WASHINGTON (CNN) -

The House of Representatives side of the U.S. Capitol is closed Thursday because of a construction-related incident, officials said.

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.