SAN FRANCISCO (CBS SF) — Strong winds blew debris off a roof, hitting pedestrians on the head and forcing the temporary closure of Market Street in San Francisco.

The debris came from a building under construction at 7th and Market Streets.

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The Fire Department said the material was Styrofoam forms used for making roofs.

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“We closed off Market Street (and) went up on the roof,” said Battalion Chief Victor Wyrsch. “There were about 100 forms up there. (We) tied them all down (and) notified the owner. The owner is going to come out and take care of the rest.”

The forms are 12-feet by four-feet, and weigh as much as 60-pounds.

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One person was taken to the hospital.