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Risks for Respirable Crystalline Silica (Quartz) Exposures in Hydraulic
Fracturing Operations
Michael Breitenstein
Eric J. Esswein
John SnawderDISCLAIMERS: THE FINDINGS AND CONCLUSIONS IN THIS PRESENTATION HAVE NOT BEEN FORMALLY DISSEMINATED BY NIOSH AND SHOULD NOT BE CONSTRUED TO REPRESENT ANY AGENCY DETERMINATION OR POLICY. MENTION OF COMPANY NAMES AND/OR PRODUCTS DOES NOT CONSTITUTE ENDORSEMENT BY THE NATIONAL INSTITUTE FOR OCCUPATIONAL SAFETY AND HEALTH.
• Mission: improve OS&H by partnering with industry, conduct innovative research, develop practical solutions
• Upstream Oil & Gas (O&G) Industry
• 3 types of companies
• Land‐based operations
• Domestic focus
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Source PA Fire Commission, Chesapeake Energy
Each phase of wellsite activity has different hazards…
ProductionCompletionsWell Construction
Site Selection& Preparation
2 5 3 3
Operator experts rated the hazards in each phase of wellsite activity on a 1‐5 index, where 5 is considered the most hazardous…
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www.cdc.gov/niosh/docs/2010‐130/pdfs/2010‐130.pdf
NIOSH O&G Field Effort ‐ Chemical Exposures
1. Field (IH) research2. Upstream Oil & Gas (O&G) Industry3. Hazard identification /
determination 4. Risk evaluation / determination 5. Risk communication6. Controls (if necessary)7. Evaluation
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5
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Industrial Hygiene Sample Collection and Analysis
• Respirable Particulates‐NMAM 0600• Respirable Silica‐NMAM 7500• Diesel Particulate Matter as Elemental Carbon‐
NMAM 5040• BTEX‐ NMAM 1500, 1501• Total VOCs (qualitative)‐NMAM 2549• PAHs/PACs‐ NMAM 5506/5800• Petroleum ethers/Naphthas‐ NMAM 1550• Drilling Fluid Aerosol‐ NMAM 5524• Elements on Wipes‐ NMAM 9102
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Sampling Equipment
BGI GK 2.69 Cyclone
Use of this company name does not imply Endorsement by NIOSH
SKC AirChek XR5000
Use of Real‐Time/Direct Reading Instruments
• 4‐gas + PID (photoionization detector) monitors with data logging and telemetry (CO, H2S, SOx, CH4, NOx, LEL, O2 and VOCs)
• Respirable Silica (Haz‐Dust)• Respirable fine particulate (diesel particulate, Haz‐Dust DPM)
• Drager Chip Measurement System (CMS: Total hydrocarbon, benzene, aldehydes, etc.)
• Field portable gas chromatograph • Advanced personal monitors• Infra‐red hydrocarbon camera
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Silica (Quartz)
• Silicon (Si) an element • SiO2 (silicon dioxide= silica, quartz)• Respirable crystalline silica (fine dusts) • Exposures regulated by OSHA• Silicosis, COPD, lung cancer, other disease • Occupational hazard of antiquity• ≈200 workers deaths per year U.S. • Preventable disease
Occupational Exposure Criteria Respirable silica (quartz)
• ACGIH TLV : 0.025 mg/m3 TWA
• NIOSH REL: 0.05 mg/m3 TWA
• OSHA PEL: 10 mg/m3 Resp. dust containing
( % silica + 2) silica
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Sand Use
• Hundreds of thousands of pounds per stage
• Proppant • Various shapes and
sizes • Virtually 100% silica
• Highest exposures are periodic. Silica exposures were found to increase during periods of heavy pumping; i.e., during hydraulic fracturing operations and/or during sand transfer.
• Traffic and site dusts are contributors to exposure.
• Prevalent winds and location in relation to the source are major determinants of exposure.
Respirable Silica Exposure
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Real‐time Respirable Silica
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Respirable Silica Results by Location
Site > ACGIH TLV* > NIOSH REL* > OSHA PEL* Total #
samples
A 24 (92.3%) 19 (73.1%) 14 (53.9%) 26
B 16 (84.2%) 14 (73.7%) 12 (63.2%) 19
C 5 (62.5%) 5 (62.5%) 4 (50.0%) 8
D 19 (90.5%) 14 (66.7%) 9 (42.9%) 21
E 25 (92.6%) 23 (85.2%) 18 (66.7%) 27
F 4 (40%) 1 (10%) 0 10
Total 93 (83.8%) 76 (68.5%) 57 (51.4%) 111
* Number of samples/%
Relative Comparisons, Geometric Means (mg/m3 ) by Job Titles
0
0.1
0.2
0.3
0.4
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Comparisons, Geometric Means, 95% Confidence Intervals
Exposure Comparisons by Job Title
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T‐Belt Operator
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Sand Mover Operator
15
Blender Operator
Hydration Unit Operator
16
Water Tank Operator
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Sand Coordinator
7 Primary Points of Dust Generation
1. Release from top hatches, sand movers 2. Transfer belt under sand movers3. Site traffic 4. Sand dropping in blender hopper5. Release from T‐belt operations6. Release from “dragon’s tail” 7. Dust ejected from fill ports on sand
movers
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19
20
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1. Eliminate
2. Substitute
3. Engineering Controls
4. Administrative Controls
5. Personal Protective Equipment
Industrial Hygiene Hierarchy of Controls
Control of Dust Generation
1. Prevention through Design (PtD)2. Remote operations 3. Substitution (ceramic vs. quartz) 4. Implement Engineering Controls 5. Passive enclosures
Stilling (staging) curtains, shrouding 6. Minimize distance that sand falls 7. End caps on fill nozzles 8. Use amended water for site dust control 9. Effective respiratory protection program
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mini‐baghouse retrofit assembly
Proposed Controls, Sand Movers
Mini Baghouse Retrofit Ass’y
Proof of concept evaluation, June 2012
Patent pending
Self cleaning
No additional power req’d.
