Thousands of evacuated residents returned to their homes and officials investigated the accidental mixing of two acids that created a toxic cloud leaving up to 85 people injured at a wire factory.

Hydrochloric acid and nitric acid were accidentally mixed at the National Standard Co. wire plant late Tuesday, creating a toxic cloud that injured up to 85 people and forced the evacuation of as many as 5,000 residents within a 3-mile radius, police said.

"The all clear went at 10 (p.m. EDT) and everyone went home," said Niles police dispatcher Russell York. "The police left the scene and so did the fire department. The National Standard people were taking care of the cleanup."

Nancy Kime, emergency services manager at Pawating Hospital in Niles, said all of the people treated at the facility were released. She said most of those treated were for minor upper respiratory problems.