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Washington State Exposure Assessment Report Finds Some Workers Have Very High Exposure to Silica Dust

Posted on January 30, 2019

Worker exposure to respirable silica for some workers is very high, reaching 130 times the permissible exposure limit (PEL), according to a recent report from the Washington State’s Division of Occupational Safety and Health (DOSH). And that was before OSHA’s new silica dust rule cut the PEL in half for general industry and maritime and even more significantly for the construction industry.

In an initiative to better support compliance efforts, DOSH analyzed and summarized worker exposure assessment information collected by industrial hygiene compliance safety and health officers (CSHOs) between 2008 and 2016. While the data is specific to Washington State, it likely reflects what’s happening in other locations as well. As such, it can help companies that deal with silica dust understand the severity of the hazard and what employees are most at risk.

Here’s a summary of the respirable silica results:

Silica dust samples accounted for >5% total samples

Over the 9-year study period, CSHOs conducted 9941 industrial hygiene compliance inspections (across all industries), collecting a total of 4,394 exposure samples. These included 239 samples of silica dust:

  • 160 of crystalline quartz
  • 79 of crystalline cristobalite

Both of these forms of crystalline silica are classified as Group 1 carcinogens by the International Agency for Research on Cancer and as Suspected Human Carcinogens by the American Industrial Hygiene Association (AIHA).

Crystalline quartz ranked #1 for maximum severity of exposure

One sample of crystalline quartz was measured at 130 times the permissible exposure limit (PEL), which was the highest exposure level for any substance. This measurement was for an abrasive blaster.

Highest severity exposures to crystalline quartz by industry:

  • Construction, mining, and forestry machinery and equipment rental
  • Showcase, partition, shelving, and locker manufacturing
  • Lessors of residential buildings and dwellings

Highest severity exposures to crystalline quartz by job title:

  • Abrasive blaster
  • Countertop installer
  • Maintenance

The maximum severity for crystalline cristobalite was 4.4, meaning that at least one sample indicated exposure at 4.4 times the PEL. Because cristobalite didn’t make the top 10 for severity, the report authors didn’t break out the results by industry or job title.

Most silica dust samples indicated exposure above the PEL

The median severity, or the halfway point in the distribution, for both substances show that most silica exposures are too high. For quartz, the median severity was 1.6, meaning that half of the samples collected were equal to or exceeded 1.6 times the PEL. For cristobalite, it was 1.0, meaning that half of the samples were at or above the PEL.

There were 21 job titles across six industries where silica was measured at or above the PEL.

Industry Job Title
Real estate and rental and leasing
  • Abrasive blaster
  • Maintenance
  • Painter
  • Countertop installer
  • Stone fabricator
  • Foundry worker
  • Machine operator
  • Laborer
  • Mason
  • Spray painter
  • Technician
  • Stone fabricator
  • Mason
  • Laborer
  • Abrasive blaster
  • Tilesetter
  • Driver
Agriculture, forestry, fishing, and hunting
  • Agriculture worker
Administrative and support and waste management and remediation services
  • Laborer
  • Landscaper
Other services (except public administration)
  • Auto detailer

Tasks associated with the highest exposure severity

  • Crystalline quartz
    • Abrasive blasting of heavy equipment parts for paint prep
    • Cutting, grinding, and polishing countertops
    • Grinding moisture barrier and concrete floor surface
  • Crystalline cristobalite
    • Grinding dry stone using hand tools in enclosed room with exhaust units
    • Cutting and grinding dry granite using hand-held angle grinders
    • Fabricating stone countertops using hand-held angle grinders

Both quartz and cristobalite were classified as AIHA exposure category 5

This is the highest exposure category. It means that the substances are uncontrolled and that workers are exposed at very high concentrations. The recommended actions for substances in this category include immediate engineering controls or process shutdown.


These results should serve as a warning to companies in high-risk industries who have workers performing high-risk tasks. If you haven’t taken steps to become compliant with the new silica dust rule, your workers are likely being exposed at very high levels. This could lead not only to fines, but also to inspectors recommending that you halt your operations until the problem is resolved.

Our industrial vacuum equipment can help you get into compliance by protecting your workers from silica dust exposure. Contact us to learn more.