Control at point of generation
Bolt‐on, low cost control
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Proposed Controls, Sand Movers
enclosure, skirting
end caps on fill nozzles
Proposed Controls, Sand Movers
Caps on fill nozzles
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Screw augur retrofit
Proposed Controls, Sand Movers
Screw augur to replace belt
Communicate the Risk • Signage
• Hazard Communication
• Include in JSA’s
• Periodic training
• Effective respiratory program
• Medical monitoring
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Conclusions• Silica: occupational health hazard for completions crews • Greater focus of “H aspects” of O&G extraction needed • Silica exposures can exceed the MUC for respirators • Numerous sources of dust generation• Respirators: workers need to be clean shaven • Simple controls: Caps on fill nozzles, close thief hatches, worksite
dust control, staging curtains, enclosures, shrouding, correct respirator use
• More involved controls: Development + implementation of engineering controls, reconfiguration of sand movers
• Prevention through Design (PtD) for sand movers & well site itself
Contact: Michael Breitenstein, NIOSH, Division of Applied Research and Technology, Cincinnati, OH(513) 533‐8290 mjb1@cdc.gov
Eric Esswein, CIH, NIOSH, Western States Office, Denver, CO(303) 236‐5946 eje1@cdc.gov
John Snawder, Ph.D., DABT, NIOSH, Division of Applied Research and Technology, Cincinnati, OH(513) 533‐8496 jts5@cdc.gov
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Respirable Dust Exposures of Workers Dowel Drilling Concrete Pavement and Evaluation of
Control Measures
Alan EchtIndustrial Hygienist
2013 Indiana Safety and Health Conference and ExpoMarch 11, 2013
National Institute for Occupational Safety and Health
Division of Applied Research and Technology
Disclaimers
The findings and conclusions in this presentation have not been formally disseminated by the National Institute for Occupational Safety and Health and should not be construed to represent any agency determination or policy.
Mention of any company or product does not constitute endorsement by the Centers for Disease Control and Prevention or the National Institute for Occupational Safety and Health.
Subhead for Section – Myriad Pro, 20pt
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BACKGROUND
Background
Silica (quartz) dust causes silicosis Exposure also associated with other diseases
• Lung cancer
• Autoimmune disease
Concrete contains quartz
Concrete is used in highway construction
Repair and demolition produce respirable dust
Highway construction workers at risk of illness from exposures
Exposures should be controlled to reduce risk
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Background
New Jersey Department of Health and Senior Services (DHSS) has received funding since 1988 from the National Institute for Occupational Safety and Health (NIOSH), under their Sentinel Event Notification System for Occupational Risks (SENSOR) Program, to conduct disease surveillance for silicosis
The DHSS SENSOR identified 11 cases of
silicosis in road and elevated highway construction
NJ DHSS developed a sampling strategy to be used at worksites of ten partner contractors
New Jersey Department of Health and Senior Services (2001). Occupational Health Surveillance Update. Trenton, NJ, February 2001
Background
11 sets of samples collected at 9 different worksites
Sites involved 7 of 10 partner contractors.
53 samples collected for 7 different tasks
jackhammering concrete clean-up
dowel drilling concrete milling
concrete sawing asphalt milling
asphalt clean-up
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Background
NJ DHSS dowel drilling results
Data and photo courtesy of Daniel Lefkowiitz, NJ DHSS
JobDuration(minutes)
RespirableDust
(mg/m3)
QuartzContent
(%)
Laborer 271 5.19 5.4
Laborer 273 1.40 6.7
Background
NIOSH Division of Respiratory Disease Studies (DRDS) also evaluated silica exposures from concrete in construction and demolition
Tasks evaluated Abrasive blasting of concrete
Dowel drilling
Concrete grinding
Concrete sawing
Pavement milling
Linch, Kenneth D (2002). Respirable Concrete Dust—Silicosis Hazard in the Construction Industry. Applied Occupational and Environmental Hygiene 17(3): 209–221.
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Background NIOSH DRDS dowel drilling results
Photos and data courtesy of Ken Linch,
JobNumber
ofSamples
Geometric Mean Respirable Dust
(mg/m3)
RangeRespirable
Dust(mg/m3)
RangeQuartz
Content(%)
Backhoe 8 1.1 0.49-2.0 ND-8.9
Driller 8 3.7 2.0-12 10-17
Background
Dowel drilling process Full depth pavement repair
• Saw cut perimeter of repair
• Break-out or lift old concrete
• Drill into perimeter of repair
Airport runway construction• Pour new slab
• Allow to cure
• Drill into edges of slab
Dowels transfer load between slabs
Photo courtesy E-Z Drill. Inc.
