Occupational Exposure to Carbon/Coke Fibers in Plants That Produce Green or Calcined Petroleum Coke and Potential Health Effects: 1. Fiber Characteristics

Abstract

Carbon/coke fibers are found in bulk samples of calcined petroleum coke. Carbon/coke and other fibers, including calcium silicate, cellulose, gypsum, and iron silicate, have been found in exposure monitoring of workers who make or handle green or calcined petroleum coke. Carbon/coke fibers are not classified or regulated as carcinogens by any agency, and the available literature (summarized in this article) has not reported significant adverse health effects associated with exposure to these fibers or dusts containing these fibers. However, available epidemiological and toxicological studies have limitations that prevent a definitive assessment of carbon/coke fiber toxicity. Therefore, it is prudent to monitor and control workplace concentrations. Analyses by transmission electron microscopy (TEM) indicate that the carbon/coke fibers are amorphous, irregularly shaped, and generally rather short (94% less than 20 μm long). Nearly all carbon/ coke fibers satisfying NIOSH 7400 B counting criteria are detectable by phase-contrast optical microscopy (PCOM), which permits the use of a highly efficient sequential sampling strategy for analysis. Data are presented on the distribution of carbon/coke structure and fiber lengths and diameters. Bootstrap resampling results are presented to determine confidence intervals for structure/fiber length and diameter. Data on time-weighted average concentrations are given in a companion article, but nearly all time-weighted average carbon/coke fiber concentrations were beneath 0.1 fibers per milliliter.

Notes

*This statement assumes that the sizes of the fibers being measured are sufficiently large that these are detectable by PCOM. For certain fibers, such as some forms of asbestos, only a fraction of the fibers are detectable with PCOM. However, structures that meet the NIOSH 7400 B criteria for respirable fibers are detectable by PCOM.