[Federal Register: May 20, 2008 (Volume 73, Number 98)]
[Rules and Regulations]
DEPARTMENT OF LABOR
Mine Safety and Health Administration
30 CFR Part 57
Diesel Particulate Matter Exposure of Underground Metal and
AGENCY: Mine Safety and Health Administration (MSHA), Labor.
ACTION: Notice of enforcement of DPM final limit; withdrawal of intent
to issue a proposed rule.
SUMMARY: This notice informs the public of MSHA's decision to implement
the diesel particulate matter (DPM) final permissible exposure limit
(PEL) of 160 micrograms of total carbon (TC) per cubic meter of air
(160TC µg/m3). MSHA has developed a practical
sampling strategy to account for interferences from non-diesel exhaust
sources when TC is used as a surrogate for measuring a miner's exposure
to DPM. The Agency will begin enforcement of the 160 TC limit under existing 30 CFR
57.5060(b)(3) on May 20, 2008. MSHA will post details of its sampling
strategy on the Agency's DPM Single Source Page prior to enforcement.
The sampling strategy is based on the best available scientific
evidence and will be specific to each mine.
DATES: Effective Date: May 20, 2008.
FOR FURTHER INFORMATION CONTACT: Patricia W. Silvey, Director, Office
of Standards, Regulations and Variances at firstname.lastname@example.org (E-
mail), 202-693-9440 (Voice), or 202-693-9441 (Fax).
MSHA measures a miner's personal exposure to DPM by analyzing the
sample for a DPM surrogate, TC. TC is the sum of elemental carbon (EC)
and organic carbon (OC). The 160 TC limit was promulgated in the 2001
final rule ``Diesel Particulate Matter Exposure of Underground Metal
and Nonmetal Miners'' which was published in the Federal Register on
January 19, 2001 (66 FR 5706) and amended on June 6, 2005 (70 FR 32868)
and May 18, 2006 (71 FR 28924).
When the Agency published the 2006 final rule, MSHA stated its
intent to issue a proposed rule to convert the 160 TC PEL to a
comparable EC PEL prior to the effective date of May 20, 2008, provided
sufficient scientific data were available to support a proposed rule.
MSHA is not issuing a proposed rule to uniformly convert the 160 TC
limit to a comparable EC limit. Instead, MSHA provides a protocol for
calculating a location specific adjustment for situations in which the
EC on the miner's personal sample is less than 160 micrograms per cubic
meter of air times the error factor (EF) for EC, and TC on the miner's
personal sample is greater than 160 micrograms per cubic meter of air
times the EF for TC. The decision not to issue a uniform conversion
factor is based on MSHA's assessment that there is still insufficient
evidence suggesting an appropriate conversion factor, and the latest
available scientific evidence regarding the relationship between TC and
EC at levels as low as 160 TC. MSHA will continue to monitor and
encourage research in this field.
The DPM rulemaking record established that a miner's exposure could
not be validated simply by adding the EC and OC of a TC sample due to
the potential for non-diesel exhaust sources to deposit on the OC part
of the sample and interfere with the MSHA sample analysis. These
interferences include environmental tobacco smoke, drill oil mist, and
ammonium nitrate/fuel oil (ANFO) vapors. When measuring EC,
interferences are not a factor in assuring the accuracy of the sample
Currently, MSHA determines a miner's exposure to the PEL of
350TC µg/m3 (350 TC) by conducting an EC analysis to
validate that the miner's overexposure to TC is not the result of
interferences. In each analysis, MSHA incorporates an error factor to
account for variability in sampling and analysis resulting from such
things as pump flow rate, filters, and the NIOSH Analytical Method
5040. If the TC measurement is above 350 TC micrograms times the error
factor for TC, MSHA looks at the EC measurement from the sample
obtained through the NIOSH Analytical Method 5040, and multiplies EC by
a conversion factor of 1.3 to produce a statistically valid estimate of
what the TC result is without interferences. MSHA issues a citation
when the EC measurement times the multiplier is above 350 micrograms
times the error factor for EC. The 1.3 multiplier that MSHA uses to
estimate TC (i.e., EC x 1.3 = estimated TC) is the median value of all
TC to EC ratios obtained from valid TC samples (i.e., without OC
interferences) collected by MSHA during the 31-Mine Study, and it is
consistent with NIOSH's determination that TC is 60-80% EC.
In the 2006 final rule (71 FR 28924, May 18, 2006), MSHA retained
the 2001 final limit of 160 TC but determined that it should be phased
in over a two-year period and stated that:
Consequently, on May 20, 2006, the initial final limit will be
308 micrograms of EC per cubic meter of air (308EC µg/m3), which is the same as the existing interim limit; on
January 20, 2007, the final limit will be reduced by 50 micrograms
and will be a TC limit of 350TC µg/m3; and on May
20, 2008, the final limit of 160TC µg/m3 will
become effective. Note that the 350TC µg/m3 final
limit and the 160TC µg/m3 final limit are
established as TC-based limits in this final rule. (Id. at 28934).
