Investigators tried to determine Friday what had caused an accident which killed a city Department of Environmental Protection worker that day in a Brooklyn sewage treatment plant.

Mayor Michael Bloomberg said Gennaro Montello, 45, was crushed when steel supports fell off a temporary conveyor belt.

It happened at the Owls Head Waste Water Treatment plant in Bay Ridge.

A second worker, Joseph DiGiovanni, was injured while trying to save Montello. He was treated at Lutheran Hospital and released.

The mayor spoke with Montello's wife and issued a statement, saying, "We typically only think of uniformed officers putting themselves on the line to serve the public. Today's accident is a tragic reminder of how many others serve our city in challenging environments and how our city could not run without them."

An investigation into the accident was underway Friday, lead by the DEP and Brooklyn Councilman Vincent Gentile, who expressed condolences over Montello's death.

Gentile said the use of temporary conveyer belts is now on hold.

"We have to take a hard look at portable conveyer belts, because equipment this big and heavy to be in a portable state raises concerns," the councilman said.

Montello's next-door neighbor, Anna Sorsaia, said she is concerned about the widow and the Montellos' two children.

"Very nice family. There's nothing I can say other than that. And what can I say? I feel so bad. Young man - he's not old. And it hurts me. It hurts me very much," said Sorsaia.

Montello had worked for the DEP since 2001.