Environmental Health, Safety and Risk Management University of Alaska Fairbanks A guide to working with Silica December 2010
Overview • Silica: crystalline vs. amorphous • Part I: Crystalline Silica • Health Hazards • Exposure Limits • Exposure Monitoring • Ways to Reduce Exposure • Online Resources
Overview (cont.) • Part II: Amorphous Silica • Examples • Exposure Limits • Synthetic Vitreous Fibers • Health Hazards • Exposure Limits • Engineering Controls • Internet Resources
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
Silica (cont.) • Silica occurs as both crystalline (structured) and non-crystalline (amorphous) forms. Diagram source: http://www.osha.gov/SLTC/etools/silica/silicosis/silicosis.html
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
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
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
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
Silicosis (cont.) • Common symptoms • shortness of breath following physical exertion • severe cough • fatigue • loss of appetite • chest pains • fever • cyanosis (bluish skin)
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
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
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
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
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
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
OSHA Crystalline Silica Exposure Standards • General Industry: 29 CFR 1910.1000 • Construction: 29 CFR 1926.55(a) • Shipyard: 29 CFR 1915.1000
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)
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
Crystalline Silica “Bottom Line” Message The more crystalline silica there is in the dust, the less of the dust you should breathe
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
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
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!
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!
Ways to Reduce Exposure: Respiratory Protection (cont’d) Source: NIOSH Publication No. 2004-108: Silicosis: Learn the Facts!
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
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.
OSHA Internet Information on Crystalline Silica http://www.osha.gov/pls/oshaweb/owadisp.show_document?p_table=DIRECTIVES&p_id=3790 http://www.osha.gov/SLTC/silicacrystalline/index.html http://www.osha.gov/dte/library/materials_library.html#silica www.cdc.gov/niosh/topics/silica www.cdc.gov/niosh/docs/2005-100/default.html
Cannot distinguish by X-ray diffraction Silica: Amorphous • Under certain conditions, heating amorphous silica results in conversion to the crystalline form
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
Silica: Amorphous (cont.) • Common examples of products containing amorphous silica: • Diatomaceous earth • Window glass • Synthetic Vitreous Fibers such as fiberglass
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
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
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
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
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)
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
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).
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.
Amorphous Silica: Synthetic Vitreous Fibers(cont.) • The primary uses of synthetic vitreous fibers are: • heat and sound insulating purposes • reinforce other materials • filtration materials
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
Amorphous Silica: Synthetic Vitreous Fibers, Health Hazards (cont.) Source: http://www.osha.gov/SLTC/syntheticmineralfibers/table2.html
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
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
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
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
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
OSHA Internet Information: Synthetic Vitreous Fibers www.osha.gov/SLTC/syntheticmineralfibers/index.html www.atsdr.cdc.gov/substances/toxsubstance.asp?toxid=185 www.cdc.gov/niosh/docs/2006-123/