Sample copies of the injury/employment data collection forms also are available from the same address. Data for contractors were included in the tables for "All Coal" and "Metal/Nonmetal" but could not be derived for the remaining tables due to changes in contractor reporting requirements.

In 1983, the U.S. Congress limited the Mine Safety and Health Administration's (MSHA) enforcement activities over surface mining and milling of stone, clay, feldspar, colloidal phosphate, and sand and gravel, as well as over independent construction contractors working at areas of all surface mines apart from the mining activity. Thus, only partial year data are available for 1983.

Data are subject to differing policies toward general enforcement of the reporting regulations and also to slight changes in the definitions; and therefore may not be solely indicative of health and safety trends in the work environment. "Surface" work location includes associated shops and yards, and is further divided into: Strip/Open pit/Quarry (opencast), Auger (screw to conveyor - coal only), Culm bank/Refuse pile (reclaimed coal fines or coal waste), Dredge (floating excavation), Other - metal/nonmetal only (placer, sluicing, hydraulicking, washing, leaching, evaporation).

Data in this directory are excerpted from the MSHA Informational Report 1132: "Summary of Selected Injury Experience and Worktime for the Mining Industry in the United States, 1931-77". The publication contains definitions and limitations of the data in more detail than can be addressed in this text. Copies may be ordered from the address shown above.

The letters, "NA" (Not Available), appear in many of these tables because certain categories of data were not collected in the earlier years. For instance, the "nondisabling" (medical treatment) cases were not collected until 1972 for coal and 1973 for metal/nonmetal operations. Although the U.S. government began collecting mining statistics in 1911 through the U.S. Bureau of Mines, it was not until 1931 that the million employee-hours of exposure was used as a base to develop comparative frequency rates. This measure continued as the industry standard through 1977. "Severity rates" were also calculated by multiplying the total lost days by 1,000,000 and dividing the product by the total hours worked. In this directory, "lost days" are calculated from the total calendar days elapsed before the employee returned to work.

The term, "Mechanical cleaning plants", is the equivalent of "Mills" or "Preparation plants" used in the other directories. In this directory and the publication, certain estimates were made for injuries, manhours and production for years prior to 1973. This is the only publication that contains 1931-1977 mining data combined for all five canvasses: coal, metal, nonmetal, stone, and sand and gravel.