I could no longer restrain my curiosity, I went outside in time to see a fifth truck pull up, the fire marshall arrive and see that the police had also blocked off the other end of the street. emilytheslayer also joined me outside and our upstairs neighbors followed soon after.
We saw people evacuating from the building two doors down, but that was it.
After much waiting, emilytheslayer (she had shoes on, I didn't) went to ask a cop what happened. This was as the firemen were packing up to leave. Apparently their hot water heater had overheated and steam came out. They thought it was smoke, panicked and called the fire department. The didn't evacuate until well after the firemen had arrived.
Late Night Fun!