British Transport Police are appealing for information after a bottle of hydrochloric acid was found on a Northern Rail train at Middlesbrough station shortly after 7 o'clock on Sunday evening.
The station was evacuated for a time and buses replaced train services.
4 fire appliances attended the incident along with 3 special appliances and 3 officers.It is believed the acid was in a soft drink bottle and caused the smell of burning when some of the liquid leaked from the container.
More top news
Chancellor George Osborne will seek to reassure financial markets on Monday morning following Britain's decision to leave the EU.
Eight crew members had to be rescued from a fishing boat after it started sinking a mile off the coast of Sunderland.
Drivers travelling north or southbound on the A1 near Newcastle and Gateshead are advised to expect delays until Wednesday morning.