Methods: Exposure
Occupational Exposure Limits
Permissible Exposure Limits. The Occupational Safety and Health Administration (OSHA) and the Mine Safety and Health Administration (MSHA) each enforce regulations that establish the legal limits of workplace exposures to pneumoconiotic agents. These legal limits are described here as permissible exposure limits (PELs), although the regulations sometimes use the term "standard" or "exposure limit". Since 1979, OSHA and MSHA began reporting exposure data for pneumoconiotic agents.
The OSHA PELs for several pneumoconiotic agents were changed on March 1, 1989, but a legal challenge to the modified OSHA PELs was upheld, and the modified OSHA PELs reverted to the previous OSHA PELs on March 23, 1993. Some pneumoconiotic agents had a substance-specific OSHA PEL only from March 1, 1989 to March 22, 1993, including: aluminum as welding fumes, respirable dust of natural graphite, mica containing less than 1% crystalline silica, tin oxide, inorganic compounds of tin oxide, fused respirable silica dust, fibrous talc not containing tremolite, talc not containing asbestos, insoluble tungsten and compounds, and welding fumes (total particulate).
The following table presents the U.S. Code of Federal Regulations (CFRs) for legal limits of workplace exposures to pneumoconiotic agents by industry. Although OSHA has PELs for the maritime industry [29 CFR 1915], very few samples have been collected and are not reported here.
| OSHA | MSHA | ||
|---|---|---|---|
| General Industry | Construction Industry | Coal Mine Industry | Non-Coal Mine Industry |
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The MSHA metal/nonmetal mining PELs for pneumoconiotic agents were adopted from the 1973 edition of the American Conference of Governmental Industrial Hygienists (ACGIH®) publication entitled TLVs® Threshold Limit Values for Chemical Substances in Workroom Air Adopted by ACGIH for 1973. MSHA has not adopted PELs for the following pneumoconiotic agents: tin oxide dust/fume, inorganic dusts of tin, insoluble tungsten dusts/fumes, and welding fumes (total particulate). A MSHA PEL of 10 milligrams per cubic meter (mg/m3) is used for welding fumes (total particulate) through 1993, but since then it has been MSHA policy not to collect samples for welding fumes.
OSHA and MSHA do not have PELs specific for crystalline silica. The PELs apply to respirable dust containing crystalline silica, and the allowable exposure to respirable dust is reduced as the crystalline silica content increases. The formulas for allowable exposure vary with the agency and the industry. In metal/nonmetal mining, the MSHA PEL is the same as the OSHA PEL for respirable dust containing at least 1% quartz:
However, OSHA adopted a PEL of 0.1 mg/m3 for quartz that was enforced from March 1, 1989 through March 22, 1993.
Since December 1972, the MSHA PEL for respirable coal mine dust has been 2 mg/m3 Mining Research Establishment (MRE)1 unless the quartz content of the respirable coal mine dust at the mine exceeds 5%. When the quartz content of the respirable dust exceeds 5% in a coal mine sample, the MSHA PEL is reduced based on the following formula:
The OSHA PEL of 2 fibers per cubic centimeter (f/cc) for asbestos was reduced to 0.2 f/cc on July 21, 1986, and to 0.1 f/cc on October 11, 1994. Therefore, asbestos exposures are presented for 1979–1986, 1987–1994, and for 1995 onwards. The MSHA PEL for asbestos has not changed from 2 f/cc since it was adopted.
Recommended Exposure Limits. NIOSH develops and periodically revises recommended exposure limits (RELs) for hazardous substances or conditions in the workplace. The RELs are then published and transmitted to OSHA and MSHA for use in promulgating legal standards. The RELs for mineral dusts and chemical hazards, including pneumoconiotic agents, are published in the NIOSH Pocket Guide to Chemical Hazards. The REL for coal mine dust was adopted in September 1995, while RELs for the other pneumoconiotic agents presented were adopted before 1979. The REL for beryllium and compounds is based on cancer, rather than pneumoconiotic effects. NIOSH has no full-shift RELs for the following pneumoconiotic agents: aluminum oxide, emery, synthetic graphite, rouge, fused respirable silica dust, titanium dioxide, and welding fumes (total particulate).
