Fibrous Glass-Lined Air Transmission Systems: An Assessment Of Their Environmental Effects

Our plain-English summary of Fibrous Glass-Lined Air Transmission Systems: An Assessment Of Their Environmental Effects, by J.L. Balzer, W.C. Cooper, D.P. Fowler (1971).

The study

• Authors: J.L. Balzer, W.C. Cooper, D.P. Fowler
• Published: American Industrial Hygiene Association Journal 32(8):512-518, August (1971)
• Type of article: Journal article
• Our copy: from Johns-Manville's own medical library, J-M no. 004952. The article is still under copyright, so we describe it here rather than post it.

In plain English

This study, from the School of Public Health at the University of California, Berkeley, measured whether air ducts lined with fibrous glass add glass fibers to the air delivered into buildings. From thirty building air systems surveyed, the authors took air samples in thirteen where they confirmed fibrous glass lining. They collected over 600 samples, several hundred of them in three buildings on the Berkeley campus. Fibers caught on filters were counted under the microscope and sorted into six categories, one of which was asbestiform minerals. The reported results concern glass fibers. Air inside the ducts consistently had lower glass fiber concentrations than outside air, and over 95% of matched samples taken the same day in the same building showed a decrease. Glass fiber levels inside buildings tracked outdoor air more closely than air leaving the ducts. Areas supplied by lined ducts had roughly 1 glass fiber per liter. The authors put this at less than one ten-thousandth of the occupational limit for glass fibers. The authors concluded that properly designed, built and maintained lined systems do not add glass fibers to the air stream. They cautioned that the results cannot be applied to all such systems. The research was supported in part by the National Insulation Manufacturers Association.

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: Field air-sampling study comparing glass fiber concentrations in air before and after it passed through fibrous glass-lined air transmission (ventilation and heating) systems, using membrane filters and microscopy
• Who was studied: Thirteen building air transmission systems, chosen from thirty surveyed, with fibrous glass lining confirmed by inspection. Over 600 samples were taken, several hundred of them in three buildings on the University of California Berkeley campus. Ambient air in the San Francisco Bay Area was also sampled. The paper was published in 1971.
• Exposure: Airborne glass fibers from fibrous glass linings in ventilation or heating ducts. Fibers were classified into six categories, including fibrous glass and asbestiform minerals.
• Main results:
  • Across the systems, air within ducts showed consistently lower glass fiber concentrations than outside air.
  • Over 95% of matched individual air samples, taken the same day in the same building, showed fewer glass fibers in duct air than in outside air or in air just after the inlet filters.
  • Glass fiber concentrations within buildings correlated more closely with concentrations in ambient air than with concentrations in air leaving the lined supply systems.
  • In San Francisco Bay Area ambient air samples, glass fiber concentrations ranged from less than 0.05 to 10 fibers per liter, with a mean of approximately 0.2 fibers per liter.
  • In areas supplied with air that had passed through fibrous glass-lined ducts, concentrations were roughly 1 fiber per liter. The authors described this as less than 1/10,000 of the threshold limit value for airborne glass fibers.
  • Glass fiber diameters ranged from less than 1.6 to 35.3 micrometers, with an estimated geometric mean of 4.5 micrometers.
• The authors' conclusion: The authors concluded that properly designed, constructed and maintained air transmission systems lined with fibrous glass do not add glass fibers to the air stream. They also concluded that the fiber concentrations measured were extremely low and do not appear biologically significant.
• Limitations the authors state:
  • The results cannot be expected to apply to all fibrous glass-lined air transmission systems, including poorly designed or maintained ones.
  • The authors did not give any numerical estimate of the method's accuracy.
  • The authors could not quantitatively describe the reproducibility of their air sampling.
  • There were too few fibers from any one system to draw a statistically valid conclusion about the size distribution of glass fibers.
  • Samples could not be taken from equivalent sites in every system.
  • The causes of the observed changes in the fiber population could not be determined with the limited data available.

Topics

Medical terms in this study, explained in our Lexicon: Asbestiform.

Browse return to medical research.