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A GUIDE TO WORKING WITH SILICA

Environmental Health, Safety and Risk ManagementUniversity of Alaska Fairbanks

December 2010

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Overview

Silica: crystalline vs. amorphous Part I: Crystalline Silica

Health Hazards Exposure Limits Exposure Monitoring Ways to Reduce Exposure Online Resources

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Overview (cont.)

Part II: Amorphous Silica Examples Exposure Limits Synthetic Vitreous Fibers

Health Hazards Exposure Limits Engineering Controls Internet Resources

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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

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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

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Part I: Crystalline Silica

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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

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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

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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

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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

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Silicosis (cont.)

Common symptoms shortness of breath following physical

exertion severe cough fatigue loss of appetite chest pains fever cyanosis (bluish skin)

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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

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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

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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

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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

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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

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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

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OSHA Crystalline Silica Exposure Standards General Industry: 29 CFR

1910.1000 Construction: 29 CFR 1926.55(a) Shipyard: 29 CFR 1915.1000

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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)

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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

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Crystalline Silica “Bottom Line” Message

The more crystalline silica there is in the dust, the less of the dust

you should breathe

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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

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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

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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!

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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!

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Ways to Reduce Exposure: Respiratory Protection (cont’d)

Source: NIOSH Publication No. 2004-108: Silicosis: Learn the Facts!

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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

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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.

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OSHA Internet Information on Crystalline Silicahttp://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

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Part II: Amorphous Silica

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Silica: Amorphous

Under certain conditions, heating amorphous silica results in conversion to the crystalline form

Cannot distinguish by X-ray diffraction

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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

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Silica: Amorphous (cont.) Common examples of products

containing amorphous silica: Diatomaceous earth Window glass Synthetic Vitreous Fibers such

as fiberglass

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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

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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

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Amorphous Silica Exposure Limits, Regulated: PEL

The PEL for amorphous silica, including natural diatomaceous earth

80 mg/m3 as % 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

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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

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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)

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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

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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).

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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 μm are 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.

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Amorphous Silica: Synthetic Vitreous Fibers (cont.) The primary uses of synthetic

vitreous fibers are: heat and sound insulating purposes reinforce other materials filtration materials

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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

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

Source: http://www.osha.gov/SLTC/syntheticmineralfibers/table2.html

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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 ZMineral Wool and Fibrous Glass

Respirable Fraction: 5 mg/m3

Total Dust: 15 mg/m3

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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

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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

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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 dust5 mg/m3

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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

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OSHA Internet Information: Synthetic Vitreous Fibers

www.osha.gov/SLTC/syntheticmineralfibers/index.htmlwww.atsdr.cdc.gov/substances/toxsubstance.asp?toxid=185

www.cdc.gov/niosh/docs/2006-123/