Updated January 1, 1 . AmFam Team
Crystalline silica is the basic component of sand, quartz, and granite rock. Airborne crystalline silica occurs commonly in both work and non-work environments. Activities, such as a sandblasting, rock drilling, roof bolting, foundry work, stonecutting, drilling, quarrying, brick/block/concrete cutting, gunite operations, lead-based paint encapsulant applications, asphalt paving, cement products manufacturing, demolition operations, hammering, chipping and sweeping concrete or masonry, and tunneling operations can create an airborne silica-exposure hazard.
Occupational exposure and inhalation of airborne crystalline silica can produce silicosis, a disabling, dust-related disease of the lungs. Even materials containing small amounts of crystalline silica may be hazardous if they are used in ways that produce high dust concentrations. Depending on the length of exposure, silicosis is a progressive and fatal disease. It may take twenty or more years of exposure before a medical exam tests positive for silicosis. Inhaling silica dust has also been associated with other diseases, such as tuberculosis and lung cancer. There is no cure for silicosis, but it is a preventable occupational disease.
This report addresses the types and sources of silica, potential health effects and symptoms of exposure, exposure assessment and control, and suggestions for reducing or preventing silicosis.
Silica is the name of a group of minerals containing silicon and oxygen in chemical combination having the general formula, SiO2. Silica may be free, in which case only SiO2 is present; or combined, in which the SiO2 is combined chemically to some other atom or molecule. The difference is important to recognize, since the silica problem exists only with free silica.
Silica dust is an inhalation hazard and workers may be at risk of silicosis when high-velocity impact shatters the sand into smaller dust particles. Labels on materials, product analysis sheets, and material safety data sheets (MSDS), must be read and instructions for use followed carefully.
Free silica may occur in many forms as amorphous-free silica or as five principal forms of crystalline-free silica. Certain materials contain both amorphous- and crystalline-free silica. Silica-related diseases are associated only with crystalline-free silica. The most common examples of crystalline-free silica are beach or bank sands. A third form of free silica is fused silica that is produced by heating either the amorphous or crystalline forms. Other forms include cristobalite and tridymite.
Quartz, a principal form of silica, is geologically the second most common mineral in the earth's crust. Quartz is readily found in both sedimentary and igneous rocks. Quartz content can vary among different rock types; for example, granite can contain anywhere from 10 to 40 percent quartz; shales have been found to average 22 percent quartz; and sandstone’s can average 70 percent quartz.
In the construction industry, sandblasting may be used to remove paint and rust from stone buildings, metal bridges, tanks, and other surfaces. The most severe worker exposure to crystalline silica results from sandblasting. Other construction activities that may produce crystalline silica dust include jack hammer operations, rock/well drilling, concrete mixing, concrete tunneling, and brick and concrete block cutting and sawing. Tunneling operations, repair or replacement of linings of rotary kilns and cupola furnaces, and setting, laying, and repairing railroad tracks are also potential sources of exposure.
Concrete and masonry products contain silica sand and rock containing silica. These products are primary materials for construction, and construction workers may be exposed to respirable crystalline silica during activities, such as the following:
Silicosis is one of the world's oldest known occupational diseases, dating back to ancient Greece. Since the 1800s, the silicotic health problems associated with crystalline silica dust exposure have been referred to under a variety of common names, including consumption, ganister disease, grinders' asthma, grinders' dust consumption, grinders' rot, masons' disease, miner's asthma, miner's phthisis, potters' rot, sewer disease, stonemason's disease, chalicosis, and shistosis. Silicosis was considered the most serious occupational hazard during the 1930s and was the focus of major federal, State, and professional attention.
Silicosis is the result of the body's response to the presence of silica dust in the lungs. The respirable fraction of the dust (particles generally considered to be smaller than 5 microns (five-millionth of a meter) can penetrate to the innermost reaches of the respiratory systems. These are the alveoli (airsacs) where the exchange of oxygen and carbon dioxide occurs. When workers inhale crystalline silica, they land on the alveoli, and white blood cells (macrophages) try to remove them. However, the particles of free crystalline silica cause the macrophages to break open. The lung tissues react by developing fibrotic nodules and scarring around the trapped silica particles. Formation of large numbers of "scars" following prolonged exposure causes the alveolar surface to become less elastic. This is noticed as shortness of breath following exertion. Symptoms seldom develop in less than five years and, in many cases, may take more than 20 years to become disabling or cause death.
A worker's lungs may react more severely to silica sand that has been freshly fractured (sawed, hammered, or treated in a way that produces airborne dust). This factor may contribute to the development of acute and accelerated forms of silicosis.
