HOUSTON — Rescuers began a block-by-block search of tens of thousands of Houston homes Thursday, pounding on doors and shouting as they looked for anyone — alive or dead — who might have been left behind in Harvey's fetid floodwaters, which have now damaged more than 87,000 homes and destroyed nearly 7,000 statewide.Elsewhere, the loss of power at a chemical plant set off explosions that prompted a public health warning, and the city of Beaumont, near the Texas-Louisiana line, lost its public water supply. The remnants of the storm pushed deeper inland, raising the risk of flooding as far north as Kentucky.More than 200 firefighters, police officers and members of an urban search-and-rescue team fanned out across the Meyerland neighborhood for survivors or bodies. They yelled "Fire department!" as they pounded with closed fists on doors, peered through windows and checked with neighbors.