A chemical train jumped its tracks Saturday, spilling formaldehyde that forced 100 families to evacuate and sending seven people to the hospital for breathing problems.

It was not immediately known how much formaldehyde leaked out when 30 cars of the 148-car train derailed near the Ohio River, but none went into the water, officials said.People who were within a mile of the site were evacuated while other nearby residents were told to remain indoors and seal off ventilation systems.

Six residents and the train's conductor were treated for breathing trouble. All of the residents were released, but the unidentified conductor remained hospitalized.

His condition was not immediately known, but none of the patients appeared to be critical, a nursing supervisor said.

Nine firefighters were sent to the hospital for a precautionary examination, but none reported serious problems.

The accident was about 50 yards from the Ohio River, in the northeastern edge of Huntington. Early reports claimed it was chlorine that spilled, but officials later said it was formaldehyde.

The train's tank cars also carried sodium hydroxide, hydrochloride acid and multon sulfur. Several coal cars were thrown from the tracks.

Hazardous materials emergency crews built a dike around the spill and contained it by late afternoon, said Gordon Merry, director of Cab-ell County emergency services.

Residents were told they would not be able to return to their homes before Sunday.