Handling silica dust poses many risks

Photo: EleSi/ Creatas Video+ / iStock / Getty Images Plus via Getty Images.

Follow these standards and best practices for inspecting and assessing suspect silica dust     

By Jon A. Barrett and Onell Gonzalez, PhD, CIEC, LEED AP OM

What are Crystalline Silica Dust, Amorphous Silica, and Quartz?
    Crystalline Silica is one of the most common minerals on earth and a major ingredient in glass and ceramic glazes. Silica is also used in the manufacture of building materials, in foundry castings, and for sandblasting, and respirable (breathable) crystalline silica particles are produced during quarrying and mining.
    Amorphous Silica can be considered Diatomaceous earth, Diatomaceous silica, Diatomite, Precipitated amorphous silica, Silica gel, and Silicon dioxide (amorphous).
    Quartz is a form of silica, it is a possible cause for concern in various workplaces.

Sources of Silica Dust
    When operating, managing, and inspecting buildings and facilities, it is important for OSH and CIH professionals, to be aware of the various sources of Silica Dust. The following information identifies several potential sources of suspect Silica Dust.
    Aggregate materials like sand, stone, concrete, and mortar contain crystalline silica. It is also used to make glass, pottery, ceramics, bricks, and artificial stone.

How is Silica Dust produced?
    Open Pit Mining and Quarries, for aggregate materials and Quartz, produce dust deposits, dust air suspensions, and dust accumulations. In the manufactured stone industry, workers may also be exposed to silica dust when opening bags of ground quartz, moving or mixing bulk raw materials, cleaning and scraping mixers, or cleaning dust collector bag houses.
    Chipping workers had the highest exposure levels and were investigated during demolition, crushing, and chipping at several Massachusetts construction sites.
    Factories like quartz crushing facilities (silica flour milling), agate, ceramic, slate pencil, glass, stone quarries, and mines, produce Silica Dust.
    Construction workers who sand drywall joint compounds are often exposed to high concentrations of dust and, in some cases, respirable silica. Drywall joint compounds are made from many ingredients (i.e., talc, calcite, mica, gypsum, silica).
    Cutting, Drilling, Scraping, Rasping, Sanding, Polishing, and Fitting, Natural Stone, Manufactured Stone, Plaster, Plaster of Paris, Drywall boards, Engineered Stone, Gypsum Boards, SheetRock, Cement boards, Fiber Cement Boards, and Tiles, also produce Silica Dust.
    Stone Countertop Fabrication and Stone industry workers in shops and on job sites throughout the United States saw, grind, polish, and drill slabs of natural (mostly granite) and manufactured (man-made, engineered, or cultured) stone as part of manufacturing, finishing, and installing countertops. Workers operating powered hand tools, such as saws, grinders, and high-speed polishers, have some of the highest silica dust exposures in the countertop manufacturing, finishing, and installation industries. These exposures come from dry cutting, grinding, edging, and contouring stone, and may occur in shop environments as well as on job sites where finishing work is completed.
    Excessive exposures were found in sandblasting, dismantling facade elements, diamond drilling, drilling hollow-core slabs, drilling with a drilling rig, priming of explosives, tiling, use of cabinless earthmoving machines, and jackhammering. Installing foundation and frame stages of new construction, yard work, interior work phases in the renovation and novel construction of apartment buildings, facade work, demolition of buildings, infrastructure construction, concrete waste, and stone crushing (pulverization)
    Particulate Matter, (PM), generating dust emissions from coal mining operations and construction poses a specific and significant threat to miners’ and construction workers’ health. PM generated in these work environments contains organic and inorganic constituents, including silica, iron, metalloids, heavy metals, PAHs, and other contaminants.

OHSA Standard for Inspecting Suspect Silica Dust
    OSHA Standard 1926.1153: Respirable Crystalline Silica, regulates all airborne occupational exposures to respirable crystalline silica in construction work, except where employee exposure will remain below 25 micrograms per cubic meter of air (25 μg/m3) as an 8-hour time-weighted average (TWA) under any foreseeable conditions. As opposed to airborne exposure, at present, a single direct relationship between silica dust sampled from a surface and potential human exposure does not exist. In addition, there is not even a protocol for surface sampling to reliably assess silica dust contamination. Even so, it is evident that contaminants’ exposed presence in occupied locations represents an obvious danger with unknown risks until these become properly assessed. Thus, important challenges exist when a need to evaluate silica dust migration and contamination presence over surface deposits.
    When Silica Dust contamination is suspected to be present over surfaces in occupiable, non-industrial locations, or non-production areas of related industries, or ongoing migration of such fiber may pose indirect, non-occupational exposures, OSH and IH professionals and facility managers may benefit from having a safety inspection procedure in place to address both air and surfaces as well. Other inspection procedures associated with these conditions beyond the scope of this article, may include, Proper Personal Protective Equipment, (PPE), per O.S.H.A. and E.P.A. guidelines, as required. A suspect Silica Dust inspection should also include a Safety Plan for emergencies, possible Confined Space training, and making sure communicating devices are operating, with a backup device and plan. A plan of action, documentation, and a communication chain of command are critical for safety and awareness. Some proposed best practices to consider for surface silica dust inspections are discussed below.

