Control of Silica Exposures During Concrete Truck Drum ChipOut

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Control of Silica Exposures During Concrete Truck
Drum Chip-Out

• Art Wickman, CIH
• Georgia Institute of Technology
• 404-894-8088
• art.wickman_at_gtri.gatech.edu

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• Tax supported function of US Dept. of Labor
  (OSHA)
• Consultation Progs. are State, not Federal,
  Agencies
• (In Georgia, at Georgia Tech)
• Voluntary compliance assistance
• Mandatory hazard correction obligation

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OSHA Special Emphasis on Silica

• One million workers routinely exposed with 250
  Worker deaths per year
• 1970s thru early 1990s data
• Silicosis
• Tuberculosis
• Heart Disease
• Lung Cancer?
• Suspected Human Carcinogen A2 (ACGIH)

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Surveys of Silica Exposures in Ready Mix Concrete
and Block Plants

• Work request of GA Concrete Products Association
• 10 site visits
• Approx. 50 air samples
• Both Ready Mix and Concrete Block Plants

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Concrete Block Plants

• Average silica exposure
• 51 of OSHA PEL
• (26 Samples)
• No fullshift TWAs exceeded PEL
• One sample was 128 of PEL
• associated with short term clean up work.
• Jobs Block machine, cubers, front end loaders,
  maintenance

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Ready Mix Concrete Plants

• Average Exposure
• 47 of OSHA PEL
• 7 samples
• No samples exceeded PEL
• Jobs Batch processors, front end loaders,
  general labor

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Hazards of Chip-out Work

• 1. Silica and total dust
• 2. Noise
• 3. Heat Stress
• 4. Other Hazards

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Noise Hazards of Chip-out Work

• TWAs in excess of 120 dBA
• Sources
• Steel chisel on steel drum
• Compressed air exhaust from chipper
• May have two workers in drum

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Heat Stress Hazards of Chip-out Work

• Elevated Temperatures
• Elevated Relative Humidity
• Heavy Work Clothes
• Respirators
• Heavy Work Load

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Other Hazards

• Intermittent Lockout of Drum
• Confined Space
• Fall hazards
• External Top entry to drum is awkward and in
  excess of 12 feet high
• Internal Jagged debris, equipment hoses,
  baffles
• Ergonomics Intense upper body vibration
• Non-standard Workshift May run overnight

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Silica Exposures

• Exposure Range 40 110 X OSHA PEL
• No ventilation, or
• Minimal ventilation using pedestal fan
• Common practice in use shown here

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Controls Local exhaust

• Exposures reduced to 16 X OSHA PEL
• Probably could improve by smoothing out duct work

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• Duct is cumbersome and awkward in confined space

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Controls Forced Dilution

• Exposures 6 13 X OSHA PEL
• Maintain exposures below or within the APF of
  designated respiratory protection

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Ventilation Fan/Ductwork
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Charge Chute Connection
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Side Hatch Connection

• Forcing air in from lower hatch, exhausting at
  upper hatch was less effective
• Exhaust air moving through breathing zone?

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Controls Wet Methods
Illinois Safety and Health Consultation Program
(1997-1999) - Donald Williams and Kwasi
Sams Documented reductions below the OSHA PEL
during chip out work
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Chipping Hammer, Materials List for Water
Suppression

• Hydraulic line
• ¼ inch ID
• 3 to 4 feet long
• w/ compression fittings
• w/ threaded ends.
• Spray nozzle
• ¼ gallon per minute (chapin 6-4824)
• Water shut off valve.

• Reducer coupling for transition from the
  hydraulic line to standard garden hose.
• Duct Tape.

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Other Wet Methods

• 1. Soak truck drum overnight
• Absorbs water up to about 2 inches
• 2. Use manual water spray at point of operation
• Garden pressure sprayer

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Constraints on Wet Methods

• 1. Freezing Temperature
• Chip out work may be scheduled for winter months
  when work is slack
• 2. Slip hazard increased
• 3. Electrical Hazard

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Silica Control during Chipout

• 1. Exhaust ventilation
• Reductions to 16 X PEL
• 2. Forced dilution ventilation
• Reductions to 6 13 X PEL
• 3. Wet Methods
• Potential reductions to below the PEL
• With some constraints on wet methods
• -

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Risk vs Frequency of Exposure

• Infrequent exposure
• Traditionally, smaller ready mix companies did
  drum chip-out in-house (by driver or volunteer)
• Exposures are infrequent (a few times per year)
• Frequent Exposure
• For large companies, subcontracting is a growing
  trend
• Frequency of exposure is much higher for
  subcontractors

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Acknowledgements

• Contributing Authors
• Ryan Langton, GTRI
• Michelle Dunham, Chris Collins, GTRI
• Mr. Joe Thornton, Joseph Thornton Associates
• Mr. Jon Swierenga at Lafarge Corporation
• Georgia Concrete Products Association

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Closing Questions