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Background
Dowel drills 1-5 pneumatic or hydraulic rock drills arranged in parallel
Frame aligns drills perpendicular to concrete surface
On-slab, on-grade, or boom mounted
Two manufacturers
Both sell optional dust controls
No documentation that they reduce exposures
Photos courtesy of E-Z Drill, Inc. (l) and Minnich Manufacturing(r)
Background
Dust controls for small pneumatic rock drills first reported in the 1920s Hay 1926
Kadco 1932
Drill-Vac 1937
Cooper, Susi, & Rempel 2012
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A LABORATORY STUDY OF DOWEL DRILL DUST CONTROLS
A laboratory study of dowel drill dust controls
Objective To determine the relative reduction in respirable dust emissions
achieved through the use of local exhaust ventilation dust control systems
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A laboratory study of dowel drill dust controls
Process description Minnich A-5SCW E-Z Drill 210-3
A laboratory study of dowel drill dust controls
Sampling strategy• Compared respirable dust emissions dust “control on” versus dust
“control off”
• Paired “control on” and “control off” trials
• Randomized “control on” and “control off” order in pairs
• A round consisted of a pair of “control on” and “control off” trials
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A laboratory study of dowel drill dust controls
Sampling procedures Respirable dust samples collected during “control-on” and
“control-off” trials at three locations around the drills at breathing zone height
Samples collected and analyzed according to NIOSH Method 0600 - pre-weighed filters were desiccated and weighed after sampling.
Samples collected using Higgins-Dewell cyclones (Model 4L, BGI, Inc. Waltham, MA) at 2.2 liters/minute
A laboratory study of dowel drill dust controls
Test procedure Position drilling machine
Position samplers
Start samplers – record start time
Close tent
Start drills by remote control
Record last drill stop time
Wait five minutes
Open tent
Stop samplers – record stop time
Purge tent
Position drilling machine
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A laboratory study of dowel drill dust controls
A laboratory study of dowel drill dust controls
Measured control parameters Measured exhaust air and bailing air (flow through the drill stem
and bit to flush the cuttings from the hole)
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A laboratory study of dowel drill dust controls
Sample size calculations Used RSD from pilot study
One sided test (i.e., only concerned about the significance of the reduction)
Log-normal distribution, split-plot design
Designed to observe a 75% emissions reduction with a power of .80 and 95% confidence
At least 4 test rounds with samples in three positions were required
A laboratory study of dowel drill dust controls
Statistical analysis Univariate procedure used to test lognormality of the data
Took natural logs (ln) of dust concentration. ln dust concentration was dependent variable
Calculated geometric mean (GM) dust concentration for each position and both conditions
Calculated GM reduction ratio (1 - GM “control on”/GM “control off”)
T-tests used to test hypothesis that “control on” ≠ “control off”
General Linear Model procedure was used to construct a model of the emissions reduction
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A laboratory study of dowel drill dust controls
Results Minnich site
• n = 42 respirable dust samples collected in 7 rounds of sampling
o 7 samples in 3 locations “control-on” condition = 21 samples
o 7 samples in 3 locations “control-off” condition = 21 samples
E-Z Drill site• n = 48 respirable dust samples collected in 8 rounds of sampling
o 8 samples in 3 locations “control-on” condition = 24 samples
o 8 samples in 3 locations “control-off” condition = 24 samples
Total n = 90 samples, 45 in each control condition.
A laboratory study of dowel drill dust controls
Number of Samples
Geometric Mean
(mg/m3)
GeometricStandard Deviation
Range(mg/m3) p-Value
E-Z Drill
Control OFF 24 54 1.3 30-82<0.0001
Control ON 24 3.0 1.5 1.9-6.0
Minnich
Control OFF 21 57 1.2 39-79<0.0001
Control ON 21 5.3 1.9 1.6-12
Overall
Control OFF 45 55 1.3 30-82<0.0001
Control ON 45 3.9 1.8 1.6-12
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A laboratory study of dowel drill dust controls
Results Emissions without dust control 14 times higher
93% reduction in emissions
Location of sample not significant (p = 0.3488)
Controls significantly reduced dust (p<0.0001)
A FIELD STUDY OF DOWEL DRILLING DUST CONTROLS
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A field study of dowel drilling dust controls
Objective Ascertain the effectiveness of the controls on job sites by
comparing exposures associated with the use of the controls to exposures without controls
A field study of dowel drilling dust controls
Site Descriptions Site 1 – Full-depth concrete pavement replacement with two 3-
drill boom-mounted dowel drills without dust collection systems
Site 2 – Full-depth concrete pavement replacement with two 3-drill boom-mounted dowel drills without dust collection systems
Site 3 – Concrete runway construction with two 4-drill slab-rider dowel drills without dust collection systems
Site 4 – Concrete runway construction with two 5-drill slab rider dowel drills with dust collection systems
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A field study of dowel drilling dust controls
Sample size calculations Based on desire to determine at least a 75% reduction in
exposures power of .80 and 95% significance
Used data from sites 1 and 2, with GSD of 1.94
Lyles, R.H., & Kupper, L.L. (1996). On Strategies for Comparing Occupational Exposure Data to Limits. American Industrial Hygiene Association Journal, 6-15.
