A 49-year-old furnace operative suffered life-threatening injuries in an explosion at the plant in March 2012.
The worker, from Rotherham, - who did not wish to be named - was injured after a control system fault caused 25 tons of molten metal to spill from a furnace.
The blast erupted at the Aldwarke Lane premises soon after the worker and a colleague hosed water onto the spilled metal.
The man staggered to safety where colleagues rushed to his aid and applied a burn shield before he was taken to hospital, said the HSE. Two other employees received minor injuries.
He was in intensive care in a specialist burns unit at Pinderfields Hospital, Wakefield, and in an induced coma for three weeks.
He went on to have numerous skin grafts and reconstructive surgery to his eyes, ears and forehead. He has since managed to return to work but can no longer work in any high-temperature area.
HSE’s investigation identified serious safety failings by Tata in recognising and dealing with risks that led to workers being exposed to unnecessary danger, according to the regulator.
It found the firm had no procedures for dealing with spillages of molten metal, no assessment of the dangers and risks had been carried out and there was no safe system of work in place,
On Tuesday, Tata Steel UK Ltd pleaded guilty at Sheffield Crown Court to two breaches of the Health and Safety at Work etc Act 1974.
Following sentencing, HSE inspector Denise Fotheringham said: “This was a horrific incident that left a worker with life-changing injuries which have had a devastating impact on him and his family.
“Tragically, it could have been avoided had Tata assessed the risks of dealing with molten metal spillages.
“The company’s business is to make steel but they had no procedures for dealing with these spillages, leading to employees using hoses to cool the metal.
“This was very dangerous but the scale of risk had not been recognised by workers who had received no other information or instruction on what to do.
“The resulting explosion was massive and a man nearly lost his life. He remains badly scarred by what happened that day.
“Tata no longer uses water to cool spillages and the risk has been eliminated. If the company had done this prior to the incident, this worker and his family would not be where they are today.”