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Directives
CPL 03-00-007 - National Emphasis Program – Crystalline Silica |
Directives - Table of Contents |
Record Type: | Instruction |
Old Directive Number: | CPL 03-00-007 |
Title: | National Emphasis Program – Crystalline Silica |
Information Date: | 01/24/2008 |
OSHA INSTRUCTION
ABSTRACT
By and Under the Authority of Edwin G. Foulke, Jr. Executive Summary
In 1996, the Occupational Safety and Health Administration (OSHA) issued a memorandum establishing a Special Emphasis Program (SEP) for Silicosis, which provided guidance for targeting inspections of worksites with employees at risk of developing silicosis . This instruction establishes a National Emphasis Program (NEP) that expands and builds upon the 1996 SEP. This instruction addresses targeting of worksites with elevated exposure to crystalline silica, as well as silica-related inspection procedures and compliance assistance. All Local Emphasis Programs (LEPs) for silica-related activities may remain in effect under this NEP. Any conflicts between an LEP and an NEP should be resolved in favor of the NEP. Significant Changes
This Instruction expands the 1996 SEP to include the following changes:
Table of Contents
List of Appendices
Appendix A. Background Information on Silica Appendix B. Industries with Potential Overexposure to Crystalline Silica Appendix C. Guidelines for Air Sampling Appendix D. Cyclone Leak Test Procedure Appendix E. Conversion Factor for Silica PELs in Construction and Maritime Appendix F. Employee Questionnaire Appendix G. Medical Monitoring Recommendations for Employees Exposed to Crystalline Silica Appendix H. CSHO Checklist for Conducting Silica-Related Inspections Appendix I. Case File Components to be Sent to the National Office Appendix J. Bibliography This appendix provides an overview of the following silica-related topics: the forms and sources of silica; common industrial uses of silica and workplaces with silica exposure; history of silicosis ; and health effects associated with exposure. The reference list at the end of this appendix, as well as the expanded bibliography in Appendix J, provide many sources that may prove useful to those interested in a more in-depth treatment of these topics. Introduction "Silica," is a term which refers broadly to the mineral compound silicon dioxide (SiO2). Silica can be crystalline or amorphous. Crystalline silica is significantly more hazardous to employees than amorphous silica. In addition to causing the disabling and irreversible lung disease known as silicosis , crystalline silica has been classified as a human carcinogen by the International Agency for Research on Cancer (IARC ) [IARC, 1997]. As it is typically used in this document, "silica" refers specifically to crystalline silica. Crystalline silica is characterized by a large scale, repeating pattern of silicon and oxygen atoms, as distinguished from the more random arrangement found in amorphous silica. Abundant in the earth's crust, crystalline silica is a basic component of most classes of rock. Naturally-occurring forms of amorphous silica include diatomaceous earth (the skeletal remains of marine organisms) and vitreous silica or volcanic glass [Markowitz and Rosner, 1995; Davis, 1996]. Forms and Sources of Crystalline Silica Crystalline silica occurs in three primary mineralogical forms, or polymorphs-quartz, cristobalite, and tridymite. Silica is also called "free silica," to distinguish it from the silicates, which are minerals containing silicon dioxide bound to one or more cations [Beckett et al., 1997]. Quartz is by far the most common form of naturally-occurring silica [Davis, 1996; IARC , 1997]. Cristobalite and tridymite, which are molecularly identical to quartz, are distinguishable by their unique crystalline structures. They are less stable than quartz, thus accounting for the dominance of the quartz form. Quartz itself exists as either of two sub-polymorphs, alpha-quartz (also known as low quartz), and beta-quartz (high quartz). Alpha-quartz is the thermodynamically stable form of crystalline silica and accounts for the overwhelming portion of naturally-occurring crystalline silica [IARC, 1997]. Quartz is a major component of soils and is readily found in both sedimentary and igneous rocks, although the quartz content varies greatly from one rock type to another. For instance, granite contains on average about 30 percent quartz, and shales contain about 20 percent quartz. Natural stone, such as beach sand or sandstone, may be nearly pure quartz [IARC , 1997; Davis, 1996]. Cristobalite and tridymite are natural constituents of some volcanic rock, and man-made forms result from direct conversion of quartz or amorphous silica that has been subjected to high temperature or pressure. Diatomaceous earth, composed of amorphous silica, crystallizes during heating (calcining), yielding a calcined product that contains as much as 75 percent cristobalite. Cristobalite is also found in the superficial layers of refractory brick that has been repeatedly subjected to contact with molten metal [Markowitz and Rosner, 1995; Ganter, 1986; Cheng et al., 1992; Bergen et al., 1994]. Major Industrial Sources of