Alpha Power n GSD RSD STDln
Limit/Exposure % Change
0.05 0.8 15 1.81 0.65 0.59 2.0 50
0.05 0.8 10 1.81 0.65 0.59 2.5 60
0.05 0.8 6 1.81 0.65 0.59 4.0 75
0.05 0.8 18 1.96 0.75 0.67 2.0 50
0.05 0.8 12 1.96 0.75 0.67 2.5 60
0.05 0.8 7 1.96 0.75 0.67 4.0 75
A field study of dowel drilling dust controls
Sampling strategy Tasked-based sampling
Partial period-consecutive samples
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A field study of dowel drilling dust controls
Sampling procedures Air sampling sites 3 and 4
• Higgins-Dewell (model 4L, BGI, Inc., Waltham, MA) cylone and pre-weighed PVC filter clipped in breathing zone and sampling pump (model 224, SKC, Inc., Eighty Four, PA) calibrated to 2.2 L/min worn at belt on worker’s waist
A field study of dowel drilling dust controls
Sampling procedures Weather monitoring
• Wind speed and direction data collected at sites 3 and 4 using tripod-mounted data-logging wind meters
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A field study of dowel drilling dust controls
Sampling procedures Measurement of dust control flow rate – site 4
Measured air flow at dust collectors of both drills using in-line mass flow meter (model 730-N5-1, Sierra Instruments, Inc., Monterey, CA)
A field study of dowel drilling dust controls
Data analyses Time weighted average (TWA) exposure data were transformed
to their natural logs (ln) and analyses were performed using lnTWA as the dependent variable
Descriptive statistics were calculated
T-tests used to assess exposure differences with and without dust controls
T-tests used to assess exposure differences between backhoe operators and drillers at sites 1 and 2
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A field study of dowel drilling dust controls
Data analyses General linear model used to assess the impact of other
variables on ln exposure
Mixed model analysis used to assess effect of control, adjusting for job and controlling for unequal exposure measurement between workers
Nonparametric analyses conducted on the effect of controls due to very small sample size
A field study of dowel drilling dust controls
ResultsPersonal Respirable Dust Exposures by Site and Job
Site Job nGM
(mg/m3)GSD
Range(mg/m3) p-Value
1 Backhoe 4 0.85 1.6 0.49-1.6
1 Driller 4 3.2 1.5 1.7-6.0
2 Backhoe 4 1.5 1.3 1.1-2.0
2 Driller 4 3.0 2.3 2.0-12
3 Driller 6 3.3 4.0 0.45-21
4 Driller 3 3.0 1.9 1.7-6.0
Total 25 2.4 2.5 0.45-21
Comparing Exposures Across Sites 1 and 2
Backhoe 8 1.1 1.6 0.49-2.00.0006
Driller 8 3.7 1.8 2.0-12
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A field study of dowel drilling dust controls
ResultsDust Control was not Significantly Different from No Control
Parametric Statistics
Dust ControlMeasures
nGM
(mg/m3)GSD
Range(mg/m3)
ProbabilityStatistic
Student’s T-test
Off 14 3.48 2.60 0.45-210.795
On 3 2.98 1.90 1.7-6.0
General Linear ModelAnalysis of Variance
R2 Estimate F Value0.795
0.0046 0.154 0.007
Mixed Model ProcedureAIC Estimate F Value
0.46244.7 0.648 0.60
A field study of dowel drilling dust controls
ResultsDust Control was not Significantly Different from No Control
Non-Parametric Statistics
Wilcoxon Rank Sums
ControlNumber
ofSamples
Mean Score
0.757Off 14 8.0
On 3 9.2
Median Scores
ControlNumber
of Samples
MeanScore
0.611Off 14 0.33
On 3 0.50
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A field study of dowel drilling dust controls
Results Simple linear regression using the General Linear Model
y=3.27-0.3x+e
Where:
y is the dependent variable, ln TWA exposure
3.27 is the intercept
-0.3 is the coefficient
x is the wind speed (mph)
e is the error
A field study of dowel drilling dust controls
Results Air flow measurements
• Worker c’s drill – 90 m3/hr
• Worker d’s drill – 96 m3/hr
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A field study of dowel drilling dust controls
Discussion and Conclusions GM respirable dust exposures with the dust control were not
significantly different from exposures without the control
Wind speed (which approached significance) had more effect on exposure reduction than the control
Performance could be due to design (low transport velocity, extensive use of flexible duct), maintenance practices, or work practices. More sites needed to find out.
EVALUATION OF A HIGH-VOLUME SAMPLER FOR SHORT-TERM TASKS
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Evaluation of a high-volume sampler for short-term tasks
Objective To design, fabricate, and test a new cyclone sampler
Evaluation of a high-volume sampler for short-term tasks
Background 19% of the samples collected during the laboratory evaluation
were less than the limit of detection (LOD), 24% were between the LOD and the limit of quantitation (the mass of analyte equal to 10 times the standard error of the calibration graph divided by the slope)
Minimum detectable concentration (MDC) = LOD/Sample Volume
Sample volume = time x flow rate
Increasing flow rate can reduce the MDC
Cyclone samplers use centrifugal force to separate particles by size
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Evaluation of a high-volume sampler for short-term tasks
Background Cyclone samplers evaluated against respirable dust convention
Particle Aerodynamic Diameter (µm) Respirable Particulate Matter
Fraction Collected (%)
0 100
1 97
2 91
3 74
Particle Aerodynamic Diameter (µm) Respirable Particulate Matter
Fraction Collected (%)
0 100
1 97
2 91
3 74
4 50
5 30
6 17
7 9
8 5
10 1
Evaluation of a high-volume sampler for short-term tasks
Background Kenny and Gussman (1997) described a scalable cyclone
design
The UK Health and Safety Laboratory (HSL) has extensive experience evaluating respirable dust samplers
Contracted with Gussman’s company and the HSL to design, fabricate, and evaluate a new
cyclone sampler
Photo and drawing courtesy of BGI, Inc.
