This report documents the re-evaluation of Hanford Tank Farm occupational exposure limits (OEL) for furan and 13 associated substituted furans identified as Chemicals of Potential Concern. Furan causes liver toxicity and cancer in laboratory animals. Recent toxicity studies in animal models have established a non-genotoxic mechanism of action and new data to support re-evaluation of the furan HTFOEL. As such, PNNL proposes to adjust the HTFOEL for furan from 1 ppb to 1.9 ppb based on a no-observed-adverse-effect level in Fischer-344 rats (the most sensitive species tested) exposed to subchronic oral administration of furan as a point of departure modified by species extrapolation of dose and route, inter- and intra-species uncertainty factors, and adjustments for life-time versus occupational exposure periods. Because of limited data and similar hypothesized mechanisms of toxicity, PNNL recommends continuing to use the furan HTFOEL as a surrogate for substituted furans until further data for substituted furans become available. Further toxicity investigations or new OELs proposed by authoritative organizations (e.g., National Institute of Occupational Safety and Health, Occupational Safety and Health Administration, and the American Conference of Government Industrial Hygienists) would warrant re-evaluation of HTFOEL for furan and substituted furans.