the top of the screen, out of nowhere, the street explodes as if a giant bomb goes off. >> you could see absolutely a terrorized expression on all these people's faces because they didn't know what it was. they probably thought it was a bomb in the subway system. >> with september 11th never far from new yorkers' minds, many think the explosion is another terrorist attack. >> yeah, you think it's terrorism. that's the first thought that goes through anybody's mind. >> people run for cover as the dirt, rocks and asphalt blasts into the sky and rains down. and after the explosion, a nonstop gigantic geyser of steam shoots up nearly 80 stories, an incredible sight to see. so loud and powerful, workers in neighboring skyscrapers feel their buildings shake. >> it was, like, it's got to be a building falling because it keeps rumbling. >> gregory's tow truck is parked right above the epicenter of one of the biggest underground