In April 1996, the National Institute for Occupational Safety and Health (NIOSH) received a request for a health hazard evaluation (HHE) from the Bureau of Alcohol, Tobacco, and Firearms (ATF), in Falls Church, Virginia, regarding respiratory hazards associated with fire investigations. ATF trains a select number of special agents as fire investigators as part of the ATF arson enforcement program. These special agents work with counterparts in state and local fire departments to investigate the origin and cause of fires. ATF special agents and local fire investigators in the northern Virginia jurisdictions were concerned about the potential respiratory health effects from conducting fire scene examinations and the adequacy of their respiratory protection. In response to this request, environmental monitoring was performed during the investigation of two house fires on February 12 and 13, 1997, in metropolitan Washington, D.C., and Prince George's County, Maryland, and three staged fires on June 3, 1997, at the Fort Belvoir military base in Alexandria, Virginia. During these fire scene examinations, environmental samples were collected for total and respirable dust, metals, hydrogen cyanide, inorganic acids, aldehydes including formaldehyde, polycyclic aromatic hydrocarbons (PAHs), elemental carbon, and volatile organic compounds (VOCs).