Crystalline Silica Exposure Crystalline silica is an important industrial material and occupational exposure occurs across a broad range of industries, including mining, manufacturing, construction, maritime, and agriculture (see Appendix B for a listing of industries and Standard Industrial Classifications with potential for significant occupational exposure). Processes associated historically with high rates of silicosis include sandblasting, sand-casting foundry operations, mining, tunneling, and granite cutting. Crystalline silica, in the form of finely ground quartz sand as an abrasive blasting agent, is used to remove surface coatings prior to repainting or treating, a process that typically generates extremely high levels of airborne respirable crystalline silica. A 1992 report published by the National Institute for Occupational Safety and Health (NIOSH) estimates that there are more than one million U.S. employees who are at risk for developing silicosis , and of these employees, more than 100,000 are employed as sandblasters. Abrasive blasting is performed in a wide variety of different industries; the construction industry employs the largest number of employees as abrasive blasters, concentrated in the special trades [NIOSH 92-102; CDC, 1997]. In addition to abrasive blasting, construction employees perform numerous other activities that may result in significant silica exposure, including tunnel and road construction, excavation and earth moving, masonry and concrete work, and demolition [IARC , 1997]. Foundry employees, primarily in iron and steel foundries, may be exposed to crystalline silica throughout the metal-casting process, including the production of sand-based molds and cores, shakeout and knockout, and finishing and grinding operations. Crystalline silica, primarily as quartz, is a major component of the sand, clay, and stone raw materials used to manufacture a variety of products, including concrete, brick, tile, porcelain, pottery, glass, and abrasives. The powdered form of quartz, also called silica flour, is used in the manufacture of fine china and porcelain. Finely ground crystalline silica is also used as a functional filler in the manufacture of paints, plastics, and other materials. The rock crystal form of quartz is of great value to the electronics industry. Agricultural employees perform activities, including plowing and harvesting, that may generate elevated silica levels. However, OSHA does not regulate crystalline silica exposure on farms with fewer than ten employees and exposure data for this population is lacking [Linch et al., 1998]. On the other hand, OSHA does regulate crystalline silica exposure in the agricultural services sector, and crystalline silica exposures have been documented in the sorting, grading, and washing areas of food processing operations for crops such as potatoes and beans. Cristobalite, as calcined diatomaceous earth, is used as a filler in materials such as paints and as a filtering media in food and beverage processing. Maintenance and trades personnel who repair and replace refractory brick linings of rotary kilns and cupola furnaces may be exposed to significant levels of quartz, as well as cristobalite and tridymite. These kilns and furnaces are found in glass, ceramics, and paper manufacturing facilities as well as foundries [Markowitz and Rosner, 1995]. The industries described above, (see Appendix B) represent the major industrial sources of crystalline silica exposure. However, there are numerous other operations in which silica may be used or otherwise encountered, and it is important to be aware of the risk of silicosis in industries not previously recognized to be at risk. History of Silicosis Silicosis is one of the world's oldest known occupational diseases; reports of employees with the disease date back to ancient Greece. By 1800, there were numerous common names for the lung disease now known as silicosis . The names frequently referred to the affected laborers' trade, such as grinders' asthma, grinders' rot, masons' disease, miners' asthma, miners' phthisis, potters' rot, sewer disease, and stonemasons' disease. Despite its different names through the centuries, silicosis is a single disease with a single cause-exposure to respirable crystalline silica dust. During the 1920s, the health risks of the "dusty" trades, in particular the granite industry, emerged as a significant public health concern, and by 1930 silicosis was considered the most serious occupational disease in the United States. During the 1930s and 1940s, the granite industry was the focus of a major effort to alleviate dusty conditions and create a safer working environment [Rosner and Markowitz, 1994]. However, as the more extreme silica hazards were brought under control, attention shifted away from silica to other occupational health hazards. Nonetheless, as the studies described below indicate, in recent decades silicosis has continued to pose a significant health threat to employees in a variety of occupations, including but not limited to construction, foundries, and sandblasting. It is important to be aware of the possible risk of silicosis in workplaces not previously recognized to be at risk.
