Investigators are looking into why a form apparently collapsed May 6 during a concrete pour on the top level of a 26-story concrete apartment building in Bal Harbour, Fla., killing three workers. Torivio Acevedo, Menes Daniel and Endy Guirand were reportedly trapped in concrete and debris and could not be rescued, according to local safety officials. The employer, Southland Forming Inc., West Palm Beach, Fla.,declined to comment until investigations are complete. “Our hearts and thoughts go out to the families of the men,” says Darrell Whiteside, company president