Occupational exposure to carbon fibers impregnated with epoxy resins and evaluation of their respirability

Our plain-English summary of Occupational exposure to carbon fibers impregnated with epoxy resins and evaluation of their respirability, by P. Lovreglio, A. Stufano, D. Mele, et al (Inhalation Toxicology, 2020).

The study

• Authors: P. Lovreglio, A. Stufano, D. Mele, P. Acquafredda, D. Cottica, F. Gardinali, L. Vimercati, L. Soleo, G. De Palma
• Journal: Inhalation Toxicology
• Published: 2020;32(2):63-67
• Cited by: 4 articles, as counted by NIH iCite
• Read it: PubMed · Publisher

Abstract

Objectives: The study aims to investigate occupational exposure to carbon fibers impregnated with epoxy resins (carbon fiber reinforced [CFR]) in workers at an airplane fuselage section construction plant, by environmental and biological monitoring.Materials and methods: Determination of airborne CFR was done by environmental sampling with active samplers, 11 of which were stationary and 19 personal samplings. The subsequent analyses were performed in the scanning electron microscope fitted with an X-ray microanalysis system (SEM-EDXA). Biological monitoring was carried out by determining CFR in exhaled breath condensate (EBC) collected from 19 male workers who wore personal environmental samplers (exposed workers) and from 10 male workers at the same factory who had no occupational exposure to CFR (internal controls). CFR analysis was done by SEM, applying the method used for determining asbestos fibers in aqueous samples.Results: The airborne CFR concentrations were found to be significantly higher (p = 0.03) at personal samplings (median value 7.01 ff/L, range 1.24-11.16 ff/L) than stationary samplings (median value 1.93 ff/L, range 0.55-10.09 ff/L). The aerodynamic diameters calculated starting from the length and geometric diameter of the sampled CFRs were always higher than 20 µm. CFR was not found in any of the EBC samples collected from the exposed workers and controls.Conclusions: Despite the evidence of occupational exposure to low concentrations of CFR, the absence of such fibers in the EBC in the exposed workers confirms their non-respirability, as expected based on their aerodynamic diameter.

In plain English

This 2014 field study measured workers' exposure to carbon fibers impregnated with epoxy resins (called carbon fiber reinforced, or CFR) at a factory making airplane fuselage sections. It did not study asbestos, but the authors adapted methods used to measure asbestos fibers. Air was sampled with 11 stationary and 19 personal samplers during sanding, drilling/reaming and rivet removal. The fibers were examined by scanning electron microscopy. The authors also looked for fibers in exhaled breath condensate (moisture collected from the breath) from 19 exposed male workers and from 10 male office workers who served as controls. Personal samples had higher fiber levels (median 7.01 fibers per liter, range 1.24 to 11.16) than stationary samples (median 1.93, range 0.55 to 10.09; p = 0.03). The fibers averaged 62.1 micrometres long and 6.4 micrometres wide. All calculated aerodynamic diameters were above 20 micrometres. No fibers were found in any breath sample. The authors concluded that the fibers were not respirable. They noted that further studies are needed to rule out that breath condensate simply cannot carry large particles like fibers.

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 study combining workplace air monitoring (stationary and personal samplers) with biological monitoring (exhaled breath condensate) in exposed workers and internal controls
• Who was studied: The study was carried out in 2014 at a factory producing airplane fuselage sections. It included 19 male workers randomly selected from those potentially exposed to CFR, and 10 male workers randomly chosen from administrative staff in a different building who had never been occupationally exposed to CFR (controls).
• Exposure: Carbon fibers impregnated with epoxy resins (CFR), released during dry-sanding, drilling/reaming and rivet removal on fuselage section walls. Ventilation systems were switched on, and workers wore face filtering half masks that filter at least 94% of airborne particles.
• Main results:
  • Airborne CFR was significantly higher (p = 0.03) at personal sampling (19 samplings; median 7.01 ff/L; range 1.24 to 11.16 ff/L) than at stationary sampling (11 samplings; median 1.93 ff/L; range 0.55 to 10.09 ff/L).
  • When broken down by working activity (sanding, drilling/reaming, rivet removal), personal sampling was higher than stationary sampling for each activity, but these differences were not significant.
  • The sampled CFRs had an average length of 62.1 ± 47.2 micrometres and an average geometric diameter of 6.4 ± 0.6 micrometres (printed as "mm" in the text).
  • All calculated aerodynamic diameters of the sampled fibers were above 20 micrometres, ranging from 20.1 to 39.7. The authors considered the fibers non-respirable on this basis.
  • No CFR was found in the exhaled breath condensate of any of the 19 exposed workers or the 10 controls.
  • The authors compared the measured levels with limits for other fibers. They described them as one order of magnitude lower than the 100 ff/L limit for asbestos in European Directive 2003/18/CE, and noted that no specific limits exist for CFR.
  • Smoking was more common among exposed workers (42.1%) than controls (10.0%), but the difference was not statistically significant.
• The authors' conclusion: The authors concluded that workers were exposed to low concentrations of CFR. They stated that the combined air and breath sampling approach seems able to confirm that CFR is not respirable, and to exclude the previously reported possibility that carbon fibers split along their long axis.
• Limitations the authors state:
  • The authors state that further studies are needed to validate the breath condensate method for carbon fibers. Such studies would also need to exclude the possibility that no fibers were found because breath condensate cannot carry large particles like fibers.
  • No established methods existed for this kind of measurement, so the authors adapted methods used for asbestos and man-made mineral fibers.

Topics

Medical terms in this study, explained in our Lexicon: Occupational Exposure.

Related studies

• Microwave polymerisation of epoxy resin: rapid processing technique in ultrastructural pathology — A.L. McLay, J.D. Anderson, et al. (1987)
• Evaluation of the size and type of free particulates collected from unused asbestos-containing brake components as related to potential for respirability — M.A. Atkinson, M. O'sullivan, et al. (2004)
• Re: Evaluation of the size and type of free particulates collected from unused asbestos-containing brake components as related to potential for respirability — D.J. Paustenbach, B.L. Finley, et al. (2006)
• Carcinogenic hazards from inhaled carbon black, titanium dioxide, and talc not containing asbestos or asbestiform fibers: recent evaluations by an IARC Monographs Working Group — R.A. Baan (2007)
• Airborne fiber size characterization in exposure estimation: Evaluation of a modified transmission electron microcopy protocol for asbestos and potential use for carbon nanotubes and nanofibers — J.M. Dement, E.D. Kuempel, et al. (2015)
• Epoxy Resins for Flooring Applications, an Optimal Host for Recycling Deactivated Cement Asbestos — F. Campanale, F. Vergani, et al. (2023)

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