Pulmonary silicosis has historically been the disease most well-known as being caused by the inhalation of respirable crystalline silica particles. Additionally, there is evidence that exposure to crystalline silica-containing dusts causes or is associated with the following conditions: lung cancer, tuberculosis, chronic obstructive pulmonary disease (including emphysema and bronchitis), autoimmune diseases or immunologic disorders, chronic renal disease, and subclinical renal changes [NIOSH, 2002]. Silicosis Silicosis is a fibrotic disease of the lungs caused by the inhalation of crystalline silica dust. It is a type of pneumoconiosis, which is a general term for chronic lung disease that occurs when certain particles are inhaled and deposited deep in the lung. There are two main types of silicosis , chronic silicosis (also called "classical" or "nodular" silicosis) and acute silicosis, medically referred to as silico-proteinosis or alveolar lipoproteinosis-like silicosis. Chronic silicosis, by far the most common form of the occupational disease, typically appears 20 to 40 years after initial exposure and tends to progress even after exposure ceases. Accelerated silicosis is a variant of chronic silicosis but develops after more intense exposure to crystalline silica; it is characterized by earlier onset (within 5 to 15 years of initial exposure) and more rapid progression of disease than chronic silicosis [Weill et al., 1994]. Acute silicosis results from an overwhelming exposure to silica and the symptoms become manifest in as little time as a few weeks after exposure. Acute silicosis appears to be distinct from the other forms of silicosis, possibly involving an immune mechanism not associated with either accelerated or chronic silicosis. This disease, though rare, is invariably fatal. Outbreaks of acute silicosis have occurred among sandblasters and silica flour mill employees [Peters, 1986]. The development of silicosis is dependent on the size of the crystalline silica dust particle, the dust concentration, and the duration of exposure. Crystalline silica particles smaller than 10 micrometers (µm) in diameter, so-called respirable particles, are particularly hazardous, because they easily pass through the tracheobronchial tree and are deposited in the deepest recesses of the lungs, the alveolar structures. Particles larger than 10 mm in diameter are trapped in the nose or the mucous lining of the airway and are removed by the mucociliary escalator. Chronic silicosis has an early manifestation of a dry or non-productive cough when there is continued exposure to the inhaled irritant. The cough then becomes prolonged and distressing, with sputum production as the disease advances. Initially, breathlessness occurs while exercising, but progresses to shortness of breath during normal activity [Porth, 1994]. Wheezing typically only occurs when conditions such as chronic obstructive bronchitis or asthma are also present. Advanced states of silicosis include pneumothorax and respiratory failure. Respiratory symptoms increase with the progression of silicosis [Wang, 1999]. A rapid increase in the rate of synthesis and deposition of lung collagen has also been seen with the inhalation of crystalline silica particles. The collagen formed is unique to silica-induced lung disease and is biochemically different from normal lung collagen [Olishifski and Plog, 1988]. Silicosis in all its forms is incurable and causes significant impairment or death. Therefore, eliminating or controlling occupational exposure to respirable crystalline silica is critical to prevention of the disease. Lung Cancer The International Agency for Research on Cancer [IARC, 1997] classifies crystalline silica inhaled in the form of quartz or cristobalite from occupational source as "carcinogenic to humans (Group 1)." However, in making the overall evaluation, the IARC Working Group noted "that carcinogenicity in humans was not detected in all industrial circumstances studied." The Working Group also stated: "Carcinogenicity may be dependent on inherent characteristics of the crystalline silica or on external factors affecting its biological activity or distribution of its polymorphs." The IARC analysis included studies of U.S. gold miners, Danish stone industry employees, U.S. granite shed and quarry employees, U.S. crushed stone industry employees, U.S. diatomaceous earth employees, Chinese refractory brick makers, Italian refractory brick makers, U.K. pottery makers, Chinese pottery makers and cohorts of registered silicotics from North Carolina and Finland. Most of these studies found a statistically significant association between occupational exposure to crystalline silica and lung cancer . Tuberculosis Epidemiologic studies have firmly established the association between TB and silicosis. Some studies have