[Federal Register Volume 73, Number 98 (Tuesday, May 20, 2008)]
[Rules and Regulations]
[Pages 29058-29060]
From the Federal Register Online via the Government Publishing Office [www.gpo.gov]
[FR Doc No: E8-11329]


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DEPARTMENT OF LABOR

Mine Safety and Health Administration

30 CFR Part 57

RIN 1219-AB55


Diesel Particulate Matter Exposure of Underground Metal and 
Nonmetal Miners

AGENCY: Mine Safety and Health Administration (MSHA), Labor.

ACTION: Notice of enforcement of DPM final limit; withdrawal of intent 
to issue a proposed rule.

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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 g/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

[[Page 29059]]

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 [email protected] (E-
mail), 202-693-9440 (Voice), or 202-693-9441 (Fax).

SUPPLEMENTARY INFORMATION:

A. Background

    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 
analysis.
    Currently, MSHA determines a miner's exposure to the PEL of 
350TC [mu]g/m \3\ (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 [mu]g/
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 [mu]g/m \3\; and on May 
20, 2008, the final limit of 160TC [mu]g/m \3\ will 
become effective. Note that the 350TC [mu]g/m \3\ final 
limit and the 160TC [mu]g/m \3\ 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 
stating:

    Moreover, we intend to convert the final limits of 
350TC [mu]g/m \3\ and 160TC [mu]g/m \3\ 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 [mu]g/m \3\ 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 
[mu]g/m \3\ interim limit before we converted it to 308EC 
[mu]g/m \3\ in the June 2005 final rule. Whereas we have evidence 
that we can obtain an accurate sample analysis of the final limit of 
350TC [mu]g/m \3\, 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 [mu]g/m \3\. (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 
230 TC.
    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

[[Page 29060]]

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 
interferences.

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 
appropriate.

    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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