Development of silicosis is influenced by several factors that include:
Workers may develop any of three types of silicosis, depending on the concentration of airborne silica:
Chronic silicosis. This usually occurs after ten or more years of exposure to crystalline silica at relatively low concentrations.
Accelerated silicosis. This occurs from exposure to high concentrations of crystalline silica and develops five to ten years after the initial exposure.
Acute silicosis. This occurs where exposure concentrations are the highest and can cause symptoms to develop within a few weeks to four or five years after the initial exposure.
Early stages of the disease may go unnoticed. Continued exposure may result in a shortness of breath on exercising, possible fever, and occasionally bluish skin at the ear lobes or lips. Silicosis makes a person more susceptible to infectious diseases of the lungs, such as tuberculosis. Progression of silicosis leads to fatigue, extreme shortness of breath, loss of appetite, pains in the chest, respiratory failure, and may cause death.
Medical evaluations of silicosis victims usually show the lungs to be filled with silica crystals and a protein material. Pulmonary fibrosis (fibrous tissue in the lung) may or may not develop in acute cases of silicosis, depending on the time between the exposure and the onset of symptoms. Furthermore, evidence indicates that crystalline silica is a potential occupational carcinogen.
The presence of crystalline-free silica in the air can be detected and measured. Generally, if dust containing crystalline-free silica can be seen, an exposure problem is likely to exist. It should be remembered that only a portion of the total dust is respirable dust and usually cannot be seen by the unaided eye. If airborne dust can be seen, however, a problem is likely to exist.
The following aspects of a construction operation should be part of the overall exposure assessment:
Employers are required to provide and assure the use of appropriate controls for crystalline silica-containing dust. Workplace exposure to crystalline-free silica can be controlled. Although there is no specific standard outlining the requirements of a "silicosis prevention program," many of the elements of such a program are outlined in other Occupational Safety and Health Administration (OSHA) standards (e.g., Hazard Communication, Respiratory Protection, Safety Training and Education, etc.). The program should be the result of analysis of the workplace assessment of exposures. The elements of an effective program depend on the type of project and the effectiveness of existing facilities and required work practices. Elements that should be included in an effective silica program include:
*Required by existing OSHA standards if an overexposure to crystalline silica exists.
There are many specific and general recommendations to reduce exposures to respirable crystalline silica on the jobsite. Workers can limit their exposure by being aware of the following:
OSHA has a national special emphasis program (SEP) to reduce worker silica dust exposures that can cause silicosis-related deaths.
This SEP will apply to all workplaces under OSHA's jurisdiction in the general industry, construction, and maritime sectors. A silicosis coordinator has been designated in each region to coordinate the special emphasis program activities. To encourage voluntary protection measures by employers, OSHA conducted an outreach program for 60 days before proceeding with enforcement under existing OSHA standards. The outreach and voluntary protection program involved the efforts of three governmental agencies. Outreach materials are currently being developed by OSHA's Office of Education and Training, working with National Institute for Occupational Safety and Health (NIOSH), and the Mine Safety and Health Administrative (MSHA).
Among the outreach materials developed are slides about hazard recognition and crystalline silica control technology, a video on crystalline silica and silicosis, and informational cards for workers explaining crystalline silica, health effects, and methods of control.
Under SEP, OSHA targets workplaces with the potential for silica exposure for inspection. Some examples of sources used by OSHA to target inspections in construction include:
To discover more ways to protect your business and employees, check out the American Family Insurance Loss Control Resource Center.
1. National Institute for Occupational Safety and Health. Preventing Silicosis and Deaths in Construction Workers. No. 96-112. Cincinnati, OH: Centers for Disease Control and Prevention, 1996.
2. Rosner, D., and G. Markowitz. Deadly Dust. Silicosis and the Politics of Occupational Disease in Twentieth Century America. Princeton, NJ: Princeton University Press, 1994.
3. Yassin, Abdiaziz. “Operational Exposure to Crystalline Silica Dust in the United States, 1988-2003.” Environmental Health Perspectives Volume 113. Number 3 (2005): 255-260.
COPYRIGHT ©2005, ISO Services, Inc.
The information contained in this publication was obtained from sources believed to be reliable. ISO Services, Inc., its companies and employees make no guarantee of results and assume no liability in connection with either the information herein contained or the safety suggestions herein made. Moreover, it cannot be assumed that every acceptable safety procedure is contained herein or that abnormal or unusual circumstances may not warrant or require further or additional procedure.