Residents of Teutopolis, Illinois who had to evacuate after a semi-truck crashed, releasing thousands of gallons of toxic ammonia, have been cleared to return home.
CNN  — 

At least five people were killed and parts of an Illinois neighborhood were evacuated due to a Friday crash involving a semi-truck carrying thousands of gallons of anhydrous ammonia.

The truck was carrying about 7,500 gallons of the toxic substance at the time of the wreck in Effingham County, according to the Illinois Environmental Protection Agency. The agency said early estimates say more than half of that – about 4,000 gallons – were released.

After officials said approximately 500 people were evacuated from the area, residents have been told it is safe to return home, Teutopolis Assistant Fire Chief Joe Holomy said in a news release Saturday night.

“Testing has indicated that the danger from the anhydrous ammonia has dissipated,” Holomy said.

Parts of Teutopolis, a village in south-central Illinois, were evacuated “due to the plume from the ammonia leak” after the crash Friday night on US Highway 40, about a half mile east of Teutopolis, Illinois State Police said.

The crashed tanker has been drained, patched and taken to a secure location to be investigated by the National Transportation Safety Board, the state emergency management agency said in a release. The Illinois State Police is also investigating the cause of the accident, it said.

CNN has reached out to the National Transportation Safety Board.

In addition to the deaths, multiple injuries have also been reported.

Emergency crews were still on scene and working to contain the leak Saturday afternoon, according to the state’s EPA.

Just before 5 p.m. a separate crash had taken place on Interstate 70 just east of Effingham, which caused traffic to be rerouted to US Highway 40.

At about 9:25 p.m. local time, authorities were notified about a crash on the highway “involving multiple vehicles, including a semi-truck that is leaking anhydrous ammonia,” police said.

Effingham County Sheriff Paul Kuhns described the scene as large and complicated.

At least five people were airlifted to local hospitals, Teutopolis Fire Chief Tim McMahon said.

Crews worked overnight to get part of the rupture on the semi-truck patched up – which slowed down the leak but did not stop it completely, according to McMahon.

Those within an estimated 1-mile radius of the crash, including northeastern parts of Teutopolis, were then evacuated, police said.

“We offer our deepest sympathies to all those affected by the accident and chemical spill,” Illinois Emergency Management Agency and Office of Homeland Security Deputy Director of Emergency Management Clayton Kuetemeyer said in a statement.

Anhydrous ammonia “is essentially pure (over 99 percent) ammonia,” according to the Occupational Safety and Health Administration. “‘Anhydrous’ is a Greek word meaning ‘without water;’ therefore, anhydrous ammonia in ammonia without water.”

Ammonia used in households is a diluted water solution that contains 5 to 10 percent ammonia, according to OSHA.

Ammonia in high levels can irritate and burn the skin, mouth, throat, lungs and eyes, according to the Centers for Disease Control and Prevention. Very high levels can also damage the lungs or cause death.

Symptoms of anhydrous ammonia exposure include breathing difficulty; irritation of the eyes, nose or throat; and burns or blisters.

Anhydrous ammonia can get into airways and attach itself to mucus and moist surfaces, Kuhns said. “It caused terribly dangerous air conditions,” he said of the leak.

Effingham County has an estimated population of about 34,000 according to the US Census Bureau, and is located about two hours south of Illinois’ capital, Springfield.

CNN’s Zoe Sottile and Raja Razek contributed to this report.