Silica Hazard Identification

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Silica Hazard Identification

• Brock Enterprises, Inc.
• I.A. (Tony) Huval, CSP
• April 7, 2005

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• Each year, 300 people die from a disease called
  Silicosis.
• Are you or any of your employees among the 2
  million people exposed to silica each year?

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The Basics of Silica

• Silica (Si02) is a mineral compound made up of
  one silicon atom and two oxygen atoms.
• Oxygen is the most abundant element in the
  earth's crust. 
• Silicon is the second most abundant.
• There are other compounds that contain silicon
  whose names are quite similar, such as silicate
  and silicone.  Do not mistake these for silica. 
  They are not the same thing.
• If the individual silica molecules are lined up
  in order and create a repeatable pattern then the
  silica is in crystal form.  We call it
  "crystalline" silica.
• If there is no order and no repeatable pattern
  then it is called amorphous silica.

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Silica Atomic Structure
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Repeating Pattern of Crystalline Silica
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Random Pattern of Amorphous Silica
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Types of Silica

• There can be more than one repeatable pattern in
  silica.  The various crystal patterns are given
  their own name.  There are
• quartz,
• cristobalite,
• tridymite,
• and other rare forms of crystalline silica. 
• Quartz is so common that the term quartz is often
  used to refer to crystalline silica.  And sand is
  often used to refer to quartz.

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Determining Silica Exposure
Because Silica is so prevalent and abundant in
our natural resources, it is possible that you
are using it without even knowing!
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Industries Using Silica

• Abrasive blasting or Sandblasting (High Risk)
• Asphalt pavement manufacturing
• Blast furnaces
• Cement manufacturing
• Ceramics, clay, and pottery
• Concrete mixing
• Concrete tunneling
• Construction (mainly cement, concrete work)
• Demolition
• Electronics industry
• Foundry industry grinding, molding, shakeout,
  core room (High Risk)
• Hand molding, casting, and forming
• Jack hammer operations
• Manufacturing abrasives, paints, soaps, and glass
  
• Mining
• Repair or replacement of linings of rotary kilns
  and cupola furnaces
• Rolling and finishing mills
• Setting, laying, and repairing railroad track
• Steelwork

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Occupations Using Silica

• Brickmason/stonemason
• Construction laborer
• Crane and tower operator
• Crushing and grinding machine operator
• Furnace, kiln, non-food oven operator
• Grinding, abrading, buffing, and polishing
  machine operator
• Hand molder/shaper (not jeweler)
• Heavy-equipment mechanic
• Janitor or cleaner
• Machinist
• Metals/plastics machine operator
• Molding and casting machine operator
• Mining machine operator
• Miscellaneous material moving equipment operator
• Millwright
• Operating engineer
• Painter who sandblasts (High Risk)
• Production supervisor
• Rock driller (High Risk)

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Materials Using Silica

• Abrasives
• Coal Dust
• Concrete
• Dirt
• Filter Aids
• Graphite, natural
• Mica
• Mineral Products
• Paints
• Pavement
• Perlite
• Plant Materials
• Plastic Fillers
• Polishing Compounds
• Portland Cement
• Sands
• Silicates
• Slag
• Soapstone

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Caution

• RememberThere is potential for danger ONLY
  when crystalline silica particles are in the
  air.  There may be materials that contain silica
  but if the operations on those materials do not
  generate dust, there is little chance of inhaling
  the silica. 
• Likewise, there may be silica particles in the
  air even though you don't see any dust.

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Airborne?
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Airborne?
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Airborne?
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So How Small is Small?
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Particulate Matter Sizes
2,000 particles, each 2.5 micrometers in
diameter, when laid end-to-end, will stretch
across the width of a small paper clip.
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Where Else to Check?

• Labels
• A product that contains silica should have a
  label that says so. 
• The machines used in the operations may also be
  labeled with warning signs indicating that silica
  is being used. 
• Manufacturer's responsibility  attach a label to
  all products that contain more than 0.1 silica
  that may be hazardous when used.
• Employer's responsibility  ensure that the label
  is not removed or defaced.

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Is That All?

