Silicosis Mortality Trends and New Exposures to Respirable Crystalline Silica — United States, 2001–2010

Ki Moon Bang, PhD; Jacek M. Mazurek, MD; John M. Wood, MS; Gretchen E. White, MPH; Scott A. Hendricks, MS; Ainsley Weston, PhD

Disclosures

Morbidity and Mortality Weekly Report. 2015;64(5):117-120. 

In This Article

Discussion

A statistically significant decline in silicosis death rates was observed during 2001–2010. However, silicosis deaths still occurred among persons aged 15–44 years. Of 28 decedents aged 15–44 years, the youngest was aged 19 years. This would be consistent with the decedent developing acute silicosis after an extremely high exposure to respirable crystalline silica. Such findings indicate the importance of educating at-risk workers and their employers regarding the dangers of exposure to respirable crystalline silica in the workplace. The disparities by sex and by race reflect differences in the composition of the workforces in the industries and occupations placing workers at risk for exposure to crystalline silica dust.**

Approximately 2 million U.S. workers remain potentially exposed to respirable crystalline silica.[5] Occupational exposures to dust containing crystalline silica have long been known to occur in mining, quarrying, sandblasting, pottery making, rock drilling, road construction, stone masonry, and tunneling operations.[1,5] Despite enforceable limits†† on worker exposure to respirable crystalline silica, substantial overexposures continue to occur in the United States.[3] Moreover, new job tasks that place workers at risk for silicosis continue to emerge.

In 2004, occupational disease surveillance programs in Michigan, New Jersey, Massachusetts, New York, and Ohio reported nine confirmed cases of silicosis among technicians who performed sandblasting in dental laboratories;[6] in 2013, there were approximately 37,000 dental laboratory technicians in the United States.§§ In a 2012 report from Israel, a 2014 report from Spain, and a 2015 report from the United States, silicosis has been documented among workers exposed to respirable crystalline silica dust during the fabrication and installation of quartz-containing engineered stone products used primarily for kitchen and bathroom countertops.[4,7,8] A 2013 report documented high levels of exposure to respirable crystalline silica during hydraulic fracturing of gas and oil wells.[3] Moreover, a 2010 study reported an excess risk for silicosis in coal miners that was associated with silica as a component of coal mine dust formed during drilling, crushing, and loading of mine material.[9] In 2013, there were approximately 204,000 oil and gas extraction industry workers and approximately 80,000 coal mining industry workers in the United States.¶¶ Finally, although not in the United States, silicosis cases have been reported in other occupational settings, including among denim sandblasters.[10]

In 1999, the Council of State and Territorial Epidemiologists made silicosis a nationally notifiable condition.*** In addition, because current permissible exposure limits for respirable crystalline silica do not adequately protect workers, the Occupational Safety and Health Administration (OSHA) has proposed amending the current standards. One of the proposed changes is a lower permissible exposure limit.[5]

The findings in this report are subject to at least three limitations. First, silicosis deaths were not validated by medical records or follow-up with health care providers, thus findings might be subject to misclassification. Second, no individual work history is reported on death certificates. Therefore, it was not possible to identify those industries and occupations where the decedents' exposures to crystalline silica occurred. Finally, inhalation of respirable crystalline silica can cause diseases other than silicosis, such as lung cancer and chronic obstructive pulmonary disease,[1,5] which are not considered in this analysis.

Effective silicosis prevention strategies for employers recommended by OSHA††† and CDC's National Institute for Occupational Safety and Health§§§ are available. Comprehensive silicosis prevention programs include substituting less hazardous noncrystalline silica alternatives when possible, implementing engineering controls (e.g., blasting cabinets, local exhaust ventilation, not using compressed air for cleaning surfaces, using water sprays to control airborne dust, and using surface wetting to prevent dust from becoming airborne when cutting, drilling, grinding, etc.), administrative and work practice controls, personal respiratory protective equipment, medical monitoring of exposed workers, and worker training. Because of the serious health and socioeconomic consequences of silicosis, new operations and tasks placing workers at risk for silicosis, and the continuing occurrence of silicosis deaths among young workers, effective primary prevention through elimination of exposure to respirable crystalline silica is critical. At the same time, because of the sometimes long latency of silicosis, with cases diagnosed years after exposure and often in retirement, ongoing silicosis surveillance is needed to track its prevalence in the United States.

**Additional information available at https://www.bls.gov/cps/wlf-databook-2013.pdf.
††Additional information available in "Lowering Miners' Exposure to Respirable Coal Mine Dust, Including Continuous Personal Dust Monitors; Final Rule" (https://www.gpo.gov/fdsys/pkg/FR-2014-05-01/pdf/2014-09084.pdf) and "Criteria for a Recommended Standard: Occupational Exposure to Respirable Coal Mine Dust" (https://www.cdc.gov/niosh/docs/95-106/pdfs/95-106.pdf).
§§Additional information available at https://www.bls.gov/oes/current/oes_nat.htm.
¶¶Additional information available at https://www.bls.gov/opub/ee/2014/ces/table1a_201401.pdf.
***Available at https://c.ymcdn.com/sites/www.cste.org/resource/resmgr/ps/09-oh-01.pdf.
†††Available at https://www.osha.gov/pls/oshaweb/owadisp.show_document?p_table=standards&p_id=12716.
§§§Available at https://www.cdc.gov/niosh/topics/silica.

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