indicated that employees who do not have silicosis but who have had long exposures to silica dust may also be at increased risk of developing TB [NIOSH, 2002]. Individuals with chronic silicosis are more susceptible to developing active tuberculosis than the general population. However, it is not clear whether low-level exposure to silica, in cases where silicosis has not developed, also predisposes employees to tuberculosis [Davis, 1996]. Chronic Obstructive Pulmonary Disorder Epidemiologic studies have shown that occupational exposure to respirable crystalline silica is associated with chronic obstructive pulmonary disease, including bronchitis and emphysema. The findings from some of these studies suggest that emphysema and bronchitis may occur less frequently or not all in nonsmokers. Epidemiologic studies have also found significant increases in mortality from nonmalignant respiratory disease, a category that includes silicosis, emphysema, and bronchitis, as well as some other related pulmonary diseases [NIOSH, 2002]. Immunologic Disorders and Autoimmune Diseases Several epidemiologic studies have found statistically significant increases in mortality from or cases of immunologic disorders and autoimmune diseases in employees exposed to silica. These disorders and diseases include scleroderma (a rare multisystem disorder characterized by inflammatory, vascular, and fibrotic changes usually involving the skin, blood vessels, joints, and skeletal muscle), rheumatoid arthritis, systemic lupus erythematosus (lupus), and sarcoidosis (a rare multisystem granulomatous disease characterized by alterations in the immune system) [NIOSH, 2002]. Renal Disease Epidemiological studies report statistically significant associations between occupational exposure to silica dust and several renal diseases or effects, including end-stage renal disease morbidity (including that caused by glomerular nephritis, chronic renal disease mortality, and Wegener's granulomatosis (systemic vasculitis often accompanied by glomerulonephritis) [NIOSH, 2002]. Stomach and Other Cancers There is some evidence from studies of various occupational groups exposed to crystalline silica of statistically significant excesses of mortality from stomach or gastric cancer. However, most of these studies did not adjust for confounding factors and possible exposure-response relationships were not assessed. Similar issues with confounding and lack of exposure-response assessment exist for the infrequent reports of statistically significant numbers of excess deaths or cases in silica-exposed employees of other nonlung cancers such as nasopharygeal or pharyngeal, salivary gland, liver, bone, pancreatic, skin, esophageal, digestive system, intestinal or peritoneal, lymphopoietic or hematopoietic, brain, and bladder [NIOSH, 2002]. Summary As these health findings indicate, crystalline silica exposure is associated with a number of diseases, in addition to silicosis. Silica exposure continues to pose substantial risks to employees, centuries after it was first identified as an occupational hazard. The only way to prevent disease is to eliminate exposure to crystalline silica or reduce crystalline silica exposure to safe levels. References ACGIH (2000) 2000 TLVs® and BEIs®. Threshold Limit Values for Chemical Substances and Physical Agents and Biological Exposure Indices. American Conference of Governmental Industrial Hygienists. Cincinnati, OH. Archer, C., Gordon, D.A. (1996) Silica and Progressive Systemic Sclerosis (Scleroderma ): Evidence for Workers' Compensation Policy. American Journal of Industrial Medicine. 29:533-538. Bang, K.M., Althouse, R.B., Kim, J.H., et al. (1995) Silicosis Mortality Surveillance in the United States, 1968-1990. Appl. Occup. Environ. Hyg. 10(12):1070-1074. Beckett, W., et al. (1997) Adverse Effects of Crystalline Silica Exposure. Statement of the American Thoracic Society, Medical Section of the American Lung Association. American Journal of Respiratory and Critical Care Medicine. 155:761-765. Bergen, E.A.V.D., Rocchi, P.S.J., Boogaard, P.J. (1994) Ceramic Fibers and other Respiratory Hazards during the Renewal of the Refractory Lining in a Large Industrial Furnace. Appl. Occup. Environ. Hyg. 9(1):32-35. Boujemaa, W., Lauwerys, R., Bernard, A. (1994) Early Indicators of Renal Dysfunction in Silicotic Workers. Scand J Work Environ Health. 