Crystalline Silica Health Hazards And Exposure Limits

The International Agency for Research on Cancer (IARC) lists crystalline silica, inhaled in the form of quartz or cristobalite, as carcinogenic to humans (Group 1) based on epidemiological studies.

The effects of continually breathing respirable silica dust are both cumulative and progressive. Overexposure to dust that contains microscopic particles of crystalline silica can cause scar tissue to form in the lungs, reducing our ability to extract oxygen from the air. Acute silicosis occurs where exposures are the highest and can cause symptoms to develop within a few weeks or months. Development of chronic silicosis, the most common form, takes place over a period of years and often goes undetected. As the disease progresses, one or more of the following symptoms may be present: shortness of breath following physical exertion, severe cough, fatigue, loss of appetite, chest pains, and fever. Since these symptoms mimic those of other illnesses, it is important to consult a physician who has expertise in lung disorders if potential overexposure is suspected.

The American Conference of Governmental Industrial Hygienists (ACGIH) has established Threshold Limit Values (2003 TLV) for the inhalation of silica (SiO2) dust. The TLV for respirable quartz dust, cristobalite, and tridymite is 0.05 milligrams per cubic meter (mg/m3); the TLV for fused silica is 0.1 mg/m3. The Occupational Safety and Health Administration (OSHA) and the Mine Safety and Health Administration (MSHA) have established Permissible Exposure Limits (PEL) based on the amount of silica present. If crystalline silica is the only type present and is one percent or greater of the total respirable fraction, the respirable crystalline silica exposure limit for general industry [29 CFR 1910.1000] and for mining operations [30 CFR 56.5001] is determined from the following formula:

PEL= 10 mg/m3
% quartz silica + 2

For cristobalite and tridymite, the PEL is half the value calculated from the formula above. The OSHA PEL for the construction industry [29 CFR 1926.55] is measured in millions of particles per cubic foot (mppcf) and is calculated from the following formula:

PEL= 250 mppcf
% quartz silica + 5

Where Do We Find Silica Dust?

Crystalline silica is the basic component of sand. Quartz, a form of silica, is the most common mineral in the Earth’s crust. Concrete and masonry products contain silica sand. More than 100,000 employees in the United States encounter high-risk silica exposures. Some of the industries and activities that pose the greatest potential risk for employee exposure are:

• Construction: sandblasting, jackhammering, rock drilling, loading, hauling, dumping, tunneling
• Mining
• Foundry work: grinding, molding, shakeout, core room
• Ceramics, clay and pottery tasks
• Glass manufacturing
• Shipyards: abrasive blasting
• Railroads: setting, laying track and ballasting
• Manufacturing of soaps and abrasives
• Stone cutting: sawing, abrasive blasting, chipping and grinding
• Agriculture

Health Hazard Control Methods

• Making a commitment to prevent silicosis in the workplace requires the cooperation of both employers and employees. The most effective engineering controls, the best personal protective equipment, and the most effective training are of little value if not used.
• Install and maintain engineering controls such as process enclosures, exhaust ventilation, control and dust collection systems. Supply vacuums with high-efficiency particulate air (HEPA) filters, water sprays, wet drilling, enclosed cabs and drill platform kits.
• Practice preventive maintenance since the abrasiveness of silica can damage engineering controls.
• Substitute less hazardous materials than crystalline silica for abrasive blasting.
• Practice good housekeeping. All cleaning should be performed using wet methods or industrial type vacuum cleaners equipped with HEPA filters. Dry sweeping and cleaning with pressurized air should be prohibited.
• Establish a written respiratory protection program. Provide medically cleared employees with appropriately selected, properly fitted, approved respirators. Ensure that respirators are kept clean and properly maintained, and that employees are trained in their use. Respirators should be used until the air monitoring results indicate that respiratory protection is not warranted or that engineering controls alone provide sufficient personal protection.
• Warning signs should be posted to mark the boundaries of work areas that present potential silica exposure.
• Perform periodic air monitoring to ensure that atmospheric concentrations of dust are kept within allowable limits. Remember that employees and the public need to be protected.

Pre- And Post-Employment Medical Exams

1. Pre-employment physicals should include a medical and occupational history to collect data on crystalline silica exposure and symptoms of respiratory disease.
2. All personnel should have a pre- and post-employment medical examination including X-rays (posterior and anterior) according to the 1980 International Labor Office (ILO) International Classification of Radiographs of Pneumoconiosis (ILO 1981). Pulmonary function tests should be a part of these examinations. Annual examinations are also recommended for personnel exposed to silica.
3. Employees whose medical background includes a history of tuberculosis, either active or arrested, and/or other pulmonary abnormalities should be evaluated annually.

As a reminder, whenever work is performed with toxic materials, it is always a sound practice to:

• Change into disposable or washable clothes at the worksite.
• Shower and change into clean clothing before leaving the worksite to avoid potential contamination of vehicles, homes and family members.
• Avoid eating (including chewing gum), drinking, using tobacco products, or applying cosmetics in work areas where there is dust or other toxic materials.
• Practice good personal hygiene by washing hands and face before eating and drinking.

XL Environmental • Risk Control Division • 520 Eagleview Boulevard, PO Box 636, Exton, PA 19341 • Phone: 800-327-1414 • Fax: 610-458-7285 • xlenvironmental.com

XL Environmental is a division of XL Specialty Insurance Company.