Also in the 2006 final rule, MSHA discussed its concerns regarding
the relationship between TC, EC and OC at lower concentrations and its
intent to conduct a separate rulemaking to determine the most
appropriate way to convert the 160 TC PEL to a comparable EC PEL by
Moreover, we intend to convert the final limits of
350TC µg/m3 and 160TC µg/m3 in a separate rulemaking by January 2007. As we said in the 2005 NPRM, if
we do not complete this rulemaking by that time, we will use the EC
equivalent as a check to validate that an overexposure to the
350TC µg/m3 final limit is not the result of
interferences. This enforcement policy, which is based on the Second
Partial Settlement Agreement and data in the rulemaking record,
would be the same that we used to implement the 400TC µg/m3 interim limit before we converted it to 308EC
µg/m3 in the June 2005 final rule. Whereas we have evidence
that we can obtain an accurate sample analysis of the final limit of
350TC µg/m3, there is no evidence in the rulemaking
record suggesting that the 1.3 conversion factor is appropriate for
substantially lower limits, such as the final limit of
160TC µg/m3. (Id. at 28976).
Although in the 2006 final rule MSHA acknowledged the limitations
of sampling a miner's exposure to TC and preferred EC rather than TC as
a DPM surrogate, the Agency did not conclude that TC could not be used
as an appropriate surrogate for measuring a miner's exposure to DPM. In
addition, the court decision in Kennecott Greens Creek Mining Company
v. Mine Safety and Health Administration, 476 F.3d 946, 956 (DC Cir.
2007), upholding the DPM standard, allows MSHA to enforce either the
160 TC PEL or a converted elemental carbon (EC) PEL. The court upheld
MSHA's selection of TC and EC as appropriate surrogates for DPM. See
Id. at 956.
Subsequent to the DPM court decision, MSHA decided to wait for
further scientific evidence regarding whether MSHA could reasonably
convert the 160 TC PEL using a fixed conversion factor such as the 1.3
conversion factor currently used. The latest available scientific
evidence is the study titled ``Relationship between Elemental Carbon,
Total Carbon, and Diesel Particulate Matter in Several Underground
Metal/Non-metal Mines'' which was published on February 1, 2007 (J. D.
Noll; A. D. Bugarski; L. D. Patts; S. E. Mischler; L. McWilliams,
Environ. Sci. & Technol., Vol. 41, No. 3: February 1, 2007, 710-716).
The authors concluded that the variability of the TC-to-EC ratio
increases below 230 TC and is high at 160 TC. Therefore, MSHA could not
identify a single, constant conversion factor for EC at any level below
In March 2007, MSHA hired an outside expert with experience in DPM
sampling methodology and analysis to advise the Agency in developing an
enforcement strategy for accurately determining a miner's exposure to
TC. The expert also reviewed the latest available data to attempt to
devise a scientific method for converting the 160 TC PEL to a
comparable EC PEL. The expert was unable to recommend such a method. As
an alternative to developing a conversion factor, the expert recommended sampling strategy options for the Agency's
consideration in enforcing the DPM final limit in a September 2007
report. MSHA was reviewing the expert's recommendations when it
published its December 10, 2007 Semi-Annual Regulatory Agenda in which
the Agency continued to state its intent to propose a rule to convert
the 160 TC limit. MSHA now has determined that insufficient data exist
to proceed with further rulemaking to convert the DPM final limit using
a single, constant conversion factor, such as the 1.3 factor currently
used for EC for all mines.
B. Notice of Enforcement of DPM Final Limit
MSHA has developed an enforcement strategy for implementation of
the DPM 160 TC PEL beginning May 20, 2008. MSHA will continue to
determine a miner's exposure to DPM based on a single personal sample
taken over the miner's full shift as specified in existing 30 CFR Sec.
57.5061 of the DPM standard. MSHA will use an EC analysis and
appropriate sampling methods to ensure that a citation for a miner's
overexposure to the 160 TC PEL is valid and not the result of
C. Reason for Withdrawal of Intent To Issue a Proposed Rule
MSHA is withdrawing its intent to issue a proposed rule to convert
the 160 TC PEL because it has determined that insufficient data exist
to support such a rule, and because it has determined that the
enforcement strategy it will begin to use on May 20, 2008, is an
accurate and effective way of enforcing the DPM standard. This
enforcement strategy will provide effective health protections for
miners at underground metal and nonmetal mines. In light of MSHA's
enforcement action, this notice does not reduce health protections for
underground metal and nonmetal miners.
Diesel Particulate Matter Exposure of Underground Metal and
Nonmetal Miners is withdrawn from the Regulatory Agenda. This document
does not preclude future agency action that MSHA may find to be
Dated: May 15, 2008.
John P. Pallasch,
Deputy Assistant Secretary for Mine Safety and Health.
[FR Doc. E8-11329 Filed 5-19-08; 8:45 am]
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