during the
Keystone trial, the Secretary objected
specifically to Lee's opinions on other issues on
the grounds that they had not been disclosed
during discovery.  K. Tr. 3781-83, 3865-66, 3883.
When Keystone questioned Lee as to whether an
increase in the water pressure of scrubbers, with
an accompanying greater water spray, would affect
the susceptibility to dislodgment of dust samples,
however, the Secretary raised no objection.  K.
Tr. 3891.  The judge then asked whether the
increase in water pressure would increase or
decrease the susceptibility, and Lee answered that
the pressure increase would decrease the
susceptibility to dislodgment.  K. Tr. 3892.  The
Secretary again failed to object to Dr. Lee's
testimony on the effect of scrubbers on
susceptibility of filters to dust dislodgment.
Indeed, the Secretary subsequently questioned Dr.
Lee as to how he arrived at his opinion on the
effect of scrubbers.  K. Tr. 4043-45.

     The portion of the transcript that the Secretary 
cites in support of his contention, K. Tr. 3894, pertains
to another matter.  He has apparently confused
questions to Dr. Lee related to whether "overall
water levels and moisture levels in the Urling One
Mine [that] increased between 1990 and 1993"
affected the susceptibility of filters to dust
dislodgment, to which he raised objections, with
earlier questions regarding the use of scrubbers
between 1989 and 1990 (see Stips. 85, 93, and
94),[58] which coincided with the general decline
in AWCs, to which he raised no objection.[59]

     In any event, even if the Secretary had timely objected
to questions regarding the effect of scrubbers, the
testimony would have been properly admitted.  As
noted with respect to the Secretary's Rule 26
objection to the testimony of Dr. Corn, the judge
stated at the Common Issues pretrial conference
that, at trial, "the expert witnesses should be
able to testify in support of their own
conclusions, their own opinions and should be able
to respond to criticism by other experts and
should be able to criticize and attack the reports
of experts on the other side."  Tr. 23-24 (Prehr'g
Conf. Nov. 17, 1992).  Dr. Lee's testimony falls
squarely within the parameters of the judge's
ruling.

     Further, the primary report submitted by Dr. Lee
in the Keystone proceeding set forth his opinion that
lower relative humidity, in existence in the
winter months, increases the susceptibility of
filters to dust dislodgment.  K. Ex. 2001, at 14.
In response to Dr. Lee's report, the Secretary's
expert, Dr. Marple, stated:

               [T]he important parameter to consider is the
               moisture content of the particles and not the 
               relative humidity of the air outside of the 
               mine or even in the mining environment.  When
               the coal is mined, there are water sprays from
               the mining machine on the coal face providing a
               very wet local atmosphere in the generated dust,
               independent of the months identified in Dr. Lee's
               report.

               K. Gov't Ex. 509, at 10.  At the Keystone trial,
               Dr. Marple testified further on the effect of
               scrubbers:  "I think the wetness of the particles
               would have a major effect which would be related
               back to water sprays."  K. Tr. 1551.  Dr. Lee's
               subsequent testimony regarding scrubbers was made
               in response to Marple's report and testimony.  See
               also K. Tr. 4042-44.  Thus, under the judge's
               pretrial ruling, which was within his discretion,
               Lee's testimony was admissible, even if not
               disclosed during discovery.[60]  See Fed. R. Civ.
               P. 26(a)(2)(B); Phil Crowley, 601 F.2d at 344.

               b.  Crediting of Dr. Lee's Opinion

     The Secretary challenges the expertise of Dr. Lee to
give an opinion on the effect of scrubber systems on dust
deposits, arguing that the issue was outside the
area in which he was qualified, and that Dr.
Marple's credentials were more directly related to
this issue.  S. Br. at 90-91.  In response,
Keystone notes that Dr. Lee was the only expert to
research systematically the effect of humidity and
water on AWC formation and that his testimony on
the effect of scrubbers was consistent with his
basic opinion that moisture content of coal was a
factor that affected susceptibility to AWCs.  K.
Br. at 86-87.  Intervenors argue that Dr. Lee's
opinion was consistent with testimony of all
experts at the Common Issues trial and that Dr.
Marple's testimony also indicated that a variety
of factors, including humidity, could affect the
threshold velocity needed to dislodge dust
particles from filters.  I. Br. at 50-52.

     The Secretary failed to lodge an objection to 
Lee's testimony on this subject during the trial. As
with the Secretary's contention that the judge
erred in admitting Lee's testimony because it was
not disclosed during discovery, the Secretary was
obliged to lodge a timely objection to the
testimony in order that the judge could consider
the issue of Lee's qualifications to give an
opinion on this issue.  See Fed. R. Civ. P. 46;
Browzin, 527 F.2d at 850 & n.15; 30 U.S.C. 
823(d)(2)(A)(iii).

     In any event, Lee was fully qualified to offer an 
opinion on this subject.  As noted, he has a doctorate
in solid state physics and was accepted as an expert
witness in physics, materials characterization and
analysis, and environmental monitoring.  15 FMSHRC
at 1488; see R. Ex. 1001A.  The R. J. Lee Group,
which Dr. Lee headed, was experienced in analyzing
air samples and particulate matter and had worked
for numerous government agencies, as well as for
private industry.  See Tr. 5923-48.  A portion of
his expert report dealt with the impact of
humidity on the susceptibility of filters to
dislodgment.  See K. Ex. 2001, at 14.  Lee's
opinions were based on his water spray experiments
performed for the Common Issues trial.  K. Tr.
3893.  The Secretary offers no persuasive argument
to support his contention that Dr. Lee's testimony
was outside his area of expertise.  See S. Br. at
90-91.  Rather, he argues that Dr. Marple, who
testified that water sprays do not reduce the
susceptibility of dust deposits to dislodgment, K.
Tr. 4145-49, was more qualified to testify in this
area.  S. Br. at 90-91.  However, "the resolution
of conflicting testimony, including that of expert
witnesses, is for the trier of fact."  Jackson,
422 F.2d at 1275 (citations omitted); see also L &
J Energy, 57 F.3d at 1088.

     Here, the judge weighed partially conflicting testimony
and determined that the use of scrubbers and water
sprays would reduce the susceptibility of filters
to dust dislodgment.  16 FMSHRC at 883.  He noted
inconsistencies in Marple's testimony regarding
the effect of water sprays.  Id. at 875.  Marple
testified that water sprays do not reduce the
susceptibility of dust deposits to dislodgment, K.
Tr. 4145-50, but he also testified that wetness of
coal dust caused by scrubbers affects
susceptibility to dust dislodgment,  K. Tr. at
1551-52.  We further note that Marple testified in
the Common Issues trial, in response to a question
from the judge, that wet particles would be more
resistant to dislodgment.  Tr. 3103-05; see also
Tr. 9498-9500.  The judge was well within his
discretion in crediting Dr. Lee's opinion over Dr.
Marple's.

     Finally, the Secretary argues that the installation
of scrubbers systems does not explain a decline in
AWCs after March 26, 1990.  S. Br. at 93.   As
noted in section C. 5. b., supra, the Secretary
mischaracterizes the Keystone Decision.  The judge
merely considered the installation of scrubbers as
one of several factors that could account for the
decline in AWCs at Urling in late 1989 and early
1990.  16 FMSHRC at 883.

     D.  Statistical Issues[61]

     In the Common Issues trial, the Secretary attempted to
establish, through the use of statistics, that AWCs were not
randomly distributed across the industry, that a sharp drop
in the rate of AWC citations across the industry occurred
after institution of an AWC void code on March 19, 1990, and
that these factors, along with other evidence, established
intentional tampering by the cited operators.[62]  In
support of his proposition that statistics can be used to
prove a causal relationship, the Secretary cited cases in
which statistics were used to prove discrimination in
employment.  The judge found that the susceptibility of
filters to dust dislodgment depended on a number of
manufacturing and other variables and that the statistical
analysis of the Secretary's expert failed to take those
variables into account.  15 FMSHRC at 1521.  He noted that
the operators' statistical evidence showed that AWCs were
non-random after the void code was instituted as well as
before and that the decline in AWC citation rate commenced
in September 1989.  Id. at 1507-08; see also id. at 1485-86.
The judge concluded that, because of the existence of many
other potential causes, the statistical evidence did not
establish that AWCs resulted from intentional tampering.
Id. at 1519-22.

