Milton fire, rescue and police all responded Monday afternoon to a report of a natural gas leak at compressed natural gas company NG Advantage.
There was no ground leak: A trailer containing four tanks of extremely pressurized, compressed natural gas was filled that morning and was awaiting transport to a customer in Putney. Just before noon, a loud hissing noise alerted employees to a problem.
There was never concern the gas would ignite, Fire Chief Don Turner said. The worry is what triggered the gas release in the first place.
“For whatever reason, it popped the caps that allow it to vent,” said Gerry Myers, NG Advantage’s vice president of safety and operations. He was at the company’s Colchester offices at the time but got to Catamount Industrial Park within 15 minutes, he said.
When emergency responders arrived, they ordered about 90 people from a nearby home and business to evacuate to the Chimney Corners park and ride as a precaution, Turner said.
The incident suspended operations at NG Advantage until the company learns why the trailer’s emergency vent system went into action seemingly unprompted. Representatives from the system manufacturer Lincoln Composite, out of Lincoln, Neb., were on their way to Vermont to investigate on Wednesday, Myers said.
A plume of white vapor was visible for about a half-hour as 350,000 cubic feet of compressed natural gas – enough to provide the heat and steam needed to make paper at Putney Paper Co. for about 10 hours – was released into the air. The normally colorless, odorless substance appeared cloud-like because of the cold air temperature, Myers said.
The reaction is actually a safety feature: Trailers vent and release the gas to avoid catastrophes, Myers said.
“If there’s a building on fire next to us and looks like it might spread to our tank, you vent the gas, and it becomes harmless,” he said.
Natural gas isn’t totally harmless; it’s extremely flammable, but being lighter than air, it dissipates quickly when vented. So if a hauler rolled over on the interstate, the vents open to release the gas away from possible ignition, Myers said.
As trained, responders made no effort to stop the gas from escaping, Turner said. The gas needs to mix with a certain ratio of oxygen to ignite; if it had caught fire, firefighters would not have attempted to suppress it.
Since the gas dissipates quickly and the breeze wasn’t too stiff Monday afternoon, Turner wasn’t concerned the gas would find a source of ignition and catch fire, he said.
Turner still called the state HAZMAT team, blocked off both ends of Gonyeau Road and evacuated all employees of Tri-angle Metal Fab and the residents of a household to the south. Power was shut off for about an hour, and firefighters tested for methane and carbon monoxide around Interstate 89 but discovered none, he added.
Milton Fire previously met with NG Advantage representatives to plan for this type of scenario, Turner said Monday.
NG Advantage began compressing natural gas from a pipeline in the Milton industrial park at the start of this year and has the one Putney customer. The gas company has four trailers like the one that malfunctioned Monday; two are in Putney, storing that business’ power source on site. NG Advantage encourages its customers maintain an oil reserve for emergencies, Myers said.
“That was one of my first calls, telling them to switch to oil for a few days until we get it sorted out,” he said. “We believe it was the right thing to do to put safety first.”
Myers estimates the escaped gas cost the company less than $5,000.