CAPE CANAVERAL, Florida (AP) - As Kennedy Space Center employees returned to work with orders to be more careful following a spate of accidents, authorities said a roofer died after falling from a warehouse.

Steven Owens, 51, had removed his safety harness and was moving to the roof's edge when he tripped on a lightning protection wire Friday, said Sam Gutierrez, a spokesman for Space Gateway Support, which holds the joint base operations contract at the space center and Cape Canaveral Air Force Station.

Owens was taken to a hospital, where he later died, authorities said.

"The goal of (the safety stand down) was to try to prevent accidents like this,'' Mike Rein, a NASA spokesman, told Florida Today. ''The bottom line is that we're doing everything we can to make sure things like this don't happen.''

The space center's director, James Kennedy, ordered work stopped for two hours Thursday while he addressed nearly 15,000 employees on safety issues over closed-circuit television.

He warned that a major accident could derail NASA's plans to complete the International Space Station and begin exploring the moon and then Mars.

"We must stop in their tracks the events that led me to call for this safety stand down,'' Kennedy said.

In January, workers did not lock down space shuttle Endeavour's nose wheel landing gear while transferring it between floor jacks, causing the orbiter to pitch forward. No serious damage was done. Later, workers put too much pressure in the water coolant loop of space shuttle Atlantis, requiring repairs.

This month, the arm of space shuttle Discovery was dented by a platform being used to clean up broken glass. The arm has been used to inspect the shuttle's exterior with a camera, build the space station, and release and retrieve satellites. NASA on Friday ordered a formal investigation.

A few days after the arm incident, an X-ray film container was dropped on Endeavour, requiring tile repairs.

And last week, workers repairing the roof of the vehicle assembly building inadvertently started a small fire. The solid rocket boosters and the external tank, which are used to launch the shuttle, were in the building but not directly under the fire. They were unharmed, said Mike Rein, a NASA spokesman.

Until this week, workers had been under pressure to finish preparations for a May launch of Discovery. But NASA officials delayed the launch until at least July so workers can replace sensors on the fuel tank.