     In Keystone, the Secretary attempted to establish, through
the use of statistics, that a sharp drop in Urling's AWC
citation rate occurred after March 26, 1990, the date the
Secretary alleges ESD personnel became aware of the void
code,[63] and that this drop established that Urling had
intentionally tampered.  As noted in section C.5.c., supra,
the judge refused to infer tampering from the statistical
evidence.  He held that March 26, 1990, was not materially
significant at Urling and that the statistical evidence did
not establish that a reduction in the mine's citation rate
resulted from MSHA's investigation of its dust sampling
program.  16 FMSHRC at 900-01.

          1.  Common Issues Decision

     In his PDR, the Secretary argues that the judge 
erred in failing to understand the significance of the
statistical evidence in supporting the conclusion that
intentional tampering was the likely cause of AWCs
because such conduct was highly consistent with a
dramatic decline in AWCs in the spring of 1990 and
other explanations are inconsistent with that decline.
PDR at 15-16.

     The Secretary states that his use of statistics in the
Common Issues trial was designed to enable the judge to
draw inferences regarding the conduct of the cited
operators and to corroborate the Secretary's other
evidence of intentional tampering.  S. Br. at 36-37
n.12; S. Reply Br. at 15.  He asserts that the judge
erred when he stated that "[s]tatistical evidence
alone . . . cannot prove causal relationships."[64]  S.
Br. at 36-37 n.12, quoting 15 FMSHRC at 1484 n.4.  He
contends that the judge had "a legally erroneous
understanding of what statistical evidence can prove."
S. Br. at 37 n.12.  He submits that very significant
weight should have been given to the statistical
evidence and cites discrimination cases, in which
courts have determined that statistics alone can
constitute prima facie proof of employment or other
discrimination.[65]  Id. at 36-37 n.12.  He also argues
that Intervenors' attempts to explain AWCs do not
comport with the Secretary's evidence that AWCs did not
occur randomly over time and across the industry.  S.
Reply Br. at 15-16.

     Intervenors respond that the inference, if any, to be
drawn from, and the weight to be given to, the statistical
evidence was within the judge's sound discretion.  I.
Br. at 56.  Intervenors and Keystone argue that the
statistical evidence deserved little weight because the
underlying data were merely allegations of tampering,
not objective evidence of such conduct.   Id. at 61-62,
referencing 15 FMSHRC at 1465-66; K. Br. at 94.  They
distinguish the discrimination cases as analyzing
fundamentally different data, i.e., objective facts,
and as providing evidence of probable relationships
between variables, not proof of causal relationships.
I. Br. at 57 & n.49.  They note that MSHA first
developed written protocols for AWC identification in
the spring of 1990 and that the criteria for
identifying AWCs also became more stringent then.  Id.
at 63.  Intervenors argue that the continuing non-
random distribution of AWCs across mines after the void
code undermines the Secretary's position.  Id. at 69.
Intervenors further argue that AWC rates had
dramatically declined for five months before
institution of the void code and that the data reveal a
continuous decline throughout the period in question.
Id. at 66.  They point out that any date selected
during the period will result in a rate that is
statistically significantly higher before that date
than after, and that the rate of decline was steeper
before the void code date than after.  Id. at 67-68.
Intervenors further note the Secretary's failure to
explain the comparable rate of decline in AWCs in the
samples taken by MSHA inspectors before and after
institution of the void code.  Id. at 68.

     The statistical evidence on which the Secretary relies
was based on cited filters submitted to MSHA between August
8, 1989, and March 31, 1992. 15 FMSHRC at 1484. The data 
base  (the "Analysis Data Set") analyzed by Dr. Miller, the
Secretary's statistical expert, contains a record of
all respirable dust compliance filters submitted to
MSHA during that period except those from operators who
pled guilty to charges related to submitting fraudulent
samples.  Tr. 3201-07; Gov't Ex. 227, at 4-6.  Miller
concluded, on the basis of a chi-square analysis, that
the data were "inconsistent with the hypotheses that
the phenomenon leading to cited cassettes is random and
that the likelihood of cited cassette generation is the
same at each mine." Gov't Ex. 227, at 18.  He also
found "a trend to decreasing cited rate over time" and
"a marked decrease in the cited rate on or about
3/19/90."  Id. at 21.


**FOOTNOTES**

     [49]:  The Secretary  also requests the Commission to accept
Marple's uncontradicted testimony  identifying threshold velocity
of dust particles, i.e., the air velocity  that  is  required  to
dislodge  dust  particles  from  the  surface  of filters, as the
single most important factor in dust dislodgment.   S. Br. at 82.
The  judge found that both filter-to-foil distance and  threshold
velocity were important factors in dislodgment.  See 16 FMSHRC at
885, 899.  There is no inconsistency in the judge's determination
that  both   factors,   one   having  to  do  with  the  physical
characteristics  of  dust  and  the   other   with  the  physical
characteristics of the filter cassette (filter-to-foil distance),
were causative.

     [50]:  The series 200,000 filters were manufactured  between
April  20,  1988,  and April 3, 1989, R. Ex. 1069; series 300,000
between April 3, 1989,  and  February  13,  1990,  R.  Ex.  1068;
series  400,000  between February 13, 1990, and October 25, 1990,
R. Ex. 1070; series  500,000 between October 25, 1990, and August
5, 1991, Gov't Ex. 259A;  series  600,000 between August 5, 1991,
and  February 15, 1992, Gov't Ex. 261A;  series  700,000  between
February  15,  1992,  and  May  28, 1992, R. Ex. 1071; and series
800,000 from May 28, 1992, through  the date of the Common Issues
trial, Gov't Ex. 265A.

     [51]:    The   graphs   provide   filter-to-foil    distance
measurements  under  two conditions, before dust was loaded  onto
the filter, and after  dust  had  been  loaded.  See Tr. 2880-81.
The judge analyzed both types of measurements  and noted that the
pre-loading  values  show  a  slight  tendency  of filter-to-foil
distance to increase in the later manufactured series.  15 FMSHRC
at 1516.  See Gov't Exs. 253A, 255A, 257A, 259A, 261A, 263A.

     [52]:   The  9  mm  ring standoff pattern is caused  by  the
filter backing pad coming  in  contact  with  the  9  mm  plastic
(standoff) supports on the cassette.  Tr. 2526-27; Gov't Ex. 328.

     [53]:   The  judge  referred to Roth's testimony and report,
which showed that cassettes  manufactured  before 1990 had an AWC
rate that was 10 times higher than cassettes  manufactured  after
1990.   See  Tr.  4128-30; R. Ex. 1041, at 3.  See also Oral Arg.
Tr. 168.

     [54]:  The four  key dates were: May 26, May 31, June 1, and
June 2, 1989.  Roth found  that,  for  all  R&P  mines  including
Urling,  the  rate  of  AWCs  for cassettes manufactured on these
dates  was  49.6%  as  compared  to   5.8%  for  other  dates  of
manufacture.  K. Ex. 2004, at 6; 16 FMSHRC at 880.

     [55]:   We  have  affirmed that determination  as  discussed
infra in section D. 2. a.

     [56]:  This section  addresses  Issues  No. 10 and 11 in the
PDR.

     [57]:   The  record  shows  that  scrubbers  were  gradually
introduced beginning in 1989 and early 1990.  See K.  Tr.  85-86,
2594, 2796-98.

     [58]:   In  their  stipulations,  the parties included facts
relating to the use of scrubbers on continuous  miners  at Urling
and  specifically  identified  those  miners  that had scrubbers.
Stip. 94.

