An investigation is under way into a toxic leak at a factory on Teesside that left one man seriously hurt and 36 others needing treatment.
A "major incident" was declared after the release of the substance, at the BASF site in Seal Sands, near Billingham, on Thursday.
One man suffered serious burns, and 16 others were treated in hospital. All but one were later released.
A further 20 workers were given medical treatment at the site.
The casualties suffered burns, skin irritation and breathing difficulties, and all had to be decontaminated.
The leak involved hexamethylenediamine, which is corrosive and can be hazardous in high concentrations.
Police are working with the Health and Safety Executive to establish how the accident happened.
Nine people were taken to the James Cook Hospital in Middlesbrough, and seven to North Tees Hospital.
The man suffering from serious burns is being treated at Newcastle's Royal Victoria Infirmary, where his condition is described as critical but stable.
Ambulance and fire crews from across the region responded to the leak, which happened at around 0930 GMT at the company's Nylon Intermediates plant.
Paul Burnage, from the Cleveland Ambulance Service, said: "When I arrived there were a number of casualties believed to be contaminated by the chemical.
"Our job was to make sure they were properly decontaminated and anyone who needed treatment was taken to various hospitals."
He added that the service was trained to deal with this type of incident, and carried out exercises on a regular basis.
The leaked chemical is used in the manufacture of a wide range of plastics.
The incident was confined to the plant and did not affect the general public.