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Crystalline Silica and Silica Exposure

Quick Tips #354

The term "silica" broadly refers to the mineral compound silicon dioxide (SiO2). Although silica can be crystalline or amorphous in form, crystalline silica is more hazardous to employees and, therefore is the focus of this document. Crystalline silica is a basic component of the Earth's crust and can be detected in soil, sand, granite and many other minerals. It is most commonly found in the form of quartz, but it is also found in substances such as cristobalite, tridymite and tripoli. Breathing crystalline silica dust poses an industrial hazard and can lead to severe health problems and even death.

Respirable size silica dust particles, or particles that are less than 10 um in diameter, pose the greatest threat to employees working with or near crystalline silica. These dust particles occur when workers chip, cut, drill or grind objects that contain crystalline silica. This occurs in workplace settings such as manufacturing, mining, construction, agriculture and abrasive blasting. Up to 2 million workers in the United States are threatened by silica exposure in the workplace with at least 100,000 of those workers being sandblasters.

Check the links below for additional information pertaining to OSHA and Canadian abrasive blasting standards:

OSHA abrasive blasting standards

Silica exposure has been linked through epidemiologic studies to chronic obstructive pulmonary disease such as bronchitis and emphysema. It has also been linked to immunologic disorders such as scleroderma, rheumatoid arthritis, and lupus in addition to renal disease and stomach or gastric cancer. Crystalline silica dust was listed in the 12th Report on Carcinogens (page 377) as a known human carcinogen. However, the most prominent disease linked to silica dust exposure is Silicosis.

Silicosis is one of the world's oldest known occupational diseases, with reports of the employees contracting the disease dating back to ancient Greece. By the 1800s common names for silicosis included grinders' asthma, grinders' rot, masons' disease, miners' asthma, miners' phthisis, potters' rot, sewer disease, sandblasting disease and stonemasons' disease.

Silicosis, is a preventable yet incurable disease that causes scar tissue to build up in the lungs leading to a reduction in the ability to take in oxygen. Respirable silica dust particles pass through the tracheobronchial tree of the lung and collect in the deepest recesses of the lung, called the alveolar structures. This accumulation leads to a significant decrease in lung function. There are three types of silicosis.

  1. Chronic or classic silicosis: results from 15-20 years of low to moderate silica exposure. Chronic silicosis causes shortness of breath and clinical signs of poor oxygen/carbon dioxide exchange in the early stages. In the late stages of chronic silicosis the individual will experience extreme shortness of breath and fatigue, as well as chest pain and respiratory failure.
  2. Accelerated silicosis: results from 5-10 years of high exposure. Accelerated silicosis results in severe shortness of breath, weakness and weight loss.
  3. Acute silicosis: the most dangerous form of silicosis, also causes severe shortness of breath, weakness and weight loss. Acute silicosis arises anywhere from a few months to two years after exposure to extremely high concentrations of silica dust. Acute silicosis is often fatal.

Because of the severe side effects resulting from silica exposure, the Occupational Safety and Health Administration (OSHA) has established a permissible exposure limit (PEL) for workers who may be exposed to silica dust. This exposure limit is dependent on the percent of respirable dust particles produced by an application. OSHA has outlined a method for calculating the PEL for silica dust in 29 CFR 1926.55 and 1910.1000. OSHA also requires that hazard communication training (outlined in 29 CFR 1910.1200) be provided to workers who may be exposed to silica dust. Additionally, OSHA stresses putting engineering controls in place to reduce the amount of silica exposure in the workplace. Some examples of these engineering controls are as follows:

  1. locating employees in an area where they will not be exposed to silica dust
  2. isolating workers from exposure with enclosures or barriers
  3. installing local exhaust ventilation systems
  4. using wet methods for cutting, chipping, drilling, sawing, grinding, etc.
  5. using HEPA equipped vacuums or wet sweeping for cleaning applications
  6. NOT using compressed air for cleaning applications
  7. substituting non-crystalline silica material when possible
  8. using tools with dust collection systems

OSHA states that it is important to consult a competent industrial hygienist or other technically qualified person when determining the engineering controls to be used. OSHA also stresses that employee exposure must be monitored. Guidelines for collecting air samples are outlined in the OSHA Technical Manual (OTM) Section II Chapter I.

When engineering controls cannot eliminate the risk of silica exposure a respirator program should be put into place. The minimum respiratory protection that is required is an N95 NIOSH approved respirator for exposures that do not exceed the assigned protection factors. Of course, as with any respirator program (see Quick Tips #195: Starting a Respiratory Protection Program), medical evaluations (see Quick Tips #143: Medical Evaluation Questionnaire, 29 CFR 1910.134) are required for employees who will be wearing the respirators.

Commonly Asked Questions

Q.   What is m?
A.   m is the abbreviation for micrometer. A micrometer is a unit of length equal to one thousandth (10-3) of a millimeter or one millionth (10-6) of a meter. Micrometer is the unit of measure used to describe the diameter of small particles.
 
Q.   What type of air monitors are used to measure silica exposure and at what level of silica exposure should a respirator protection program be enforced?
A.   The type of air monitor used to measure silica exposure and the level of silica exposure requiring respiratory protection is dependent on the size of the silica particles being generated by an application. The parameters of determining how to monitor for silica exposure can be found in the OSHA Technical Manual (OTM) Section II Chapter I. To calculate the permissible exposure level please refer to 29 CFR 1926.55 and 1910.1000 Table Z-3.
 
Q.   Can I use a disposable respirator for protection during sandblasting?
A.   Disposable dust masks will not protect the worker from silica exposure during sandblasting. Effective engineering controls such as substitution, automation, enclosed systems, local exhaust ventilation, and wet methods should be used. In addition a properly operated and maintained approved abrasive blasting respirator may provide adequate protection to the wearer.
Sources

For additional information regarding silica exposure in the workplace please visit the OSHA website:
http://www.osha.gov/Publications/osha3176.html

(Rev. 1/2012)

 

Find even more information you can use to help make informed decisions about the regulatory issues you face in your workplace every day. View all Quick Tips Technical Resources at www.grainger.com/quicktips.

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Please Note:
The content in this newsletter is intended for general information purposes only. This publication is not a substitute for review of the applicable government regulations and standards, and should not be construed as legal advice or opinion. Readers with specific compliance questions should refer to the cited regulation or consult with an attorney.

©2012 W.W. Grainger, Inc.

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