20:180-3. Centers for Disease Control and Prevention. (1998) Silicosis Deaths Among Young Adults - United States, 1968-1994. MMWR 47(16):331-335. Centers for Disease Control and Prevention. (1997) Silicosis Among Workers Involved in Abrasive Blasting - Cleveland, Ohio, 1995. MMWR 46(32):744-747. Checkoway, H., Heyer, N.J., Demers, P.A., et al. (1993) Mortality among workers in the diatomaceous earth industry. Brit. Jour. Ind. Med. 50:586-597. Cheng, R.T., McDermott, H.J., Gia, G.M., et al. (June 1992) Exposure to Refractory Ceramic Fiber in Refineries and Chemical Plants. Appl. Occup. Environ. Hyg. 7(6):361-367. Davis, G.S. (1996) "Silica," in Occupational and Environmental Respiratory Disease, Mosby-Yearbook Inc., St. Louis, MO, eds. Harber, P., Schencker, M. B., Balmes, J.R. Gantner, B.A. (1986) Respiratory Hazard from Removal of Ceramic Fiber Insulation from High Temperature Industrial Furnaces. Am. Ind. Hyg. Assoc. J. 47(8):530-534. Goldsmith, D.F. (1994) Silica exposure and pulmonary cancer. In: Epidemiology of Lung Cancer, 245-298, Samet, J.M. ed. New York: Marcel Dekker, Inc. IARC . (1997) IARC Monographs on the Evaluation of Carcinogenic Risks to Humans. Silica, Some Silicates, Coal Dust and para-Aramid Fibrils. Vol. 68. Lyon, France. International Agency for Research on Cancer, World Health Organization. Linch, K.D., Miller, W.E., Althouse, R.B., Groce, D.W., Hale, J.M. (1998) Surveillance of Respirable Crystalline Silica Dust using OSHA Compliance Data (1979-1995). American Journal of Industrial Medicine. 34:547-558. Lippmann, M. (1995) Exposure Assessment Strategies for Crystalline Silica Health Effects. Appl. Occup. Environ. Hyg. 10(12):981-990. National Institute for Occupational Safety and Health, Publication No. 92-102 (1992) Hazard Alert: Preventing Silicosis and Deaths from Sandblasting. Olishifski, L.B.; Plog, B.A. (1988) Overview of Industrial Hygiene, Fundamentals of Industrial Hygiene 3rd ed. Chicago, National Safety Council. Peters, J.M. (1986) Silicosis. Occupational Respiratory Diseases. Division of Respiratory Disease Studies, Appalachian Laboratory for Occupational Safety and Health, ed. J.A. Merchant, published by the National Institute for Occupational Safety and Health. Porth, C.M. (1994) Pathophysiology: Concepts of Altered Health States, 4th ed. Unit V, Ch. 26 & 27, J.B. Lippincott Co., Philadelphia. Proctor, N.H., Hughes, J.P., Fischman, M.L. (1988) Chemical Hazards of the Workplace. 2nd ed. J.B. Lippincott Co. Philadelphia. Rapiti, E., Speranti, A., Miceli, M., et al. (1999) End Stage Renal Disease Among Ceramic Workers Exposed to Silica. Occup. Environ. Med. 56:559-561. Rosenman, K.D., Reilly, M.J., Kalinowski, D.J., Watt, F.C. (1997) Silicosis in the 1990s. Chest. 111(3):779-782. Rosenman, K.D., Reilly, M.J., Rice, C., et al. (1996) Silicosis Among Foundry Workers: Implications for the Need to Revise the OSHA Standard. Am. J. Epidemiol. 144(9):890-900. Rosner, D., Markowitz, G. (1994) Deadly Dust: Silicosis and the Politics of Occupational Disease in Twentieth-Century America. Princeton: Princeton University Press. Schluter, D.P. (1994) Silicosis and Coal Worker's Pneumoconiosis. Occupational Medicine. eds. Zens C., et al. 3rd ed. St Louis, Mosby-Year Book, Inc. Starzynski, Z., Marek, K., Kujawska, A., Szymczak, W. (1996) Mortality Among Different Occupational Groups of Workers with Pneumoconiosis: Results From a Register-Based Cohort Study. Am. J. of Ind. Med. 30:718-725. Steenland, K., Mannetje, A., Boffetta, P., Stayner,L., Attfield, M., Chen, J., Dosemeci, M., DeKlerk, N., Hnizdo, E., Koskela, R., and Checkoway, H. (2001). Pooled exposure-response analyses and risk assessment for lung cancer in 10 cohorts of silica-exposed workers: an IARC multicentre study. Cancer Causes and Control 12:773-784. Walsh, S.J. (1999) Effects of Non-mining Occupational Silica Exposures on Proportional Mortality from Silicosis and Systemic Sclerosis. The Journal of Rheumatology. 26(10):2179-2185. Wang, X., Yano, E., Nonaka, K., et al. (1997) Respiratory Impairments Due to Dust Exposure: A Comparative Study Among Workers Exposed to Silica, Asbestos, and Coal Mine Dust. Am. J. of Ind. Med. 31:495-502. Wang, X., Yano, E. (1999) Pulmonary Dysfunction in Silica-Exposed Workers: A Relationship to Radiographic Signs of Silicosis and Emphysema. Am. J. of Ind. Med. 36:299-306. Weill, H., Jones, R.N., Parkes, W.R. (1994) Silicosis and Related Diseases, in Occupational Lung Disorders, 3rd ed., Butterworth-Heinemann Ltd., Oxford, England. Weill, H., McDonald, J.C. (1996) Exposure to Crystalline Silica and Risk of Lung Cancer: The Epidemiological Evidence. Thorax. 51:97-102. Winter, P.D., Gardner, M.J., Fletcher, A.C., Jones, R.D. (1990) A mortality follow-up study of pottery workers: Preliminary findings of lung cancer. In: Occupational Exposure to Silica and Cancer Risk (IARC Scientific Publications, No. 97), 83-94, Simonato, L., et al. eds. International Agency for Research on Cancer. Lyon. This appendix contains a list of industries in which employees may be exposed to elevated levels of crystalline silica. The list is based on a review of inspection data from OSHA's Integrated Management Information System (IMIS) for crystalline silica (quartz), for the period January 1996 through March 2007. This table is intended to show the range of industries in which crystalline silica exposure may occur, but should not be considered to be an exhaustive listing. Employee exposure to crystalline silica may occur in industries not listed here. Likewise, crystalline silica exposure does not occur in all establishments encompassed within these North American Industry Classification System (NAICS) or Standard Industrial Classification (SIC) codes.
