OBJECTIVE: Disasters are complex events making epidemiologic studies and determination of accurate denominators difficult due to the poor nature of available records. However, these data are essential to perform useful calculations and accurate descriptions of disaster medical impacts. This study was undertaken to identify the availability and utility of various information sources in the analysis of a mass casualty disaster. In addition, characteristics of cases presenting for care are described. DESIGN: This is a retrospective cohort study abstracting medical records and other documents relating to an explosion and fire. Public domain documents are obtained by written request or by filing a Freedom of Information Act (FOIA) request. SETTING: A rural EMS and tertiary hospital. CASES: Individuals directly exposed to the forces of the explosion. OUTCOME MEASURES: The number of cases detected by various information sources. In addition, the demographics, dispositions, and nature of the physical injuries of the cases are reported. RESULTS: Seven sources of case information were identified. The most cases were identified by investigative agencies (33) and the fewest by medical records (18). Rates include; injury 0.68, admission 0.20, and operative 0.14, with no deaths. Case locations during the explosion were determined for all cases. No association was noted between admission and location in the building. CONCLUSIONS: This study demonstrates the availability and usefulness of data in the public domain. Using FOIA requests or partnerships with public or private agencies may more clearly define denominator data in epidemiologic evaluations of disasters.