Two firefighters died from injuries sustained while fighting a June 2, 2011, fire in a multi-story, single-family dwelling in San Francisco. NIST used its Fire Dynamics Simulator and visualization software to investigate the circumstances and fire behavior that led to untenable conditions on the first floor, where the downed firefighters were found. After failure of windows in the basement, where the fire began, an adjoining stairway became a “chimney for hot gases” that poured onto the first floor. For more, read the NIST study report (NIST TN 1856).