A cracked plastic valve on a propane tank was the source of a leak that sent thousands of gallons of toxic, flammable liquefied propane gas into a Shirley neighborhood and forced the pre-dawn evacuation of about 2,000 residents, Suffolk Executive Steve Levy said last night.

Levy said there’s no indication of criminal misconduct behind the Kohl’s shopping center on Montauk Highway, but Suffolk police arson detectives will investigate what went wrong.

“It could have been a terrible disaster, a terrible explosion, but fortunately we had seasoned, trained professionals who did their jobs very well and averted a tragedy,” Levy said.

Brookhaven Town fire marshals and the town attorney will also look into whether the owner of the propane tank has followed proper permit requirements, town Supervisor Mark Lesko and board member Daniel Panico said. No one was seriously hurt, but two people were given oxygen at the scene.

The disruption was massive and traumatic for the residents forced to leave their homes in the pre-dawn hours of New Year’s Day.

One resident, Rosemary Henninger, 51, her daughter and her grandchild were roused in darkness by the police, who then hustled the family away from their home.

Her fear was heightened by the overpowering odor of gas.

advertisement | advertise on newsday

“It was so bad it took your breath away,” Henninger said. “It was so strong it burned the back of your throat.” Henninger’s daughter Beth Lombardo, 27, took nearly no supplies when she hurriedly left her home with her 4-month-old son. They all went directly to William Floyd High School shelter.

The Long Island Rail Road halted service along nearby tracks, electrical power was cut off to many homes and businesses, and the streets were emptied of vehicle traffic as Suffolk police officers went door to door on foot to alert residents.

The police even resorted to riding bicycles, not wanting to risk sparks from vehicles that might ignite the gas, as they evacuated 900 homes near the Kohl’s shopping center on Montauk Highway, site of the leaking tank. In neighborhoods adjacent to the immediate evacuation zone, residents were asked to leave voluntarily but not forced out, said Dan Aug, a spokesman for Levy.

“This is the kind of event they have trained for and they carried it off in an exemplary way,” Levy said.

Many evacuees waited for hours at a makeshift Red Cross shelter at the high school for word that the danger had passed.

That finally came at 8:15 p.m. when Capt. William Silva, of the county police crisis action team, told the families, “The area has been deemed safe. You can go back into your homes.”

The police then gave back to the families the keys to their homes, which officers had earlier collected to allow them to check propane levels inside houses in the so-called “hot zone.” They wanted to make sure that the heavier-than-air propane hadn’t concentrated in basements or other areas.

“The ignition of a pilot flame, a pilot light could potentially ignite propane if it was to fill a basement,” Panico, the town board member, said in an interview.

The leak was discovered at 1:15 a.m. yesterday. A propane truck was making a delivery when the driver heard a disturbing sound and noticed gas emanating from a tank below ground. The driver was able to shut down his delivery vehicle and alert authorities.

The underground propane tank, used to heat the retail space, was about 200 feet behind the Kohl’s store in a grassy, fenced-off area.

advertisement | advertise on newsday

Mastic Fire Department Chief Dwight Blankenship was among the first to arrive at the scene, where the clouds of gas rose at least 3 feet into the air, like a fog.

“I knew I had a major leak here. I was scared. I knew I was way too close to the scene but I had to stay to get my assets in place and get the evacuation under way,” Blankenship said.

Panico, the town board member, said the fire chief showed bravery in dire circumstances.

“He’s truly a hero. He was doing his job with a cloud of vapor up to his shoulder,” Panico said.

Natalie Farrell, who also lives on Pinelawn Avenue, was on her way to a pay phone about 1:30 a.m. to call her daughter, who was at a friend's house, when she said she smelled the odor of gas. So she walked back home to get two of her children — Jeremy Lavarco, 18, and Angela Lavarco, 12.

advertisement | advertise on newsday

“I smelled gas,” Farrell said. “It was very strong.”

“I was very nervous,” Farrell said while waiting to find out when she could go home. “I am still nervous.”

Firefighters who worked within a quarter-mile radius of the leak wore breathing gear. Mastic fire officials said firefighters made several attempts to seal the tank but were unsuccessful. They estimated that from 7,000 to 9,000 gallons of propane had leaked from the 30,000-gallon tank.

At about 1:30 p.m., four large trucks from Industrial Propane Reclamation, of New Jersey, arrived at the scene with a state police escort to try to fix the leak.

John Stearns, the company owner, said his machinery was able to suck in the propane vapor leaking from the broken tank and convert it safely back to liquid propane with a cooling system based on a series of condensing fans.

Another team of workers from a Smithtown company, Paraco Gas, did the preparatory work by lowering the temperature of the tank and its contents.

Paraco “froze everything down, so we were able to reach in and close the valves,” Stearns said.

Meanwhile during the day, Levy spoke of the trauma many area residents were going through. At a news conference, he said, “It is a very difficult way for some folks in the Mastic-Shirley area to begin the new year.” He said that police, fire and emergency service personnel coordinated to help out in the situation.

During the day, the Red Cross gave evacuees blankets and hot coffee, and the county SPCA set up shop at the high school because many evacuees brought pets with them. The pets were being cared for by the SPCA in a mobile unit outside the high school.

A Suffolk police spokesman said that officers from the Seventh, Sixth and Fifth precincts were involved in the evacuation. An LIRR spokesman said service was suspended between Speonk and Patchogue. He said buses were being used to transport people between the stations.

At the high school, some of those evacuated lay down on cots. Others stood about talking to neighbors about when they might return home.

“I just want to go home,” said Tami Houmis, who was awakened at 5 a.m. by a loud knock on her front door. “I want them to fix this.” She said she was concerned about water damage from her refrigerator, which began leaking after power was shut off. She and her husband, Steve, said they have no idea where they would go.

Bill Cunningham, who rents a room on Clinton Avenue, near the site of the leak, said, “I don’t know what to do. This is horrible.”

Duane Consalvo said he saw power go out at one home after another on Pinelawn Avenue, where he lives with his family across the street from Kohl’s.

“It’s like a sci-fi movie,” Consalvo said.

With Carl Corry, James Berstein, Joseph Mallia, Emily Dooley, Patrick Whittle, Nicholas Spangler and Matthew Chayes