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Exposure Assessments

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NIOSH publication 77-173 Occupational Exposure Sampling Strategy Manual (Yellow Book) ... NIOSH 77-173 'In statistical terms, the employer should try to attain 95 ... – PowerPoint PPT presentation

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Title: Exposure Assessments


1
Exposure Assessments
  • Paul Wambach, CIH
  • DOE, Worker Safety Health Policy (HS-11)
  • Phone 301-903-7373
  • Email Paul.Wambach_at_hq.doe.gov

2
Exposure Assessment and Management
3
Proving Exposures are Unacceptable Regulatory
Action Level
  • NIOSH publication 77-173 Occupational Exposure
    Sampling Strategy Manual (Yellow Book)
  • An OSHA Inspector assumes the workplace is safe
    until proven unsafe
  • Very few industrial operations have day-to-day
    environmental GSDs less than about 1.2
  • . . . If one measured daily exposure average is
    at one half the standard then . . . at least 5
    of unmeasured true daily averages exceed the
    standard.
  • One measurement can prove that working conditions
    are unsafe.

4
Proving Exposures are Acceptable
  • NIOSH 77-173 In statistical terms, the employer
    should try to attain 95 confidence that no more
    than 5 of employee days are over the standard.
  • Tuggle -1982 Assessment of Occupational Exposure
    Using One-Sided Tolerance Limits
  • Hewett and Ganser 1997 Simple Procedures for
    Calculating Confidence Intervals Around the
    Sample Mean and Exceedance Fraction . . .

5
Similarly Exposed Group (SEG)
  • AIHA 2006 A group of workers having the same
    general exposure profile for an agent because of
    the similarity and frequency of the task(s) they
    perform, the similarity of the materials and
    processes with which they work, and the
    similarity of the way they perform the task(s).
  • Rappaport 1991 Ratio of the 97.5tile mean
    to the 2.5tile mean 4 or equivalently the
    between worker geometric standard deviation (GSD)
    is 1.4

6
Theory
  • Prove SEG Exposures are Unacceptable
  • Null hypothesis 95 of exposures lt OEL
  • Accept alternative if 95-95 UTL gt OEL
  • Rule-of-thumb, any value gt ½ OEL
  • Prove SEG Exposures are Acceptable
  • Null hypothesis 95 of exposure gt OEL
  • Accept alternative if 95-95 UTL lt OEL
  • Rule-of-thumb, 10 values lt 1/10 OEL
  • Uncertain if neither of the above are true

7
Problems
  • SEGs are the exception rather than the rule
  • Tasks, locations, materials, and tools vary,
    especially for service and construction workers
  • For mature programs, recognized exposures are
    being controlled and the usual determinants of
    exposures are not good predictors job, task and
    location.
  • Materials with no OELs
  • If a high percentage of exposure monitoring
    results are non-detects many samples are needed

8
Line Fit Plot for 533 Samples for 23 Beryllium
Machinist During an ORR
9
Needed Solutions
  • Methods for heterogeneous groups.
  • Groups based on the organization structure used
    to administer health protection programs
  • Must be large enough for non-parametric
    statistics (greater than 60 samples per year)
  • Methods for establishing provisional OELs
  • EPA IRIS, AIHA WEEL, etc standard methods for
    converting animal data to limits
  • Conservative default for unstudied materials
  • Data Quality Objectives
  • Sufficient number of samples to answer the
    question
  • Laboratory reporting limits arent arbitrarily
    set too high.

10
Exposure SurveillanceSecondary Use of
Information
  • Public health surveillance
  • Health information collected from patient
    encounters analyzed to detect unusual events or
    pattern of events
  • LaMontagne 2002
  • Occupational exposure surveillance is the
    ongoing collection, management, and aggregate
    analysis of exposure data, and in turn the
    application of findings to guide workplace
    prevention and control efforts.
  • Are health risk management programs preventing
    exposures above OELs?

11
Examples Jones and Nicas 2005 Validity of COSHH
Essentials
  • Under-control With recommended controls, the
    upper limit of the control band was exceeded in
  • 78 (139/179) of vapor degreasing and
  • 48 (76/159) of bag filling operations
  • Over-control Without recommended controls,
    concentrations were within the control band
  • 61 (102/167) at vapor degreasing and
  • 8 (3/26) at bag filling operations

12
Example Marchant et al 2009 Database for
Synthetic Vitreous Fibers
13
Example DOE Beryllium-Associated Worker
Registry (BAWR)
14
BAWR Percent Exceeding 0.2 mg/m3 by Work
Activity Category
15
Conclusions
  • Proving compliance is more difficult than proving
    non-compliance.
  • Data quality objectives are different.
  • Establish the exposure profile.
  • Exposure surveillance provides a conceptual
    framework for progress.
  • Computerized information management makes routine
    analyses of aggregated data feasible.
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