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Evaluation of a high-volume sampler for short-term tasks
Methods Measured aerosol penetration through the sampler
Measured the challenge aerosol
Compared the two to characterize the sampler
Evaluation of a high-volume sampler for short-term tasks
Methods Measured aerosol penetration through the sampler
• Generated polydisperse aerosol of glass beads in sampling chamber
• Connected sampling tube to cyclone
near inlet
• Particle size distribution measured with
aerosol particle sizer (APS)
Photo courtesy Andrew Thorpe, Health and Safety Laboratory
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Evaluation of a high-volume sampler for short-term tasks
Methods Measured the challenge aerosol
• Prepared an identical set of tubing without the cyclone attached
• Collected a series of 1-minute samples
• Alternated between cyclone and reference
samples with 1-minute break to clear tubing
Photo courtesy Andrew Thorpe, Health and Safety Laboratory
Evaluation of a high-volume sampler for short-term tasks
Data Analyses Particle concentrations measured with and without cyclone
(reference aerosol) were averaged at each particle size
Cyclone:Reference ratio is measure of penetration
Normalized the penetration to 1 at 1 micrometer to compensate for APS characteristics for particles less than 1 micrometer
Used bias map technique to assess the difference between the sampler and the respirable dust convention
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Evaluation of a high-volume sampler for short-term tasks
Results Measured D50 values
FlowRate
(L/min)
D50
Test 1 Test 2 Test 3 Mean SDCOV (%)
7 4.90 4.90 4.88 4.89 0.012 0.24
8 4.37 4.28 4.38 4.34 0.055 1.27
8.5 4.18 4.05 4.05 4.09 0.075 1.83
9 3.99 3.87 3.88 3.91 0.067 1.70
9.5 3.70 3.67 3.65 3.67 0.025 0.69
10 3.52 3.45 3.43 3.47 0.047 1.36
Evaluation of a high-volume sampler for short-term tasks
Results Measured D50 values versus flow rate
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Evaluation of a high-volume sampler for short-term tasks
Results Bias Maps
At 8.5 L/min, sampler was
within 2% of target
85% of bias was within +/-10%
of target value
Evaluation of a high-volume sampler for short-term tasks
Results Bias Maps
At 9.0 L/min, sampler was
within 2% of target
85% of bias was within +/-10%
of target value
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Evaluation of a high-volume sampler for short-term tasks
Results Bias Maps
At 9.5 L/min, sampler was
within 2% of target
85% of bias was within +/-10%
of target value
Evaluation of a high-volume sampler for short-term tasks
Discussion and conclusions Cyclone agrees with sampling convention at 3 flow rates
Simpler, cheaper, better, and made in USA (and tested in the UK) versus French and German high-flow personal samplers
Drawings from Arelco and Gesellschaft für Schadstoffmessung und Auftragsanalytik) Messgerätebau GmbH,
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Evaluation of a high-volume sampler for short-term tasks
Discussion and Conclusions New cyclone will be able to detect and quantify respirable
particles, such as quartz, in a much shorter time
Suitable for short term tasks or breaking down larger tasks into components for exposure evaluation
Subject to overloading in dusty environment
For more information please contact Centers for Disease Control and Prevention1600 Clifton Road NE, Atlanta, GA 30333Telephone, 1-800-CDC-INFO (232-4636)/TTY: 1-888-232-6348E-mail: cdcinfo@cdc.gov Web: www.cdc.gov
Alan EchtEngineering and Physical Hazards BranchDivision of Applied Research and TechnologyNational Institute for Occupational Safety and Health4676 Columbia Parkway, R-5Cincinnati, Ohio 45226-1998AEcht@cdc.gov(513) 841-4111 phone(513) 841-4506 fax
National Institute for Occupational Safety and Health
Division of Applied Research and Technology
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Engineering Controls to Prevent Silica Exposure during Asphalt Pavement Milling
Duane Hammond, M.S., P.E.
2013 Indiana Safety and Health Conference and ExpoMarch 11, 2013
National Institute for Occupational Safety and Health
Division of Applied Research and Technology – Engineering and Physical Hazards
Disclaimer: “The findings and conclusions in this presentation are
those of the author(s) and do not necessarily represent the views of
the National Institute for Occupational Safety and Health.”
2
Presentation Outline
Silica hazard
Cold milling in highway construction and repair
Background – Forming the Partnership
2003-2006 individual milling studies Evaluated water-spray controls
Millfest studies 2008 Marquette, Michigan airport (four manufacturers)
2010 Shawano, Wisconsin (five manufacturers)
2011 tracer gas studies of ventilation controls
2012 field testing of ventilation controls
What is silica?
Silicon dioxide (SiO2) Occurs in crystalline or non-crystalline form
Forms of crystalline silica alpha quartz (most common)
beta quartz
tridymite
cristobalite
keatite
coesite
stishovite
moganite
Ampian SG, Virta RL [1992]. Crystalline silica overview: Occurrence and analysis. Washington, DC: U.S. Department of the Interior, Bureau of Mines, Information Circular IC 9317.
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How are workers exposed?
Silica is commonly found in rocks, sand, and construction materials.
Silica dust is generated by rock drilling, concrete sanding or cutting, tuck pointing, concrete sawing, concrete grinding, and abrasive blasting.
Lung disease called silicosis develops by breathing respirable crystalline silica particles.
Asphalt milling
rotating cutter drum to grind and remove the pavement to be recycled
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Silica exposure during asphalt milling
Road milling has been shown to result in overexposures to respirable crystalline silica Linch KD [2002]. Respirable concrete dust – silicosis hazard in the construction industry. Appl OccupEnviron Hyg 17(3):209–221.
Rappaport SM, Goldberg M, Susi P, Herrick RF [2003]. Excessive exposure to silica in the U.S. construction industry. Ann Occup Hyg 47(2):111–122.
