On 14 July 1991, at 2150 h, a train derailment occurred near the Cantara rail curve about six miles above Dunsmuir in Northern California. The derailment spilled approximately 19,000 gallons of metam-sodium into the Sacramento River. When mixed with loater, metam-sodium degrades to methylisothiocyanate (MITC) and other gases. The contaminated river water passed the town of Dunsmuir and other occupied areas exposing residents to MITC gas.

From 15 July to 20 July (five days), a total of 360 people underwent triage. The majority of patients displayed minor exposure symptoms that did not require hospital care. Mercy Mt. Shasta Hospital, a small rural hospital close to Dunsmuir, received the majority of patients. As of 29 July, 15 days after the incident, Mercy Mt. Shasta Hospital had seen 244 exposed patients in its emergency department, and had admitted five. Three had symptoms that could have been spill-related. Three Regional Poison Control Centers provided medical toxicology advice.

Medical management of the emergency medical services (EMS) response to the event was piecemeal and weak. There did not appear to be a medical operations component at local Emergency Operations Centers (EOC). Most health care personnel interviewed complained about inadequate information about the substance and the situation. Local fire service mutual- aid agreements to obtain additional fire service and ambulance personnel worked well. It is important to emphasize that everyone who believed they had been exposed to the chemical underwent triage and received appropriate acute medical care.