The death of California firefighter Kirk Schafer has left his fire department not only full of sadness, but full of questions about what caused the bizarre explosion that killed him.

Schafer, 36, had been with the North Central Fire District in Fresno County for five years. Before that, the second-generation firefighter served as a volunteer.

Schafer was doing basic pump operations on a new truck behind Station 45 Thursday. The pumper was hooked up to a 500-gallon water tank that supplies water for the fire station.

The water tank "somehow became pressurized, then airborne," said Chief Lee Daugherty.

The 300-pound tank flew about 100 feet into the air and then crashed down onto the pumper.

Schafer was struck by the debris and immediately taken to University Medical Center in Fresno, where he died Friday afternoon. The chief said they are speculating that Schafer was getting out of the cab when the explosion occurred, because of the injury to the back of his head.

Schafer is survived by his wife Lilly and their five year-old son Kaleb. He also leaves behind his father, a retired firefighter from the same department, and his brother, also a firefighter at North Central.

The chief described Schafer as having a very positive attitude a great work ethic.

"He was one of those people everybody would like to have in their organization. He was kind of born in this department - he spent a lot of time here as a child," Daugherty said.

Capt. Wayne Van Ornam remembered the firefighter for his sense of humor and desire to help the community.

The incident is under investigation by the fire department and the California Occupational Safety and Health Administration. Daugherty said they are looking at all possibilities, and don't know whether the problem lies with the water tank, the new apparatus, or something else.

The Central States pumper had only been with the department for two days before the accident.

"We were supposed to be excited but it turned into a tragedy," Van Ornam said. The $240,000 pumper sustained about $20,000 in damage.

This is the first line of duty death the department has experienced in about 40 years. "This is all completely new to us. We've never had to deal with this before," said a dispatcher for the department.

The dispatcher described Schafer as a great person and friend. "He always had a smile for you no matter what," she said.

Visitation will take place Wednesday, August 1 from 10 a.m. to 7 p.m. at 538 South Madera Ave in Kerman.

The funeral was on Thursday, August 2 at 10 a.m. at People's Church, 7172 North Cedar Ave in Fresno. The burial will follow at Fresno Memorial Garden at 175 South Cornelia Ave in Fresno.