Airborne fiber concentrations during splitting open and boxing bags of asbestos

Our plain-English summary of Airborne fiber concentrations during splitting open and boxing bags of asbestos, by N.A. Esmen, M. Corn (Toxicology and Industrial Health, 1998).

The study

• Authors: N.A. Esmen, M. Corn
• Journal: Toxicology and Industrial Health
• Published: 1998;14(6):843-56
• Cited by: 7 articles, as counted by NIH iCite
• Read it: PubMed · Publisher

Abstract

Measured airborne concentrations of asbestos are often unavailable to assess different epidemiologic estimates of past personal exposure levels or concentrations near specific operations involving handling asbestos. The purpose of this study was to assess the potential use of a laboratory study in estimating exposure to asbestos in operations that ceased for many years. The asbestos transfer operations were simulated by splitting and boxing 4.5-kg paper bags of chrysotile asbestos in an enclosed chamber ventilated at 28.2 air changes per hour (ACH). Two recirculation fans achieved chamber air mixing. The airborne concentration of asbestos fibers was determined by sampling air through membrane filters at a rate of 10 l/min and by analysing fibers by phase contrast optical microscopy to determine 15-min average airborne concentrations. Samplers were located at four equidistant locations from the operation. Opening a maximum of seven bags in 15 min was associated with an asbestos-in-air concentration of less than 2 x 10(-6) fibers/m3 (f/m3) in splitting open and boxing and less than 0.85 x 10(-6) f/m3 in boxing of pre-split bags. The measured airborne asbestos concentration exhibited a linear trend with the number of bags opened per 15 min. The empirical results were utilised to model fiber concentrations for various ventilation rates. It was concluded that the distribution of the operation within the workday and the ventilation rate are the two most important variables in the determination of the estimated time-weighted average concentration. Splitting open and boxing 32 bags of asbestos over an 8-h period at a rate of 4 bags/h over an 8-h period results in a calculated time-weighted average exposure of about 1 x 10(-6) f/m3 in a work space with 20 ACH and approximately 7 x 10(-6) f/m3 in a work space with 2 ACH. Splitting open and boxing at a rate of 12 bags/h for 2 h and 45 min yielded calculated concentrations less than one-half of the above mentioned values. These results should serve as a useful benchmark for epidemiologists concerned with the magnitude of exposure in historically dusty industrial tasks.

In plain English

This was a laboratory experiment, not a study of workers. The authors simulated a historical factory task, opening bags of asbestos, to test whether experiments can help estimate past exposures. In 33 runs inside a ventilated chamber, 2 to 7 paper bags each holding 4.5 kg of loose chrysotile were either split open on a saw-blade splitter and slid into a box, or pre-cut and only boxed. Air was sampled at four points, and the chamber air tested as well mixed. Fiber concentrations fit a straight-line pattern with the number of bags used. The authors then used the results in a model of splitting and boxing 32 bags in an 8-hour day. Calculated 8-hour averages ranged from 0.29 to 21 fibers per cubic centimetre, depending on ventilation and scheduling. Work timing alone changed results 2- to 3-fold and ventilation 5- to 8-fold. The authors concluded that ventilation and how the task is spread over the workday matter most. They also concluded that a simple model can estimate past exposure within an order of magnitude.

We wrote this plain-English summary from the full article with the help of AI, and a second AI model checked each sentence against the article. It is not the authors' wording; the abstract and the article are their own account.

What the study did and found

• Design: Laboratory simulation experiment with mathematical exposure modelling; the authors state the main purpose was methodological
• Who was studied: No people were studied. There were 33 experimental runs, each using 2 to 7 bags, in a ventilated chamber measuring 1.8 m by 2.2 m by 2.2 m. The acknowledgments say the work was done years earlier at the University of Pittsburgh and presented in 1993.
• Exposure: Loose chrysotile asbestos in 4.5-kg heavy-duty paper bags. Bags were either split open on a circular saw-blade splitter and slid into a cardboard box, or pre-slit with a scalpel and boxed only. The chamber was ventilated at 28.2 air changes per hour. Each run was sampled for 15 minutes at four points, and fibers longer than 3 micrometres were counted by phase contrast optical microscopy.
• Main results:
  • A chi-square test of where the highest and lowest readings occurred indicated that the chamber air was well mixed.
  • Airborne asbestos concentrations could be fitted to a linear model with the number of bags used in each experiment.
  • As printed, the average fiber release per unit volume was 2 x 10^-6 f/m3 (standard deviation 0.78 x 10^-6) for splitting open and boxing, and 0.85 x 10^-6 f/m3 (standard deviation 0.24 x 10^-6) for boxing only. The units and exponent appear inconsistent with the tables (see text_problems).
  • The batch frequency correction functions for splitting and boxing and for boxing only did not differ significantly (p greater than 0.05), so the authors pooled the results.
  • The authors assumed workplace ventilation of 0.2 to 10 air changes per hour and 100% chrysotile. On that basis they calculated a peak (15 minutes or less) exposure range of 0.6 to 80 f/cm3. They stated this agreed reasonably well with peak exposures reported in the literature for mixing and similar tasks.
  • The authors modelled splitting and boxing 32 bags in six scheduling scenarios at 0.5 to 30 air changes per hour. Calculated 8-hour time-weighted averages ranged from 0.29 to 21 f/cm3 (Table 5).
  • In the modelled scenarios, the scheduling of releases alone introduced 2- to 3-fold variability in expected time-weighted average concentrations, and the range of ventilation rates introduced 5- to 8-fold variability.
• The authors' conclusion: The authors concluded that the distribution of the operation within the workday and the ventilation rate are the two most important variables in estimating time-weighted average concentration. They also concluded that a simple semi-empirical model with modest experimental effort can satisfactorily predict past exposure within an order of magnitude.
• Limitations the authors state:
  • The fiber collection and analysis method was non-standard. It was chosen for sensitivity and cost over NIOSH 7400 or electron microscopy.
  • The chamber ventilation rate was higher than is typical in general industry.
  • Historically, asbestos came in jute or heavier paper bags rather than the grocery-type bags used here. The authors stated their opinion that this would not influence the results.
  • The standard error of the fitted constants was about 33%.
  • The literature sources used for comparison did not report ventilation rates, so the authors had to assume them.
  • The results reflect bag opening without local exhaust ventilation. With effective local exhaust, exposures would be substantially lower.

Topics

Medical terms in this study, explained in our Lexicon: Chrysotile, Time-Weighted Average (TWA).

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