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NIOSH Respiratory Diseases Research Program

Evidence Package for the National Academies' Review 2006-2007

NIOSH Programs > Respiratory Diseases > Evidence Package > 3. Interstitial Lung Diseases > 3.2 Silica-Induced Respiratory Diseases

3.2a) Reduction in Silicosis Deaths through Research and Policy Statements

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For more than a century, silicosis has been recognized as a plague on dust-exposed U.S. workers in mining and other industry sectors. A major U.S. Public Health Service effort in the 1930s did much to raise awareness and effect prevention. Somewhat forgotten, silicosis remained a major cause of occupational disability and death. Nevertheless, soon after its establishment under the Occupational Safety and Health Act of 1970, NIOSH initiated work on a Criteria Document, “Occupational Exposure to Crystalline Silica,” which was completed and disseminated in 1974. Many HHEs and other field studies conducted by RDRP scientists documented widespread and sometimes very egregious problems with excessive occupational exposures to silica and case-after-case of debilitating and fatal cases of silicosis, sometimes among workers only in their thirties. A former NIOSH Director publicly expressed outrage at what he referred to as the obscenity of continuing silicosis.39

By 1991, RDRP had established a system for national surveillance of silicosis (and other pneumoconioses, as well). The surveillance data revealed that, while annual silicosis deaths had been generally declining since 1968 (the earliest year for which data was available), the decline had ceased in the 1980s.40 This plateau, along with other inputs including the ongoing reminders from various case reports and workplace studies that severe silicosis was continuing to occur, motivated RDRP to undertake a major initiative on silicosis research and prevention.


RDRP scientists adopted a multi-disciplinary approach to reducing morbidity and mortality due to silica exposure. Laboratory and aerosol scientists developed methods to collect airborne dust in the workplace and to quantitate the levels of crystalline silica in samples. Industrial hygienists evaluated silica levels in various worksites. Biologists conducted in vitro and animal model studies to elucidate mechanisms and define dose-response. Physicians and epidemiologists documented the incidence of disease associated with workplace exposures. Risk assessors modeled dose-response to recommend exposure limits. Engineers developed improved dust controls.

In addition to research, RDRP fully engaged in an initiative to move others to action in silicosis prevention. Emphasis was placed on partnering with OSHA and MSHA, but additional partnering was also undertaken. An Interagency Working Group on Silicosis Prevention that included NIOSH, Bureau of Mines (later transferred into NIOSH), MSHA, OSHA, and the U.S. Geologic Survey was established in the mid-1990s.

Outputs and Transfers

RDRP scientists have produced hundreds of abstracts for presentations at scientific conferences and publications in the peer-reviewed literature (a total of 416, of which 249 were published in the last 10 years) in the area of silica and silica-induced lung disease, which have supported NIOSH policy. A listing of key publications is given at the end of chapter 3.2g and an extended listing is given in the appendix (A3-33).

Based on RDRP research, NIOSH has published 12 official policy documents on silica in the workplace. These documents include a 1974 Criteria Document on “Occupational Exposure to Crystalline Silica” which set a REL for crystalline silica in the workplace, documents for analytical and sampling methods for workplace airborne silica, and Current Intelligence Bulletins and Alerts documenting high-risk occupations (A3-1, A3-34, A3-35, A3-36). In 2002, NIOSH reassessed data on silicosis, conducted an updated risk assessment, and reaffirmed NIOSH REL of 0.05 mg/m3 for silica (lower than the OSHA PEL of 0.1mg/m3) in a major NIOSH Hazard Review document entitled “Health Effects of Occupational Exposure to Respirable Crystalline Silica(A3-37).

RDRP generated a Joint Campaign on Silicosis Prevention, formalized in 1996 as a partnership of the American Lung Association, MSHA, OSHA, and NIOSH.41 This national public education campaign, “If It's Silica, It's Not Just Dust” (A3-38), to prevent silicosis resulted in a National Conference to Eliminate Silicosis in 1997, which engaged many additional partners from industry, labor, and academia, and involved more than 600 participants form 40 states and five foreign countries.42 In 1998, as part of the joint campaign, NIOSH sponsored a workshop at which RDRP and external experts drafted a “Proposed National Strategy for the Prevention of Silicosis” (A3-39). This document promoted a high level of continued planning/coordination among NIOSH, OSHA, and MSHA. The campaign ultimately produced a multitude of widely disseminated educational materials on silica and silicosis prevention from each of the major partnering agencies separately and jointly. Various educational booklets, pocket cards, Fact Sheets, hardhat stickers, and videos were produced to raise awareness among workers and employers. RDRP and its partners conducted a massive outreach/education program to alert workers of the health risks associated with exposure to silica. Examples include the brochure “Silicosis-Learn the Facts” that includes a Spanish translation “Silicosis No Más!” that serves as an outreach effort to Hispanic construction workers (A3-40, A3-41). A newspaper release on silicosis prevention generated more than 600 newspaper articles in 30 states with an estimated readership of 37 million. Coordinated distribution of radio spots on silicosis prevention were carried on nearly 600 radio stations in 50 states with a potential audience of 100 million listeners.