This appendix summarizes the procedures for collecting air samples of respirable crystalline silica, contained in OSHA sampling and analytical method ID-142. Although OSHA ID-142 applies to the collection of quartz and cristobalite, tridymite can also be collected and analyzed using this method if the appropriate reference material and diffraction pattern are used. Compliance Safety and Health Officers (CSHOs) should consult the method directly for detailed information. Additionally, information on respirable dust samplers and crystalline silica sampling is contained in the OSHA Technical Manual, Section II: Chapter I. Sampling Equipment 1. A 5-µm pore size, 37-mm diameter polyvinyl chloride (PVC) filter, preceded by a 10-mm nylon Dorr-Oliver cyclone, is used with a personal sampling pump for the collection of airborne respirable crystalline silica. Note: SKC metal cyclones shall not be used for sampling respirable dust (OSHA Instruction TED 01-00-015 {TED1-0.15A}). The metal cyclones do not "cut" the appropriate particle size as required by the OSHA standard. 2. CSHOs may obtain pre-weighed PVC filters by contacting OSHA's Salt Lake Technical Center (SLTC) or Cincinnati Technical Center (CTC). Sampling Instructions 1. Calibrate the personal sampling pump to a flow rate of 1.7 liters per minute (L/min), with a representative sampler assembly (cyclone, filter, etc.) in-line. The pump shall be calibrated before and after each use. Refer to the OSHA Technical Manual (OTM), Section II: Chapter 1, for detailed information on pump calibration when sampling with cyclones. The recommended and maximum sampling time is 480 minutes (resulting in a sample air volume of 816 liters at 1.7 L/min.), and the minimum sample time is 240 minutes (408 liters collected at 1.7 L/min.). 2. Before and after each use, clean the cyclone gently, taking care not to scratch it. A leak test must be conducted on a cyclone at least once a month with regular usage. Refer to the OSHA OTM Section 1: Chapter 1. Also, Appendix D summarizes the Cyclone Leak Test Procedure. 3. The cyclone shall be positioned outside of the employee's personal protective equipment but within the breathing zone. Do not allow the cyclone to be inverted during or after sampling. Maintain the cyclone in an upright position until the filter is removed from the cyclone. 4. Check the pump and sampling assembly periodically, to verify pump performance and monitor particulate loading on the sample filter. Filters should be replaced when employees move to another task or activity, or if observation during sampling suggests possible filter overload (greater than 3 mg.). [Note: The CSHO should not enter an area while the abrasive blasting operation is active.] 5. When submitting the sample to the laboratory, indicate whether the requested analysis is for quartz, cristobalite, or both. Operations in which the material has been heated to high temperatures generally should be analyzed for both. When other airborne compounds are known or suspected to be present, such information, including the suspected identities, should be provided to the laboratory. Where possible, a copy of the MSDS should be submitted to aid in identifying interferences. Potential analytical interferences are listed in Appendix A of OSHA ID-142. A partial listing follows:
7. Obtain bulk samples in accordance with standard procedures described in the OTM, Section II: Chapter 1. The bulk sample should be representative of the airborne silica content of the work environment, e.g., from settled dust. A bulk sample of the raw material should be collected to evaluate compliance with the Hazard Communication standard. The type of bulk sample shall be stated on the OSHA-91 form and cross-referenced to the appropriate air samples. Determining Compliance with the PEL for Respirable Crystalline Silica The General Industry permissible exposure limit (PEL) for respirable dust containing crystalline silica (as quartz), codified at 29 CFR 1910.1000, is determined individually for each sample, according to the following formula: The PEL can be calculated either by following the steps below, or by accessing the "Advisor Genius" on-line at the OSHA web site. The Advisor Genius performs the calculations for a respirable dust sample and yields three values: the PEL for the sample, the respirable dust exposure result, and the severity. To determine the PEL for an air sample containing respirable