     [59]:   The  judge was unable to draw conclusions  from  the
evidence before him  concerning  the increased moisture levels in
the mine in 1993 as compared to 1989  and 1990 and the decline in
AWCs in late 1989 and 1990.  16 FMSHRC at 883.

     [60]:  The cases on which the Secretary  relies,  S.  Br. at
90,  to  support  the  proposition that his testimony should have
been  excluded are inapposite.   See  Weiss  v.  Chrysler  Motors
Corp.,  515  F.2d 449, 457-58 (2d Cir. 1975); Freund, 956 F.2d at
356-59.

     [61]:  This section addresses Issues No. 7 and 8 in the PDR,
which are set  forth  in  terms  of  the  Keystone Decision.  The
Secretary  "concurrently  objected  to"  related   findings   and
conclusions in the Common Issues Decision.  PDR at 10 n.1; S. Br.
at 40 n.15.

     [62]:   The  Secretary  states:  "The institution of the AWC
void  code  was  the first official notification  to  the  mining
industry that samples with AWC characteristics were considered by
MSHA  to  be  abnormal   and   that   some   kind  of  government
investigation into the AWC matter was under way."  S. Br. at 8-9.

     [63]:  In the Common Issues case, the Secretary  used  March
19, 1990, the date on which the void code notices were issued  by
MSHA,  asserting  that  this was the date on which operators were
advised of the voiding of  filters with AWCs.  15 FMSHRC at 1460,
1486; S. Br. at 8-9.  In Keystone,  he  used  March 26, 1990.  16
FMSHRC at 878.

     [64]:   Dr.  Miller  conceded  at  the Common Issues  trial,
however, that none of his studies allowed  him  to  conclude that
the presence of an AWC on a filter "establishes that  the  weight
of the coal dust on that filter was intentionally altered .  .  .
."  Tr. 3740; see also Tr. 3806-07.

     [65]:   The Secretary relies on such discrimination cases as
Hazelwood School  District v. United States, 433 U.S. 299, 307-08
(1977); International  Brotherhood of Teamsters v. United States,
431 U.S. 324, 339-40  (1977); Barnett v. W.T. Grant Co., 518 F.2d
543, 549 (4th Cir. 1975);  Wetzel v. Liberty Mutual Ins. Co., 508
F.2d 239, 259 (3d Cir. 1975), cert. denied, 421 U.S. 1011 (1975);
United States v. Jacksonville  Terminal  Co.,  451  F.2d 418, 442
(5th  Cir.  1971), cert. denied, 406 U.S. 906 (1972); Alabama  v.
United States,  304  F.2d  583,  586  (5th  Cir. 1962), aff'd per
curiam, 371 U.S. 37 (1962).  S. Br. at 35-36.



     Preliminarily, we agree that the data here are 
not objective.  The Secretary asserts that the AWC
citations constitute objective data because the judge
found Thaxton's AWC determinations to be consistent for
purposes of the Common Issues case.  The judge found in
his Common Issues Decision that Thaxton's
classifications were consistent and that his
determinations as to whether filters should be cited
under his tamper codes "were sufficiently consistent so
that I must consider whether an AWC establishes a
violation."  15 FMSHRC at 1466-67, 1469.  The judge
declined, however, to credit Thaxton's opinion on AWC
causation, finding that his opinion was not supported
by systematic scientific experiments.  16 FMSHRC at
897; see 15 FMSHRC at 1513, 1521.  We have affirmed
that conclusion.  Thus, the data analyzed by Dr. Miller
were merely allegations of tampering.[66]

     We find no error in the judge's determination that
the statistical evidence on non-randomness was not
persuasive of intentional tampering.  Differences in
AWC rates across mines do not necessarily prove
tampering.

     Further, the drop in citation rate for the industry
as a whole on March 19, 1990, derives from data as to 
two different groups of mines.  The data were analyzed
based on certain "before" and "after" periods.  The
"before" period included mines that submitted filters
with AWCs before March 20, 1990, and the "after" period
included mines that submitted filters with AWCs after
March 19, 1990.  See Gov't Ex. 241, at 1.  The "before"
data included filters from 300 mines that did not
submit filters during the "after" period.  15 FMSHRC at
1507; Tr. 4036-38.  The "after" period contained data
on 762 mines that were not considered in the "before"
period.  Id.  Of the 2,677 mines in the Secretary's analysis,
more than 1,000 were included in only one period, not both.
15 FMSHRC at 1507-08; Tr. 4036-38.  Thus, the data can
prove nothing as to a change over time for one group of
mines or the other.


**FOOTNOTES**

     [66]:  The judge was correct in determining  that  this case
is  not  analogous to a discrimination case.  15 FMSHRC at  1464.
Use of data  derived from Thaxton's decisions, even if consistent
as to which filters to cite, stands in marked contrast to the use
of statistical  data  in  employment  discrimination cases, where
statistics are generally used to compare objective data as to two
groups.  See, e.g., Teamsters, 431 U.S.  at 336-42.  For example,
the racial makeup of a particular category of a company's workers
is compared to the racial makeup of the qualified  and  available
labor  pool.   Absent  discrimination, the percentages should  be
similar.  The data used  by  the  Secretary  in this case are not
objective  and,  moreover,  they are not compared  to  a  second,
control group.


     Moreover, the drop in the citation rate for the coal
mining industry does not prove a drop in the citation rate
for all operators in the Common Issues proceeding.  Some
operators had submitted their only cited sample some
months before the void code date.[67]  Others received
their only citation for a sample taken many months
after that date.[68]  In fact, many operators who
received multiple citations had not yet taken their
first cited sample as of that date.[69]  The
statistical evidence presented by the Secretary in the
Common Issues trial did not even prove that many cited
operators experienced a drop in citation rates at or
near the void code date.

     The Secretary has not alleged that the operators in
this consolidated case were engaged in a conspiracy or were
in any way acting in concert to violate the Mine Act.
Yet he has attempted to use statistics on the citation
rate for the coal mining industry as a whole not only
to prove a drop in the citation rate for all operators
but to prove that the drop occurred because operators
learned of the AWC void code and, as a result, ceased
deliberate tampering.  The Secretary is essentially
asserting that a drop in the rate of allegations
against coal mine operators as a group provides legal
support for the underlying allegations against
particular operators.  We conclude that, absent a
conspiracy charge, a drop in the citation rate for the
industry as a whole cannot, as a matter of law, be used
to draw inferences regarding the conduct of all
operators or to support a finding of deliberate
misconduct on the part of any.  Based on that
determination, we conclude that the judge did not err
in finding that the statistical evidence did not
establish that AWCs resulted from intentional
tampering.  See 15 FMSHRC at 1520.


**FOOTNOTES**

     [67]:  For example, Big  Fork  Coal  Co., Mine ID # 4401969,
received its only citation for a sample taken  on  September  22,
1989; C&N Coal Co., Mine ID # 1516336, received its only citation
for  a  sample taken on November 17, 1989; and Big Hill Coal Co.,
Mine ID #  1513300, received its only citation for a sample taken
on October 4, 1989.  See Gov't Ex. 272.

     [68]:  For example, Bullion Hollow Enterprise, Inc., Mine ID
# 4404871, received its only citation for a sample taken on April
2, 1991; LJ's  Coal  Corp.,  Mine ID # 1516637, received its only
citation for a sample taken on  October  25,  1990;  and  Wampler
Brothers  Coal,  Inc.,  Mine  ID  #  1516722,  received  its only
citation for a sample taken on September 25, 1990.  See Gov't Ex.
272.

     [69]:   For  example,  Trojan  Mining,  Mine  ID  # 1502091,
received its first of 12 citations for a sample taken on July 11,
1990;  Double M. Coal Co., Mine ID # 4405661, received its  first
of five  citations  for  a  sample taken on October 22, 1991; and
Soldier Creek Coal Co., Mine ID
# 4200077, received its first  of  three  citations  for a sample
taken on June 11, 1990.  See Gov't Ex. 272.

