environmental health safety and risk management university of alaska fairbanks n.
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A guide to working with Silica

A guide to working with Silica

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A guide to working with Silica

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  1. Environmental Health, Safety and Risk Management University of Alaska Fairbanks A guide to working with Silica December 2010

  2. Overview • Silica: crystalline vs. amorphous • Part I: Crystalline Silica • Health Hazards • Exposure Limits • Exposure Monitoring • Ways to Reduce Exposure • Online Resources

  3. Overview (cont.) • Part II: Amorphous Silica • Examples • Exposure Limits • Synthetic Vitreous Fibers • Health Hazards • Exposure Limits • Engineering Controls • Internet Resources

  4. Silica • Silica (SiO2, silicon dioxide) is one of the most common minerals in the earth’s crust and is a major component of sand, rock and mineral ores • Silica is used in the manufacturing of a variety of products from kitty litter to fiber optic cables to cosmetics and food additives

  5. Silica (cont.) • Silica occurs as both crystalline (structured) and non-crystalline (amorphous) forms. Diagram source:

  6. Part I: Crystalline Silica

  7. Silica: Crystalline • Has a diagnostic X-ray diffraction* pattern *analytical technique which reveals information about the crystallographic structure, chemical composition, and physical properties of materials • Most common types (formed under different pressures and temperatures) • Quartz (alpha & beta) • Cristobalite • Tridymite

  8. Silica, Crystalline,Health Hazards,Silicosis • Silicosis is a disabling, nonreversible and sometimes fatal lung disease caused by overexposure to respirable* dust containing crystalline silica *respirable means deposited in the gas-exchange region or deepest part of the lungs • Overexposure to dust that contains respirable crystalline silica can cause scar tissue to form in the lungs, which reduces the lungs’ ability to extract oxygen from the air

  9. Silicosis (cont.) • Inhalation of crystalline silica particles has been associated with other diseases, such as bronchitis, emphysema, and tuberculosis • Some studies also indicate an association with lung cancer, immunologic disorders, autoimmune diseases, renal disease and stomach and other cancers

  10. Silicosis (cont.) • There are 3 types of silicosis: • CHRONIC silicosis, which usually occurs after 10 or more years of exposure at relatively low concentrations. This is the most common form of silicosis • ACCELERATED silicosis, which develops 5 to 10 years after the first exposure • ACUTE silicosis, which develops after exposure to high concentrations of respirable crystalline silica and results in symptoms within a period ranging from a few weeks to 5 years after the initial exposure

  11. Silicosis (cont.) • Common symptoms • shortness of breath following physical exertion • severe cough • fatigue • loss of appetite • chest pains • fever • cyanosis (bluish skin)

  12. Silicosis: Who is at risk? Do you work in: • construction • mining, quarrying • foundry work • ceramics, clay, and pottery • stone cutting • glass manufacturing • agriculture • shipyards • railroad • manufacturing and use of abrasives (including sand blasting denim to “age” it!) • dental laboratories • manufacturing of soaps and detergents

  13. Silicosis, Special Emphasis Program • In 1996, OSHA established a Special Emphasis Program (SEP) for Silicosis, which provided guidance for targeting inspections of worksites with employees at risk of developing silicosis

  14. Crystalline Silica, National Emphasis Program • Effective January 24, 2008, OSHA implemented a National Emphasis Program (NEP) to identify, reduce, and eliminate the health hazards associated with occupational exposure to crystalline silica • Why? Because silica-related illnesses and fatalities continue to occur

  15. National Emphasis Program (cont.) • The NEP is a written compliance directive incorporating updated information and policies and procedures adopted since 1996 • Expands 1996 Special Emphasis Program • Provides updated research results on silica exposure hazards

  16. National Emphasis Program (cont.) • Details inspection procedures, including follow-up inspections where overexposure found • Addresses targeting of worksites and provides updated NAICS (North American Industrial Classification System ) codes for industries with worker exposure to crystalline silica

  17. National Emphasis Program (cont.) • Explains calculation of PELS (Permissible Exposure Limits) in General Industry, Construction, and Shipyard • Establishes program evaluation procedures • Provides for Regional and Area Office outreach programs

  18. OSHA Crystalline Silica Exposure Standards • General Industry: 29 CFR 1910.1000 • Construction: 29 CFR 1926.55(a) • Shipyard: 29 CFR 1915.1000

