ORRINGTON — A worker who turned off a critical safety mechanism was the cause of Monday night’s release of 1,700 pounds of toxic chlorine gas from the HoltaChem facility, company spokeswoman Beryl Wolfe said Tuesday.

The incident occurred at the plant’s rail yard, where chlorine is loaded into railroad cars to be shipped out. While one car was being loaded with the chemical, which is produced at the plant, another car began moving slowly toward it.

Two things went wrong Monday night, Wolfe said.

The first was that the second car never should have been on the same track as the car being filled. The second error occurred when the operator turned off the safety mechanism that would have derailed the slow-moving car before it could collide with the other one.

Instead, the tanker moved at about 1 mph until it hit the car that was still being loaded with chlorine. When the two collided, the chlorine line ruptured, releasing a cloud of green gas.

HoltraChem workers addressed the leak quickly, fire and environmental officials said, turning off the valves that let the gas out of the building. Winds of up to 10 miles per hour dissipated the gas, and emergency personnel at the scene characterized the incident as a minor one.

Wolfe said the company was “very apologetic” for the “inconvenience and concern” the chlorine release caused.

She reiterated the company’s earlier statement that rail cars are loaded routinely with no history of a similar incident, and added that all safety procedures were followed Monday with the exception of one operator mistake.

“It’s a simple case of human error, as unfortunate as it is,” she said. The worker who turned off the safety mechanism will be disciplined if necessary, she said.

The company Tuesday began retraining employees involved with loading chlorine and moving rail cars, and intends to look at all its safety procedures to see if any new procedures should be added.

No one was seriously injured as a result of the chemical release. The eight people who sought medical evaluation Monday night all were treated and released that night, according to a spokeswoman for Eastern Maine Medical Center. Two other people also went to the hospital to ask questions about the chlorine release.

“They were evaluated, cared for and able to go home,” said Nancy Ballard, director of community relations for Eastern Maine Health Care.

Workers at the chemical facility, which employs 70 people, found that approximately 1,700 pounds of chlorine escaped when one rail car bumped another as the second was being filled with the chemical.

“When 1,700 pounds of liquid chlorine turns into a gas, a pure gas with no air in it, the green cloud would be in the vicinity of 6 cubic meters,” explained Cleve Leckey, an oil and hazardous materials specialist for the Maine Department of Environmental Protection. “If was spherical, like a ball, it would be pretty close to 2 meters in diameter” at the widest point. A meter is about the same size as a yard.

Despite the technically small leak, Leckey of DEP said Tuesday that the incident “could have been more minor than it was.”

“When you have as many as 10 people involved … [who] think they’ve been exposed, that’s not the most minor spill I’ve ever attended to.”

One of the people who checked in at EMMC Monday night was a neighbor of the chemical facility who wanted to know why the community was not informed that the leak had occurred.

The town of Orrington and HoltraChem each cover half the cost of an emergency siren mounted at the plant. The siren does not go off automatically; emergency officials must decide to turn it on.

On Monday night, that decision rested with Orrington Fire Chief Leslie Grover. He determined that the situation was not serious enough to warrant sounding the siren.