PHILADELPHIA — A natural gas-fueled explosion destroyed a West Reading chocolate factory building in March, the National Transportation Safety Board said in a preliminary report Tuesday. Seven people were killed and 11 were injured in the R.M. Palmer blast that rocked the tight-knit borough of about 4,500 people. The source of the likely gas leak was not laid out Tuesday, and will be a focus of the ongoing investigation, according to the NTSB report. Still, the preliminary information laid out by investigators forms the clearest picture of what happened the day of the explosion, just 65 miles ...