Reporting of data. Exposure data is presented two ways: yearly and by Agency regions/districts with state detail. For the Agency regions/districts tables, the data is reported in four groupings: (1) Most recent five years, (2) 15 years prior to the most recent five years, (3) all remaining years prior to the 15 years, (4) all years.
Data Selection
MSHA Coal Mine Dust. Coal mine dust samples presented here met all of the following criteria:
- Samples were obtained in the U.S. or one of its territories;
- Samples were designated by MSHA as valid;
- Samples were coded as "designated occupation", "non-designated occupation", "designated work position", "non-designated work position" with valid occupation codes, or "designated area" other than "intake air"; and
- Samples were not an optional operator sample.
MSHA Coal Mine Quartz. Coal mine quartz data presented here were obtained from MSHA. The MSHA LIMS Database (often used by other investigators) only includes some specific samples sent from the Pittsburgh database for special analysis prompted by specific actions. Coal mine quartz samples presented here met all of the following criteria:
- Samples were obtained in the U.S. or one of its territories;
- Samples were designated by MSHA as valid;
- The sample duration was greater than zero;
- The quartz content was greater than or equal to zero;
- Samples were coded as "designated occupation", "non-designated occupation", "designated work position", "non-designated work position" with valid occupation codes, or "designated area" other than "intake air"; and
- Samples were not an optional operator sample.
MSHA Metal/Nonmetal Mine Data (MNMD). MNMD presented here met the following criteria:
- Samples were obtained in the U.S. or one of its territories; and
- Samples were not duplicated by another record, as determined by a comparison of all data fields.
NIOSH staff edited the MNMD provided by MSHA to remove duplicate records and records with internal inconsistencies, similarly to the methods previously used by the U.S. Bureau of Mines for updates prior to December 2005.
The respirable quartz exposure data includes the following MSHA respirable dust contaminant codes: 121 (listed nuisance dust, respirable fraction, less than 1% silica), 131 (unlisted dust, respirable fraction, less than 1% silica), 521 (respirable dust, quartz fraction not analyzed), and 523 (quartz, respirable crystalline silica fraction, greater than or equal to 1% quartz). Codes 121, 131, 521, and 523 are all respirable silica dust personal air samples. The specific code is assigned based on the laboratory's analytical result, matched to the definition of the code.
OSHA Integrated Management Information System (IMIS) and OSHA Information System (OIS). The IMIS and OIS samples presented here met all of the following criteria:
- The state code was one of the 50 U.S. states, Washington, DC, American Samoa, Guam, Puerto Rico, or the U.S. Virgin Islands;
- The sample type was "area" or "personal" (excludes: "bulk", "wipe", "screen", "blood", and "urine" samples);
- The exposure type was "time-weighted average" or "not detected" (excludes: "ceiling", "peak", "dose", "sound reading", "not analyzed", and "not valid"); and
- The indicated OSHA PEL and units were applicable to the contaminant indicated by the substance code for the recorded date of sampling.
MSHA Coal Mine Districts. Geographical areas of the U.S. are divided into MSHA coal mine districts. Over time, some of the MSHA districts changed and some mine assignments to those districts changed. When a county was assigned to more than one of the current MSHA coal mine districts, we determined the appropriate district assignment for this study. All samples for a given mine where assigned based on the geographical location (county) of the mine to the MSHA coal mine district as indicated in the table below.
