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

NIOSH DREAM Workshop

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

Sampling strategies

Strategy development

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

Area Survey Monitors

• Real-time counters– Geiger-Muller– Ion chamber– Proportional

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

Mass monitors

• Area versus personal• May have integrated filter for subsequent analysis

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

Respirator Fit-testing

• Aerosol monitor used to determine appropriateness of personal protection

Ergonomics

• NIOSH lifting equation• Capabilities for measuring

force strength on actual muscles

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.

pearce.terri@dol.gov

Oklahoma City Area Office55 N. Robinson, Suite 315Oklahoma City, OK 73102

405-278-9560