Ken Joyce, 53, of Lanchester, County Durham, was working for Allan Turnbull, trading as A&H Site Line Boring and Machining, when the incident happened on 2 December 2008.
He was dismantling the structural steelwork of the roof of the Burning Hall at the Swan Hunter Shipyard in Wallsend, Newcastle.
During a four-week trial at Newcastle Crown Court, a jury heard how Joyce was working from one cherry picker while two colleagues were working from another cherry picker and a crane.
They were dismantling the structure and were using a crane to lower the steel beams to the ground.
While removing a beam brace connecting two plate girders, one of the plate girders struck the basket of the cherry picker in which Joyce was standing, knocking the equipment over.
Joyce fell to the ground below and suffered serious head injuries. He was pronounced dead soon after.
A joint investigation carried out by Northumbria Police and the HSE established that North Eastern Maritime Offshore Cluster Ltd (NEMOC) had subcontracted the dismantling work to Allan Turnbull.
The jury was told that NEMOC and its director Christopher William Taylor failed to ensure the safety of its employees and sub-contracted workers by neglecting to check that Turnbull had the necessary competence to carry out the work.
The investigation also found that Turnbull had failed to adequately plan the work after identifying a lack of suitable and sufficient lifting plans to ensure a safe system of work was in place for the dismantling of the structural steelwork.
Turnbull, 61, of Tow Law, County Durham, was found guilty of gross negligence manslaughter following the trial after pleading guilty earlier to safety breaches.
He was sentenced to three years in prison.
North Eastern Maritime Offshore Cluster Ltd (NEMOC), which had been operating from the Swan Hunter Yard, was fined £1 for each offence after it was found guilty of safety breaches.
The company is now in liquidation.
Christopher William Taylor, 51, of Newcastle, was found guilty of safety breaches and was fined a total of £30,000 and ordered to pay £50,000 costs.
After the case, which was brought by the Crown Prosecution Service, HSE Inspector Emma Scott, said: “This was a tragedy that could easily have been prevented had a safe system of work been in place.
“Instead Ken Joyce lost his life as a result of collective failures which included not preparing in advance a detailed plan of how the work should be carried out and no lifting plans to ensure the safe removal of the beams.
“Allan Turnbull was also prosecuted in November 2005 after an employee sustained serious leg injuries while dismantling a redundant brick manufacturing plant.
“I hope other companies can learn from this and ensure they take the necessary action to deal with the high risk involved with work of this nature.”
Chief Inspector Mark Anastasi, of Northumbria Police, said: “This is a tragic case. Ken left home to go to work and never returned.
“He left behind his partner Eva and his family who never saw him again. They have been very supportive of the investigation and have shown their love for Ken throughout.
“Swan Hunter shipyard formed a major part of the local community and sadly, at the end of an era, during the dismantling process Ken lost his life as a result of the mismanagement of the work.
“The failures from both the individuals and the company showed a total disregard for safe working practices.
“Ken’s employer failed to improve his work following a similar incident in 2005, yet he continued to perform dismantling work.
“This complex and lengthy enquiry has shown that Northumbria Police and the HSE, with the support of the Crown Prosecution Service, will work in partnership to ensure offenders are brought to justice.”
In a statement, Joyce’s family said: “As his family, we are striving to honour Kenneth’s memory and are still coming to terms with the void his absence has left in our lives over the past four years.
“Above all else we have hoped for justice for him and for the intensity of the sadness and grief created by his untimely passing, to ease and lessen with the aid of this justice, along with the healing passage of time.”