The worst accident in Disneyland's history in terms of technical failure and legal impact was the 2003 Big Thunder Mountain Railroad derailment. On September 5, 2003, a locomotive became detached from the passenger cars as the train entered a tunnel, causing the first car to slam into the underside of the locomotive. This accident killed 22-year-old Marcelo Torres and injured ten other passengers. An investigation by the California Division of Occupational Safety and Health (Cal/OSHA) determined the cause was improper maintenance, specifically a failure to tighten and secure bolts on the left guide wheel. This tragedy led to a massive overhaul of Disney’s maintenance protocols and remains a somber case study in theme park safety. Other notable fatal incidents include the 1998 Sailing Ship Columbia accident, where a heavy metal cleat tore free and struck a guest, and several "behavior-based" fatalities on the Matterhorn Bobsleds and the now-defunct PeopleMover in the 1960s and 70s.