What do we know about the Ohio train derailment and toxic chemical leak?

Crews released toxic chemicals from derailed tanker cars to prevent an explosion. Photograph: Gene J Puskar/AP

A train carrying hazardous materials heading from Pennsylvania to Illinois derailed in early February, causing a major fire and alarm over a possible imminent explosion. The situation has local people worried, despite reassurances from officials, and has highlighted how vulnerable many Americans are to similar incidents.

Up to 2,000 residents living in the immediate area were evacuated as chemicals being carried by the train, run by Norfolk Southern Corporation, were released to prevent an explosion.