KISSIMMEE, Fla. -

A high-voltage electrical transformer exploded Sunday morning at a Kissimmee Utility Authority substation, leaving one contractor dead and two utility employees with second- and third-degree burns.

Officials said calls started coming in around 9:30 a.m. for a report of an explosion and dark black smoke coming from 1100 Davis St., which is a Kissimmee Utility Authority substation.

When firefighters arrived, they found thick black smoke coming from the control house on the property, officials said.

Medical helicopters were called to transport two patients, who suffered from burns, officials said. They were later identified as 60-year-old John Johnson, who has worked at KUA since July 1995, and 43-year-old Robert Treasure, who was hired by KUA in September 1998.

Johnson and Treasure were airlifted to Orlando Regional Medical Center for treatment. Johnson was listed in critical condition.

The contractor, an employee of Reinhausen, was pronounced dead at the scene by Osceola County emergency officials. Her name has not been released.

?Our thoughts and prayers are with the families right now,? said Jim Welsh, KUA?s president and general manager. ?This is a tragic event and a difficult time for all of us.?

The transformer was a new piece of equipment, having only been in service a few months at the substation.

The accident remains under investigation.

Officials said there were no power outages because of the incident.

Founded in 1901, KUA is Florida's sixth largest community-owned utility, providing electric and telecommunication services to 64,000 customers in Osceola County.