Occupational Health: Silica Exposure and Spirometry Requirements

The 2016 OSHA silica standard on respirable crystalline silica in the workplace reduced the permissible exposure limits (PEL) from 250 ug/m3 to 50ug/m3 over an 8-hour time-weighted average (TWA). The new rules went into effect on June 23, 2017 and enforcement began on September 23, 2017. Crystalline Silica Standard 29 CFR 1926.1153 applies to all exposures of respirable crystalline silica, except where exposure will stay below the OSHA action level of 25 ug/m3 over an 8-hour TWA.

How does silica damage the lungs?

Inhalation of respirable crystalline silica causes silicosis, a progressive fibrotic disease. In addition to silicosis, the exposures can increase the risk for chronic obstructive lung disease, tuberculosis, renal disease, autoimmune disease, and lung cancer. More recently diagnosed cases are related to construction and mining. Other emerging areas of exposure include manufacturing and installation of engineered stone countertops, gas hydraulic fracturing, and highway repair. In the United States, approximately 1-2% of workers are exposed to respirable silica (>2 million workers). Data collected in Michigan from 1988-2016 and published by Reilly et. al November 2018 found that 62% of sites inspected had silica exposures above the PEL and only 11% of the companies had screened their workers for silicosis. OSHA mandates medical surveillance of workers above the permissible limit. Affected workers should be referred to a pulmonologist or occupational medicine physician for further evaluation.

Why is spirometry required in the evaluation of silica exposure?

Spirometry is included in the medical surveillance requirements every three years. The spirometry may be normal or demonstrate a restrictive or obstructive pattern. Although the data from Michigan found normal results in only 24% of ever smokers and 28% of never smokers. It is important to note that an obstructive pattern may be the only pulmonary function abnormality even though silicosis is generally classified as a restrictive lung disease. The mandate also specifies that any individual administering the spirometry testing must complete a NIOSH approved spirometry course and maintain their certificate after completion of the course. This mandate applies regardless of professional training and background. All spirometry data should be collected based on the current published standards from the American Thoracic Society and European Respiratory Society.

Spirometry results should include the FVC, FEV1, and FEV1/FVC%. The NHANESIII (Hankinson 1999) reference normal should be used to interpret the data. The interpretation includes an assessment of test quality, review of both the volume-time and flow-volume loops in addition to the numeric results and their relation to the lower limit of normal (LLN).

Need NIOSH spirometry certification?

Reilly MJ, Timmer SJ, Rosenman, RD. The Burden of Silicosis in Michigan: 1988-2016. AnnalsATS Volume15, Number 12, December 2018.