Pam Tucker, Columbia County’s emergency and operations director, said in an e-mail that the placement of the charge by Martin Marietta caused a louder-than-normal boom, registering at a 130-decibel air blast level. The legal limit is 142 decibels, she said.
The company also started its blasting earlier than expected, at 10:30 a.m. instead of noon, Tucker said.
Though some thought the boom might have come from an earthquake, Tucker said none had been detected by either the Savannah River Site Geotech Group or the U.S. Geological Survey.
There had been widespread reports of a loud noise as far away as North Carolina. One person responding to a Facebook post reported hearing the noise in Wrens, Ga.
Blasting is what Columbia Middle School secretary Wendy Prickett assumed she heard Tuesday.
“It kind of shook our doors,” she said.
The school is next to the Dogwood Quarry, so people at the school are accustomed to hearing blasts. Typically, though, they occur at the end of the workday, when the quarry usually dynamites rock for removal.
On Ray Owens Road, about four miles away, “At first we thought somebody was on the roof working,” said North Columbia Elementary secretary Nancy Kensinger. Teachers later said the boom shook the interactive boards in their classrooms.
“It kind of felt like a large gust of wind slamming into the side of our building,” said a Martinez-Columbia firefighter at Fire Rescue Station 10 on Ray Owens Road.