THOMASTON – A 6,000-gallon chemical spill at Dragon Products’ cement plant injured two people Tuesday and prompted a voluntary evacuation within a half-mile of the plant.

Emergency crews converged on the U.S. Route 1 site shortly after 9:30 a.m. to stabilize the rush of ammonium hydroxide into a nearby quarry.

Two workers were taken by ambulance to Penobscot Bay Medical Center in Rockport, according to Terry Veysey, Dragon executive vice president. The men are employed by F.L. Schmidt of Allentown, Pa., which is a major supplier of equipment to the cement industry.

The workers were transferring the chemical from a tanker truck to Dragon equipment for a trial process aimed at controlling emissions from the plant.

Veysey could not identify the men, but said both were treated, then released from the hospital by midafternoon. He did not know the extent or nature of their injuries.

No Dragon employees or public safety personnel were injured.

Glen Wall, a state Department of Environmental Protection spokesman, said the spill was completely contained in the onsite quarry and did not pose a threat to the environment or residents.

Veysey said Dragon did not know precisely what caused the spill.

As a precautionary measure, Thomaston Fire Chief Michael Leo called for a voluntary evacuation of residents within a half-mile of the spill, which occurred near the plant’s pre-heater – the tallest tower on the property.

A temporary shelter was established at the Williams-Brazier American Legion post, Police Chief Kevin Haj said. About 20 people responded, most of them children from a day care center on nearby Old County Road.

Wall said the entire content of the tanker was dumped into a catch basin, then traveled into a quarry at the plant.

“We believe all of it has leaked,” he said, and “it’s contained right here.”

Ammonia can be dangerous, he said, but ammonium hydroxide contains 19 percent ammonia and 81 percent water.

Ammonium hydroxide is a corrosive chemical that can affect people if they breath it. It can irritate the nose, throat and lungs, causing coughing, wheezing or shortness of breath. Skin contact can cause dryness, itching and redness or dermatitis.

It took Thomaston fire and Rockland hazmat personnel about an hour to set up equipment and gear, Leo said, and two more hours to stabilize the spill. About 25 people responded to the incident.

A Dragon truck dumped some 20 yards of limestone dust near the spill, Leo said, and a Thomaston firefighter clad in protective gear spread the material over the chemical with a bucket loader.

Haj and other officers went door to door, asking residents of High and Marsh streets, Old County Road and the Creek Hill area to voluntarily evacuate their homes and businesses. Besides the day care center, Creek Hill service station closed for several hours.

DEP was still considering what happens next.

Wall indicated that DEP needs to talk to professionals who have dealt with this type of spill to learn what further steps should be taken. It was not known Tuesday how much the cleanup will cost.

Plant manager Stuart Guinther said the chemical was to be used in the cement-making process to lower emissions. “It’s something we haven’t tried before,” he said.

Dragon environmental engineer Ann Thayer is confident the use of ammonium hydroxide will prove to be successful in reducing oxides of nitrogen emissions.

NOx or nitrogen oxides are toxic to plants and nitrogen dioxides can cause breathing difficulties in humans, according to an Environmental Protection Agency Web site. Nitrogen oxides are one of the main precursors of ground level ozone, which can also affect breathing and damage crops and vegetation, according to the Web information.

“We did some initial testing that was quite positive,” Thayer said.