NATCHEZ — A potentially lethal gas leaked into an unoccupied building at the port last week, but emergency responders contained the gas before any harm was done.

Natchez City Engineer David Gardner said hydrogen sulfide — a poisonous, flammable and explosive — gas leaked into the former Farmers Electric building at the port from a sewer line.

Gardner said he believes that a chemical from one of the industries at the port entered the sewer line, mixed with the sewage and created hydrogen sulfide gas. The gas, Gardner said, escaped from the line because water in the P-traps of the building’s plumbing had evaporated, allowing the gas to likely escape through a sink.

Gardner said the property owner contacted authorities when the owner noticed an odd odor in the building. Hydrogen sulfide gas smells like rotten eggs.

Atmos Energy was contacted, Gardner said, and the company’s staff used devices to determine the gas was hydrogen sulfide.

Adams County Emergency Management and the Natchez Fire Department also responded, and firefighters placed exhaust fans in the building to disperse the gas, Gardner said.

No residences or residential sewer or water lines were in danger, Gardner said. He said the gas was only present in a line from the port to the Natchez Wastewater Treatment Facility.

The gas, Gardner said, was discovered by the property owner and contained before it reached the treatment facility, where staff likely would have smelled it.

The gas reached a 3-percent concentration, Gardner said, which is dangerous. Worse-case scenario, Gardner said, would have been that the gas was ignited inside the unoccupied building.

Gardner said it has not been determined from which industry operation at the port the hydrogen sulfide originated.

“We can’t really prove that it came from any particular one,” he said. “And we get stuff like that all of the time from the port, but usually it’s not gaseous, it’s liquid.”

Gardner said all industries at the port were contacted about leak and asked to adjust their operations if necessary to prevent any future incidents.

“Hopefully the industrial customers down at the port, they’ll recognize a problem and hopefully can take some measures to not let it happen again,” he said. “But I do want to stress that no one was in harm’s way. We were on top of that and had good response from EMA and the fire department.”

A backflow prevention device was installed in the building after the incident, Gardner said, which should stop any future contamination or pollution caused by backflow.