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Intra-workday fluctuations of airborne contaminant concentration and the time-weighted average.

Air contaminant concentrations vary between and within workdays and are often measured across a workday by passing a known air volume through a collection device. Laboratory analysis determines the contaminant mass trapped, providing a time-weighted average air concentration (CTWA). This approach wa...

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Published in:Journal of Occupational & Environmental Hygiene Vol. 19; no. 12; pp. 742 - 759
Main Author: Smith, Philip A.
Format: CEU equations & formulas pictorial research tables/charts Journal Article
Published: Taylor & Francis Ltd Dec2022
Online Access:View this record in EBSCOhost
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      issn: 15459624
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      dt: Dec2022
      vid: 19
      iid: 12
      pid: 377
      pub: Taylor & Francis Ltd
      place: Philadelphia, Pennsylvania
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        10.1080/15459624.2022.2132258
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        atl: Intra-workday fluctuations of airborne contaminant concentration and the time-weighted average.
      aug:
        au: Smith, Philip A.
        affil: Occupational Safety and Health Administration, U.S. Department of Labor Directorate of Technical Support and Emergency Management, Washington, DC, USA
      sug:
        subj:
          Air Pollutants, Occupational Analysis
          Occupational Exposure Evaluation
          Environmental Monitoring
          Work Environment
          Occupational Health
          Human
          Hygiene
          Gases Analysis
          Precision
          Automation
          Internet of Things
          Descriptive Statistics
          Education, Continuing (Credit)
      ab: Air contaminant concentrations vary between and within workdays and are often measured across a workday by passing a known air volume through a collection device. Laboratory analysis determines the contaminant mass trapped, providing a time-weighted average air concentration (CTWA). This approach was driven by the best technologies available as exposure measurement processes developed and accuracy and measurement precision were sought. However, all integrated concentration•time (C•t) values determining CTWA are equally weighted in assessing exposures, intra-workday concentration variability is unknown, and results are available days later. At times inappropriately, an occupational exposure limit (OEL) expressed as a CTWA also requires equal weighting of all C•t values across an exposure period following concepts of Haber's law. Continuous monitoring (real-time detection) informs both the CTWA and the variability of C during sampling, which are needed for stressors where a ceiling or peak OEL exists, for dangerous exposures to permanent gas-type contaminants, and for immediately dangerous to life or health (IDLH) conditions. Selective and accurate real-time detection instruments are not available for all air contaminants, but exposure magnitude information may be provided. The large amounts of data from continuous monitoring and the ability to correlate exposure maxima to specific tasks are also important. An exposure assessment role exists for selective and nonselective monitors, and in some cases, similar accuracy and precision are provided compared to laboratory analyses. Continuous monitoring may be of value when the alternative is the collection of a few CTWA data points. Digitized personal monitor data can support the automation of some exposure control decisions or allow such decisions to be made by people in near real-time. The emerging Internet of Things (IoT) offers opportunities to integrate digital exposure data into decision-making to increase both efficiency and safety. The perceived and real uncertainty associated with real-time exposure assessments may be lessened with work to rule out the presence of know interferents and confirm the presence of target analytes.
      pubtype: Academic Journal
      doctype:
        CEU
        equations & formulas
        pictorial
        research
        tables/charts
        Journal Article
      ougenre: Article
    language: English
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