          2.  Keystone Decision

     The judge, refusing to infer tampering from the 
statistical evidence, held that March 26, 1990, was not 
materially significant at Urling.  He was unable to conclude
on the basis of the statistical evidence that the
reduction in the citation rate at Urling was related to
MSHA's investigation of the dust sampling program at
the mine.  16 FMSHRC at 901.

     In his PDR, the Secretary argues that the judge 
erred in failing to understand the significance of the
statistical evidence in supporting the conclusion that
intentional tampering was the likely cause of AWC
formation because such conduct was highly consistent
with a sharp decline in AWCs on March 26, 1990, and
other explanations are inconsistent with that decline.
PDR at 15-16.  Further, the Secretary asserts that the
judge erred in his analysis of the statistical evidence
"by focusing, inter alia, on the bimonthly sampling
period rather than recognizing the self-evident and
paramount importance of March 26, 1990, as a discrete
and most logical date for evaluating rates of AWCs."
Id. at 16.

     In support of the petition, the Secretary argues that
the record establishes that Urling submitted 74 filters
with AWCs during the seven months preceding March 26,
1990, but only one AWC after that date, and that AWC
rates for other R&P mines were similar.  S. Br. at 37-
38.  The Secretary asserts that whatever was causing
the AWCs effectively ceased on March 26, 1990, and the
most likely explanation was the response of R&P
employees to the AWC void code.  Id. at 37-40.  The
Secretary further argues that, even assuming R&P
employees had sufficient knowledge of the MSHA
investigation to consider altering their conduct prior
to March 26, 1990, that date is of critical importance
because it is when they learned that tampering would no
longer yield positive results for R&P.  Id. at 45-46.
He also argues that the analysis of AWCs on a bimonthly
basis masks a dramatic decline after March 26, 1990.
Id. at 46-48.  Finally, the Secretary asserts that
Keystone's attempts to explain the occurrences of AWCs
are unsatisfactory.  S. Reply Br. at 15-16; see also
id. at 20, 26, 27.

     Keystone responds that substantial evidence supports
the judge's decision.  It asserts that the Secretary's
analysis is flawed.  It states that the date on which
Keystone was alleged to have gained knowledge of the
void code, March 26, 1990, is irrelevant because their
personnel were aware almost two months prior to that
date of a criminal investigation into dust sampling
conducted by MSHA.  K. Br. at 94-99.  Keystone also
argues that, even if these flaws in the Secretary's
analysis are ignored, the statistical evidence does not
establish that AWCs resulted from tampering.  Id. at
94.

               a.  Significance of March 26, 1990

     The judge concluded that March 26, 1990, was not 
the most logical cutoff point for comparing AWC rates. 
16 FMSHRC at 900.  He found that "the evidence shows
that the ESD personnel and Keystone management
were aware of the investigation . . . 6 weeks or
more before the notification of the void code 
. . . ."  Id.

     In early February 1990, Dennis Hellgren, the 
Director of Safety for R&P mines, learned that MSHA 
was investigating R&P's dust sampling program.  16
FMSHRC at 888.  He had received a telephone call
from the superintendent of the Florence No. 2
mine, who related that two foremen, Charlie
McGinnis and Norm Thompson, had been contacted by
MSHA special investigators, who were looking into
R&P's dust sampling program.  Both foremen had
taken notes of their interviews with the MSHA
investigators, and those notes were sent to
Hellgren.[70]  Hellgren knew that special
investigators normally handled criminal
investigations.  K. Tr. 2490-91.  From his review
of the notes, Hellgren knew that the investigators
were asking questions concerning cassettes with
white centers and tampering.  K. Tr. 2476-78,
2492-97; see 16 FMSHRC at 888.  He called the
superintendents of other R&P mines to find out
whether MSHA investigators had contacted their
foremen about the dust sampling program and asked
them to report back to him.  K. Tr. 2477-78, 2486-
88; K. Ex. 2073; see 16 FMSHRC at 888.

     Hellgren called but was unable to reach the MSHA 
agent in charge of special investigations at the local
district office; instead, he spoke to an
investigator, who confirmed that MSHA was
collecting information but who refused to explain
the reason.  K. Tr. 2478-79.   On February 2,
while Hellgren was present, Edward Onuscheck, a
former vice-president of safety and a consultant
to R&P, had a telephone conversation with Jerry
Spicer, an MSHA supervisor.  Spicer said that a
preliminary inquiry, on a nationwide basis, was
being made into respirable dust sampling.  K. Tr.
2479-84; K. Ex. 2073; see 16 FMSHRC at 888.

     On or about February 3, after reviewing Thompson's
and McGinnis's notes, Hellgren showed them to Donald
Eget, supervisor of R&P's ESD laboratory, and
asked Eget what he thought the investigators were
seeking.  K. Tr. 2299-2300, 2497-98; see 16 FMSHRC
at 888.   Other employees of the ESD laboratory
also learned of the MSHA investigation.  Dust
technician, Robert Bollinger, Sr., knew about the
investigation because MSHA investigators came to
his home looking for his son, who was a foreman at
an R&P mine.  K. Tr. 3016-19.  Shawn Houck, who
worked under Eget's supervision, learned of an
MSHA investigation from Bollinger.  K. Tr. 2120-
21.  Foreman McGinnis told Thomas Hollern, a dust
technician in the R&P laboratory, about the MSHA
investigation in early February.  K. Tr. 3256-58,
3294.  Douglas Snyder and Herbert Gleditsch, other
dust technicians, also learned of the MSHA
investigation and knew that investigators were
talking to foremen.  K. Tr. 1908-11, 2677-78,
2728.

     On February 20, 1990, an MSHA investigator, Joe
Totorio,  telephoned Hellgren to set up a meeting with
R&P officials.  Totorio indicated to Hellgren that
MSHA was working with the U.S. Attorney's office
in investigating dust cassettes with white spots
in the centers.  Hellgren asked Totorio which of
the R&P mines were being investigated and was told
that Urling was one.  In a second telephone
conversation that day, Totorio identified the
lawyer from the U.S. Attorney's office with whom
he was working.  K. Tr. 2499-2507; K. Ex. 2074;
see 16 FMSHRC at 888.  Following these
conversations, Hellgren told R&P's legal
department that the company was "under
investigation by the U.S. Attorney."  K. Tr. 2507-
08.  Hellgren also told Eget about the
conversation with Totorio.  K. Tr. 2300-01, 2508-
09; see 16 FMSHRC at 888.

     To summarize, beginning in early February 1990, 
officials at R&P, from its top management to its 
first-line supervisors, had knowledge of MSHA's
investigation into dust cassette tampering.  A mine
superintendent first telephoned R&P's safety
director to report MSHA's efforts to interview
foremen, and he in turn put every R&P mine
superintendent on notice to report any MSHA
contacts with foremen.  The safety director's
February 20 telephone conversation with an MSHA
investigator confirmed that the investigation
involved allegations of criminal misconduct.  In
early February and again on the 20th, details of
the investigation were passed along to Donald
Eget, whom the judge found had an opportunity to
tamper with dust cassettes.  16 FMSHRC at 888-89,
901; K. Tr. 2495-98, 2508-09.  These
communications diffused knowledge of the
investigation among R&P managers.  ESD laboratory
employees, including dust technicians, also became
aware of the investigation.  16 FMSHRC at 890-92;
K. Tr. 1908-11, 3016-19, 3355-59.