  19. Crystalline Silica Exposure Limits, OSHA PELs • OSHA regulates silica exposure using the permissible exposure limit (PEL), which is the maximum amount of airborne dust an employee may be exposed to during a full work shift.The PEL is dependent on • the % silica content of the dust from a sample collected over an 8 hour time period • whether it is respirable or not • the composition (quartz, cristobalite or tridymite)

  20. Crystalline Silica Exposure Limits: Other Guidelines • ACGIH (American Conference of Governmental Industrial Hygienists) Threshold Limit Value (TLV) for respirable quartz (alpha) and cristobalite: 0.025 mg/m3 • NIOSH (National Institute for Occupational Safety and Health) Recommended Exposure limit (REL) for respirable crystalline silica: 0.05 mg/m3

  21. Crystalline Silica “Bottom Line” Message The more crystalline silica there is in the dust, the less of the dust you should breathe

  22. Crystalline Silica: ExposureMonitoring • Exposure monitoring (air sampling) • Measures worker exposures to respirable crystalline silica and helps select appropriate engineering controls and respiratory protection • Monitors effectiveness of the controls • Determines if exposures are in excess of permissible exposure levels (PELs) • Performed when an employee is experiencing symptoms or health effects that may be attributable to crystalline silica • If you believe you need to have an exposure assessment conducted, contact EHS&RM at 474-6771 or 474-5197

  23. Ways to Reduce Exposure to Crystalline Silica: Engineering Controls • Substitute materials that have no crystalline silica • Locate employees as far as possible from dust-generation source • Isolate employees OR the source • Control rooms • Enclosures • Barriers

  24. Ways to Reduce Crystalline Silica Exposure: Engineering Controls (cont’d) • Use local exhaust ventilation (LEV systems) • Use tools with dust-collecting systems • Use wet methods • Cutting • Chipping • Drilling • Sawing • Grinding • Clean surfaces with HEPA vacuums or wet sweeping—no compressed air!

  25. Ways to Reduce Crystalline Silica Exposure: RespiratoryProtection • And if other controls are not sufficient— Use Proper Respiratory Protection Source: NIOSH Publication No. 2004-108: Silicosis: Learn the Facts!

  26. Ways to Reduce Exposure: Respiratory Protection (cont’d) Source: NIOSH Publication No. 2004-108: Silicosis: Learn the Facts!

  27. Ways to Reduce Exposure: Respiratory Protection (cont’d) • When respirators are used, the employer must establish a comprehensive respiratory protection program, required in the OSHA respiratory protection standard (29 CFR 1910.134 and 1926.103) and as outlined in the NIOSH Guide to Industrial Respiratory Protection (NIOSH 1987a) • The respiratory protection program should be evaluated regularly by the employer

  28. Ways to Reduce Exposure: Respiratory Protection (cont’d) • Important elements of this standard are • periodic environmental monitoring • regular training of personnel • selection of proper NIOSH-approved respirators • an evaluation of the worker's ability to perform the work while wearing a respirator • respirator fit testing • maintenance, inspection, cleaning, and storage of respiratory protection equipment.

  29. OSHA Internet Information on Crystalline Silica

  30. Part II: Amorphous Silica

  31. Cannot distinguish by X-ray diffraction Silica: Amorphous • Under certain conditions, heating amorphous silica results in conversion to the crystalline form

  32. Silica: Amorphous (cont.) • Common examples of naturally occurring amorphous silica: • Diatom cell walls (a prolific group of algae that live in oceans, freshwater and soils) • Volcanic glass

  33. Silica: Amorphous (cont.) • Common examples of products containing amorphous silica: • Diatomaceous earth • Window glass • Synthetic Vitreous Fibers such as fiberglass

  34. Silica: Amorphous, Health Hazards • Studies have found amorphous silica to be biologically inert when ingested and inhaled, with the exception of certain synthetic vitreous fibers (to be discussed later) • Studies have found that exposure to amorphous silica is not associated with the development of silicosis

  35. Amorphous Silica Exposure Limits, Regulated • The PELs (permissible exposure limits) for amorphous silica is found in the following regulations: • General Industry: 29 CFR 1910.1000 Z-3 • Construction: 29 CFR 1926.55 Appendix A • Shipyard : 29 CFR1915.1000

