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

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
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OVERVIEW (CONT.)
 Part II: Amorphous Silica
 Examples
 Exposure Limits
 Synthetic Vitreous Fibers
 Health Hazards
 Exposure Limits
 Engineering Controls
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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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CRYSTALLINE SILICA
Most common types
(formed under different
pressures and temperatures)
 Quartz (alpha & beta)
 Cristobalite
 Tridymite
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
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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
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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
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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
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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)
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SILICOSIS (CONT.)
X-ray of normal lungs (left) and the lungs of a person with silicosis (right).
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SILICOSIS:
WHO IS AT RISK?
DO YOU WORK IN:
 construction
 mining, quarrying
 shipyards
 railroad
 foundry work
 manufacturing and use of
 ceramics, clay, and pottery abrasives (including sand
blasting denim to “age” it!)
 stone cutting
 dental laboratories
 glass manufacturing
 manufacturing of soaps
 agriculture
and detergents
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OSHA CRYSTALLINE SILICA EXPOSURE
STANDARDS
 Current regulations are found
under 29 CFR 1910.1000 (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
1910.1053.
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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/m3, but it has
not gone into effect yet. The action level will be 0.025
mg/m3 (more on this later).
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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 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/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
The coal used at the UAF Power Plant and the ash
produced there typically contain from 2-7%
respirable quartz.
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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 474-6771
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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 > 0.025
mg/m3 (over the action level)
 Every 3 months if employee exposures are >0.05
mg/m3 (over the PEL)
 If employee exposures are below the action level, then
additional air sampling is only needed if procedures or
work conditions change.
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REDUCING EXPOSURE TO
CRYSTALLINE SILICA: ENGINEERING
CONTROLS
 Substitute materials that do not contain
crystalline silica
 Locate employees as far as possible from the dustgenerating source
 Isolate employees OR the isolate the source
 Control rooms
 Enclosures
 Barriers
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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!
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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
1910.134)
The respiratory protection program should be evaluated
regularly by the employer.
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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
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TYPES OF RESPIRATORY
PROTECTION
Source:
NIOSH
Publication
No. 2004108:
Silicosis:
Learn the
Facts!
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TYPES OF RESPIRATORY PROTECTION
(CONT.)
Source: NIOSH Publication
No. 2004-108: Silicosis:
Learn the Facts!
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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.
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MEDICAL SURVEILLANCE (CONT.)
Physicals shall focus on:
 Lung function and the respiratory system
 Screening for tuberculosis
 Other signs and symptoms associated with silicarelated 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.
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PART II: AMORPHOUS
SILICA
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SILICA: AMORPHOUS
Cannot distinguish
by X-ray diffraction
 Under certain conditions,
heating amorphous silica
results in conversion to
the crystalline form
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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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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
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AMORPHOUS SILICA:
EXPOSURE LIMITS
The OSHA PEL for amorphous silica, including natural
diatomaceous earth is:
80 mg/m3 divided by the % silica content of the dust
So if your dust contains 8% amorphous silica, then the
PEL would be 80 mg/m3 divided by 8, or 10 mg/m3
The NIOSH REL for amorphous silica is
6 mg/m3
ACGIH has withdrawn the TLV for amorphous silica
due to insufficient data
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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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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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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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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.
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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
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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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SYNTHETIC VITREOUS FIBERS:
EXPOSURE LIMITS (CONT.)
OSHA General Industry—29 CFR 1910.1000 Table Z-3 "Inert
or Nuisance Dust”
 Respirable Fraction: 5 mg/m3
 Total Dust: 15 mg/m3
NIOSH
 Fibers with diameter  3.5 µm and length 10 µm: 3
fibers/cc
 Total dust: 5 mg/m3
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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/m3
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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
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THANK YOU!
QUESTIONS?
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