How to Effectively Sample Silica in the Workplace

13 Mar How to Effectively Sample Silica in the Workplace

Exposure to silica dust is a severe hazard in rock mining, whether it is a granite vein in coal, copper, diamond mine, or other rock cutting activities (i.e., granite cutting, stone dust). Because of hydraulic fracturing, silica can also be a problem in the oil and gas industry. Lung cancer, silicosis, and chronic pulmonary obstructive disease can result from exposure to silica dust, so it is essential to have adequate personal and area dust monitoring equipment to limit worker exposure.

Like the majority of laboratory sample analysis, a sample needs to be collected from the work environment, in particular, those locations that exhibit the biggest risk.  The Respirable Silica sample can include silica, coal dust, and diesel particulate, and is sent to an approved laboratory for analysis, usually using X-ray diffraction techniques (XRD).

What is Needed for Sample?

Related Article OSHA Publishes Silica FAQ

Sampling Methods

OSHA.gov

U.S. Government/Gobierno de los Estados Unidos [Public domain]

The website of the Occupational Safety and Health Administration (OSHA) describes the process for the collection of a sample to measure airborne silica as follows:

  • A trained specialist, such as a certified industrial hygiene specialist, will use a Dust Sampler to collect dust particles.
  • The wearable dust monitoring sampler is placed on an employee with a collection tube within 8 to 10 inches of the employees’ mouth. The tube usually runs through the employee’s clothing and attached to the back or in a safety vest pocket.
  • The employee will wear the device for 8 hours during the work shift to obtain a Total Weighted Average (TWA).
  • All employees can be equipped with the sampling device or can be fitted on only a few select employees closest to the silica source. A certified industrial hygienist can help determine what best way for sampling is.
  • At the end of the sampling period, the unit should be deactivated, and the filters removed for analysis by a certified laboratory.

Analytical Methods

The certified laboratory must have approved procedures specified in one of the following analytical methods:

Cheerful Woman in Laboratory

Cheerful Woman in Laboratory. Photo by FreePik

  • OSHA ID-142 (XRD)
  • NMAM 7500 (XRD)
  • NMAM 7602 (IR)
  • NMAM 7603 (IR)
  • MSHA P-2 (XRD)
  • MSHA P-7 (IR)

The laboratory must also be accredited to ANS/ISO/IEC Standard 17025:2005 and about Respirable Crystalline Silica (RCS) must also be compliant with ISO/IEC Standard 17011:2004 for implementation of quality assessment programs including their internal Quality Control (QC) program.

The laboratory must use the National Institute of Standards and Technology (NIST) traceable standards for instrument calibration and verification.

The sample is analyzed for polymorphs of crystalline silica, quartz, and cristobalite, which have been classified as Group 1 carcinogens by the International Agency for Research on Cancer (IARC).  The sampling methods eliminate the non-RCS components that might obscure the analysis.  Once the sample is determined to be “clean,” quantitative detection of the Permissible Exposure Limit (PEL) is based on sample air volume.

Silica is Dangerous for Worker’s Health

OSHA has determined that employees exposed to respirable crystalline silica at previous permissible limits of exposure face significant health risks and have amended its existing standards. OSHA’s Final Rule for the Protection of Workers from Exposure to Respirable Crystalline Silica offers two standards, one for Construction and one for the General Industry and Maritime Industry.

  • Reduces the PEL for respirable crystalline silica to 50 micrograms per cubic meter of air, which is averaged over an 8-hour shift.
    Worker sweeping at MountainWest PreCast wearing the DustCount 8899

    Worker sweeping at MountainWest PreCast wearing the DustCount 8899

  • Requires employers to:
    • Make use engineering of regulations (such as ventilation or water) to reduce worker exposure to PEL
    • Provide enough respirators whenever engineering controls cannot sufficiently limit exposure
    • Access to high exposure areas should be limited, and a respirator should be worn
    • A written exposure control plan should be developed that provides medical examinations for high exposure workers, and train workers on the risks of silica and how to limit exposure
    • Provides medical examinations to monitor and inform highly exposed workers about their lung health
  • Allows flexibility to help employers – particularly small companies – protect workers from exposure to silica

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