A GUIDE TO WORKING WITH SILICA Environmental, Health, Safety, and Risk Management University of Alaska Fairbanks May 2015

OVERVIEW  Silica: crystalline vs. amorphous  Part I: Crystalline Silica  Health Hazards  Exposure Limits  Exposure Monitoring  Ways to Reduce Exposure  Medical surveillance 2

OVERVIEW (CONT.)  Part II: Amorphous Silica  Examples  Exposure Limits  Synthetic Vitreous Fibers  Health Hazards  Exposure Limits  Engineering Controls 3

SILICA  Silica (SiO 2, 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 4

SILICA (CONT.)  Silica occurs as both crystalline (structured) and non-crystalline (amorphous) forms. 5 Diagram source:

PART I: CRYSTALLINE SILICA 6

CRYSTALLINE SILICA Has a diagnostic X-ray diffraction* pattern due to an orderly crystalline structure * analytical technique which reveals information about the structure, chemical composition, and physical properties of materials 7 Most common types (formed under different pressures and temperatures )  Quartz (alpha & beta)  Cristobalite  Tridymite

CRYSTALLINE SILICA AND DISEASE: SILICOSIS  Overexposure to dust that contains respirable* crystalline silica can cause scar tissue to form, reducing the lungs’ ability to extract oxygen from the air  This can result in a disease called silicosis  Silicosis is a disabling, nonreversible, and sometimes fatal lung disease  *respirable dust particles are small enough to travel to the deepest part of the lungs, where gas-exchange occurs 8

CRYSTALLINE SILICA AND DISEASE (CONT.)  Inhalation of crystalline silica particles has been associated with other diseases, such as bronchitis, emphysema, and tuberculosis  Some studies have shown an association with lung cancer, immunologic disorders, autoimmune diseases, kidney disease, and stomach and other cancers 9

SILICOSIS  There are 3 types of silicosis:  CHRONIC silicosis  usually occurs after 10 or more years of exposure at relatively low concentrations. This is the most common form of silicosis.  ACCELERATED silicosis  develops 5 to 10 years after the first exposure  ACUTE silicosis  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 10

SILICOSIS (CONT.)  Common symptoms  shortness of breath following physical exertion  severe cough  fatigue  loss of appetite  chest pains  fever  cyanosis (bluish skin) 11

SILICOSIS (CONT.) 12 X-ray of normal lungs (left) and the lungs of a person with silicosis (right).

SILICOSIS: WHO IS AT RISK?  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 DO YOU WORK IN:

OSHA CRYSTALLINE SILICA EXPOSURE STANDARDS  Current regulations are found under 29 CFR (Air contaminants)  OSHA has proposed a new rule that covers Crystalline Silica. It is currently in the process of being finalized.  It will be found under 29 CFR

EXPOSURE LIMITS FOR CRYSTALLINE SILICA OSHA regulates silica exposure using the permissible exposure limit (PEL) The PEL is the maximum amount of airborne dust an employee may be exposed to during a full 8-hour work shift. The current OSHA PEL is dependent on  the % silica content of the dust  whether it is respirable or not  the composition (quartz, cristobalite or tridymite) OSHA has proposed a new PEL of 0.05 mg/m 3, but it has not gone into effect yet. The action level will be mg/m 3 (more on this later). 15

CRYSTALLINE SILICA EXPOSURE LIMITS: OTHER GUIDELINES  ACGIH (American Conference of Governmental Industrial Hygienists) Threshold Limit Value (TLV) for respirable quartz (alpha) and cristobalite: mg/m 3 TWA (8 hour time weighted average)  NIOSH (National Institute for Occupational Safety and Health) Recommended Exposure limit (REL) for respirable crystalline silica: 0.05 mg/m 3 16

CRYSTALLINE SILICA “BOTTOM LINE” MESSAGE The more crystalline silica there is in the dust, the less of the dust you should breathe The coal used at the UAF Power Plant and the ash produced there typically contain from 2-7% respirable quartz. 17

CRYSTALLINE SILICA: EXPOSURE MONITORING Exposure monitoring (air sampling)  Measures worker exposures to respirable crystalline silica  Helps determine appropriate engineering controls and respiratory protection  Monitors effectiveness of the controls  Determines if exposures are in excess of PELs  Is 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 EHSRM at

CRYSTALLINE SILICA: EXPOSURE MONITORING (CONT.) Exposure monitoring (air sampling)  According to proposed OSHA standard for crystalline silica, additional exposure monitoring must be done:  Every 6 months if employee exposures are > mg/m 3 (over the action level)  Every 3 months if employee exposures are >0.05 mg/m 3 (over the PEL)  If employee exposures are below the action level, then additional air sampling is only needed if procedures or work conditions change. 19

