A SUSPICIOUS white, powdery substance delivered in the mail yesterday to the office of U.S. Sen. Pat Toomey, R-Pa., in a Center City skyscraper - sparking a homeland security and hazmat scare - turned out to be cornstarch, police said.

An intern opened a letter containing the powder in Toomey's office, on the 17th floor of 8 Penn Center, said Officer Tanya Little, a police spokeswoman.

Department of Homeland Security, fire and hazmat officials were on the scene at 17th Street and JFK Boulevard to investigate about 3 p.m. About an hour later, they determined that the substance was harmless, Little said.

The offices of several other members of Congress, including House Speaker John Boehner, R-Ohio, started receiving letters with a white powdery substance on Tuesday.

The substance in all incidents so far has proved to be harmless.

"Although all letters received thus far have proved harmless," Senate Sergeant-at-Arms Terrance Gainer said Wednesday in a memo to Senate offices, "it is essential that we treat every piece of suspicious mail as if it may, in fact, be harmful."