Valiante DJ, Schill DP, Rosenman KD, Socie E [2004]. Highway repair: a new silicosis threat. Am J Public Health 94(5):876–880.
Asphalt Partnership
Originated in 1994 with the asphalt fume study
Seven engineering studies were conducted between 1994 and 1997.
The 1990’s research resulted in the publication of engineering control guidelines: ENGINEERING CONTROL GUIDELINES
FOR HOT MIX ASPHALT PAVERS (1997)http://www.cdc.gov/niosh/asphalt.html
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Engineering Controls were put on all new highway class pavers
* The asphalt fumes studies were led by NIOSH researchers Kenneth R. Mead, Ph.D., P.E. and R. Leroy Mickelson, M.S., P.E.
Formation of Silica/Milling Machines Partnership
April 5, 2002 NIOSH meeting to propose silica partnership Association of Equipment Manufacturers (AEM) Compaction and Paving Machinery Technical Committee
July 23, 2002 NIOSH phone call to propose partnership National Asphalt Pavement Association (NAPA) The Asphalt Institute Harvard
January 15, 2003 NAPA meeting The silica/milling machines partnership was formed Shared many of the members as the asphalt fumes partnership
Milling studies began later in 2003 in Wisconsin.
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SILICA/MILLING MACHINE PARTNERSHIP MEMBERS
National Asphalt Pavement Association (NAPA)
Wirtgen Caterpillar Terex Roadtec Volvo Payne and Dolan Midwest Paving/Delta Paving Northeast Asphalt E&B Paving Inc. L&L Astec Industries Sakai America, Inc. Bomag Colas Inc Midwest Asphalt Corporation NIOSH
OSHA Association of Equipment
Manufacturers (AEM) International Union of Operating
Engineers (IUOE) Federal Highway Administration (FHWA) Dynapac Delta Companies, Inc. Barrett Paving Materials, Inc. Tilcon Connecticut Inc. Laborers' Health Safety Fund of North
America (LHSFNA) Asphalt Recycling & Reclaiming
Association (ARRA) Upper Plains Contracting Inc. (UPCI) Asphalt Paving Association of California
(APACA) Laborers’ International Union of North
America (LIUNA)
Initial project goals
Determine if existing water-spray systems used to cool cutting teeth could also control respirablecrystalline silica exposures.
Improve dust controls by modifying water-spray flow, nozzle pressure and nozzle location.
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Area sampling methods
Continuous-monitoring, data-logging optical particle counters (pDR instruments) were mounted at fixed locations on each machine.
Two battery-operated sampling pumps, each connected through flexible tubing to a sampling head consisting of a standard 10-mm, nylon, respirable size-selective cyclone followed by a pre-weighed, 37-mm diameter, 5-micron (μm) pore-size polyvinyl chloride filter.
Area dust sampling setupArea dust sampling setup
pDR Instantaneous dust monitor (one sample every 10 sec)
pDR Instantaneous dust monitor (one sample every 10 sec)
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Conveyor TopConveyor Top ConveyorConveyor
Cutting Drum BackCutting Drum Back
OperatorOperator
Cutting Drum Front
Cutting Drum Front
Ten Respirable Dust Sampling LocationsTen Respirable Dust Sampling Locations
Four of Ten Dust Sampling LocationsFour of Ten Dust Sampling Locations
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2003 Pilot Study
Two day study on US Route 12 in Wisconsin
Evaluated higher flow water-spray nozzles
Measured respirable dust and respirable quartz exposures in personal and area samples
Reductions were not statistically significant
2004 Silica/Milling Machines Partnership Study
Asphalt Milling of US Route 22 and SR 64 in Wisconsin Increasing the water flow
Cutter drum spray bars from 5 gallons per minute (gpm) to 9 gpm
2 gpm to 3 gpm at the conveyor sprays Resulted in an overall reduction in respirable dust
emissions of about 50%, and nearly as great a reduction in respirable quartz emissions.
Results varied by location with the greatest reduction occurring at the conveyor sampling location.
Six trials are not sufficient to make good predictions
10
2006a Silica/Milling Machines Partnership Studies
U.S. Highway 2 resurfacing project Minnesota, June 20-22, 2006 Increased the water-flow rates to the spray nozzles
at the cutter drum from 16 gpm to 18.5 gpm. Resulted in no clear reduction in respirable dust
concentrations at area air monitoring locations around the machine.
Factors affecting the studySmall difference in the water flow rates Interruption in the flow of trucks removing the
milled asphaltSubstantial down time in the actual milling
2006b Silica/Milling Machines Partnership Studies
South Dakota Highway 79 South Dakota, August 15-17, 2006 Increasing the total water flow to the water-spray
nozzles from 12.5 gpm to 18.8 gpm . 41% average reduction based on the results of the
time-integrated air sampling method 53% mean reduction based on the real-time data-
logging instrumentation Both of these reductions were statistically
significant at the 95% confidence level (or the p < 5% level).
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2006c Silica/Milling Machines Partnership Studies
New York State Thruway (Interstate Highway 90) resurfacing project Hamburg, New York, September 25-26, 2006
Increased the total water flow to the water spray nozzles from about 12.5 gpm to about 20 gpm
Did not result in overall reductions in respirable dust and quartz concentrations at area air-monitoring locations around the machine.