• Material Safety Data Sheets (MSDS)
• These sheets contain data for all materials or
  products containing hazardous substances that are
  used at a business in quantities greater than
  what a consumer would use. 
• If a material or product contains crystalline
  silica in quantities greater than 0.1, there
  must be a safety data sheet for it. 
• Manufacturer's responsibility  shall obtain or
  develop a safety data sheet for each hazardous
  chemical they produce or import. 
• Employer's responsibility  ensure access to
  safety data sheets for all hazardous materials at
  the workplace.

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Measuring Airborne Silica
Now that you suspect Silica is being used and
that it may be in the air, you need to know just
how much of it there is.
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Sampling

• The sampling pump will be placed on an employee,
  who will wear the device throughout the work
  shift for up to 8 hours.
• All employees may be fitted with the sampling
  device or just a select few who are closest to
  the silica source may be fitted.  An industrial
  hygienist can help you determine what will be
  most appropriate.

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Laboratory Analysis

• Your main task here is to select a competent
  laboratory that does quality work.  The work from
  the previous step will be wasted if the samples
  are mishandled or analyzed incorrectly. You
  should ask the following questions and get
  positive answers before deciding to go with a
  particular lab.
• Can the laboratory describe the positives and 
  negatives of the techniques they use to analyze
  samples?
• Do they maintain accreditation with a recognized
  authority?
• Does the laboratory report the results in a
  format that is understandable and provides all of
  the information required to perform the exposure
  calculations?
• Does the laboratory have a quality assurance
  program?
• Do they participate in a proficiency testing
  program for crystalline silica to assure
  consensus and adequate performance?
• Do they analyze quality control samples to assure
  that their procedures are performing correctly?
• Does the laboratory staff appear knowledgeable
  about your workplace operations, including the
  other substances you use that could interfere?

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Exposure vs. Limits
Finding and comparing the actual exposure against
the permissible limit will let you know if you
need to take action or not
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Comparing Samples to the PEL

• There is not one crystalline silica exposure
  limit for all cases.  Rather, the limit is
  derived from a calculation that takes into
  account the percentage of quartz, cristobalite,
  tridymite, and respirable dust specific to your
  particular work-site.
• 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 amount of crystalline
  silica that is present in the dust. For the most
  part, OSHA is more concerned with the respirable
  fraction of the sample because it is more
  hazardous however, both respirable and total
  dust equations are shown.

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Oh No, Math!

• The following parameters are necessary to
  calculate the PEL and the exposure level.
• crystalline silica in the air samples (if the
  lab reports the silica concentrations in units of
  mass convert the mass to percent e.g., sample
  weight (mg) dust weight (mg) 100 )
• quartz
• cristobalite
• tridymite
• Total weight of the dust collected in the air
  samples in milligrams
• Total volume of air sampled for each sample in
  cubic meters (1000 liters 1 cubic meter)
• Total sampling time for each air sample in
  minutes

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More Math !

• PEL Equations
• PEL (respirable fraction) 10 quartz (
  cristobalite 2) ( tridymite 2) 2
• PEL (total dust) 30 quartz (
  cristobalite 2) ( tridymite 2) 2
• The total dust sample is normally taken using the
  same sampling technique described previously, but
  without a cyclone.

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More Math ((!

• Exposure Equation
• Exposure (mg/m3(1) time(1)) (mg/m3(2)
  time(2)) ... (mg/m3(n) time(n)) 480
  minutes
• This is the formula, now lets work thru an
  example (are we never going to finish with this
  math?)

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Sample Lab Results
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I Hate math

• Step 1. Calculate the percentage of quartz,
  cristobalite, and tridymite in the particulate
  collected.
• Quartz 5.2 (0.855/1.474) 4.8
  (0.619/1.474) 3.0 2.0 5.0
• Cristobalite 2.3 (0.855/1.474) 1.7
  (0.619/1.474) 1.3 0.7 2.0
• Tridymite none detected 0
• Step 2. Calculate the PEL for the mixture.
• PEL(mixture) 10 mg/m3 quartz (
  cristobalite 2) ( tridymite 2) 2   10
  5 (2.0 2) ( 0 2) 2 10 11.0
  0.91 mg/m3

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It Just Keeps Following Me

• Step 3. Calculate the employee's exposure (8
  hour TWA).
• Exposure (mg/m3(1) time(1)) (mg/m3(2)
  time(2)) ... (mg/m3(n) time(n)) 480
  minutes (2.1 238) (1.9 192) 480 1.8
  mg/m3
• Step 4. Calculate the severity of the exposure.
• Severity 1.8 mg/m3 0.91 mg/m3 2.0
• If the severity number is higher than 1.0 you are
  above the limit.  If the severity number is less
  than 1.0 you are below the limit.