| District | State Covered |
|---|---|
| 02 | Connecticut, Maine, Massachusetts, New Hampshire, New Jersey, New York, Pennsylvania, Rhode Island, Vermont |
| 03 | Delaware, Maryland, Ohio, Northern West Virginia (WV counties: Barbour, Berkeley, Brooke, Calhoun, Doddridge, Gilmer, Grant, Hampshire, Hancock, Hardy, Harrison, Jackson, Jefferson, Lewis, Marion, Marshall, Mason, Mineral, Monongalia, Morgan, Ohio, Pendleton, Pleasants, Preston, Randolph, Ritchie, Roane, Taylor, Tucker, Tyler, Upshur, Wetzel, Wirt, Wood) |
| 04 | Southeastern West Virginia (WV counties: Boone, Braxton, Clay, Fayette, Greenbrier, Kanawha, Monroe, Nicholas, Pocahontas, Putnam, Raleigh, Summers, Webster) |
| 05 | Eastern Kentucky (KY counties: Garrard, Greenup, Harlan, Harrison, Jackson, Jessamine, Johnson, Kenton, Knott, Knox, Laurel, Lawrence, Lee, Leslie, Letcher, Lewis, Madison, Magoffin, Martin, Mason, Menifee, Montgomery, Morgan, Nicholas, Owsley, Pendleton, Perry, Pike, Powell, Robertson, Rockcastle, Rowan, Whitley, Wolfe), Virginia |
| 07 | Alabama, Georgia, Florida, Central Kentucky (KY counties: Adair, Allen, Anderson, Barren, Boone, Boyle, Carroll, Casey, Clinton, Cumberland, Franklin, Gallatin, Grant, Green, Hart, Henry, Larue, Lincoln, Marion, McCreary, Mercer, Metcalfe, Monroe, Nelson, Owen, Pulaski, Russell, Scott, Shelby, Spencer, Taylor, Washington, Wayne, Woodford), Mississippi, North Carolina, Puerto Rico, South Carolina, Tennessee, Virgin Islands |
| 08 | Illinois, Indiana, Iowa, Michigan, Minnesota, Northern Missouri (MO counties: Adair, Andrew, Atchison, Audrain, Boone, Buchanan, Caldwell, Callaway, Carroll, Cass, Chariton, Clark, Clay, Clinton, Cooper, Daviess, Dekalb, Gentry, Grundy, Harrison, Holt, Howard, Jackson, Johnson, Knox, Lafayette, Lewis, Lincoln, Linn, Livingston, Macon, Marion, Mercer, Monroe, Montgomery, Nodaway, Pettis, Pike, Platte, Putnam, Ralls, Randolph, Ray, Saline, Schuyler, Scotland, Shelby, St. Charles, Sullivan, Warren, Worth), Wisconsin |
| 09 | Alaska, Arizona, Arkansas, Colorado, Kansas, Southern Missouri (MO counties: Barry, Barton, Bates, Benton, Bollinger, Butler, Camden, Cape Girardeau, Carter, Cedar, Christian, Cole, Crawford, Dade, Dallas, Dent, Douglas, Dunklin, Franklin, Gasconade, Greene, Henry, Hickory, Howell, Iron, Jasper, Jefferson, Laclede, Lawrence, Madison, Maries, McDonald, Miller, Mississippi, Moniteau, Morgan, New Madrid, Newton, Oregon, Osage, Ozark, Pemiscot, Perry, Phelps, Polk, Pulaski, Reynolds, Ripley, Scott, Shannon, St. Clair, St. Francois, St. Louis, St. Louis City, Ste. Genevieve, Stoddard, Stone, Taney, Texas, Vernon, Washington, Wayne, Webster, Wright), Montana, New Mexico, North Dakota, Oklahoma, Texas, Utah, Washington, Wyoming |
| 10 | Western Kentucky (KY counties: Ballard, Breckinridge, Bullitt, Butler, Caldwell, Calloway, Carlisle, Christian, Crittenden, Daviess, Edmonson, Fulton, Graves, Grayson, Hancock, Hardin, Henderson, Hickman, Hopkins, Jefferson, Livingston, Logan, Lyon, Marshall, McCracken, Mclean, Meade, Muhlenberg, Ohio, Oldham, Simpson, Todd, Trigg, Trimble, Union, Warren, Webster) |
| 12 | Southwestern West Virginia (WV counties: Cabell, Lincoln, Logan, McDowell, Mercer, Mingo, Wayne, Wyoming) |
Data Analysis
The reported number of samples for an agent was the total number of samples meeting the above criteria. The percent of samples exceeding the PEL for an agent category was calculated as the number of samples in that category with measured exposures exceeding the PEL enforced at the time the sample was collected, divided by the total number of samples for the agent, and finally multiplying by 100. The percent of samples exceeding the REL for an agent was calculated as the number of samples in that category with measured exposure exceeding the REL, divided by the total number of samples for the agent, and multiplying by 100.
