A large, three-story building in the middle of downtown exploded following a fire. A pedestrian walking by smelled smoke, and by the time he called 911, the building had become fully engulfed in flames. He said the smoke was black in color. As the fire trucks were pulling up to the front of the building, it exploded, and three firefighters were killed. The time from the pedestrian smelling smoke to the building being fully engaged was about 45 seconds, based on the time of the 911 call. While the pedestrian was on the telephone, he yelled that flames were coming out of the top floor of the three-story building. The explosion seemed to come from the first floor of the building. The firefighters were killed when building material fell on them or was exploded through their bodies.