Overview

Industrial ventilation can partially address silica exposure issues, provided that dust hoods, ductwork, and airflow are designed effectively.

Many industries generate fine or "inhalable" silica dust during production processes, posing potential health hazards to employees. Silica is most commonly found in quartz, one of the most common minerals on Earth. Quartz can be hazardous when finely cleaved. Silica risks can exist in occupations involving the mining, production, or handling of sand, clay, and rock, including concrete and asphalt production, stone cutting and stonemasonry, glass and paint processing, road construction and shipbuilding, and oil and gas production. Health Risks

Silica dust is linked to silicosis, lung cancer, kidney and autoimmune diseases, and chronic obstructive pulmonary disease (COPD). Silicosis is a respiratory disease that damages the lungs and reduces their oxygen-carrying capacity. Inhalable silica has been classified as a carcinogen since 1996. 2. Affected Industries

The Occupational Safety and Health Administration (OSHA) has regulated silica exposure for years, and recently updated its regulations. Stricter regulations were implemented for the construction industry in September 2017, and on June 23, 2018, the scope was further expanded to conventional industries and the marine sector. Regulations on silica exposure in hydraulic fracturing operations will be implemented in 2021.
3. For covered mining activities, the Mine Safety and Health Administration (MSHA) is drafting its own silica exposure regulations, which are expected to be similar to those of OSHA.
4. Exposure Limits

OSHA's regulations update requirements for exposure assessment, respiratory protection, medical monitoring, hazard communication, and record keeping. They also halved the Permissible Exposure Limit (PEL) to no more than 50 micrograms per cubic meter (µg/m³). If the concentration of silica in the air exceeds 25 µg/m³ over an eight-hour period, the employer must take action to reduce potential exposure.

Mitigation Measures

The Occupational Safety and Health Administration (OSHA) has issued numerous guidelines to help employers across industries understand and comply with the new regulations. 3.5 Listed silica exposure management strategies include the following common strategies:

Work Practice and Procedure Changes: Modify processes to reduce dust levels and/or restrict access to high-exposure areas;

Well-designed Controls: Control dust through barriers, enclosures, or wetting devices, and/or capture it through local exhaust ventilation; and

Personal Protective Equipment (PPE): Provide NIOSH-approved full-face respirators if other controls are insufficient or in the process of being installed.

The Role of Dust Removal

OSHA standards list local exhaust ventilation systems (dust removal systems) as an engineered control. Properly designed and maintained dust removal systems help reduce airborne dust levels and can be used as part of a larger-scale mitigation strategy.

Identifying an Effective System

Silica dust control involves more than just dust collectors. It requires managing three key aspects at different points within the facility:

Exposure: Reducing the concentration of dust in the ambient air around employees;

Efficiency: Filtering captured dust using dust collector technology tailored to the application;

Emissions: Minimizing the amount of dust released into the atmosphere.

Key Components

To address the issues in all three areas, an effective dust collection system includes well-designed fume hoods and ductwork to maintain recommended capture and conveying speeds; highly efficient dust collection technology; fans suitable for the system's airflow and pressure design requirements; and appropriate working methods for managing dust and maintaining the system. More details are provided below:

1: Design and Placement of Fume Extractors

For fume hoods placed at all dust-generating locations, design and deployment are the most critical steps in effectively controlling dust. The performance of the fume hood in controlling harmful dust emissions determines the highest performance achievable by the entire dust control system. If the fume hood can only capture 20% of the dust, the efficiency of the local exhaust ventilation system will only reach 20%. The efficiency of the dust collector component refers only to its ability to filter harmful dust captured by the fume hood and conveyed to the dust collector. 2. Duct Airflow

Maintaining recommended capture and conveying velocities is equally important for all types of dust. For heavy or toxic dust, higher capture velocities are needed to draw particles into the dust collector hood, and higher conveying velocities are required to transport the dust through the duct system to the dust collector. A qualified industrial ventilation designer should advise on the initial layout and modifications to the ventilation system. Adding a dust collector hood or duct may disrupt the delicate balance of airflow within the system.

3. Collector Efficiency

When operating under steady-state conditions, the dust collector should efficiently remove dust from the treated dust-laden airflow. During continuous operation under steady-state conditions, a dust cake will accumulate on the filter bag surface. During cleaning cycles, the dust cake detaches from the filter bags, and the dust concentration around the filter bags will be significantly higher than the inlet dust concentration. Because it is difficult to ascertain the actual accumulated dust content, relying on the theoretical performance efficiency of a new filter cartridge (e.g., a Minimum Reported Efficiency Value (MERV) of 14) may not accurately reflect overall performance. Monitoring employee exposure levels and vent emission levels would be better performance metrics.

Professional Design Knowledge

The *Industrial Ventilation Design Handbook* published by the American Federation of Industrial Hygiene Experts (AFI) contains best practices for dust collection design. Qualified industrial ventilation designers can use these practices to develop dust collection systems. Good design requires sufficient control space at each exhaust hood to contain and control dust from each emission source. From a design perspective, a delicate balance needs to be managed, and you can disrupt this balance if you try to exploit it with additional ductwork. It's a good idea to have an industrial designer advise on any modifications.

Compliance Expertise

Process owners should engage appropriate experts to advise them on silica regulation compliance. Given the unique aspects of specific facilities and processes, knowledgeable Employee Health and Safety (EHS) professionals can help accurately explain which regulations apply and how best to implement them. Trained industrial hygienists can help test and monitor exposure levels to verify that the ventilation system is operating within design parameters and can recommend additional measures or work practices to reduce silica exposure. It's best to have an industrial designer advise on modifications to existing facilities.