     Substantial evidence in the record supports the
judge's finding that R&P employees were aware of MSHA's
criminal investigation some six to seven weeks
prior to MSHA's notification that dust sample
filters with AWCs would be voided.  16 FMSHRC at
900.  Further, we reject the Secretary's argument
that, even if R&P employees knew of the
investigation earlier, March 26, 1990, is critical
because they learned on that date that tampering
would no longer be beneficial.  The Secretary has
presented us with no evidence of why, if R&P
personnel had been tampering with dust cassettes,
they would have been more likely discouraged by
the institution of the void code than by the
special investigation and the prospect of criminal
prosecution.  We also note that, from early
February 1990, the time the judge found R&P's
employees had knowledge of the investigation,
until March 26, 1990, Urling's citation rate
actually rose sharply, from zero in the sampling
weeks of February 5, 12 and 26, to 50% in the week
of March 19, 1990.  K. Gov't Ex. 501.

     Significant to the judge's rejection of Miller's
analysis of the rate of AWCs at Urling before and after
March 26, 1990, was the unexplained overall decline in
the rate of AWCs from September of 1989 through
April of 1990.  16 FMSHRC at 900.  Indeed, in
other periods prior to March 1990, the rate of
AWCs also decreased, sometimes more sharply than
it did after March 26.  See 16 FMSHRC at 905 (App.
A); K. Ex. 2129B; K. Gov't Ex. 500, at Attach. A1.
Although the Secretary states in his brief that
"the data picked the date," S. Reply Br. at 21,
Dr. Miller testified that the date March 26, 1990,
was given to him by the Secretary's trial counsel
for use in his analysis.  K. Tr. 788-789.  The
Secretary offered no explanation, see Oral Arg.
Tr. 116-17, to distinguish earlier declines in the
rate of AWCs from the decline that occurred after
March 26, 1990, which he asserts is indicative of
the cessation of intentional tampering.

     We affirm the judge's conclusion that the date 
March 26, 1990, is not materially significant in the
Keystone proceeding and that the drop after that
date in Urling's citation rate does not establish
intentional tampering.

               b.  Use of Bimonthly Data[71]

     The Secretary challenges the statistical analysis 
of the rate of AWCs by Keystone's expert, Dr. Roth,
because it was based on bimonthly data, which the
Secretary alleges masks the decline after March
26, 1990.[72]  S. Br. at 46-48.  The judge
accepted Roth's approach in using bimonthly data
because operators carry out dust sampling on a
bimonthly basis.  16 FMSHRC at 900; see 30 C.F.R.
 70.207(a) & 70.208(a) (1994).

     Miller conceded that, once March 26, 1990, loses
its significance as the date on which  R&P employees
became aware of the MSHA investigation, as the
judge held and we have affirmed, there was nothing
"necessarily wrong" with using a two-month period
to analyze the rate of AWCs.  K. Tr. 845-47.  It
is also apparent, from the judge's consideration
of Urling's AWC rate before and after March 26,
1990, that he also examined weekly data and did
not rely exclusively on Roth's bimonthly analysis.
16 FMSHRC at 900, 905 (App. A).  Thus, we conclude
that the judge did not err in relying in part on
Dr. Roth's analysis based on bimonthly data.

     E.  Exclusion of Third-Party Criminal Evidence[73]

     Prior to the Common Issues trial, the operators sought to
exclude the testimony of five individuals on the Secretary's
witness list who were expected to testify about methods by
which dust could be deliberately dislodged from filters or
fraudulent samples created.  Mot. to Exclude S. Case-
Specific Witnesses from the Common Issues Trial, filed Nov.
12, 1992; Tr. 79-80, 85-88 (Prehr'g Conf. Nov. 17, 1992).
Those individuals included Randy Thomas, a former R&P
employee, and a principal and an employee of Triangle
Research Corporation ("Triangle").
S. Witness List filed Oct. 30, 1992.  At the pretrial
hearing, the judge granted the operators' motion, excluding
the testimony because it was not relevant to the issue to be
determined in the Common Issues trial, i.e., whether "an AWC
on a cited filter cassette . . .  establishes that the
operator intentionally altered the weight."   Tr. 82-83, 89
(Prehr'g Conf. Nov. 17, 1992).

     At the Common Issues trial, the Secretary, in examining
Mr. Thaxton on filters classified as tamper code 10, sought
to question him regarding Triangle and offered exhibits
involving guilty pleas of individuals and entities in
criminal cases involving Triangle and its employees and
other operators.[74]  Tr. 294-96.  He offered the evidence
to show "the accuracy of Mr. Thaxton being able to discern
which cassettes [had] been deliberately altered," and "also
discern the method by which they were altered."  Tr. 296-97.
The Secretary asserted that evidence of those guilty pleas
would show that, at least as to tamper code 10, Mr. Thaxton
was very accurate.  Tr. 296-97. The judge sustained the
operators' objection and excluded the evidence.  Tr. 307.
He let stand Thaxton's testimony that tamper code 10 filters
came from a particular geographical area (Kentucky,
Virginia, and West Virginia) and were largely submitted by
Triangle.  Tr. 305.  During redirect examination of Thaxton,
the Secretary renewed his request that the evidence be
admitted, again urging that it would show Thaxton's ability
to identify filters that had been deliberately altered.  Tr.
1115-20.  Again, the judge sustained the operators'
objection, finding the evidence irrelevant and not necessary
to rehabilitate Thaxton as a witness.  Tr. 1119-20.  The
Secretary made offers of proof regarding the five
individuals whose testimony was excluded at the pretrial
hearing as well as several other documents involving
criminal pleas.  Excluded Exs. 330-34; Tr. 307-11, 1120; S.
Statement and Intro. to Offers of Proof Reg. Potential
Testimony of Pysher, Murray, Thomas, Ellis, and White, filed
Jan. 7, 1993.

     In the PDR, the Secretary asserts that the judge erred
in the Common Issues trial in excluding evidence of criminal
tampering and evidence from those who had witnessed or
participated in tampering because it would have played a
substantial role, when weighed with other evidence, in
establishing that intentional tampering was the most likely
cause of AWCs and was "clearly relevant to the general
question of motive in tampering . . . ."  PDR at 20-21.  He
further contends that the evidence of criminal conduct was
relevant to showing the opportunity and the incentive to
tamper by R&P personnel, S. Br. at 101, S. Reply Br. at 49-
50, and that the judge's ruling  precluded "the possibility
of consideration of most of this evidence at the [Keystone]
hearing."  S. Br. at 100.

     Intervenors argue that the evidence was properly excluded
under the terms of the September 1992 Order, which provided
that evidence of intent by individual mine operators was not
an issue in the Common Issues proceeding.  I. Br. at 53-54.
Keystone and Intervenors also argue that the evidence was
properly excluded at the Common Issues trial because it was
neither relevant nor probative and because evidence
concerning operators who were criminally liable could not be
used to establish that other operators acted in a similar
manner.  Oral Arg. Tr. 198-99; K. Br. at 52; I. Br. at 54.

     We conclude that the judge did not err in excluding the
evidence at the Common Issues trial.  As noted in section B.
3., supra, the judge, in the September 1992 Order, set forth
the issue to be determined in the Common Issues trial as whether
an AWC "establishes that the operator intentionally altered
the weight of the filter."  14 FMSHRC at 1677.  "The intent
of a particular mine operator or group of operators [was]
not an issue in the common issues trial . . . ."  Id.
Moreover, evidence that some AWCs were caused by deliberate
conduct would not have established that all or even most
AWCs were caused by deliberate conduct.  We conclude that
the judge's evidentiary ruling is consistent with the
September 1992 Order and was not an abuse of discretion.


**FOOTNOTES**

     [70]:  Thompson's notes are dated January 25, 1990,  K.  Ex.
2075,  while  McGinnis's are dated February 1, 1990, K. Ex. 2076.
McGinnis's notes indicate that he was interviewed at his home and
shown dust filters  with AWCs.  Id.; see K. Tr. 2496-97.  Neither
Thompson nor McGinnis testified at trial.

     [71]:  Bimonthly  analysis  has  the effect of smoothing the
data  over time.  16 FMSHRC at 880.  Compare  16  FMSHRC  at  905
(App. A) with Id. at 906 (App. B).