crystalline silica: 1. Obtain the respirable dust concentration for the sample. The weight of the respirable dust in the air sample (expressed as mg or µg) is the net filter weight gain, as determined by the industrial hygienist or the laboratory. The sample air volume is then used to express the concentration of respirable dust in air, as mg of respirable dust per cubic meter of air (mg/m³), as follows: 2. Obtain the percent respirable crystalline silica (e.g., as quartz) in the respirable dust sample, determined analytically by the laboratory and derived as follows: 3. Calculate the PEL for the sample, using the reported percent respirable quartz, from no. 2 above, as follows: 4. To determine whether there is an overexposure, compare the PEL, calculated in no. 3, with the sample respirable dust reading (from no. 1). The severity ratio is determined by the following formula: 5. Calculate the Lower Confidence Limit (LCL) by subtracting the Sampling and Analytical Error (SAE) from the severity: LCL = Severity - SAE If the LCL is greater than 1, there is a greater than 95% confidence that the sampled employee's exposure exceeded the PEL, and the employee was, therefore, overexposed to respirable dust containing crystalline silica as quartz. Other factors may have to be considered before arriving at a final exposure value. For example, the Time Weighted Average (TWA) calculation may require combining two or more sample results and adjusting to an 8-hour workday. Consult the OTM, Section II: Chapter 1 for procedures to determine the PEL when the employee is exposed to different types of respirable crystalline silica (i.e., quartz, cristobalite, and tridymite) during the course of a single work shift. References Occupational Safety and Health Administration (OSHA). OSHA ID-142. Quartz and Cristobalite in Workplace Atmospheres (XRD). December 1996. Occupational Safety and Health Administration (OSHA), OSHA Technical Manual TED 01-00-015 (TED 1-0.15A). Section II: Sampling, Measurement Methods and Instruments, Chapter I: Personal Sampling for Air Contaminants, Appendix II:1-5. Sampling for Special Analyses, Samples Analyzed by X-Ray Diffraction, Air Samples, January 20, 1999. This section summarizes procedures for leak testing of the Dorr-Oliver cyclone samplers used for collecting respirable dust. Further details on this procedure are contained in the Cyclone Leak Test Procedure (CLTP) available through the OSHA Cincinnati Technical Center (OSHA, 1997). Compliance Safety and Health Officers (CSHOs) should review the entire leak test procedure before conducting the leak test as summarized below. See the CLTP for more specific procedures regarding leak tests. Nylon Part Inspection
Final Pump-Fault Leak Test
Occupational Safety and Health Administration (OSHA). Cyclone Leak Test Procedure. OSHA Cincinnati Technical Center. September 15, 1997. The crystalline silica permissible exposure limits (PELs) for the construction and maritime industries, at 29 CFR 1926.55(a) and 1915.1000 respectively, are expressed in terms of millions of particles per cubic foot (mppcf). These PELs are based on a particle count method long rendered obsolete by respirable mass (gravimetric) sampling, which yields results reported in milligrams per cubic meter (mg/m3). In contrast with the construction and maritime PELs, the crystalline silica PELs for general industry are based on gravimetric sampling, and are the only methods currently available to OSHA compliance personnel. Since the construction and maritime PELs are expressed in terms of mppcf, the results of the gravimetric sampling must be converted to an equivalent mppcf value. In order to determine a formula for converting from mg/m3 to mppcf, OSHA requested assistance from the National Institute for Occupational Safety and Health (NIOSH). Based on its review of published studies comparing the particle count and gravimetric methods, NIOSH recommended a conversion factor of 0.1 mg/m3 respirable dust to 1 mppcf. OSHA has determined that this conversion factor should be applied to silica sampling results used to characterize exposures in construction and maritime operations. The following examples illustrate how the conversion factor should be applied to enforce the current PEL for crystalline silica (quartz) in the construction and maritime industries. Reference Formulas
This questionnaire, when completed, may be considered a medical record and must be used in accordance with 1913.10 - Rules Concerning OSHA Access to Employee Medical Records. The questionnaire is intended to provide Compliance Safety and Health Officers (CSHOs) with a form they may fill out when interviewing employees to evaluate the employer's medical monitoring program. CSHOs should consult with the OSHA Office of Occupational Medicine regarding any findings of potential silicosis.