RDRP-developed engineering controls and other recommendations to reduce occupational silica exposures that have been disseminated in the form of technical reports. More than 80 of these publications relate to dust monitoring and control in mining (e.g. a canopy air curtain system to lower exposure to roofbolters in underground mines, improvements to the Rotoclone dust collector on drills used by highwall drill operators at surface mines, and cab-enclosure/filtration systems).43 Additional technical reports, many in the form of Hazard Controls and Hazard IDs, cover control of silica exposures in industry sectors other than mining (e.g. foundries, masonry, and blast-hole drilling in construction).44

Gehl is a leading U.S. manufacturing company that produces agricultural and construction equipment ( [External link]). In their operator manual for a skid steer loader they warn of silica hazards by citing a NIOSH Silica Hazard Review (NIOSH numbered document 2002-129) that was prepared by RDRP staff (A3-41s).

Intermediate Outcomes

As a result of the RDRP initiated joint campaign on silicosis prevention, OSHA went on to develop a Special Emphasis Program to reduce occupational exposures to silica and eliminate the incidence of silicosis.45

MSHA likewise undertook enhanced efforts to reduce occupational exposures to silica and eliminate the incidence of silicosis. Motivated by RDRP research over the previous decade, in 1994 MSHA established improved regulations for more effective enforcement of dust control on drilling rigs and then engaged in special industry-wide inspection “sweeps” of surface mines along with MSHA-funded health examinations for surface coal miners.46,47  The latter led directly to the extension of MSHA’s Miners' Choice examination program for surveillance of coal miners (October 1999 through September 2002) to include surface coal miners (at particular risk for silicosis associated with drilling of overburden rock) in addition to underground coal miners.48

An RDRP-authored WHO report49 represented a fundamental step in the launching of an ongoing ILO/WHO International Programme on the Global Elimination of Silicosis in 1995, which aims at the global reduction and eventual elimination of silicosis worldwide.50  

Progress Towards End Outcomes

In the past 15 years, significant gains in fighting silicosis through exposure reductions have been realized across the mining industry, (shown above in a Table 8 from NIOSH Mining Program Briefing Documents prepared from MSHA data for a 2006 NA review): annual silicosis deaths in the U.S. declined 83 percent from 1968 to 2003, and the total number of silicosis deaths for 1999-2003 (the most recent five-year period for which data is available) is only 52 percent of the corresponding number for the five-year period from 1985-1989.51

What’s Ahead

RDRP staff will provide expert comments in 2006 and 2007 on the anticipated new OSHA standard on silica before its public release (Schuman letter A3-42). Silicosis surveillance will continue and findings will be presented in the “WoRLD Surveillance Report” series (due to be updated in 2007) and its associated Web-based format (A3-43). Work in progress to develop standards for use of digital radiographs in classification of chest films for pneumoconiosis as described in the section on CWP will also be relevant to silicosis. Work is also in progress to evaluated utility of lung sound analysis in lung diseases, also potentially relevant to silicosis. Development of a biomarker for early development of the silicosis disease process will be accomplished through research collaboration with South Africa’s National Center of Occupational Health, on “A Biomarker Study for Silicosis in Gold Miners” (Murray letter A3-44).

39. NIOSH Update [1992]. NIOSH Issues a Nationwide Alert on Silicosis. November 18, 1992 [].

40. NIOSH [1991]. Work-Related Lung Disease Surveillance Report. Cincinnati, OH: U.S. Department of Health and Human Services, Public Health Service, Centers for Disease Control and Prevention, National Institute for Occupational Safety and Health, DHHS Publication No. 91-113.

41. U.S. Department of Labor [1996]. Labor secretary calls for an end to silicosis. Press Release, October 31, 1996. [].

42. National Conference to Eliminate Silicosis [1997]. March 25-27, 1997, Washington D.C. [].

43. NIOSH [2006]. Dust Monitoring and Control Downloadable Mining Publications Web site. [].

44. NIOSH [2006]. NIOSH Hazard Controls and Hazard IDs Web site [].

49. Wagner GR [1996]. Screening and surveillance of workers exposed to mineral dusts. Geneva, World Health Organization, ISBN 92-4-154498-8.

50. Fedotov I [2005].  The ILO/WHO International Programme on the Global Elimination of Silicosis (GPES).  Presentation at IOHA International Scientific Conference.

51. NIOSH [2006]. National Occupational Respiratory Mortality System (NORMS).  U.S. Department of Health and Human Services, Public Health Service, Centers for Disease Control, National Institute for Occupational Safety and Health, Division of Respiratory Disease Studies, Surveillance Branch. []. Date accessed, August 30, 2006.

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