     [72]:   In  the  Common Issues proceeding, Dr. Roth analyzed
weekly data.  See R. Ex. 1041, Attachs. B & C.  In that case, Dr.
Miller used March 19, 1990,  rather  than  March 26, 1990, as the
pivotal time in his analysis.  15 FMSHRC at  1485.   We note that
both  experts  tailored  their analyses to the issues before  the
judge in the respective cases.

     [73]:  This section addresses Issue No. 14 of the PDR.

     [74]:  Tamper code 10 was developed in the fall of 1990,
after initiation of the void code.  Filters classified under
this  code had a slightly darker center, less  than  6mm  in
diameter,  surrounded by a broad lighter ring.  15 FMSHRC at
1462; Tr. 292-93, 8264-65.


     We also agree with Keystone and Intervenors that the
evidence concerning guilty pleas by several operators could
not properly be used to establish motive, opportunity,
incentive, or the likelihood of intentional tampering as to
others because such evidence does not prove that operators,
in general, had acted similarly.

     Further, it  is  not  apparent  that, if  the  testimony 
regarding Triangle and the challenged exhibits had been admitted
into evidence, the judge would have analyzed tamper  code 10
filters differently.  The  evidence  was  proffered  for  the
purpose of confirming Mr. Thaxton's ability to identify and
categorize AWCs, particularly those in tamper code 10.  The
judge found the evidence neither relevant to the case nor
"necessary to rehabilitate Mr. Thaxton as a witness."  Tr.
1119-20.  In fact, the judge found that "classification of
AWCs by Thaxton under his tamper codes was consistently
applied . . . ."  15 FMSHRC at 1513.  Moreover, the judge
allowed testimony from Thaxton that the vast majority of
tamper code 10 filters came from mines serviced by Triangle,
whose principal and employee were parties to a criminal plea
agreement.  Tr. 295, 305.  Thus, the judge had before him
evidence of criminal activity with respect to tamper code 10
filters and referred to the criminal convictions in the
Common Issues Decision.  15 FMSHRC at 1520.

     Contrary to the Secretary's argument, S. Br. at 100-101,
Oral Arg. Tr. 205, the judge's exclusion of the proffered
evidence in the Common Issues trial did not preclude its
consideration in Keystone.  Randy Thomas, one of the
individuals whose testimony was excluded from the Common
Issues trial, testified as the Secretary's witness in
Keystone.  K. Tr. 1307; 16 FMSHRC at 892, 902.  Further, at
trial, after Keystone had cross-examined Thaxton using
exhibits relating to the criminal pleas involving Rushton
Mining Company and Peabody Coal Company, those exhibits were
accepted into evidence on the Secretary's motion.  K. Tr.
1212-16, 1295-97; K. Exs. 2117, 2118.  Keystone Exhibit 2118
included criminal indictments and plea agreements relating
to Peabody and made up a portion of the Secretary's Exhibit
334, which was offered and excluded at the Common Issues
trial.  The Secretary did not offer into evidence any other
testimony or exhibits on this issue that were excluded from
the Common Issues trial.  Thus, the Secretary's argument on
review, that the judge's exclusion of this evidence in the
Common Issues proceeding precluded its consideration in
Keystone, is without merit.

     F.  Other Keystone Issues

          1.  Handling of Sampling Equipment at ESD[75]

     The judge found that changes in the handling of 
sampling equipment at ESD could have been a factor in the
decrease of AWCs at Urling in the spring of 1990.  16
FMSHRC at 884.  He found that ESD supervisor Donald
Eget, who handled the equipment more roughly than other
ESD personnel, did not handle samples or sampling
equipment from April 9 until May 10, 1990, and that
dust technician Douglas Snyder and the other
technicians were more careful in their handling of the
equipment as a result of MSHA's investigation.  Id.

     The Secretary contends that substantial evidence does
not support a finding by the judge that changes occurring
on or about March 26, 1990, in handling of dust
sampling equipment at ESD explained the decline in AWCs
after that date.  PDR at 18; S. Br. at 96-100.  To
support his argument, the Secretary states that both
Eget and his laboratory assistant Shawn Houck admitted
that they had not modified their handling practices
after March 26, 1990.  S. Br. at 97.  He also argues
that Snyder could not identify the time at which he
made changes in his handling of the sampling units.
Id.  Keystone counters that the judge found handling
changes in the spring of 1990 to be only one of many
possible explanations for the decline. K. Br. at 103-07.

     In asserting that the judge relied on changes in handling
to explain the decline of AWCs after March 26,  1990,  the
Secretary mischaracterizes the Keystone Decision.  The
judge found that handling changes by ESD personnel, in
addition to other phenomena at Urling, "could have been
factors in the decrease in the number of cited AWCs in
the Spring of 1990."  16 FMSHRC at 884; see also id. at
882-86.  Substantial evidence supports that finding.

     Eget, Houck, and Snyder testified that the sampling units
had been subjected to rough handling by ESD personnel.
For example, Snyder testified that, in transporting
pumps, he dropped the pumps, caught protruding hoses on
door latches, and slammed hoses in doors.  K. Tr. 1838,
1849-51.  Houck testified that the dust technicians
often left the pumps in disarray at the ESD with pumps
piled on top of each other and hoses tangled together.
K. Tr. 2084-86, 2159-60.  Eget was rough in his
treatment of the pumps; for example, he carelessly
threw pumps into his vehicle when transporting them and
swung pumps onto the table at the ESD laboratory.    K.
Tr. 2178-80, 2244-48, 2250-52.

     Houck testified that, although he did not know of any
changes in the conduct of the respirable dust program
and that it was hard to reduce the rate of accidentally
dropped cassettes, he thought everyone, including the
technicians, became "a little bit more careful of the
handling of the pumps."  K. Tr. 2179, 2203, 2214-15.
Although Eget did testify that he had not changed his
behavior after March 26, 1990, he did not handle pumps
from early April until May 10, 1990.  K. Tr. 2319-20,
2362, 2384.  Snyder could not pinpoint exactly when his
behavior changed, but he testified that he became more
careful in his pump handling.  See K. Tr. 1921.  Other
ESD dust technicians also testified to using greater
care.  Dust technician Herbert Gleditsch, who at times
sampled at Urling, testified that he handled pumps more
carefully.  K. Tr. 2713-14, 2733-34.  Dust technician
Thomas Hollern, who sampled at R&P's Heshbon mine,
testified that he became more careful after the AWC
investigation.  K. Tr. 3272-76, 3283-84.

     We conclude that substantial evidence supports the 
judge's finding that changes in the handling practices of
ESD personnel did occur and we affirm that finding.  We
also affirm the judge's conclusion that these changes
"could have been factors" causing the decrease in cited
AWCs in the spring of 1990.

          2.  Optional Quartz Samples[76]

     The judge drew no conclusions with respect to the fact
that no AWCs were noted or cited by MSHA on the "optional
quartz samples"[77] concurrently submitted by Urling
and other R&P mines.  16 FMSHRC at 887-88.  The
Secretary asserts that the judge erred in failing to
accord weight to this evidence.   PDR at 14-15; S. Br.
at 48-55.  He contends that the Urling and R&P quartz
sample filters did not display AWCs even though they
were taken in the same manner, under the same
conditions, and at the same time as the respirable coal
dust samples that exhibited AWCs.  Id.  The Secretary
asserts that the absence of AWCs on the quartz samples
indicates tampering because, for a quartz sample to be
accepted as valid by MSHA, it must be sufficiently
heavy and, thus, R&P would not have had the same
incentive to remove dust from a quartz sample as from a
compliance sample.  S. Br. at 49-51; see K. Tr. 1109,
1122-24.  Keystone responds that the judge properly
rejected the Secretary's evidence on optional quartz
samples because the appearances of those filters could
not be evaluated.  K. Br. at 90-92.

