Control of Silica Exposures During Concrete Truck Drum ChipOut - PowerPoint PPT Presentation
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Title: 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
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