real-time exposure assessment terri a. pearce, ph.d. occupational safety and health administration...
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Real-time Exposure Assessment
Terri A. Pearce, Ph.D.
Occupational Safety and Health AdministrationOklahoma City Area Office
Real-Time
• Instantaneous– Absolute, Average, Rolling average
• Near real-time– Processor delay, lag for data transmission
• Adjusted– After data interpolation
Exposure Assessment
• Source– Contaminant– Route of Entry– Monitoring method efficacy
• Receptor– Proximity– Dose– Physiological construct
Six Monitoring Categories
• Noise• Radiation• Gases and Vapors• Aerosols• Ergonomics• Biomonitoring and Surface Sampling
AIHA Survey
• 684 respondents (640 users) with most respondents from manufacturing and services sectors
• 546 reported using DRMs as supplements to laboratory analysis with 445 also using DRMs as alternatives to conventional methods
• Particle monitors used most often followed by gas and vapor monitors
Choosing a DRM
Top is number of respondents Bottom is percent of total 1 2 3 4
Comparability to standard assessment methods 255(47%)
88(16%)
91(17%)
105(19%)
Cost 50(9%)
120(23%)
160(30%)
203(38%)
Ease in accessing and interpreting data 168(31%)
204(38%)
106(20%)
61(11%)
Portability 133(23%)
175(30%)
161(28%)
108(19%)
Future Needs
• More contaminant specific• Multiple contaminants• More user friendly • Less cumbersome• Less expensive• Specific to unique hazards
Types of Monitoring
• Hazard zones • Emission points• Controls (pre- and post-implementation)• Tasks (work practice)• Exposure assessment
Hazard Zones
• Go/no go, safe/not safe• Accuracy, precision, and bias not as important
if error is on side of most conservative (protective) decision
• Established technology with good accessibility for workers
Emission Points
• Yes/no, high/low• Process emissions versus leak detection• May need to know background contaminant levels• Sensitivity may not be as important as specificity
Controls
• Before/after• Accuracy or bias may not be as important as precision• May follow-up with area
or personal monitoring
Tasks
• Tasks/overall TWA• Process emissions versus work practice• Accuracy, precision, and bias all important• Comparability across
monitors if evaluating more than one worker
Exposure Assessment
• Above/below OEL• Accuracy, precision, and bias are important,
specificity is good too• Results consistent across time
and concentration• Comparability among
monitors and with conventional method
Selecting a Method
• Understand mission/objective• Regulatory requirements• Capabilities of the technology• Calibration status• User friendliness
AIHA Real Time Detection Systems Committee
Selection Logic
Birch, M.E., T.A. Pearce, and C.C. Coffey: Direct-Reading Instruments for Gas and Vapor Detection (Publ. No. ASI18). American Conference of Governmental Industrial Hygienists (ACGIH): Cincinnati, OH, 2009.
Monitor Selection• Active/Passive• Size• Weight• Durability• Alarms• Display• Intrinsic safety• Price• Ease of calibration/bump test• Sensor availability
AIHA Real Time Detection Systems Committee
Sensor Selection
• Compatibility with monitor• Specificity for agent of interest• Service life• Price
AIHA Real Time Detection Systems Committee
Noise
• Area versus personal sampling• Continuous versus impulse noise• Measurement mimics the physiological
response
Personal Dosimeters
• Microphone placed in proximity to the ear• Provides the cumulative exposure over the course of the exposure period• Display allows for administrative control
Sound Level Meters
• Provides for identifying noise source and contributing frequency• Better at measuring impulse noise
Applicability of Noise Monitor
• Yes– Hazard zones– Emission points– Controls pre- and post-implementation– Hazards associated with specific tasks – Exposure assessment
Radiation
• Area versus personal sampling• Real-time and Near real-time• Measurement equates to the physiological response
Personal Dosimeters• Real-time– Pocket dosimeter– Digital electronic dosimeter• Audible alarm rate meter
• Near real-time– Film badges– Thermoluminescent dosimeters
Applicability of Radiation Monitor
• Yes– Hazard zones– Emission points– Controls pre- and post-implementation– Hazards associated with specific tasks – Exposure assessment
Gases and Vapors
• Area versus personal sampling• Single versus multiple gases• Not a direct measure
of physiological effect
Single gas monitors
• Mercury• Specific Sensors– carbon monoxide, chlorine, chlorine dioxide, hydrogen cyanide, hydrogen sulfide, nitrogen dioxide, phosphine and sulfur dioxide
Multi-gas monitors
• Configured with multiple sensors• Capable of detecting properties of individual
gases– Photoionization– Flame ionization– Infrared– Gas chromatography– Mass spectrometry
4-gas Monitors
• Confined Space Regulation – Oxygen deficiency – Combustible gases and vapors (LEL)– Toxics• Carbon Monoxide• Hydrogen Sulfide
Applicability of Gas/Vapor Monitor
• Yes– Hot zones versus safe zones
• Maybe– Emission points– Controls pre- and post-implementation– Hazards associated with specific tasks
• No– Exposure assessment
Aerosols
• No monitor is particle specific• Measure in mass or particle count/volume of
air• Not a direct measure of physiological effect
Particle counters
• Area monitors only• Total versus size differentiating• Coincidence errors at high concentrations
Applicability of Aerosol Monitor
• Maybe– Hot zones versus safe zones – Emission points– Controls pre- and post-implementation– Hazards associated with specific tasks
• No– Exposure assessment
Biomonitoring
• Personal sampling only• Parameter measured is or approximates the physiological response
Surface Sampling
• Area versus personal sampling• Connections to physiological response may be possible
Terri A. Pearce, Ph.D.
Oklahoma City Area Office55 N. Robinson, Suite 315Oklahoma City, OK 73102
405-278-9560