Exposures are commonly log normally distributed, rather than normally distributed. For this reason geometric mean exposures are presented. To calculate a geometric mean exposure, samples less than the minimum quantifiable concentration (MQC) were assigned a value, either the (MQC/2) or (MQC/√2), depending on the distribution of samples that were quantifiable.2 The analytical methods used to calculate the MQC for selected pneumoconiotic agents are presented in the Selected Pneumoconiotic Agent Categories table below. The calculation assumes a sample duration of 7 hours.
The Occupational Safety and Health Administration (OSHA) and Mine Safety and Health Administration (MSHA) asbestos MQCs changed over time since 1979; therefore, appropriate MQCs were used for each time period.
The MSHA respirable coal mine quartz data are based on analyses of respirable coal mine dust samples. Not every respirable coal mine dust sample is analyzed for quartz. Therefore, the percent of respirable coal mine dust samples exceeding the MSHA PEL were calculated using the MSHA PEL of 2 mg/m3 MRE for respirable coal mine dust containing no more than 5% quartz.
For the MSHA respirable coal mine quartz data, the quartz concentration is used in calculating the geometric means. The quartz concentration is calculated using the formula:
The geometric means of exposure to quartz are reported for OSHA samples. However, the reported percentage exceeding the PEL compares only the respirable dust samples containing at least 1% quartz to the PEL for respirable dust containing at least 1% quartz. The exception is from March 1, 1989 through March 22, 1993, when OSHA enforced a PEL of 0.1 mg/m3 for respirable quartz. During this period the percentage greater than the PEL compares the exposure to quartz to 0.1 mg/m3.
| Pneumoconiotic Agent Category (as defined for eWoRLD) | MSHA Agents in Category | OSHA Agents in Category |
|---|---|---|
| Asbestos | Asbestos, fibers >5 µm in length (3MgO.2SiO2.2H2O) | Asbestos [actinolite, anthophyllite, chrysotile, crocidolite, tremolite] Talc, containing fibrous tremolite |
| Coal Mine Dust | Respirable coal mine dust | |
| Quartz | Respirable coal mine dust, >5% quartz Respirable dust, >1% quartz Nuisance dust (respirable fraction), <1% quartz** Unlisted particulate (respirable fraction), <1% quartz** Respirable dust (not analyzed or below detection limit)** |
Respirable crystalline silica (as quartz) Respirable crystalline silica/tripoli (as quartz) Respirable coal dust, >5% quartz |
| Other | Aluminum oxide dust (as Al2O3) Aluminum oxide fume (as Al2O3) Beryllium dusts (as Be) Beryllium fumes (as Be) Cobalt dusts (as Co) Cobalt fumes (as Co) Iron oxide fume (as Fe2O3) Titanium dioxide dust (as TiO2) Titanium dioxide fume (as TiO2) |
Aluminum (as Al), metal (total dust) Aluminum (as Al), welding fumes Antimony and compounds (as Sb) Beryllium and compounds (as Be) Cobalt, metal, fume and dust (as Co) Iron oxide fume (as Fe2O3) Tin, inorganic compounds, except oxide (as Sn) |
| MSHA - Mine Safety and Health Administration; OSHA - Occupational Safety and Health Administration | ||
| * No data reported for this agent in the most recent provisional data. | ||
| ** See Limitations. | ||