A. Personal Information
B. Job-Related Information
C. Brief Medical History
Appendix G: Non-Mandatory Medical Monitoring Recommendations for Employees Exposed to Crystalline Silica
This non-mandatory checklist is intended as a quick reference tool for Compliance Safety and Health Officers (CSHOs) conducting silica-related inspections. The CSHO may wish to review the checklist before completing the inspection to make sure that none of the essential elements have been overlooked. The checklist addresses all of the topics discussed in Section XI(B), Inspection Procedures, of this directive.
1. OSHA 1 2. OSHA 1A 3. OSHA 1B/IH for overexposures to silica. 4. Engineering Controls (including failed ones) used to control silica exposures. See section XI. D. - Follow-up and Monitoring for additional information. ACGIH. 2004. Industrial Ventilation, A Manual of Recommended Practice. 25th Edition. American Conference of Governmental Industrial Hygienists. Cincinnati, OH. Akbar-Khanzadeh, F., and R. L. Brillhart. (2002). Respirable Crystalline Silica Dust Exposure during Concrete Finishing (Grinding) using Hand-held Grinders in the Construction Industry. Ann. Occup. Hyg. 46(3):341-346. Alpaugh, E.L.; rev. Hogan, T.J. (1988) Particulates. Fundamentals of Industrial Hygiene. Ed Plog, B.A. 3rd ed. Chicago, National Safety Council, 141. Amandus, H., Costello, J. (1991) Silicosis and Lung Cancer in U.S. Metal Miners. Arch. Environ Health. 46:82-89. Archer, C., Gordon, D.A. (1996) Silica and Progressive Systemic Sclerosis (Scleroderma): Evidence for Workers' Compensation Policy. 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A Abatement Verification Abrasive Blasting Alliances Application Assigned Protection Factor B Background Bricks Bronchitis Bulk Samples C Carcinogen Case File Submission Cement Boards Complaints Compressed Air Construction PEL Consultation Programs Contaminated Clothing Conversion Factor Coordination Crushed Stone CSHO Checklist Cylcone Leak Testing D Deletions E Employee Questionnaire Employee Records Engineering Controls Evaluation Expanding Inspection Scope Exposure Monitoring F Federal Agencies Federal Program Change Follow Up Forms of Silica G Goals of NEP GPRA H Hazard Communication Health Effects of Silica House Keeping Hygiene Practices I IARC IMIS Coding Instructions Industrial Sources of Crystalline Silica Exposure Industry Identification Inspection Procedures Inspection Scheduling L Lung Cancer M Master List Medical Monitoring Recommendations Minimum Respiratory Protection MSHA N Non-English Speaking Groups O Outreach P Partnerships PEL Calculations Purpose of NEP R Recordkeeping References Referrals Renal Disease Resource Allocation Respiratory Protection S Sampling Equipment Sampling Instructions Scheduling Scleroderma Severity Ratio SIC Codes Silica Sources Silicosis Silicosis History Site Selection Stomach Cancer T Targeting Sources/Audiences Thoracic samples Tuberculosis V Ventilation W Work Practice Controls |
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