Provo Fire & Rescue explained Wednesday what caused fireworks to launch into the crowd during Stadium of Fire festivities last year on the Fourth of July.

The incident happened during the national anthem and F-35 flyover portion of the event inside LaVell Edwards Stadium at Brigham Young University.

The firework fiasco left 27 people injured, according to Provo Fire Marshal Lynn Schofield. Initially, officials reported 18 were hit.

“We identified four people who were hit directly by the devices that suffered injuries as a result,” Schofield told reporters at a press briefing Wednesday.

The mishap stemmed from an uncontrolled deflagration or combustion of the whistle composition in two tubes in the 36-shot “Howling Tails to Hammer” device, creating “a catastrophic failure” and causing the firework to erupt into the crowd.

The firework contains 36 separate tubes that each fire individual shots in “rapid succession,” the report states.

Schofield said the device is activated by an electrical impulse from an initiator controller from the computer that sets the choreography of the show, and once activated, there is no way to halt it from discharging all 36 shots.

Initially, the Howling Tails firework discharged the first six or seven shots vertically until an explosion happened that caused damage to the casing where the tubes were housed. Seven other tubes did not fire.

“And so you have the rest up to 22 shots that went where they weren’t supposed to go,” Schofield said.

Investigators used an X-ray to examine two of the tubes and believe some sort of failure in the whistle portion of the device occurred, which caused the fireworks to launch sideways into the crowd.

Several injuries were reported from the stadium fiel,d including a sound technician and dancer who were struck or nearly struck by projectiles.

Others reported being struck by shrapnel on the field, the report said.

“The rest of the reported injuries were most likely from shrapnel that scattered across the east stands and one being reported in the west stands as well,” investigators said in the report.

Investigators concluded that the most probable cause for the incident was the breakdown of whistle composition into smaller particles within the tubes that failed.

“There is no evidence that the devices were mishandled from the time that the device left the warehouse in Kansas to the time of the malfunction,” the report stated.

The fire marshal listed a number of recommendations and suggestions to prevent a similar instance from occurring.

Those include more detailed product lists, clear labeling of self-propelled projectiles, increased separation distances and stringent safety briefings.

With the next Stadium of Fire less than six months away, Schofield said talks with fire crews and fireworks vendors are underway to implement increased safety protocols.

“Nobody intended for this to happen. Nobody is happy that this happened, and we will learn from this experience,” he said. “We will move forward and we will make the changes that we need to make to ensure that everybody has a safe event, wherever they are.”

A full report from the investigation is available on Provo City’s website.