     Paul Parobeck, chief of the instrumentation and analytical
branch at the PHTC laboratory and overseer of quartz
sampling and the Secretary's only witness on this
issue, testified that none of the quartz sample filters
submitted by Urling and other R&P mines from August
1989 through March 31, 1991, had AWCs.  K. Tr. 1124-30.
Parobeck's testimony was based on computer records, not
on his personal examination of the filters.  K. Tr.
1124-30, 1140; K. Gov't Ex. 506.  The PHTC employees
who had reviewed the filters were not called as
witnesses.  16 FMSHRC at 887-88; see K. Tr. 1140-42.
Moreover, the filters were no longer in existence[78]
and no photographs of them were introduced at the trial
or made available for examination prior to the trial.
16 FMSHRC at 887; see K. Tr. 1128-30, 1140-41; K. Gov't
Ex. 506.  Thus, the operators' experts did not have an
opportunity to examine the filters and compare them
with cited filters or form opinions about them.  We
conclude that the judge did not err in according no
weight to the Secretary's evidence regarding Urling's
quartz sample filters or in refusing to infer from such
evidence that Keystone or R&P personnel had engaged in
tampering.

          3.  Credibility of ESD Personnel[79]

     Keystone, unlike the Common Issues case, involved
allegations of tampering by the employees of a specific
operator.  The judge's evaluation of the credibility of
employee witnesses was critical and properly assumed a
significant role in his decision.  See 16 FMSHRC at
903.  The judge heard the testimony of 33 witnesses
from Keystone and the ESD laboratory; all employees of
ESD during 1989 and 1990 testified.  16 FMSHRC at 859,
888, 901; see generally K. Tr.  The judge accepted as
truthful the testimony of these employees that they did
not tamper with dust samples.  16 FMSHRC at 903.

     The Secretary argues that the judge erred in several
respects in his credibility determinations as to ESD
personnel.  PDR at 18-19.  He asserts that the judge
gave undue weight to the testimony and credibility of
ESD witnesses and contends that the judge's credibility
determinations are undermined because that testimony
conflicts.  He objects to the judge's finding that ESD
personnel lacked incentive to tamper and he objects to
the judge's failure to credit the testimony of Randy
Thomas and Jack Szentmiklosi.  Id. at 19.  He also
asserts that the judge's credibility determinations
conflict with the overwhelming weight of the other
evidence.  Id. at 19-20.  Keystone responds that the
judge's credibility determinations are fully
substantiated by the record and, in accordance with
longstanding precedent, are entitled to significant
weight.   See K. Br. at 36-45, 53-57.

     The Commission has long held that a judge's 
credibility determinations are not to be overturned 
lightly and are entitled to great weight.  Farmer v.
Island Creek Coal Co., 14 FMSHRC 1537, 1541 (September
1992); Quinland Coals, Inc., 9 FMSHRC 1614, 1618
(September 1987); Penn Allegh Coal Co., 3 FMSHRC 2767,
2770 (December 1981); Hollis v. Consolidation Coal Co.,
6 FMSHRC 21, 25 (January 1984).  "Since the ALJ has an
opportunity to hear the testimony and view the
witnesses he is ordinarily in the best position to make
a credibility determination."  Ona, 729 F.2d at 719.
The Ona court observed that, "as a general rule courts
are bound by the credibility choices of the ALJ, even
if they `might have made different findings had the
matter been before [them] . . . de novo.'" Id. at 719,
citing Gulf States Mfrs., Inc. v. NLRB, 579 F.2d 1298,
1329 (5th Cir. 1978).

     The judge, noting several elements of demeanor that 
must be considered in determining credibility, also 
recognized that his credibility determinations must take
into account the extensive factual, scientific, and
statistical evidence and the witnesses' prior knowledge
of sanctions for tampering.  16 FMSHRC at 901.  His
analysis focused on Eget and Houck because he
determined that only they, among ESD personnel, had
substantial opportunity to tamper.  Id.  In evaluating
their testimony, the judge stated that he was
"impressed [with] the backgrounds of Eget and Houck and
their forthrightness on the witness stand" and that he
"carefully considered their testimony."  Id. at 902.
We conclude from our review of this record that the
judge did not make these credibility resolutions
lightly.  The judge found these individuals to be
truthful witnesses and his acceptance of their denials
of tampering is linked to his careful consideration of
the other evidence.  See id. at 903.  Thus, the judge
properly based his credibility determinations on his
evaluation of the witnesses and their demeanor and did
so in the context of the record before him.

     The Secretary argues that, in crediting ESD personnel,
the judge overlooked a number of inconsistencies in their
testimony.  S. Br. at 109-11 & n.38.  The Secretary
identifies two points on which Eget and Houck differed:
Eget did not regard his handling as rough, whereas
Houck did; Houck recalled performing a dust removal
experiment that Eget did not remember.  See PDR at 18,
citing 16 FMSHRC at 862, 890; S. Br. at 109-10.
Neither of these differences provide reason to
discredit the witnesses or overturn the judge's
determination.  The perception of one's own behavior
frequently differs from how it is perceived by others.
Eget's failure to recall one experiment does not make
his testimony that he had not tampered unworthy of
belief by the judge, who had the opportunity to listen
to his testimony and observe his demeanor.  We conclude
that such insignificant differences in testimony do not
provide sufficient basis to overturn the judge's
credibility determinations.

     The Secretary also argues that the judge erred in basing
his decision to credit ESD personnel on their lack of
incentive to engage in tampering because they knew that
tampering could subject them to punishment.  S. Br. at
106-07.  Specifically, the Secretary contends that the
judge erred by: (1) failing to recognize that, on both
"an economic plane" and "a psychological plane,"
employees have an incentive to help their employer; and
(2) by stating that R&P's small number of respirable
dust violations indicates a lack of incentive.  Id. at
107-09.  The judge expressly recognized that mine
operators and agents had pled guilty to criminal
tampering.  16 FMSHRC at 901.  The judge's statement as
to lack of incentives responded to the Secretary's
asserted motivation for ESD personnel to engage in
tampering, i.e., to avoid penalties, to avoid
resampling, and to avoid the enormous potential costs
of non-compliance.  Id. at 902.  The judge rejected
these asserted incentives as very weak and, when
considered with R&P's relatively small history of dust
violations, to be almost non-existent.  Id.  It was in
this context that the judge referenced the employees'
knowledge of criminal sanctions and found, on balance,
that the evidence showed a lack of incentive rather
than an incentive to tamper, as argued by the
Secretary.  Id.

     In addition, the record reveals that ESD supervisor Eget
had a strong concern relating to MSHA investigations into
tampering and possible sanctions.  See K. Tr. 2322-26.
In 1982, Eget wrote a memo cautioning safety personnel
of the possibility of criminal investigations and
advising them to conduct themselves "in a responsible
manner and beyond reproach."  K. Ex. 2036.  Because of
an earlier MSHA investigation, Eget kept a logbook to
record the appearance of every sample sent to MSHA.  K.
Tr. 2260-61, 2377-80.  Eget's logbook noted that two of
the filters (369468 and 294719) submitted to MSHA and
later cited would be voided for having been taken on a
low production shift.  K. Ex. 2006A; K. Tr. 2279-80.
We find no apparent incentive for Eget to remove dust
from filters that he knew were going to be routinely
voided by MSHA.  Thus, the judge's finding of lack of
incentive is supported as to Eget.

     As to other ESD personnel, dust technician Robert
Bollinger, Sr. testified that he and others who worked under
Eget's supervision had nothing to gain from tampering.
K. Tr. 3035-36.  Dennis Hellgren, R&P's Director of
Safety, testified that he knew of no incentive for
personnel to tamper.  K. Tr. at 2540.  Hellgren also
stated that Eget would not have put up with tampering
and that Hellgren would have fired Eget if he had
tampered with filters.  K. Tr. at 2541.

     Further, a review of the record indicates that, before
the judge, the Secretary neither offered evidence on, nor
argued his theory regarding, employees' incentive to
help their employers.   We do not accept the
Secretary's theory as true on its face because even if,
in much of their behavior, employees have an incentive
to help their employers, it is not evident that, in
general, they would engage in tampering or other
illegal behavior to help their employers. Consequently,
we reject the Secretary's theory as a basis for reversing
the judge.

