The Friday night blast at the Concept Sciences Inc. facility at the Lehigh Valley Industrial Park, about three miles southwest of Allentown and 50 miles north of Philadelphia, could be felt miles away and left at least 13 others injured.
Lehigh County Coroner Scott Grimm said the dead were among seven people in the building at the time of the explosion. Two others were pulled from the debris, including one who was in critical condition. The condition of the other was not known.
Authorities believed the explosion was triggered during the distillation of the volatile chemical hydroxylamine, a substance used by the company for processing salt in water heaters, said John Conklin, director of the Lehigh County Emergency Management Office. They also believed another chemical, potassium hydroxide, was involved in the explosion.
The explosion created a 4-foot crater in the building and blew out 25-feet-high concrete walls and caused two stories of concrete ceiling to collapse.
The morning light showed just how devastating the explosion was. Twisted steel and chunks of concrete littered the area for at least 100 yards in each direction and only parts of the steel framework stood; three other adjacent buildings were damaged, with windows blown out and siding torn from the structures. Cars in an adjacent parking lot were covered in rubble.
Rescue crews in protective air masks and clothing searched all night for the missing people, but they were hampered by the unstable remains of the structure, as well as fatigue and temperatures in the 20s.
Infrared equipment was used by search and rescue specialists from the Philadelphia and Harrisburg fire departments to pinpoint where they believed the victims were, while crews used small hand tools to dig through the rubble.
Janice Nisbet, spokeswoman for the Lehigh County Emergency Management Office, had said that workers had gone "through every air pocket" looking for any survivors.
Thirteen unidentified people, including five rescue workers, were taken to area hospitals. Conklin said most were treated and released.
David Lesak, chief of the Lehigh County hazardous materials team, said most of the injuries "were blast related as opposed to chemical related."
By daybreak, Lesak's crew had decontaminated about 80 workers with a water and soap solution.
There were reports of a chemical cloud that drifted toward Allentown, and people within a one-mile radius were asked by police going door-to-door to stay indoors for about two hours Friday night. Conklin said the blast released a mixture of the chemicals into the air, but no one was ever in any danger.
Concept Sciences officials could not immediately be reached for comment.
By Genaro C. Armas