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The National Institute for Occupational Safety and Health (NIOSH)





Statistical Methodology
Keywords: Statistical analysis
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Commodity Differences for Type of Employer (Mine Operators vs. Independent Contractors)
Injury Data Inclusion Criteria
Calculation of Injury Rates
Determining the Type of Incident Associated with the Injury
MSHA Data Compared to Mining-related Data of Other Surveillance Systems

Data were obtained from the Mine Safety and Health Administration (MSHA) databases of reported employment and cases of accident/injury/illness for mine operators as well as independent contractors working on mine property as required under CFR 30 Part 50. According to CFR 30 Part 50, mine operators and independent contractors (whose employees perform certain types of work on mine property) are required to file a Mine Accident, Injury, and Illness Report (MSHA Form 7000-1) for reportable incidents within 10 working days after the accident or injury, or 10 working days following the illness diagnosis. The term “reportable injury” as defined by MSHA, includes all incidents that require medical treatment, or result in death, or loss of consciousness, or inability to perform all job duties on any workday after the injury, or temporary assignment or transfer to another job. Injuries involving “first-aid only” are not reportable. (First-aid only is defined as one-time treatment and subsequent observation of minor scratches, cuts, burns, splinters, and so forth, which do not ordinarily require medical care, even if it was provided by a physician or a registered professional person.) Information reported on MSHA Form 7000-1 includes demographics of the injured/ill worker such as age, sex, years of total mining experience, and years of experience at current mine, as well as information related to the mine location where the incident occurred (i.e., underground, surface, plant/mill), days away from work, days of restricted work activity, source of the injury, body parts injured, and a narrative description of the incident.
Also, under CFR 30 Part 50, mine operators and independent contractors (whose employees perform certain types of work on mine property) are required to file a Quarterly Mine Employment and Coal Production Report (MSHA Form 7000-2) within 15 days after the end of each calendar quarter. This information is reported in the address/employment files and includes the address and other contact information, production of clean coal tonnage, average number of persons employed during the reporting period, and the corresponding number of hours worked for each type of operation (designated by MSHA as operational subunits, which include underground operations, strip operations, plants or mills, etc.).


Commodity Differences for Type of Employer (Mine Operators vs. Independent Contractors)
The five commodities of coal (anthracite and bituminous), metal, nonmetal [1], stone, and sand & gravel (S&G) are based on a modification of the six “canvass classes” designated by MSHA for mine operators. The only modification combines anthracite coal and bituminous coal into coal. Because independent contractors may work at multiple mining operations associated with a diversity of commodities, a specific “canvass class” is not designated for independent contractors. Rather, independent contractors report employment under two aggregates: (1) all coal locations, and (2) all metal, nonmetal, stone, and sand & gravel locations. The latter aggregate is referred to by MSHA as metal/nonmetal locations and from here on will be designated as M/NM locations. (At times, this aggregate may also be referred to as noncoal locations.) As a result of these reporting differences, fatality and injury rates for independent contractors can only be computed for coal and M/NM locations. However, within these two aggregates, independent contractors report employment separately for each type of operation (designated by MSHA as operational subunits which include underground operations, strip operations, plants or mills, etc.). Consequently, both fatality and injury rates can be computed for both mine operators and independent contractors by type of operation.

