Police spokeswoman Kimberly Schneider said the incident is confined and not suspicious. A piece of ceiling fell down around 3 a.m., exposing a chemical substance in a work area.
Schneider did not know if the ceiling fell on a container, or whether the substance is liquid. Hazardous materials crews were on the scene.
Laura Condeluci, spokeswoman for the Architect of the Capitol, said there was a "potential release" during "asbestos abatement work" on the House of Representatives side.
"Samples have been collected to determine whether there was potential exposure," Condeluci said.
(Paul Courson and Deirdre Walsh, CNN)
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