Police were called at about 4:30 p.m. Saturday to a home the 300 block of Hillendale Road.
There, Pennsylvania State Police say 22-year-old Jim McGovern was testing rocket fuel for small homemade rockets when he died in a fiery explosion.
"He was mixing rocket fuel in his front yard, apparently he does it as a hobby," Trooper Pascal DiJoseph said.
Neighbor Efren Rebollo who lives a couple hundred yards away from the site of the blast heard the explosion.
"We thought it was a car accident or something like that," Rebollo said.
Investigators say McGovern was testing a fuel combination when the blast occurred. He was not launching a rocket.
They wouldn't reveal which chemicals he mixed.
McGovern was a volunteer firefighter for the Longwood Fire Company. His fellow firefighters say he was a respected member of the Company, and a better friend.
A counselor is being brought in to help the fire department cope with this tragedy.
Bunting was hung from the fire trucks and the flags flew at half staff.
McGovern's family did not want to comment on the tragedy.
Longwood Fire Chief Matt Ruoss told the Daily Local News of West Chester that McGovern was a member of the fire company and called him "one of the top responders last year."
The Associated Press contributed to the report.