Thomas Meyer was sitting outside his Lehman Street apartment building a little after 10 a.m. Thursday when he heard a huge bang.

"I heard a big explosion and there was smoke. Everything was flying," said Meyer, who lives on the first floor of the two-story building. "I never seen anything like this except in movies."

What he saw and heard was an explosion caused by vapors from as many as 31 cans of aerosol bug bombs that are believed to have ignited from a pilot light of a gas stove in a second-floor apartment, authorities said.

Seventeen cans of bug bombs were found on the second floor, 12 cans on the first floor and two in the basement, said David Eggert, a deputy fire commissioner.

The bug bombs were being used because landlord John Light had been issued code-violation notices for roach and bedbug infestation, Eggert said.

Tim Balsbaugh, a second-floor tenant, said he was getting ready to set off the bug bombs when another tenant, Dennis Morgan, grabbed some and took them into his apartment.

"He was not supposed to be setting them off yet," Balsbaugh said "I told him, 'Don't do anything' -- I hadn't gotten up there yet."

When the explosion occurred, Balsbaugh said, "I came flying out the side, getting hit with stuff."

He was released after treatment for breathing difficulties at Good Samaritan Hospital.

Karen Light, a second-floor tenant, was on the ground, Balsbaugh said. She was listed in good condition in Penn State Milton S. Hershey Medical Center on Thursday, and Morgan was in fair condition, a hospital spokeswoman said.

"We're all lucky," Balsbaugh said.

Zuleyka Torres, who lives next door, said she was awakened by the house shaking from the explosion.

"They took us all out because of the smoke," which she said was coming into her house from the attic.

Residents of adjacent buildings were allowed back in their homes Thursday afternoon after the air was tested.

Barry Fisher, Lebanon's fire commissioner, said one person had fallen from the balcony and one was on the balcony when firefighters arrived.

The aerosol vapors in bug bombs are flammable, Fisher said, and instructions on the cans tell users to make sure there are no open flames.