TACOMA, Wash. (AP) - A worker at a Tacoma Tideflats bleach plant likely is responsible for the chlorine gas leak this week that prompted evacuation of the industrial area, according to George Karscig, the manager of the Pioneer Americas plant.

Karscig said the incident was an operator error and no equipment failure was involved in the release.

It's unclear how much chlorine escaped to the air when the gas leaked from a valve. Karscig said it was almost 900 pounds. Tacoma Fire Department deputy chief Jolene Davis said it was 1,264 pounds.

Karscig said the accident occurred on Monday evening during the transfer of pressurized, liquid chlorine from a 90-ton rail car to a 1-ton chlorine cylinder.

According to Karscig, fire personnel transported 18 people to hospitals for medical evaluation, but none required treatment.