Commonly asked questions about silica, silica exposure, and the OSHA Silica Standard.
Where is silica found?
The Center for Disease Control (CDC) considers crystalline silica dust a carcinogen. The Occupational Safety and Health Administration (OSHA) recommends that it be treated as hazardous in an airborne state. Respirable silica particles are very small. Once they enter the deepest part of the lungs, they cannot be removed or expelled. Exposure over time can cause lung disease.
How is crystalline silica created?
Materials at risk for silica exposure include rock, concrete, brick, block and mortar. Any high-energy operation such as cutting, sawing, grinding, polishing, drilling and crushing stone can create respirable crystalline silica.
Additional risky activities for generating inhalable silica include:
- sweeping dirty areas
- using compressed air to clean
- driving or operating heavy equipment on dirt roads
- demolishing structures
- abrasive blasting with sand
- transferring dry materials that include silica
What are the sources of silica?
There are three types of silica: quartz, cristobalite and tridymite. Materials like sand, concrete, brick, concrete block, stone, sheet rock, aggregate, tile, grout and mortar all contain crystalline silica as an element.
Measuring Silica with Gravimetric Sampling and Real-Time Monitoring
How is gravimetric sampling done for respirable crystalline silica?
A sample pump collect an air sample by pulling air through a cyclone. Different cyclones allow differently-sized particles to pass through. The pump captures larger particles while smaller particles collect on a filter. Collected particles then go to a lab for analysis.
Gravimetric samples are required at the beginning of an assessment for a calibration factor and at the end to prove OSHA compliance.
Why not just do gravimetric sampling all the time?
The collection, processing, and lab analysis of a gravimetric sample can take weeks. The OSHA standard requires silica dust sampling a specific time intervals and frequencies for alternative compliance methods. If engineering controls change, the sampling process must begin again until workplace exposure is within compliance to the standard. Repeated testing and re-testing makes gravimetric sampling time consuming and expensive, especially for large organizations.
Real-time monitoring is a faster and less costly method to adjust controls. By verifying the effectiveness of those adjustments before final gravimetric sampling, it is possible to avoid expensive surprises.
Why perform real-time monitoring if gravimetric sampling is required as reference data by OSHA?
Real-time, direct reading instruments provide a shorter path to compliance. Making assessments and adjustments to engineering controls before collecting final gravimetric samples is more efficient.
Real-time instruments provide immediate information about exposure levels. Instant alerts warn your staff of unsafe conditions as they happen. The detailed data produced by real-time instruments enables accurate reporting and instant validation of changes to engineering controls. With real-time results, employers move through the assessment process faster and at a lower cost, while protecting workers and reducing risk.
OSHA requires gravimetric sampling to prove compliance to the silica standard. Using real-time monitoring ensures confidence in the final lab analysis of a gravimetric sample. It also demonstrates successful management of and compliance with silica exposure rules.
For more questions and details on silica dust exposure, read Silica Exposure Measurement in Real-Time for Construction
Silica Exposure Measurement Instruments
Do TSI instruments measure total respirable silica?
Not directly. TSI instruments use light scattering photometric technology to measure the amount of total respirable dust in the air. When properly calibrated, the instrument can determine the amount of crystalline silica in the aerosol sample. The photometric calibration factor adjusts the photometric reading of the instrument to the known silica content in the dust. This allows the instrument to display a representative level of respirable silica exposure (to a worker) that is very close to what one would expect from a gravimetric sample.
Where should we locate real-time instruments on the job site?
Your process, materials, and site are some of the variables that go into these decisions. In some cases, a professional IH consultant may be necessary. An IH consultant can help develop a written exposure control plan that identifies the tasks and locations for monitoring.
Silica OSHA Compliance
How does OSHA define a competent person to handle a silica exposure program?
OSHA defines a competent person as someone who can identify existing and foreseeable respirable crystalline silica hazards. This person has the authority, knowledge and ability to promptly minimize or eliminate silica hazard. He or she will implement the written exposure control plan to the employer's specifications. The competent person is responsible for frequently and regularly inspecting job sites, materials and equipment.
Can an employer have more than one competent person on staff?
Yes. The standard does not outline specific training criteria. Employers can designate any employee to be a competent person if the employee is qualified. Qualifications may change depending on the required tasks and equipment. It is a common best practice to assign a competent person to every shift, at every job site. The final number of competent persons depends on the company and/or project size.
What is the best way to begin a sampling program?
Your two most important tools are baseline references and knowledge of industry standards and regulations. The OSHA silica standard includes the requirement and guidance for developing your written exposure control plan.
A comprehensive written exposure control plan describes potential workplace exposure risks and ways to reduce exposure. These methods include engineering controls, housekeeping, work practices, and/or restricting access to high exposure areas. OSHA requires that the written plan includes:
- all tasks that employees perform that could result in exposure to respirable crystalline silica dust
- all factors that affect exposure, including materials and environment where the task is being performed
Real-time instruments can quickly identify where respirable dust exposure is the highest and where the possible sources of silica are located.
In many instances, a company will choose to hire an IH consultant to develop a written exposure control plan.
Where can I find qualified consultants and accredited analytical laboratories to help with silica exposure monitoring?
The America Industrial Hygiene Association (AIHA) provides links to industry consultants on their website (www.aiha.org). AIHA-LAP, or AIHA Laboratory Accreditation Programs, LLC (www.aihaaccreditedlabs.org) publishes a directory of accredited laboratories.
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