Nine Seattle firefighters were injured in an apparent natural gas explosion that leveled at least three businesses in the Greenwood neighborhood early Wednesday morning. The explosion happened in the area of the Greenwood Quick Stop Market at N. 85th Street and Greenwood Avenue N. just before 1:45 a.m. Firefighters were sent to the building about 40 minutes earlier for a report of a natural gas leak. While they were investigating the source of the leak, the building exploded, according to Seattle Fire officials.