REDUCING EXPOSURE TO CRYSTALLINE SILICA: ENGINEERING CONTROLS  Substitute materials that do not contain crystalline silica  Locate employees as far as possible from the dust- generating source  Isolate employees OR the isolate the source  Control rooms  Enclosures  Barriers 20

REDUCING CRYSTALLINE SILICA EXPOSURE: ENGINEERING CONTROLS (CONT.)  Use local exhaust ventilation (LEV systems)  Use tools with dust-collecting systems  Use wet methods for:  Cutting  Chipping  Drilling  Sawing  Grinding  Clean surfaces with HEPA vacuums or wet sweeping— use compressed air will soon be prohibited by law under the new regulations! 21

REDUCING CRYSTALLINE SILICA EXPOSURE: RESPIRATORY PROTECTION If engineering controls are not sufficient to keep exposures down, then proper respiratory protection must be used. When respirators are used, the employer must establish a comprehensive respiratory protection program, required in the OSHA respiratory protection standard ( 29 CFR ) The respiratory protection program should be evaluated regularly by the employer. 22

REDUCING EXPOSURE: RESPIRATORY PROTECTION (CONT.)  Important elements of this standard are  periodic environmental monitoring  regular training of personnel  selection of appropriate NIOSH-approved respirators  a medical evaluation of the worker's ability to wear a respirator  annual respirator fit testing  maintenance, inspection, cleaning, and storage of respiratory protection equipment 23

TYPES OF RESPIRATORY PROTECTION 24 Source: NIOSH Publication No : Silicosis: Learn the Facts!

TYPES OF RESPIRATORY PROTECTION (CONT.) 25 Source: NIOSH Publication No : Silicosis: Learn the Facts!

MEDICAL SURVEILLANCE Employees exposed to respirable crystalline silica at or above the PEL for 30 days or more per year must:  Receive an initial physical, including chest x-ray  Receive a follow up physical at least every 3 years Chest x-rays are repeated every 5 years, or more often depending on the length of time the employee has had exposure to respirable crystalline silica. 26

MEDICAL SURVEILLANCE (CONT.) Physicals shall focus on:  Lung function and the respiratory system  Screening for tuberculosis  Other signs and symptoms associated with silica- related disease Physicals are provided at no cost to the employee and at a time and location that is convenient to the employee. The medical provider must provide a written opinion within 30 days, and medical records are retained for the duration of employment plus 30 years. 27

PART II: AMORPHOUS SILICA 28

SILICA: AMORPHOUS  Under certain conditions, heating amorphous silica results in conversion to the crystalline form 29  Cannot distinguish by X-ray diffraction

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 30

SILICA: AMORPHOUS (CONT.) Common examples of products containing amorphous silica:  Diatomaceous earth  Window glass  Synthetic Vitreous Fibers such as fiberglass 31

AMORPHOUS SILICA: 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 32

AMORPHOUS SILICA: EXPOSURE LIMITS The OSHA PEL for amorphous silica, including natural diatomaceous earth is: 80 mg/m 3 divided by the % silica content of the dust So if your dust contains 8% amorphous silica, then the PEL would be 80 mg/m 3 divided by 8, or 10 mg/m 3 The NIOSH REL for amorphous silica is 6 mg/m 3 ACGIH has withdrawn the TLV for amorphous silica due to insufficient data 33

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) 34

SYNTHETIC VITREOUS FIBERS (CONT.) 35 Source: “Toxicological Profile for Synthetic Vitreous Fibers”, U.S. Department of Health and Human Services, Agency for Toxic Substances and Disease Registry, September 2004

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) 36

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 travel into the lower respiratory tract.  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. 37

SYNTHETIC VITREOUS FIBERS (CONT.) The primary uses of synthetic vitreous fibers are:  For heat and sound insulating purposes  To reinforce other materials  For filtration materials 38

SYNTHETIC VITREOUS FIBERS: HEALTH HAZARDS Results from animal experiments have led to conservative classifications of certain synthetic vitreous fibers as possible human carcinogens 39

SYNTHETIC VITREOUS FIBERS: EXPOSURE LIMITS (CONT.) OSHA General Industry—29 CFR Table Z-3 "Inert or Nuisance Dust”  Respirable Fraction: 5 mg/m 3  Total Dust: 15 mg/m 3 NIOSH  Fibers with diameter  3.5 µm and length  10 µm: 3 fibers/cc  Total dust: 5 mg/m 3 40

SYNTHETIC VITREOUS FIBERS: EXPOSURE LIMITS (CONT.) 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 fiber/cc  Continuous filament glass fibers (not classifiable as a human carcinogen):  Respirable: 1 fiber/cc  Inhalable (deposited anywhere in the respiratory tract): 5 mg/m 3 41

SYNTHETIC VITREOUS FIBERS: ENGINEERING CONTROLS Engineering controls include:  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 42

THANK YOU! QUESTIONS? 43