Summary of PBZ Air-Sampling Results(pre-2008)
PBZ Air Sampling:Summary of Results (mg/m3)
Mfr. AWisconsin 2004
Mfr. BMinnesota 2006
Mfr. CSouth Dakota 2006
Mfr. DNew York state2006
Maximum / GM concentrations:Respirable dust, high H2O flow, operator
1.60.90
0.250.15
0.440.11
2.31.14
Maximum / GM concentrations:Respirable dust, high H2O flow, ground man
0.570.36
1.060.87
0.300.14
0.890.79
Maximum / GM concentrations: Respirable crystalline silica, high H2O flow, operator
(0.07)0.053
NDND
NDND
0.370.18
Maximum / GM concentrations: Respirable crystalline silica, high H2O flow, ground man
(0.04)0.022
(0.058)0.048
NDND
0.160.14
# Exceedances of 0.05 mg/m3 silica / # samples: High H2O flow, Low H2O flow
3/64/6
2/61/6
0/120/10
6/62/4
# Exceedances of PEL / # samples:High H2O flow, Low H2O flow
0/62/6
0/60/6
0/120/10
6/61/4
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2008 Silica/Milling Machines Partnership Studies – Mill Fest I & II
Abandoned airport runway in Marquette, MI during June and August of 2008
Four manufacturers, each with multiple water spray configurations and one with a ventilation control
Water spray controls indicated reductions in respirable dust emissions of approximately 43%
Ventilation controls indicated reductions in respirable dust emissions of approximately 65%
2010 Silica/Milling Machines Partnership Study –Mill Fest III
Wisconsin State Hwy 47 south of Bonduel, WI Five manufacturers, each with multiple water spray
configurations and one with a ventilation control Water spray configurations that indicated reductions in 2008,
did not show similar reductions in 2010 when more trials were completed
Wet drum water spray controls tested in 2010 indicated reductions in respirable dust emissions of approximately 32% but were not statistically significant due to high variability
Ventilation controls indicated reductions in respirable dust emissions of 81%
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2012 Silica/Milling Machines Partnership testing
Laboratory/Factory tracer gas testing Manufacturer A (Racine, WI) August 2-3, 2011
Manufacturer D (Oklahoma City, OK) August 16-17, 2011
Manufacturer B (Chattanooga, TN) April 17, 2012
Manufacturer C (Minnesota) August 23, 2012
Field testing Manufacturer A - vacuum cutting system (VCS)
• June 26 – August 1, 2012 (11 days spread over four sites)
Manufacturer E – prototype wet drum• August 17-18, 2012 (2 days of testing including 19 trials)
Manufacturer B local exhaust ventilation (LEV)• September 18 – October 13, 2012 (10 days spread over seven sites)
Tracer gas testing at each manufacturer’s facility
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Tracer gas set-upWood blocks and cardboard allowed space for test equipment under edge protection plates
Wood blocks and cardboard allowed space for test equipment
Oil boom under front gradation control beam
Set-up continued
Rear scraper blade was flush to the ground
15
Tracer gas methods
Smoke Release Chauvet Category 2 Hurricane” fog machine
Tracer Gas (TG) Sulfur Hexafluoride (SF6)
Measured in the duct downstream of the fan
CSF6 = mean concentration TG released under the drum
CSF6 = mean concentration when TG released in duct
Smoke test
Provides visual check of large leaks
Released under the cutting drum 8 foot long, 2 inch diameter PVC pipe
16, ¼ inch holes drilled along the length
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Tracer gas test
Cylinder of pure SF6 with CGA-590 pressure regulator
Omega mass flow controller
¼ in diameter Teflon tubing with Swagelok connections
Quick-release connection for switching between 100% capture release point and the cutting drum release point.
100% capture injection location
Tracer gas distribution pipe inserted here
Tracer gas sampling
¼ in dia copper probe located in the duct downstream of the fan.
Two gas meters were used to pull samples simultaneously from the air stream. Miran SapphIRe infrared spectrometer
Brüel & Kjær multigas monitor
17
Manufacturer A laboratory tracer gas capture efficiency results from 2011
Trial Capture Efficiency (B&K)
Capture Efficiency (Miran SapphIRe)
1 91.6% 92.3%
2 93.2% 94.0%
3 93.4% 93.6%
4 93.0% 94.2%
5 92.4% 93.3%
Average 92.7% 93.5%
Lower 95% confidence
limit
92.0% 92.7%
Manufacturer D laboratory tracer gas capture efficiency results from 2011
Trial Capture Efficiency (B&K) Capture Efficiency (Miran SapphIRe)
1 (900 acfm) 99.5% 100%
2 (900 acfm) 99.3% 99.6%
3 (900 acfm) 99.8% 100%
4 (900 acfm) 100% 100%
Average 99.7% 99.9%
Lower 95% confidence limit
99.3% 99.7%
Trial Capture Efficiency (B&K)
Capture Efficiency (Miran SapphIRe)
1 (1300 acfm) 100% 100%
2 (1300 acfm) 100% 100%
1 (600 acfm) 97.1% 98.2%
2 (600 acfm) 97.0% 97.4%
1 (900 acfm)* 99.2% 100%
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Manufacturer B laboratory tracer gas capture efficiency results
Trial Capture Efficiency (Photoacoustic
monitor)
Capture Efficiency (Miran SapphIRe)
1 99% 100%
2 99% 99%
3 98% 99%
4 96% 95%
5 100% 100%
Average 98% 99%
Lower 95% confidence
limit
97% 97%
Manufacturer C laboratory tracer gas capture efficiency results
Fan Speed (RPM) Trial 1 Trial 2 Trial 3 Mean
Lower 95% confidence
limit
3,500 100.0% 97.0% 97.4% 98.1% 95.7%
3,000 99.4% 99.4% 93.8% 97.5% 95.1%
2,500 95.6% 93.3% 95.3% 94.7% 92.3%
2,000 87.5% 91.3% 87.0% 88.6% 86.2%
19
LEV control field studies
Field Testing Goals
The aim is to determine whether the exposures are below the NIOSH REL of 0.05 mg/m3 and the ACGIH TLV of 0.025 mg/m3, which can be demonstrated if the upper confidence limits for each occupation’s arithmetic mean is less than the REL and TLV.
