The South Philadelphia headquarters of Democratic presidential nominee Sen. Barack Obama were evacuated for about an hour yesterday after an envelope bearing threats and a suspicious powder was delivered to the building, at 15th and Christian Streets.

The incident was first reported at 4:45 p.m., and investigators from several agencies, including the Secret Service, FBI and the Fire Department, responded, Executive Fire Chief Daniel Williams said. Appearing on the envelope, which had a San Diego postmark, were the words

No Obama

. The letter contained threatening language, including the phrase

death to Obama

, Williams said.

The department's hazardous-materials team examined the the powder and ruled out anthrax or any radioactive substance. Just before 5:45 p.m., the 20 people who had voluntarily evacuated returned to the building. Although some had touched the material, none asked to go to the hospital, Williams said.

In the end, the white powder was harmless. "It turned out to be sugar," Williams said. But he added that the precautions were warranted. "Until you can identify it," he said, "it's dangerous."

- Anthony R. Wood