Crystalline silica is a mineral found in the earth’s crust, present in materials like sand, stone, concrete, mortar, and brick. When these materials are mechanically disturbed by processes such as cutting, grinding, drilling, or crushing, they release tiny particles known as respirable crystalline silica (RCS). These particles are invisible and capable of penetrating deep into the lungs when inhaled. Inhaling RCS dust is associated with several serious diseases, including silicosis, an incurable condition that scars the lungs, lung cancer, and chronic obstructive pulmonary disease (COPD). Reducing workplace exposure to this fine dust is the primary method for preventing these serious health consequences.
Controlling Dust at the Source
The most effective method for controlling silica exposure is to prevent the dust from becoming airborne, a process achieved through engineering controls. These controls focus on reducing the hazard at its source before it can reach a worker’s breathing zone. A common strategy involves using wet methods, which apply water directly to the point where dust is generated. For instance, a constant stream of water can be sprayed onto the tip of a tool or integrated into a saw blade to suppress the dust before it is released into the air.
Water suppression is effective because it binds the fine silica particles together, causing them to fall to the surface instead of floating in the air. Where water is impractical or insufficient, dust collection systems are utilized. Local Exhaust Ventilation (LEV) systems capture the dust cloud as soon as it is created, using a hood or shroud positioned directly over the work area. These systems draw the contaminated air away and filter it before exhausting clean air back into the environment.
A highly effective form of LEV involves on-tool dust collection systems, which are power tools fitted with integrated shrouds connected to a vacuum. These vacuums must be equipped with High-Efficiency Particulate Air (HEPA) filters, which are capable of trapping the extremely small respirable silica particles. For operators of large machinery like excavators, positive pressure enclosed cabs are used to seal the outside environment and filter the air entering the workspace, preventing contaminants from reaching the operator.
Workplace Procedures and Hygiene
Administrative controls supplement engineering solutions by establishing procedures that limit the duration of exposure and prevent the spread of dust. A foundational rule involves strict prohibitions on cleaning methods that re-aerosolize settled dust, such as dry sweeping or using compressed air on surfaces or clothing. Instead, cleanup procedures must rely on wet methods, like washing down dusty areas, or using HEPA-filtered vacuums to collect the particles.
The physical work environment should be managed by establishing regulated areas where silica-generating tasks are performed. These areas must be clearly marked and have access restricted to only those personnel performing the work to minimize the number of people exposed. Limiting the amount of time workers spend on high-exposure tasks can also reduce overall exposure levels, often achieved through work rotation policies.
Personal hygiene practices are necessary to prevent workers from carrying dust to other areas or home to their families. Workers should avoid eating, drinking, or using tobacco products in dusty areas to prevent ingestion of silica particles. Workers should change out of dusty work clothes at the worksite and wash their hands and face before leaving for the day. Providing disposable or washable coveralls ensures that silica dust does not contaminate personal vehicles or homes.
Personal Protective Equipment
When engineering and administrative controls are unable to reduce silica levels sufficiently, Personal Protective Equipment (PPE) serves as a layer of protection for the worker. This equipment is typically used as a last resort or as an interim measure while more effective controls are being implemented. The primary form of PPE for silica is respiratory protection, but standard filtering facepieces, such as N95 respirators, are often inadequate for the high concentrations of silica dust present.
For effective protection, workers require a P100 or N100 respirator, which is designed to filter out 99.97% of airborne particles. Any respirator used must be approved by the National Institute for Occupational Safety and Health (NIOSH) and administered through a comprehensive respiratory protection program. This program includes mandatory fit-testing to ensure the respirator forms a proper seal against the worker’s face, as well as a medical evaluation to confirm the worker is physically able to wear the device.
In addition to respirators, workers should use protective clothing, such as disposable coveralls, to minimize skin contact with the dust. This clothing prevents dust from settling directly onto personal garments, which reduces the risk of secondary exposure outside of the work area. The use of protective gear must be consistently enforced, ensuring it is properly maintained and worn correctly to provide the intended level of protection.