Around 11 a.m. Saturday morning, a small truck convoy left Sussex, N.J., under police escort, bound for Brookhaven Calabro Airport, where authorities had set up an emergency command post to deal with a potential disaster.

A 30,000-gallon tank in Shirley was leaking propane. If exposed to a spark or flame, the chemical could produce a fireball. The convoy - four trucks carrying tools and employees of a company called Industrial Propane and Reclamation - was coming to make sure that didn't happen.

John Stearns, the burly 47-year-old who heads the company, immediately on arrival went into a briefing with town, county and emergency officials.

The mood was "confident" but tense, Stearns said. Propane is colorless; in liquid form, it is stored under pressure and has a boiling temperature of minus 44 degrees Fahrenheit. When exposed to warmer temperatures or lower pressure, it turns to gas, which expands to 270 times its liquid volume.

The Mastic Fire Department had slowed the leak by spraying water over the tank that froze and made a partial seal, but gas was still leaking.

Nobody knew how much had leaked, but they did know it could burn, if exposed to flame or even a spark from an engine. "Had that lit," Stearns said, "there would have been a momentary, very impressive ball of fire that engulfed the whole parking lot, then retracted back to its source and burned at the tank."

Twenty minutes after arriving at the command post, Stearns headed with firefighters to the tank. They stopped their truck several thousand feet away and walked.

The tank was buried 2.5 feet below ground, but workers had partially dug it out. Stearns looked down at it and he saw a "bubbling liquid-filled pit of water and propane" and chunks of ice.

He had done hundreds of similar jobs in the last two years, but this time he had no diagrams to work with.

But, looking down into the pit, he thought he spotted the valve handles. There were three, two for vapor lines and one for liquid - the one he needed to shut off the leak, though he couldn't tell which was which through the murk. He pried the ice off with a firefighter's tool and took a wrench to each valve in turn, until the process of elimination showed him which valve was for liquid.

By around 3 p.m., the leak was stopped.

For the next three hours, Stearns used a patented truck-born contraption of his own invention to capture the propane remaining in the tank and transform the gas back into liquid by passing it through a series of vapor traps, condensers and refrigerators.

He pulled out about 1,200 gallons and turned most of it over to a local delivery truck - the fuel was still, after all, perfectly good.

And by that evening he was done, ready for the long drive back to New Jersey.

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