Respirable crystalline silica

In July, the Mine Safety and Health Administration published a proposed rule that would lower the permissible exposure limit for respirable crystalline silica. The potential standard is aimed at ensuring miners “have at least the same level of protections as workers in other industries.”

Exposure to respirable crystalline silica, however, is present in many other industries and work tasks. So, what is respirable crystalline silica, and why is it so dangerous? We spoke with experts from NIOSH, and others, to learn more about it and how to prevent on-the-job exposure: David Weissman, director of the Respiratory Health Division Barbara Alexander, engineer in the Division of Field Studies and Engineering Researchers from the NIOSH Mining Program (Spokane Mining Research Division and Pittsburgh Mining Research Division).

Silica facts

Silica is another name for the chemical compound silicon dioxide (SiO₂). It’s a mineral commonly found in the environment and exists in two main forms: crystalline and amorphous (non-crystalline silica). The most common type of crystalline silica is quartz, contained in stone, sand, concrete and mortar.

Respirable crystalline silica is 100 times smaller than a grain of sand, allowing it to get into the lungs when inhaled.

The small particles can get trapped in lung tissue, causing inflammation and scarring while inhibiting the lungs’ ability to take in oxygen, said Natalie Fox, CSP, a certified industrial hygienist.

That can lead to medical conditions such as black lung disease, chronic obstructive pulmonary disease and silicosis, defined by NIOSH as “an irreversible but preventable lung disease.” Breathing in crystalline silica also can lead to kidney failure and autoimmune diseases such as rheumatoid arthritis and progressive systemic sclerosis, the NIOSH experts added.

“Additionally, silicosis affects the immune system, which can increase the risk of lung infections such as tuberculosis,” Fox said.

Who’s at risk?

At-risk activities include cutting and crushing stone; abrasive sandblasting, tunneling, sanding or drilling into concrete walls; sawing brick or concrete; and manufacturing bricks, concrete blocks, ceramic products and stone countertops. Workers in hydraulic fracking and foundries also can be exposed.

Overall, around 2.3 million U.S. workers are at risk for exposure, according to OSHA. The agency revived its National Emphasis Program on respirable crystalline silica in 2020 in an effort to safeguard workers in the cut stone and stone products manufacturing industry.

It also launched a new Regional Emphasis Program last year – covering workers in Colorado, Montana, North and South Dakota, Utah, and Wyoming who handle engineered stone used to make household countertops. The move came after the release of a 2019 report in which Centers for Disease Control and Prevention researchers warned of “an emerging public health threat” after they identified an increase in cases of silicosis among workers handling engineered stone.