A utility truck's elevated bucket collapsed during a school demonstration, killing a utility company employee and injuring a teacher as about 600 children watched, authorities said.

The pair had been lifted 20 to 30 feet in the air Thursday when the boom separated from its base and fell, Police Chief Steve Dunnagan said. They were thrown from the bucket when it hit the ground outside Hiawatha Elementary School in this central Washington town.

The Avista Utilities employee was identified as Bob Smith, 50, who apparently suffered head injuries.

The teacher, Melissa Martinez, was hospitalized with non-life-threatening injuries, authorities said.

The pair were participating in an annual "egg drop" science demonstration when the accident occurred. The demonstration involves protecting eggs in various containers and dropping them from a certain height to see which land intact.

Besides hundreds of children from kindergarten through sixth grade, staff members and some parents were watching, said George Juarez, Othello School District superintendent. He said the children were "a good distance away."

Avista spokeswoman Jessie Wuerst said the company would investigate the cause of the accident. The state Department of Labor and Industries was also investigating, Dunnagan said.