Injury Data Inclusion Criteria
Unless stated otherwise, only cases that were coded as a degree of injury 1-5 were included. This excludes reportable incidents not associated with an injury (degree of injury 0), injuries requiring medical treatment not resulting in time lost from work (degree of injury 6), illnesses (degree of injury 7), and nonoccupational injuries and illnesses that are maintained in the MSHA files due to their occurrence on mine property. Of those cases coded degree of injury 1-5, office workers were excluded from analyses by excluding both employee hours and injuries reported for office locations (MSHA subunit code = 99). Office workers are excluded because they do not experience the same hazards and risks as mine workers. Data reported as “Nonfatal Lost-time Injuries” would include those cases coded degree of injury 2-5.
Selection criteria for fatalities
The number of occupational fatalities used for the analyses varies slightly from the number of fatalities reported in the publicly released MSHA accident/injury/illness databases as follows:
Fatalities attributed to independent contractors and associated with a contractor code of “ZZZ” were excluded from all analyses prior to the 2006 data. While these fatalities occurred on mine property, the victims were not employees of either an independent contractor or of a mine operator. Rather, these victims were on mine property for other reasons (e.g., visitors, customers) when they were fatally injured. Beginning with the 2006 data, each “ZZZ” fatality is examined to determine whether or not it should be excluded when analyzing the data. In addition, fatalities attributed to mine operators and independent contractors were excluded from all analyses when the victims were minors less than 17 years of age.
Number of fatalities determined by NIOSH not to be occupational and excluded from analysis by year: 1983 (n=1), 1985 (n=2), 1987 (n=2), 1988 (n=1), 1989 (n=1), 1991 (n=3), 1992 (n=5), 1993 (n=2), 1994 (n=3), 1995 (n=3), 1996 (n=1), 1998 (n=2), 2000 (n=1), 2002 (n=1), 2008 (n=1), 2009 (n=1), 2010 (n=1), 2012 (n=1), 2014 (n=1), 2015 (n=2), and 2016 (n=1).
Prior to the 2006 data, fatalities identified by MSHA after the files were closed out were not included. Beginning with the 2006 data, records for fatalities charged back after the data files were closed out and released to the public are added to the NIOSH version of the data files and are included in all published and presented data.
Number of fatalities identified after release of yearly closeout files that NIOSH included in analysis by year: 2006 (n=1), 2007 (n=1), 2009 (n=1), and 2010 (n=1).
Selection criteria for lost workday cases
Lost workday cases include only those cases which resulted in total or partial permanent disabilities, actual days away from work and/or days of restricted work activity (MSHA degree of injury codes 2 through 5). The number of lost workday cases was computed by taking the larger of either the statutory days OR the sum of the actual days lost plus the days of restricted work activity.

Calculation of Injury Rates
Injury rates were computed using employment estimates as derived from total hours worked. Full-time equivalent workers (FTE) were calculated by dividing total hours by 2,000 hours/worker. Nonfatal injury rates were constructed per 100 FTE, and fatal injury rates per 100,000 FTE. Of note, MSHA publishes both fatal and nonfatal injury rates based on 200,000 hours, which is equivalent to 100 FTE.

Determining the Type of Incident Associated with the Injury
MSHA's accident/injury/illness classification (Variable: AII) scheme was used to establish the type of incident associated with a fatality or nonfatal injury. The type of incident is a new variable named "Accinj" and is identical to MSHA's accident/injury/illness classification with the two following exceptions:
(1) Both fatal and nonfatal cases classified as a “Fall of face, rib, pillar, side, or highwall (from in place)” (AII=06) or as a “Fall of roof, back, or brow (from in place)” (AII=07) are combined and recoded into a new variable for Type of Incident with a value label of “Fall of ground (from in place).”
(2) Nonfatal injury cases classified under “Machinery” (AII=17) were reclassified as a “Fall of ground (from in place)” if the source of the injury (Variable: SOURCINJ) was “caving rock, ore, etc.” (SOURCINJ=90). This reclassification is consistent with how MSHA classifies similar incidents which resulted in a fatal injury. In 2005, MSHA addressed this coding inconsistency by applying the same classification to fatal and nonfatal injuries.  NOTE: Beginning in 2009, NIOSH statistical methodology includes surface as well as underground work locations when recoding machinery-related groundfalls.

MSHA Data Compared to Mining-related Data of Other Surveillance Systems
The mining industry data collected by MSHA may differ from data presented by other sources. This is due to the utilization of multiple industry classification systems. For example, the Bureau of Labor Statistics (BLS) used the Standard Industrial Classification (SIC) to categorize fatal injuries by industry until 1997. At that time, BLS began to utilize the North American Industry Classification System (NAICS). Both the SIC and NAICS classification schemes include oil and gas extraction in the mining industry. Note that MSHA data excludes oil and gas extraction. This is because OSHA regulates the oil and gas extraction industry, while MSHA is the designated regulatory authority for the other extraction industries.
In addition, the MSHA data include only incidents that occur on mine property. Therefore, an injury occurring during the course of work, but off mine property, is excluded from the MSHA data. An example of this MSHA exclusion would be a flyrock injury that occurred to a passing motorist on a road adjacent to mine property.
NOTE [1]: Depending on the context, the term "nonmetal" may refer to either (1) the class of nonmetallic minerals which includes clays, salt, phosphates, etc. or (2) nonmetallic minerals, stone, and sand &  gravel. In the current context, the first definition applies.

See Also
Data & Statistics
Page last reviewed: November 3, 2022
Page last updated: August 23, 2016
Content source: National Institute for Occupational Safety and Health, Mining Program
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