Investigators were combing through a New York City shipyard on Saturday trying to find the cause of a fire and an explosion that killed one person and injured more than 30 firefighters and other first responders. Firefighters were called to the shipyard about 3:30 p.m. Friday on reports that there was a fire, heavy smoke and two workers trapped in a basement area, city Fire Commissioner Lillian Bonsignore said. Less than an hour later, as firefighters and emergency medical personnel were working the scene, an explosion rocked the site, officials said.