| NOTE: The following documents were reviewed to identify pneumoconiotic agents: ACGIH® Documentation of TLVs®, 6th edition; Occupational Respiratory Diseases Report, National Institute for Occupational Safety and Health (NIOSH) Pub. No. 86-102; the NIOSH Pocket Guide to Chemical Hazards, NIOSH Pub No. 2005-149; and NIOSH Criteria Documents. | ||
| Pneumoconiotic Agent Category (as defined for eWoRLD) | MSHA Agents in Category | MSHA Analytical Method |
|---|---|---|
| Asbestos | Asbestos, fibers >5 µm in length (3MgO.2SiO2.2H2O) | NIOSH 7400 |
| Coal Mine Dust | Respirable coal mine dust, <=5% quartz | NIOSH 7603/MSHA P7 |
| Quartz | Respirable coal mine dust, >5% quartz Respirable dust, >1% quartz Nuisance dust (respirable fraction), <1% quartz* Unlisted particulate (respirable fraction), <1% quartz* Respirable dust (not analyzed or below detection limit)* |
MSHA coal: MSHA P7/NIOSH 7300 MSHA metal/nonmetal: MSHA P2/NIOSH 7500 |
| Other | Aluminum oxide dust (as Al2O3) Aluminum oxide fume (as Al2O3) Beryllium dusts (as Be) Beryllium fumes (as Be) Cobalt dusts (as Co) Cobalt fumes (as Co) Iron oxide fume (as Fe2O3) Titanium dioxide dust (as TiO2) Titanium dioxide fume (as TiO2) Welding fumes (total dust) |
OSHA 121/125 |
| Cristobalite (respirable fraction) | MSHA P2/NIOSH 7500 | |
| Talc, nonfibrous, <1% quartz | NIOSH 0600 (gravimetric)/MSHA P8 (impinger) | |
| MSHA - Mine Safety and Health Administration; NIOSH - National Institute for Occupational Safety and Health; OSHA - Occupational Safety and Health Administration | ||
| * See Limitations. | ||
| Pneumoconiotic Agent Category (as defined for eWoRLD) | OSHA Agents in Category | OSHA Compliance Analytical Method (SLCTC) | OSHA Consultation Analytical Method (WOHL) |
|---|---|---|---|
| Asbestos | Asbestos [actinolite, anthophyllite, chrysotile, crocidolite, tremolite] Talc, containing fibrous tremolite |
ID-160 | WOHL method (based on NIOSH 7400 and OSHA ID-160) |
| Quartz | Respirable crystalline silica (as quartz) Respirable crystalline silica/tripoli (as quartz) Respirable coal dust, >5% quartz |
D-142 | WOHL method (based on NIOSH 7500 and OSHA ID-142) |
| Other | Antimony and compounds (as Sb) Beryllium and compounds (as Be) Cobalt, metal, fume and dust (as Co) Iron oxide fume (as Fe2O3) Tin, inorganic compounds, except oxide (as Sn) |
ID-125G | WW001.3.1 |
| Silica, respirable cristobalite | ID-142 | WOHL method (based on NIOSH 7500 and OSHA ID-142) | |
| Welding fumes (total dust) | SOP for nuisance dust | WW001.6.0 (5µm PVC filter) | |
| ID - Identification number of the OSHA sampling and analytical method NIOSH - National Institute for Occupational Safety and Health OSHA - Occupational Safety and Health Administration PVC - Polyvinyl chloride SLCTC - Salt Lake City Technical Center SOP - Standard operation procedure WOHL - Wisconsin Occupational Health Laboratory |
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REFERENCES:
1 The MRE designation refers to the Mining Research Establishment of the National Coal Board, London, England. MSHA's PELs for respirable coal mine dust and respirable coal (Return to text)
2 Hornung R, Reed L. Estimation of average concentration in the presence of nondetectable values. Appl Occup Environ Hyg 1990;5:46–51. (Return to text)