  36. Amorphous Silica Exposure Limits, Regulated: PEL • The PEL for amorphous silica, including natural diatomaceous earth 80 mg/m3as% silica content of the dust from a sample collected over an 8 hour time period • The PEL applies to General Industry, Construction and Shipyard Standards

  37. Amorphous Silica: Exposure Limits, Other Guidelines, REL & TLV • The NIOSH REL for amorphous silica is 6 mg/m3 • ACGIH has withdrawn the TLV for amorphous silica largely because the TLV was derived from studies on diatomaceous earth , and did not take into account the crystalline silica content of the diatomaceous earth

  38. Amorphous Silica: Synthetic Vitreous Fibers • Synthetic vitreous fibers (SVF) are a group of fibrous inorganic materials that contain aluminum or calcium silicates and other trace oxides and metal • SVFs are made from rock, slag, clay, or glass • They are sometimes called Synthetic Mineral Fibers (SMF)

  39. Amorphous Silica: Synthetic Vitreous Fibers(cont.) Source: “Toxicological Profile for Synthetic Vitreous Fibers”, U.S. Department of Health and Human Services, Agency for Toxic Substances and Disease Registry, September 2004

  40. Amorphous Silica: Synthetic Vitreous Fibers(cont.) • To be considered a fiber, the particle must: • be at least 5 micrometers long (1 micrometer equals 1/1,000,000 of a meter and has the symbol μm) • have an aspect ratio of at least 3 to 1 or sometimes 5 to 1 (the aspect ratio is the ratio of a fiber’s length to its diameter).

  41. Amorphous Silica: Synthetic Vitreous Fibers(cont.) • The diameter of a fiber is an important property because very thin fibers are more easily suspended in air than thick fibers, and they can be breathed in and deposited deep in the lungs. • Only very thin fibers with diameters < 3 μmare able to be breathed into the lower respiratory tract of humans. • In general, glass wool, rock wool, slag wool, and refractory ceramic fibers have the smallest diameters, while continuous filament glass fibers have the largest diameters.

  42. Amorphous Silica: Synthetic Vitreous Fibers(cont.) • The primary uses of synthetic vitreous fibers are: • heat and sound insulating purposes • reinforce other materials • filtration materials

  43. Amorphous Silica: Synthetic Vitreous Fibers, Health Hazards • Results from animal experiments have led to conservative classifications of certain synthetic vitreous fibers as possible human carcinogens

  44. Amorphous Silica: Synthetic Vitreous Fibers, Health Hazards (cont.) Source:

  45. Synthetic Vitreous Fibers:Exposure Limits, Regulated, PELs • General Industry : 29 CFR 1910.1000 Table Z-3"Inert or Nuisance Dust” and • Shipyard: 29 CFR 1915.1000 Table Z Mineral Wool and Fibrous Glass • Respirable Fraction: 5 mg/m3 • Total Dust: 15 mg/m3

  46. Synthetic Vitreous Fibers:Other Guidelines: ACGIH • Glass wool, rock wool and slag wool fibers and special purpose glass fibers (confirmed animal carcinogen with unknown relevance to humans): 1 fiber/cc (cubic centimeter) • Refractory ceramic fibers (suspected human carcinogen) 0.2 fibers/cc

  47. Synthetic Vitreous Fibers:Other Guidelines: ACGIH (cont.) • Continuous filament glass fibers (not classifiable as a human carcinogen): • Respirable 1 fiber/cc • Inhalable (deposited anywhere in the respiratory tract) 5 mg/m3

  48. Synthetic Vitreous Fibers:Other Guidelines: NIOSH • TWA (8 hour average) • Fibers with diameter £3.5 µm and length ³ 10 µm 3 fibers/cc • Total dust 5 mg/m3

  49. Engineering Controls for Synthetic Vitreous Fibers • Local exhaust ventilation • Wet methods for activities such as installation, removal, cutting, grinding, sawing • Use of plastic sheeting to enclose or encapsulate • Clean up with a high-efficiency particulate air (HEPA) vacuum cleaner followed by wet wiping • And if other controls are not sufficient— Use Proper Respiratory Protection

  50. OSHA Internet Information: Synthetic Vitreous Fibers