Occupational Exposure to Carbon/Coke Fibers in Plants That Produce Green or Calcined Petroleum Coke and Potential Health Effects: 2. Fiber Concentrations

We monitored exposure to various fibers among workers in eight plants operated by ConocoPhillips that produce green or calcined petroleum coke. Carbon/coke and other fibers, including calcium silicate, cellulose, gypsum, and iron silicate, were found in occupational samples. Carbon/coke fibers were found in bulk samples of calcined petroleum coke, the probable source of these fibers in occupational samples. Time-weighted average (TWA) total fiber concentrations were approximately lognormally distributed; 90% were ≤ 0.1 f/ml. Although consistently low, TWA total fiber concentrations varied with plant, job (tasks), and type of coke. This was expected given the substantial differences in plant configuration, technology, and workplace practices among refineries and carbon plants. Carbon/coke fibers (identified and measured using transmission electron microscopy [TEM]) were found at all plants producing all types of calcined coke and not detected at any plant producing only green coke. Approximately 98% of all carbon/coke TWAs were ≤ 0.1 f/ml. Analysis of task length average (TLA) data by various statistical techniques indicates that the average carbon/coke TLA is certainly ≤ 0.05 f/ml and probably < 0.03 f/ml.