In May 1991, the Secretary of Labor directed the Mine Safety and Health Administration (MSHA) to conduct a thorough review of the program to control respirable coal mine dust, and to develop recommendations on how the program could be improved. This request followed the announcement the previous month of widespread tampering with respirable dust samples taken by mine operators. The Coal Mine Respirable Dust Task Group (Task Group) was established by the Assistant Secretary for Mine Safety and Health to review the respirable coal mine dust program and to make recommendations for improving it. Because of the disclosure of widestread operator tampering in the dust program raised concerns about the validity of existing information on miner exposure, the Task Grup developed a short-term respirable dust Spot Inspection Program (SIP) and a Monitoring Inspection Program (MIP) to supplement existing data. The SIP was intended to measure dust concentrations to which miners were actually exposed, to determine the extent and effectiveness of dust controls actually in use, and to assess the miners' and operators' knowledge and proficiency with respect to the dust program. This information was obtained during unannounced visits by MSHA inspectors and consisted of dust sampling, measurement of production and dust controls, and interviews with mine personnel. The MIP was intended to evaluate the operators' sampling program through MSHA observation of the operators' sampling and dust control practices. It consisted of special visits made by inspectors to mines during their mandatory bi-monthly sampling cycles. At these visits, which consisted of one shift, the inspector acted as a passive observer of the operators' sampling process but recorded data on dust controls in place, similar to that obtained in the SIP. In both the SIP and MIP, MSHA inspectors also recorded dust control plan specifications for comparison with the dust controls in place during dust sampling. SIP inspections used in the present statistical analysis were completed on October 31, 1991 and involved 723 Mechanized Mining Units (MMU's) at 565 underground coal mines. Also included in this analysis are results from MIP inspections involving 717 MMU's at 545 underground coal mines, many of which were also included in the SIP. The MIP ended on December 30, 1991. The Statistical Team was one of six task teams established by the Task Group to assist in its comprehensive review of all aspects of the coal respirable dust program. The SIP and MIP data collection instruments, the selection criteria for MMU's to be included in the two programs, and the protocol for the mine visits were all designed by a team responsible for mine audits, prior to formation of the Statistical Team. The general mission of the Statistical Team was to utilize data obtained through the coal mine operators' respirable dust sampling program, the special SIP and MIP inspections, and MSHA's routine respirable dust inspections to evaluate the effectiveness of the operator and MSHA programs in monitoring respirable dust exposures and compliance. To this end, the Statistical Team met and communicated extensively with the Task Group and representatives of the other teams to determine issues and questions that should be addressed through statistical analysis of the available data. Three databases were created in support of the analysis: a SIP database, a MIP database, and, for comparison with prior dust concentrations and production levels obtained through normal operator sampling, an Operator Sample database (POPERAT). The SIP and MIP databases were developed by staff from MSHA's Denver Safety and Health Technology Center (DSHTC), and POPERAT was developed from the statistical team's specifications by staff from MSHA' s Information Systems Center (ISC). In order to provide an ample historical baseline against which SIP and MIP results can be compared, POPERAT contains underground coal dust sampling data, corresponding shift productions as provided by the operator, and quartz-adjusted dust standards from the last bimonthly sampling cycle of 1989 through the last bimonthly cycle of 1991. (Cycles are staggered for designated area samples, relative to designated occupation samples.) In particular, POPERAT contains results for samples taken during the MIP inspections. A fourth database utilized in the analysis is the existing MSHA Inspector Sample database (PINSPECT), provided directly by ISC. PINSPECT contains dust-sample data, corresponding shift productions as determined by the inspector, and quartz-adjusted dust standards for underground respirable coal dust samples taken by MSHA inspectors between October I, 1989 and July 31, 1992. In particular, PINSPECT includes results of all the SIP inspections. Finally, in order to take effects of mine size into account, DSHTC staff constructed an underground coal Mine Employment database (PMINE_EM) from quarterly employment data provided by operators under 30 CFR Part 50. The Statistical team utilized information in these five databases so as to respond to the following questions and issues: 1. What are the dust concentrations to which underground coal miners are exposed? With what frequency is the respirable dust standard exceeded? How frequently do exposures of other miners on the section exceed that of the designated high risk miner? Dust concentrations reported by the SIP, MIP, and PINSPECT samples are presented in Section I, Summary or Data, along with a general description and analysis of other data compiled for this study. Section I also contains statistics on non-compliance with the dust standard, based on both single and average SIP samples. Estimation of noncompliance rates and dust exposures when samples are not being collected is discussed in Parts C and D of Section IV, The Mine Environment. 2. How do ordinary operator samples and inspector dust samples compare with samples obtained through MSHA's special Spot Inspection and Monitoring Program' Section II, Comparison of Sampling Programs, makes these comparisons and estimates the differences. 3. How have Low Weight Gain (LWG) samples affected respirable dust exposure estimates and MSHA compliance determinations? Section III, Low Weight Gain Samples, addresses this question and also compares the frequency of L WG samples in the SIP, MIP, PINSPECT, and POPERA T data. 4. How do production rates and dust controls in effect during operator and inspector sampling compare with normal production rates and MSHA-approved dust control plan? How representative of normal operating conditions an dust concentrations obtained from operator or inspector samples? An attempt to address these issues is made in Section IV, The Mine Environment. 5. What level of knowledge, training, and proficiency is evident among miners and certified samplers interviewed as part of MSHA's special SIP? Results of the SIP interviews are presented in Section V, Knowledge, Training, and Proficiency. Section VI of the report summarizes Findings supported by the available data. Section VII, Appendices, includes Appendix A, a collection of descriptive statistical tabulations discussed in the narrative, and Appendix B, a detailed description of all five databases.