An explosion and fire ripped through an explosives manufacturing plant Wednesday, injuring seven people and damaging four buildings, the Utah County sheriff's office said.

Five of the seven injured were treated for minor injuries and released from Mountain View Hospital in Payson, following the explosion at the Trojan Corp., located at the mouth of Spanish Fork Canyon.The two others were treated at the scene and released. They were identified as Jerry Purkey, Spanish Fork, and Dennis Pearson, Payson.

The explosion in Building 20 occurred at 6:30 a.m., causing windows to shatter a mile away. The blast was felt as far away as Provo, about 10 miles from the scene.

"It was like a big gun going off," said Allen Leifson, a clerk at the Chevron Station a mile away. "It was like a real big gun."

The sheriff's office reported the fire was under control by 8 a.m. However, people were not allowed in the 100-acre plant because of the potential for other explosions.

Workers later secured the plant and chemists and engineers were to enter it and stabilize chemicals, said Sgt. Craig Turner.

At 11 a.m. Trojan officials said, "We have no comment as to what occurred or how it occurred. (But) at this time we can assure the general public that no further incidents are impending and we are in the process of getting ourselves back into production as quickly as possible, with safety being the primary objective."

Pam White, public relations coordinator at Mountain View Hospital, identified those hurt as Larry Lewis, 40, Spanish Fork, who suffered a jaw injury; Greg Marshall, 25, and Don Aitken, 25, both of Spanish Fork, who suffered back pain; and David Hall, 34, Springville, who suffered an elbow injury.

Leonard Steggell, 41, Spanish Fork, was treated for minor head trauma. He told reporters, "They don't want us saying a whole lot about the accident. I am not opening my mouth.

Said White, "They were all really lucky. If they had been in the building when it exploded, there would have been a lot of fatalities."

According to the sheriff's department, the employees who had been working in the building were returning to work in a bus following a break. The bus was about 50 yards from the building when the explosion occurred.

Those injured were in the bus, which was damaged by the blast. Three other buildings were also damaged.

Sheriff officials said Building 20 is used to manufacture "boosters" and "primaries," which contain TNT. Boosters and primaries are used as dynamite replacements. Damage to the plant was extensive. Structures outside the area were also damaged.

Bruce Banks said the Oak Crest Inn, owned by his mother, suffered about $2,000 damage.

Provo resident Randy Horrocks, said he was getting ready to leave for work when he felt the blast. "My door between the house and the garage just shook for about 5 seconds."

In April 1987, a pipe from Trojan Powder Corp. that was taken to the Swenson Salvage Yard exploded, killing one man and critically injuing another. He recovered from the accident.