To the Editor: The article "Confined Space Hazards: Combined Exposure to Styrene, Fiberglass and Silica" by Shields et al1 was read with interest and a degree of resignation. The authors have assumed that the presence of fiberglass at the work site has contributed to an occupational illness. This article, without justification, has joined others that date back to the 1940s and which continue this erroneous practice.
Glass fibers have been investigated since the late 1930s to the present, using increasingly sophisticated animal research, human mortality and morbidity studies, and industrial hygiene evaluations.2-5 This extensive ongoing research has not demonstrated any reasonable link between exposure to airborne fiberglass and pulmonary disease.6 Glass fibers and other fibers of sufficient diameter (> 5 microns) will cause a primary irritation.7 This most often occurs on the skin, but will occasionally present as upper respiratory tract irritation. The glass mat described in the article is composed of continuous filament glass fibers. These fibers have a diameter of 12 to 15 microns and are too large to be respirable.
The authors correctly identify a number of airborne contaminates that were likely present in the air of the confined workspace. These include styrene, silica, epoxy material, and fiberglass. They mentioned in passing that the epoxy material was troweled on, which in practice could have liberated methylethylketone and other substances during the stages of cure.
There was no effective general or local ventilation and the limited use of respiratory protection devices in the confined space were not protective. The cured surface was power-ground smooth. The airborne dust reportedly obscured vision. One can only guess at the gravimetric airborne dust concentration. Because measurements are not available, it is assumed that the dust consisted of silica and cured epoxy material, but very few nonrespirable glass fibers.
The wall of the tank was, in effect, a steel outer shell with a fiberglass reinforced epoxy plastic inner shell. The continuous filament glass fiber used in these applications is too large to be respirable.8 Even when cut or ground, fiberglass can only split crosswise to its long axis.9 Published data from industrial hygiene sampling in operations in which fiberglass-reinforced plastic materials were cut and ground demonstrate no respirable glass fibers and few nonrespirable glass fibers.10
In summary, probably no respirable glass fibers and few nonrespirable glass fibers were airborne in the tanks during the renovations. The respiratory mischief was more likely caused by extremely high levels of styrene and other components of the uncured epoxy system, enhanced by massive respiratory overloading with airborne nonfibrous particulate.
Editor's Note: Dr Shields chose not to reply.
Joel R. Bender, PhD, MD
Health, Safety & Environmental Affairs; Owens-Corning; Toledo, OH
1. Shields PG, McCunney RJ, Chase KH. Confined spaces hazards: combined exposure to styrene, fiberglass, and silica. J Occup Environ Med.
2. Marsh GM, Enterline PE, Stone RA, Henderson VL. Mortality among a cohort of U.S. man-made mineral fiber workers: 1985 follow-up. J Occup Med.
3. Chiazze L, Watkins D, Fryar C, Kozono J. A case-control study of malignant and non-malignant respiratory disease among employees of a fiberglass manufacturing facility. II. Exposure assessment. Br J Ind Med.
4. Hughes J, Jones R, Glindmeyer H, Hammad Y, Weill H. Follow up study of workers exposed to man made mineral fibres. Br J Ind Med.
5. Bunn W, Bender J, Hesterberg T, Chase G, Konzen J. Recent studies of man-made vitreous fibers. J Occup Med.
6. Proceedings. Symposium on synthetic vitreous fibers: scientific and public policy issues. Reg Toxicol Pharmacol.
7. Reference not provided.
8. Reference not provided.
9. Reference not provided.
10. Reference not provided.
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