What is Silica?
Silica, scientifically called silicon dioxide (SiO₂), is a chemical compound that ranks among the most plentiful minerals in the Earth’s crust, and is essential in numerous industrial sectors, such as glass production, construction materials, and electronics. When silica is drilled, cut, or crushed, tiny particles called silica dust can be released into the air.
Forms
Silica can exist in two forms as follows:
Crystalline
Crystalline silica is the most common type and features a well-ordered, repeating atomic structure, making it more stable and giving it distinct physical characteristics. It is usually found as quartz, widely used in industrial applications for its durability and heat-resistant qualities.
It can be further divided into three subtypes:
- Quartz: Found in sandstone, granite, and other rocks.
- Tridymite: Forms in high-temperature settings like volcanic eruptions, and used in ceramics.
- Cristobalite: Produced from quartz or tridymite, this is common in foundries and glass manufacturing.
Under excessive pressure, all crystalline silica can create fine dust called Respirable Crystalline Silica (RCS). These tiny particles can be inhaled deeply into the lungs, potentially causing serious health problems.
Amorphous (Non-crystalline)
The opposite of crystalline silica is amorphous silica, which has no fixed atomic structure. It is commonly used as an absorption or thickening agent in cosmetics, pharmaceuticals, and food production. Although it generally has fewer health risks than its counterpart, it should still be managed carefully in occupational settings.
Sources
Silica is commonly sourced from the following:
Natural Sources
Silica is naturally present in rocks, clay, sand, and soil. Dust particles containing silica are formed through natural processes like erosion and windblown dust.
Industrial and Commercial Sources
Silica dust can also be generated during industrial processes such as the following:
- Mining and quarrying activities
- Crushing, drilling, or grinding rocks containing silica
- Construction work, particularly when cutting, sawing, chipping, or drilling materials like concrete, brick, mortar, and stone
- Manufacturing of glass, ceramics, and other silica-containing products
- Use of sandblasting equipment
Exposure Sources
The general population may also be exposed to silica through the following channels:
- Air: Dust from construction sites, mining, and other activities can contain respirable silica particles.
- Indoor Dust: Certain indoor dust types, particularly from concrete, can also contain silica.
- Consumer Products: Some household items, including cleansers and skin care products, may contain silica.
Health Risks of Exposure
Exposure is almost inevitable, given that silica can be found in everyday materials and activities. Prolonged or high-level exposure can lead to significant health risks, particularly in occupational settings.
Some risks associated with silica seen in recent years include the following:
- Respiratory Issues: Inhaling respirable dust can cause immediate irritation to the respiratory tract. Silica dust is also classified as a carcinogen, causing breathing difficulties and even lung cancer for those who inhale crystalline silica dust over time.
- Silicosis: Prolonged exposure can lead to silicosis, a serious and incurable lung disease.
- Kidney Disease: Silica exposure has been linked to an increased risk of developing kidney disease.
Due to the different risks associated with silica, its dust is often called the “new asbestos.” Asbestos was banned in different countries in 1983, and restrictions have been continuously imposed since then.
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Regulations
To ensure workplace and consumer safety, regulations and standards have been established to manage and mitigate the health risks associated with silica exposure. Here is an overview of key rules:
International
- World Health Organization (WHO): In 1997, WHO established a guideline for air quality standards on particulate matter (PM), which includes silica.
- International Labour Organization (ILO): The ILO has set the occupational exposure limit (OEL) value for respirable silica to 0.05 mg/m³ in its current guidelines.
US
- Occupational Safety and Health Administration (OSHA)
- There are OSHA standards to reduce silica exposure for construction, general industry, and maritime sectors.
- Under its Respirable Crystalline Silica Rule, the Permissible Exposure Limit (PEL) is reduced from 100 µg/m³ to 50 µg/m³ (micrograms of silica per cubic meter of air).
- Mine Safety and Health Administration (MSHA): MSHA regulates mine safety to reduce exposure to high levels of silica dust from quartz.
- Centers for Disease Control and Prevention (CDC): There are no current regulations from them yet regarding silica safety, but they have a list of safe practices that companies should follow.
