Bomb Maker Wounded by Blast in Vista : Explosives: Investigators find 16 guns, drug paraphernalia in home after accidental explosion of an illegal pipe bomb that critically injured the builder.

A Vista man was critically injured Tuesday when an illegal pipe bomb he was making exploded, authorities said.

Frank James Hardesty, 30, a self-employed mechanic, underwent surgery at Palomar Medical Center for a shattered right arm, shrapnel wounds to his liver, pancreas and spleen, and severe burns, hospital spokeswoman Christine Foor said.

Startled neighbors awoke shortly after 5 a.m. to “a big bang” and Hardesty’s screams, San Diego County Sheriff’s officials said.

“It was excruciating just listening,” said Janet Mohrman, who lives across the street in the 2200 block of San Clemente Avenue, where Hardesty and his girlfriend share a small guest house behind his mother’s home. Mohrman’s husband, Jim, called 911, then went to aid Hardesty.

Hardesty was conscious as he sat on a porch bench 30 feet from the explosion. A towel was draped over his right shoulder and he was gingerly covering gashes to his stomach and side, Jim Mohrman said.

Mohrman, who has training in emergency medical treatment, applied pressure to the body wounds and a tourniquet to Hardesty’s arm until paramedics arrived.

The San Diego County Sheriff’s Department and investigators from the federal Bureau of Alcohol, Tobacco and Firearms had not determined Tuesday what Hardesty intended to do with the bomb. A similar device found undetonated Monday in a public water pipe in Bonita did not appear to be connected to this explosion, sheriff’s officials said.

During a routine search for bomb remnants, investigators found 11 assault and hunting rifles at the house. Agents also found drug paraphernalia, including two balance scales and an undisclosed amount of marijuana in the guest quarters, said Jim Stathes, agent in charge of the San Diego office of the federal Bureau of Alcohol, Tobacco and Firearms.

After a federal search warrant was issued Tuesday afternoon, detectives found five handguns locked in a safe, Strathes said.

Hardesty faces charges of illegal manufacture of explosives and drug possession and trafficking, sheriff’s officials said.

Hardesty had been handling the pipe bomb in a small work shed connected to the garage, said sheriff’s Lt. Brian Roberts. A small cap-sized hole was blown through the door of the shed, and bits of pipe were scattered throughout the area.

Detectives said the pipe bomb was in a vise clamp when the explosion occurred. Hardesty may have been screwing on the seal when friction between the cap and pipe threads sparked the explosion, Stathes said.

The Hardestys have lived on San Clemente Avenue for more than a decade--their sprawling ranch-style home was one of the first built in the area. The family has had little contact with neighbors, residents said.

Janet Mohrman said that, even after living across the street for eight years, she had no strong impression of Hardesty. “Living in a rural area, seems like we’re all out here just doing our own thing.”