Conducting a visual inspection and surface sampling, for silica dust in project areas
    Silica content is part of many building materials. Disturbance, impact, handling, and use of such materials may pose exposure risks directly to workers on site and secondary exposures from potential migration, deposition, and resuspension of such mineral fibers at other nearby locations. We can think of it in terms of, for example, the uncontrolled production of silica dust at a residential renovation project where concrete substrates are being impacted, and such silica dust is migrating to the adjacent residential unit where it gets settled down over miscellaneous horizontal surfaces. Then it becomes resuspended with typical occupants’ activities. Even though the presence of silica in settled dust is not regulated, once resuspended in the air, the dust may become a major source of silica exposure. The level of silica contamination can be used as an indicator of past exposure, and good/bad housekeeping, and potentially identify a source of dust contamination.
    The practicality of this proposed surface sampling is primarily to aid in establishing surface conditions at suspected areas regarding settled concentrations of quartz, a common form of silica, a major mineral component of cement, and thus a typical surrogate for assessing Portland cement dust contamination. In addition, a detailed ocular assessment may focus on documenting surface dust contamination signs as well as susceptible pathways potentially enabling contaminants’ migration from identifiable suspected sources. Due to the lack of a specific industry standard for the collection of Surface Samples for Silica Dust, a settled dust sampling could reference ASTM Standard E1728: Standard Practice for Collection of Settled Dust Samples Using Wipe Sampling Methods for Subsequent Lead Determination and ASTM Standard D6966: Standard Practice for Collection of Settled Dust Samples Using Wipe Sampling Methods for Subsequent Determination of Metals. In addition, references can also made to the NIOSH Manual of Analytical Methods (NMAM), 4th Edition; Silica, Crystalline, by XRD: METHOD 7500, and OSHA ID-142.
    Because there are no established regulatory and risk ranking levels for settled silica dust concentrations, the analysis results’ interpretation could be based on a semi-quantitative “presence” versus “non-detection” evaluation of the said contaminant over the representative surfaces assessed. At present, a single direct relationship between silica dust sampled from a surface and potential human exposure does not exist. Even so, it is evident that contaminants’ exposed presence in occupied locations represents an obvious danger with unknown risks until these become properly assessed.
    Even though membrane filters’ size poses important handling challenges during this proposed protocol, surface samples might be collected, to the extent possible, based on ASTM Method E1728 – 16, using 5um PVC membrane filters (no cassette) as quartz wipes and disposable templates measuring 10 cm by 10 cm. The cited method comprises the following steps:
    • A clean pair of gloves is used per sample.
    • A disposable template measuring 10 cm by 10 cm is placed over the identified area.
    •The wipe is removed from its package and inspected.
    • The wipe is moistened with methanol before sample collection.
    Positioning the hand open and flat with the fingers together the wipe is placed on the surface to be sampled; the selected surface area is wiped side to side, in an overlapping “S” or “Z” pattern while applying pressure to the fingertips; the surface is wiped until the entire selected surface area is covered.
    The wipe is folded in half with the collected dust side folded inward; the preceding wiping procedure is repeated within the selected sampling area using an up-and-down overlapping “S” or “Z” pattern.
    The wipe was folded in half again with the collected dust side folded inward, and the wiping procedure was repeated one more time, concentrating on collecting settled dust from all corners within the selected surface area.
    The wipe is folded again with the collected dust side folded inward and inserted into a sample container. The sample containers are resalable, rigid-walled, 50-mL minimum volume.
    The disposable gloves are disposed of after each sample.
    One (1) field blank sample is managed for quality control per the referenced method. An unexposed wipe is removed from their packaging and placed into sample containers.

Recommendations and best practices, for elimination of sources of silica dust
    Eliminating, decreasing, and limiting all sources of Cutting, Grinding…etc will help prevent Silica Dust. After inspecting for suspect Silica Dust projects and areas, an initial plan of action can be created and implemented. Several recommendations for decreasing sources of Silica Dust may include:
    Inspect all HVAC air conveyance units and ductwork for proper operation, calibration, any air leakage, and open penetrations
    Inspect all roofing, roof hatches, windows, exhaust fans, entrances, and exit doorways for proper sealing out of weather elements and open penetrations
    Inspect all PPE, work clothing, street clothing, shoes, bedding, curtains, containers, boxes, bags, Lighting, Wall Pictures, furniture, carpet, and floors, for Silica Dust accumulations and re-suspensions
    Dispose of, or HEPA vacuum and or wash clean, PPE, work clothing, street clothing, shoes, bedding, curtains, containers, boxes, and bags, Lighting, Wall Pictures, furniture, carpet, and floors, for Silica Dust accumulations and re-suspensions
    These best practices and recommendations for inspecting suspect Silica Dust will allow a property owner to have better knowledge, to inspect for suspect Silica Dust, in government, industrial, and commercial properties, and will help prevent secondary damages to their property. These best practices and recommendations will also allow safe planning and execution of future suspect Silica Dust inspections, in government, industrial, and commercial properties, for OSH professionals, Certified Industrial Hygienists, and Certified Remediators.