Environmental justice advocates in the US and internationally have argued that hazardous materials industries are a source of significant community disruption and environmental hazard. Few of these studies, however, have examined firms' accident frequencies or how accidents are distributed across metropolitan regions. This research argues that accident frequencies differ significantly among firms, and they are an important part of understanding industries and their distribution within metropolitan regions. The accident records of the risk management plan (RMP) facilities in southern California provide an illustration for the discussion. Statistical tests demonstrate that previous accident counts correlate with future counts. The research heightens the usability of the existing accident record for local governments in the US. (C) 2007 Elsevier B.V. All rights reserved.