Mine Safety and Health Research Data Analysis Methods
Commodity Differences for Type of Employer (Mine Operators versus Independent Contractors)
The five commodity groups of coal (anthracite and bituminous), metal, nonmetallic minerals (nonmetal), stone, and sand and gravel are based on a slight modification of the Mine Safety and Health Administration’s (MSHA) six canvass classes, which are general product classifications based on the Standard Industrial Classification (SIC) [OMB 1987]. The only modification combines anthracite and bituminous into one coal category. Because independent contractors may work at multiple mining operations associated with a diversity of commodities, a canvass class is not designated for independent contractors. Instead, independent contractors report employment under two categories: (1) all coal locations and (2) all metal, nonmetal, stone, and sand and gravel locations. As a result of these reporting differences, fatality and injury rates for independent contractors can only be computed for coal and metal/nonmetal locations.
Work Location
Employment and injuries reported within the underground operational subunit are designated as underground work locations. All other operational subunits (surface areas at underground mines, strip/open pit operations, culm banks, auger mining, dredging operations, other surface mines, independent shops, coal preparation plants or mills) are combined under surface work locations with the exception of the office subunit, which is excluded from all analyses.
Selection Criteria for Fatalities
The number of fatalities used for the analyses varies slightly from the number reported in the publicly released MSHA accident/injury/illness database because of the following: (1) injuries to nonemployees have been excluded from analysis; and (2) injuries identified by MSHA after the files were closed out are not included.
Employment Size of Mining Operations
The annual average number of employees (excluding office employees) reported by mining operations was used to categorize these operations by employment size. Employee hours used to compute fatality rates within categories of employment size also excluded employee hours reported for these office workers.
Selection Criteria for Lost-Workday Cases
Lost-workday cases include only those cases that resulted in total or partial permanent disabilities, actual days away from work, and days of restricted work activity (i.e., MSHA degree of injury codes 2 through 5). The number of lost workdays was computed by adding the days away from work and days of restricted work activity, with one exception. MSHA assigns scheduled lost-workday charges for permanent partial disabilities as a means to determine the relative severity of certain injuries regardless of the days lost [MSHA 2002]. For injuries resulting in total or partial permanent disabilities, lost workdays were the statutory days charged to the incident whenever the statutory days exceeded the lost workdays reported or when lost workdays were unreported.
Calculation of Rates
Injury rates were computed using employment estimates derived from total hours worked (excluding office employees). Full-time equivalent workers were calculated by dividing total hours by 2,000 hours per worker. Nonfatal injury rates were calculated per 100 full-time equivalent workers, and fatal injury rates were calculated per 100,000 full-time equivalent workers, excluding office workers.
Injury/Illness and Mining Experience Data Inclusion Criteria
Counts within categories of total years of mining experience included all reported injuries and illnesses (i.e., MSHA degree of injury codes 1 through 7) for the years 1991 through 2000 (Figures 4–16 and 4–17). Excluded were cases for which total mining experience was not reported.
Determining the Type of Incident Associated with the Injury
MSHA’s accident/injury/illness classification scheme, which identifies the circumstances contributing most directly to the fatal or nonfatal injury, was used to establish the type of incident associated with a fatal or nonfatal injury [MSHA 2002]. The type of incident is identical to MSHA’s accident/injury/illness classification with two exceptions:
