MIAMI (AP) - Miami-Dade rescuers are trying to reach a worker who officials believe fell 140 feet into a silo containing tightly packed cement dust after a roof collapse.
    
Miami-Dade Fire Rescue responded to a call Friday morning from the Titan America cement plant in Medley. A head count was performed after the collapse, and one worker, whose name wasn't immediately released, was missing.
    
A Fire Rescue spokesman says there have been no signs of life, but all rescues are conducted with the assumption that the person is alive. The man was wearing a helmet, but he didn't have any communication equipment.
    
The Miami Herald (http://hrld.us/PucgBZ ) reports that rescuers brought two 200-foot cranes and a bucket lift to the factory Friday afternoon.
    
Officials are trying to determine what caused the roof collapse.
    
___
    
Information from: The Miami Herald, http://www.herald.com

(Copyright 2012 The Associated Press. All rights reserved. This material may not be published, broadcast, rewritten or redistributed.)