20
Personal breathing zone (PBZ) sampling methods
Full-shift time weighted average personal breathing zone sampling was conducted for respirable crystalline silica.
Respirable dust cyclones (model GK2.69, BGI Inc., Waltham, MA) at a flow rate of 4.2 liters/minute (L/min) were attached to the breathing zone of the operator and ground man.
Crystalline silica analysis of filter samples was performed using X-ray diffraction in accordance with NIOSH Method 7500.
Manufacturer A vacuum cutting system (VCS) summary results
11 days of sampling over four sites
Operator and ground man PBZ
22 PBZ samples
Ranged from 0.003 mg/m3 to 0.013 mg/m3
Silica content ranged from 7% to 23%
21
Manufacturer A vacuum cutting system (VCS) statistical results
Occupation Arithmetic mean (AM),
mg/m3
Relative Standard
Deviation (RSD) between sites
Relative Standard
Deviation (RSD), within sites
Simultaneous Upper 95% Confidence Limits (AM) for both Occupations, mg/m3
Operator 0.0071 22% 47% 0.011
Ground man 0.0066 11% 38% 0.0093
Data treated as lognormally distributed
Data treated as normally distributed
Occupation Arithmetic mean
(AM), mg/m3
Geometric mean (GM),
mg/m3
Geometric standard deviation
(GSD), between sites,
mg/m3
Geometric standard deviation
(GSD), within sites, mg/m3
Simultaneous Upper 95% Confidence Limits**(AM)
for both Occupations,mg/m3
Operator 0.0075 0.0061 1.37 1.76 0.019Ground
man0.0068 0.0061 1.13 1.59 0.013
Manufacturer E - wet drum % reduction results
19 short-term trials were conducted to compare reductions in respirable dust concentrations between the wet drum and baseline water configurations.
Ratio = Wet drum/baseline
Ratios with upper 95% confidence intervals greater than 1 were not statistically significant.
Lower 6 Operator Conveyor Top
Estimated Ratio (GM) 0.63 0.73 1.15
(lower conf limit, upper conf limit) (0.39,1.01) (0.46,1.18) (0.72,1.86)
Geometric mean ratios and 95% confidence limits
22
Manufacturer E - wet drum personal breathing zone results
Personal breathing zone samples were also collected during the two days of sampling for the operator and the ground man.
Operator 0.085 mg/m3 on day 1
0.028 mg/m3 on day 2
Ground man 0.040 mg/m3 on day 1
0.043 mg/m3 on day 2
Bulk samples contained 14% quartz, 0.51% cristobalite
Manufacturer B - local exhaust ventilation (LEV) summary results
10 days of sampling over seven sites
Operator and ground man PBZ
20 PBZ samples
Ranged from 0.002 mg/m3 to 0.013 mg/m3
(except for 1 day at 0.024 mg/m3 with partly clogged LEV)
Silica content ranged from 5% to 12%
23
Manufacturer B - local exhaust ventilation (LEV) statistical results
OccupationArithmetic mean (AM),
mg/m3, from models
Relative standard deviation (RSD),
between sites
Relative standard deviation (RSD), within
sites
Simultaneous Upper 95% Confidence
Limits(AM) for both Occupations , mg/m3
Ground man 0.011 61% 26% 0.018
Operator 0.0049 52% 35% 0.0083
Occupation
Arithmetic mean (AM),
mg/m3, from model
Geometric mean (GM),
mg/m3
Geometric standard deviation (GSD),
between sites, mg/m3
Geometric standard deviation (GSD), within
sites, mg/m3
Simultaneous Upper 95% Confidence Limits (AM) for both Occupations ,
mg/m3
Ground man 0.011 0.00871.76 1.39
0.0246
Operator 0.0053 0.0043 0.012
Data treated as normally distributed
Data treated as lognormally distributed
Summary
The LEV systems of manufacturer’s A and B have the potential to significantly reduce worker exposure to respirable crystalline silica during pavement milling operations.
NIOSH researchers recommend that manufacturers of half-lane and larger cold milling machines should implement dust controls that include local exhaust ventilation as a control for silica exposures.
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NIOSH Team
NIOSH Cincinnati Duane Hammond, M.S., P.E.
Leo Blade, M.S., C.I.H.
Stanley Shulman, Ph.D.
Alan Echt, M.S., C.I.H.
Liming Lo, Ph.D.
Mike Gressel, Ph.D., C.S.P.
Kenneth R. Mead, Ph.D., P.E.
Nick Trifonoff
NIOSH Pittsburgh Andrew Cecala
Jay Colinet
Jeanne Zimmer
Gregory Chekan, B.S., MinE
Gerald Joy, C.I.H., C.S.P.
Duane Hammond, M.S., P.E.National Institute for Occupational Safety and Health4676 Columbia Pkwy MS R-5Cincinnati, OH 45226(513) 841-4286
Questions?
National Institute for Occupational Safety and Health
Division of Applied Research and Technology – Engineering and Physical Hazards
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