EU
The European Food Safety Authority (EFSA) has regulations for using silica as a food additive (E551), permitting only the use of synthetic amorphous silica and not other forms. There is also the Directive 2004/37/EC set by EU-OSHA, which provides a guide for managing worker exposure to carcinogens, mutagens, and reprotoxic substances such as silica.
UK
The Health and Safety Executive (HSE) abides by international laws and has also set Workplace Exposure Limits (WEL) to control worker exposure to hazardous substances. The HSE has also created construction-specific safety guidelines for silica use and safety to support workers when dealing with construction dust.
Australia
In Australia, the use of silica has long been regulated by Safe Work Australia’s Model Work Health and Safety (WHS) Regulations. Included in these guidelines are the proper safety measures to follow, the right equipment to use, and the current exposure limit for RCS at 0.05 mg/m3, based on an eight-hour time-weighted average.
All jobs that involve working with materials containing at least 1% crystalline silica are also required to be strictly controlled. With the rise of silica-related health risks, Safe Work Australia is calling for stronger implementations of their safety standards, as well as better risk assessment practices. Following this, an amendment was made in 2024 to the Model WHS Regulations, requiring a silica risk control plan to be prepared for any task involving engineered stone processing.
Mitigations
Regulations are there to protect workers, but it is also essential to take preventive measures at the workplace. Here are various measures to mitigate silica exposure:
Hierarchy of Controls
The Hierarchy of Controls method prioritizes control measures from the most effective to the least based on the following:
- Elimination: Removing hazards entirely.
- Substitution: Replacing silica with safer alternatives.
- Engineering Controls: Using technologies like ventilation to isolate the hazard.
- Administrative Controls: Implementing safe work practices and scheduling to limit exposure.
- Personal Protective Equipment (PPE): Using gear like respirators as a last defense.
Asset Management
Proper management and maintenance of equipment and tools are crucial in controlling silica dust. For efficient asset management, companies should:
- monitor and track equipment usage;
- schedule regular maintenance and cleaning; and
- replace worn-out parts to prevent dust leakage.
Medical Monitoring Programs
Monitoring the health of workers exposed to silica is essential for early detection of any adverse effects. These programs involve regular health screenings and assessments, enabling prompt intervention and treatment to ensure worker safety.
Compliance with Safety Regulations
Adhering to established safety standards and regulations ensures workplaces follow the best silica exposure control practices. Comply with safe levels of exposure and provide necessary training for employees on handling silica dust safely.
Air Quality Monitoring
Silica air quality monitoring is necessary in many workplaces, especially in construction, mining, and manufacturing, where exposure is a risk. For instance, OSHA requires employers to monitor air quality to ensure silica exposure remains below the PEL. Companies can use tools like real-time monitors and air quality sensors to measure silica levels in the air.
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Monitoring Tools for Silica Dust
Various monitoring tools can help measure and control silica exposure levels. Some common sensors that do this are the following:
- Real-Time Air Quality Monitors: These devices continuously measure the concentration of silica dust in the air, providing instant data that helps businesses maintain safe air quality levels.
- Personal Dust Monitors: These monitors, worn by employees during their shifts, track individual exposure to silica dust throughout the day.
- IoT Sensors: Integrated into workplace environments, these sensors offer advanced monitoring by connecting to networks for real-time data analysis and alerts.
FAQs about Silica
Silica dust and asbestos exposure can both lead to severe, irreversible diseases, such as lung diseases. However, while they are both used for construction, they are different minerals. Silica is found in sand, stone, and quartz, while asbestos is used for fire resistance. Safety measures for silica involve dust control and monitoring, whereas asbestos has stricter rules for handling and disposal.
Recovery from silica exposure is not guaranteed, as silicosis and other related diseases are often irreversible and progressive. Early detection and intervention can help manage symptoms but cannot be reversed once lung damage occurs.
Recommended PPE for protection against silica dust includes respirators with proper filtration capabilities, protective clothing to minimize skin exposure, and eye protection to prevent irritation from dust particles.
Air quality monitoring in workplaces with silica exposure should be conducted regularly. The frequency depends on exposure levels and regulatory guidelines, typically daily to weekly checks.
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