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General Industry vs. Other Standards

• So you are covered by the Construction or
  Maritime Standards. So what? Here is what OSHA
  says about it.
• OSHA regulation 1910.1000 Table Z-3 is used to
  determine the exposure limits for crystalline
  silica. Though this regulation is under the
  General Industry Standard, crystalline silica
  exposures in the Construction and Maritime
  Industries are subject to this same limit.
  Regulating these industries under the General
  Industry Standard is specifically addressed in
  Appendix F of the OSHA Special Emphasis Program
  (SEP) for Silicosis.

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Take Action to Protect
Now that I know there is a silica hazard, what do
I do?
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Hierarchy of Controls

• Use a silica substitute
• Use engineering controls
• Improve work practices
• Use PPE

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Use a Substitute

• The most sure way to eliminate the silica hazard
  is to eliminate the silica! This is especially
  important for sandblasters, where the abrasive
  blasting is often done outside and in different
  locations, making it impossible to install an
  engineering control.  The most severe silica
  exposures occur in abrasive blasting.
• Advantages
• Complete elimination of any health hazard related
  to silica
• Eliminates the need to implement or maintain
  engineering controls
• These substances are not as dense as silica
  products which makes them easier to transport
• They can be moved from job site to job site
• Disadvantages
• May be slightly more expensive than silica
  products
• These substances are generally not as hard as
  silica products which may mean more is needed to
  do the job

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Engineering Controls

• If silica products must be used, OSHA requires
  engineering controls to be used wherever
  possible.  This type of control involves a
  mechanical process to eliminate exposure to
  silica dust.  Some of these controls may be very
  simple, as can be seen in the examples below
• Install a water hose to wet down the dust at the
  point of generation
• Install local exhaust ventilation
• During rock drilling, flow water through the
  drill stem
• Install dust collection systems onto machines or
  equipment that generates dust
• Use concrete/masonry saws that provide water to
  the blade

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Improve Work Practices

• If workers know about silica and understand the
  severity of its health hazard, they will be more
  likely to do the following
• Know which work operations can lead to silica
  exposure
• Participate in any air monitoring or training
  programs offered by the employer
• If possible, change into disposable or washable
  work clothes at the worksite shower (where
  available) and change into clean clothing before
  leaving the worksite.
• Do not eat, drink, use tobacco, products, or
  apply cosmetics in areas where there is dust
  containing crystalline silica.
• Wash your hands and face before eating, drinking,
  smoking, or applying cosmetics outside of the
  exposure area.
• If using respirators, do not alter the respirator
  in any way. 
• Use type CE positive pressure abrasive blasting
  respirators for sandblasting
• For other operations where respirators may be
  required, use a respirator approved for
  protection against crystalline silica-containing
  dust.
• If using tight-fitting respirators do not grow
  beards or mustaches

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Personal Protective Equipment

• Personal protective equipment against silica
  includes respirators and masks.  Respirators
  should be used only when the dust controls cannot
  keep dust levels below the NIOSH Recommended
  Exposure Level.
• There are many types of respirators,  from
  air-purifying to air-supplying and from a nose
  and mouth covering to a full body respirator. 
  You can receive guidance on selecting a
  respirator from OSHAs Respiratory Protection
  Safety and Health Topics page.
• The OSHA ventilation standard (1910.94) contains
  specific respiratory protection requirements for
  abrasive blasting operations.

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Choices

• By evaluating your workplace for potential silica
  hazards and then taking appropriate actions,
  employers and employees will be able to avoid
• Silicosis, a 100 preventable disease.
• The often deadly consequences of silicosis.
• Non-compliance with legal standards and possible
  citations.
• OSHA is ready to help you protect your employees.

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Ignore or Comply?