The collapse happened about 6:30 a.m. at the quarry off Belmont Ridge Road. The business said the federal Mine Safety and Health Administration was aiding in the search, along with the Loudoun County Sheriff’s Office.
Engineers and riggers worked with cranes to stabilize the silo, said Loudoun County Assistant Fire Chief Keith Johnson. The silo’s contents, a flourlike mineral filler used in asphalt and road construction, is dangerous to inhale, he added.
“We’re really concerned that removing one bit of product can cause the whole silo to fall,” Johnson said.