     The Secretary argues that the judge's reasoning with
regard to the effect on incentives of  R&P's small history
of respirable dust violations is circular in nature,
because the small history itself may have resulted from
tampering.  S. Br. at 107-08.  In deciding to credit
denials of tampering by ESD witnesses, the judge relied
primarily on his evaluation of their truthfulness and
their demeanor in the context of the other evidence.
16 FMSHRC at 901-03.  Before taking into consideration
R&P's small history of dust violations, he found the
Secretary's asserted incentives to be minimal.  Id. at
902.  Moreover, his determination as to ESD employees'
credibility was based only marginally on their lack of
incentive.  Thus, any error by the judge in relying on
R&P's violation history is harmless.

     We also reject the Secretary's assertion that the judge
failed to give his reason for discounting the testimony
of Jack Szentmiklosi, that he had heard a conversation
between Bollinger and R&P's then Vice-President of
Operations, Robert Anderson, on the subject of the
tampering investigation.  S. Br. at 110 n.39.  As the
judge explained, both Anderson and Bollinger testified
that they did not recall such a conversation.  16
FMSHRC at 891, 893.  In choosing to credit Bollinger
and Anderson, the judge referenced the same reasons he
had set forth earlier for crediting Eget and Houck.
Id. at 903.  The PDR further takes issue with the
judge's discounting of the testimony of Randy Thomas,
who testified to alleged tampering at ESD some 15 years
earlier, PDR at 19; K. Tr. 1316-19, but the Secretary
offers no support in his briefs for this objection.  We
conclude that the judge did not abuse his discretion in
weighing Thomas's testimony against that of Gary
Foehrenbach and in determining that Thomas
misunderstood what he saw or that his recollection was
dimmed by the passage of time.  16 FMSHRC at 902.

     Finally, we reject the Secretary's assertion that the
judge's credibility determinations "are entitled to no
deference" because they are irreconcilable with the
weight of the evidence.   S. Br. at 103.  The contrary
evidence of tampering referenced by the Secretary,
which he characterizes as "overwhelming," i.e., "that
nothing explains the sudden and dramatic decline in
AWCs except the fact that on March 26, 1990, R&P
learned that MSHA believed that the existence of AWCs
indicated tampering," id., provides no basis on which
to overturn the judge's credibility determinations.  We
have affirmed the judge's findings and conclusions as
to the scientific and statistical evidence as well as
the handling of sampling equipment at ESD.  Thus, in
our view, the judge's crediting of ESD employees'
testimony that they did not engage in tampering is not
irreconcilable with the record evidence but is in
accord with it.

     The Secretary's contentions do not compel the 
extraordinary step of overturning the judge's credibility
determinations.[80]  See Hollis, 6 FMSHRC at 25.

                               III.

                            Conclusion

     We have concluded that the judge articulated and 
applied the appropriate burden of proof in both the Common 
Issues Decision and in the Keystone Decision.  We have
determined that the judge did not abuse his discretion
in rejecting Mr. Thaxton's opinion on AWC
causation, in crediting Dr. Lee's opinion on AWC
causation, in admitting and crediting Dr. Corn's
opinions on the effect of filter-to-foil distance and
the size and shape of dust particles, and in admitting
and crediting Dr. Lee's opinion on the effect of
scrubbers.  We have found that substantial evidence 
supports the judge's findings that manufacturing 
variables affect the susceptibility of filters
to AWC formation and could have been a factor,
among others, in the decline of AWCs.


**FOOTNOTES**

     [75]:  This section addresses Issue No. 12 in the PDR.

     [76]:  This section addresses Issue No. 6 in the PDR.

     [77]:  If a  ine's atmosphere contains more than 5% quartz,
the maximum level  of  respirable  dust permitted  is  reduced
below 2.0 milligrams per cubic meter.   K.  Tr.  1104-05; 30
C.F.R.   70.101, 71.101, 90.101 (below 1.0 milligrams  per
cubic meter where a Part 90 miner is exposed).  If more than
5% of quartz  is detected in a sample drawn by an inspector,
an operator is  given  the  option  of submitting additional
samples for evaluation.  K. Tr. 1119.   The  results  of the
optional  quartz  samples  drawn  by  the  operator are then
averaged  with  the  results  of  the  inspector samples  to
determine the mine's respirable dust standard.  K. Tr. 1119.

     [78]:   The  quartz evaluation process itself destroys the
quartz sample filters.  K. Tr. 1112-13.

     [79]:  This section addresses Issue No. 13 in the PDR.

     [80]:  We have considered the cases on which the Secretary
relies  for  extending  diminished  weight  to  the  judge's
credibility determinations.   S.  Br. at 28-30, 102-05, 110.
Those cases offer no support for the  Secretary's  position;
they  recognize  the  general  rule that, absent exceptional
circumstances, appellate courts  do  not  overturn  findings
based on credibility resolutions.  Medline Industries,  Inc.
v.  NLRB.,  593  F.2d  788,  795 (7th Cir. 1979); Breeden v.
Weinberger,   493   F.2d   1002,  1010   (4th   Cir.   1974)
(administrative law judge has  unique  advantage  in  making
credibility  determinations);  NLRB v. Brooks Cameras, Inc.,
691 F.2d 912, 915 (9th Cir. 1982)  (weight  is  given to the
administrative law judge's determinations of credibility for
obvious  reasons).   None  of the exceptions to the  general
rule on review of credibility resolutions presented in those
cases apply here.  The judge's determinations were not self-
contradictory (Ona Corp., 729  F.2d  at 719), were not based
on irrational criteria (Breeden, 493 F.2d  at 1010), and did
not contradict the evidence (Medline, 593 F.2d  at 795; NLRB
v.  Huntington  Hospital, Inc., 550 F.2d 921, 924 (4th  Cir.
1977)).  Unlike many  of  the  Secretary's  proffered cases,
see,  e.g.,  NLRB v. Interboro Contractors, Inc.,  388  F.2d
495,  501 (2d Cir.  1967)  (credibility  determinations  not
supported  by  record);  Victor  Products Corp. v. NLRB, 208
F.2d  834, 839 (D.C. Cir. 1953) (sense  of  record  did  not
support finding), the judge's credibility determinations are
supported by the record.



     We have also affirmed the judge's conclusion that
the statistical evidence did not establish that AWCs
resulted from intentional tampering or that, in
Keystone, a reduction in the mine's citation rate
resulted from MSHA's investigation of its dust sampling
program.  We have concluded that the judge did not err
in excluding evidence of criminal tampering from the
Common Issues trial and that its exclusion did not
preclude its consideration at the Keystone trial.

     As to Keystone, we have found that substantial 
evidence supports the judge's finding that changes in the
handling of sampling equipment occurred at Urling and
that those changes could have been factors in the
decrease in cited AWCs.  We have also concluded that
the judge did not err in according no weight to the
Secretary's evidence as to quartz samples and have
declined to overturn the judge's credibility
determinations as to ESD personnel.

     Accordingly, we affirm both the Common Issues Decision
and the Keystone Decision.  The 75 citations at issue in
Keystone are vacated.

     The judge's determination in the Common Issues Decision,
i.e., that the presence of an AWC on a filter does not,
in itself, prove deliberate conduct and a violation of
section 209(b),  applies to all citations in Master
Docket 91-1.  It serves as precedent on that issue in
other dust cases, not on the Master Docket, that have
been stayed pending the outcome of this case.

     Within 45 days after issuance of this decision, the 
Chief Administrative Law Judge shall issue an order in the
cases on stay, setting forth a schedule for submissions
from the parties as to disposition of those cases.


                                   ______________________________
                                   Joyce A. Doyle, Commissioner

                                   ______________________________
                                   Arlene Holen, Commissioner


     Commissioner Marks dissents and will file his opinion
later.