The fire that started near a Jersey Shore ice cream shop and quickly consumed a swath of boardwalk, destroying more than 50 businesses as it burned for eight hours, was caused by electrical failure of aging equipment damaged by Sandy, officials said.
Authorities said the fire appeared to originate under a structure that housed the ice cream shop and a candy store. The equipment that failed was under the boardwalk beneath that structure, and was flooded during the storm nearly a year ago.
"During the storm this wiring and these connections became fully submerged in saltwater and subject to sand and wave action, contrary to intended use," said Ocean County Prosecutor Joseph Coronato.
After the storm, those compromised connections and the 1970s-era wiring eroded further, officials said, and exposed wires somehow came into contact with each other, causing an electrical arc that is believed to have started the fire last Thursday. It was in an inaccessible area under the boardwalk stores.
As far as how the wires contacted each other, Coronato said: "we will never know."
A state official dismissed speculation that inspectors may have missed potential wire problems just because they were inaccessible, telling NBC 4 New York that the fire appears to be a freak accident and that the wires had been exposed to storm and sand and salt for years.
The boardwalk had only recently been repaired from the damage it sustained during Sandy.
Officials announced their findings at a news conference Tuesday, and said foul play had been ruled out after the 40-hour investigation.
Authorities even pulled financial records of the businesses involved in the blaze to make sure no one had a financial motive to start a fire.
"We left no stone unturned," said Coronato. "This was not a suspicious fire."
They recommended that seaside businesses and homeowners whose electrical systems were flooded by Sandy have them inspected and replaced if necessary.
The problem could be widespread, authorities said.
"I'm sure on every boardwalk, everywheres all around, that there may be some compromised -- we had a major storm, that wiring, obviously wiring could be affected," Coronato said.
Coronato said officials were not trying to cause panic.
"If you are a property owner and you believe that your electrical system came in contact with water and sand, the right thing to do is to have it inspected by the electrical officials," he said.
Seaside Heights Mayor William William Akers said there is no issue with potentially compromised wiring on the surviving sections of the boardwalk.
"We did a total rebuild. All 16 blocks got all new wiring," he said.
In Point Pleasant Beach, one of the approximately half-dozen Sandy-ravaged towns where businesses with electrical connections are located on the boardwalk, Mayor Vincent Barrella said streetlight wiring is all new in a section of the boardwalk that was rebuilt last winter.
But he said about half the boardwalk, including sections in front of businesses, still needs to be redone this winter. After the prosecutor issued his warning, Barrella said he instructed borough officials to work with the local electric company and identify any wiring that might need to be replaced as part of the upcoming work.
Brian Thompson contributed to this report.