The train operator of the Pittsburg bound train reported that a patron had discharged some type of chemical inside the lead car of the train. A patron activated the emergency door release, stopping the train about 150 yards short of the platform. Nine patrons then self-evacuated to the right of way and stood on the tracks to get fresh air. The train operator got the patrons to re-board the train and the train moved to the platform, where officers intercepted the train. Officers determined that a female patron on the train had accidentally triggered a canister of pepper spray that was inside her purse while looking for another item. Patrons on the crush load train panicked and activated the door release. The release of pepper spray was determined to be accidental and no one reported any injuries. The lead car of the train was taken out of service, but the train re-boarded and continued normal service. There was about a 10 minute delay in service. TSOC notified.