Four firefighters and the 6-year-old son of a firefighter were injured. The most seriously injured was a woman firefighter, Patricia Turner, who suffered a split lip and burns to her face when she was hit in the mouth by a rocket, Knill said.
All five of the injured were treated at the scene and declined to be transported by ambulance to the hospital, he said.
Turner later went to Jefferson Memorial Hospital as a precaution and then was released, Knill said.
Her mouth remained sore but the she managed to go to work on Sunday, he said.
Other burning fireworks struck a nearby van storing fireworks for the show and caused them to ignite at once like a "fireworks finale," Knill said.
The scene was chaotic as firefighters rushed to get out of the way of the blasts, treat their injured companions and put out the fires - all at the same time, Knill said.
The van did not explode, but the fire from the exploding fireworks totaled the vehicle, Knill said.
An ambulance has been stationed at the scene as another precaution, Knill said.
The fireworks were to be shot over the Shannondale Lake as part of the subdivision's Fourth of July celebration, Knill said.
The "freak accident" occurred when one of the fireworks apparently blew out of the side instead of firing out of the top, Knill said.
The fireworks were fired from about 100 feet from the firefighters, Knill said.
About 35 firefighters were at the scene.
The fireworks had initially been checked out by the firefighters before the show started, Knill said. No defects were found.
Knill estimated the crowd at about 250 people.