The unsupported steel ring crushed the employee between the toppled metal section and a shipping container.
A Health and Safety Executive (HSE) investigation found that 48-year-old Michael Dwyer and his son Jordan were involved in the dismantling of a three-core reactor vessel at RS Bruce Metals and Machinery's March Street depot in Attercliffe, Sheffield when the incident happened on 4 March 2013.
The Star reported that the vessel was being cut into sections to sell for scrap metal. The tower had already been cut into 1.5 m-long rings, most of which were further dissected in the cutting shed at the site.
As the final three rings from the bottom of the tower were too heavy for the shed's gantry crane, they had to be cut up outside.
Father and son were cutting up the final section when a piece of metal, weighing around 1.3 tonnes, sheared off and fell on the father. Despite attempts to remove the heavy piece of metal and administer first aid, Dwyer died at the scene.
Lawyers acting for the firm claimed consideration had been given to workers' safety during toolbox talks with employees by a senior manager. They added that the company, which uses techniques to remove, recover and recycle precious metals, had an excellent safety record over the 30 years it has operated in the UK and internationally.
But prosecutors had told the court there had been a "fundamental failure of planning and forethought".
The company pleaded guilty to breaching s 2(1) of the Health and Safety at Work Act at Sheffield Crown Court and was fined £65,000. It must also pay £15,000 costs.
According to The Star, RS Bruce Metals and Machinery, part of the Bruce Group of companies founded in 1974 in Sheffield, has a £2.5m turnover and reported a £65,000 profit in 2018.
Judge Graham Reeds agreed with the prosecution that the fatal incident was avoidable and that the breach was a significant cause of Dwyer's death. "I find it as fact that at least one other worker (Dwyer's son) was exposed to the same risk of death," he said.
After the hearing, HSE inspector Tim Johnson said: "A suitable and sufficient risk assessment would have clearly identified the risk of serious injury from falling sections and should have prompted the company to put in place adequate, properly designed support and devise a safe system of work for employees to carry out the dismantling operation".