Mark Priestley, 34, was pinned against a skip by the beam at the Halifax factory of Elland Steel Structures Ltd on 31 January 2011.
The weight of the beam crushed his spine and torso, leaving him with irreversible spinal and nerve damage.
Mr Priestley, of Claremount, Halifax, was in hospital for five months. Although he regained some movement in his legs, he is largely confined to a wheelchair, still needs intensive therapy and is unlikely to be able to work again.
The incident was investigated by the Health & Safety Executive (HSE), which prosecuted Elland Steel Structures.
Bradford Crown Court heard that Mr Priestley had been working with a colleague to weld pin connections to the 23m-long beam. The beam had to be rotated several times so the welding could be done, which meant lifting it using chain slings.
HSE found that it was likely that one or both of the chain slings next to the beam had snagged it as it was about to be lifted in preparation for slinging. As the chain was being raised, it caught the beam which became unbalanced and toppled sideways onto Mr Priestley's back as he attempted to get out of the way.
The court was told the company had failed to assess the risks for lifting operations so they were not properly planned or supervised. The chain slings and technique used were also unsuitable for the load.
Elland Steel Structures pleaded guilty to breaching Section 2(1) of the Health and Safety at Work etc Act 1974. It was fined £8,000 and ordered to pay £20,000 toward costs.
After the hearing, HSE inspector Geoff Fletcher said: "What happened was devastating for Mr Priestley and his family. He now has a permanent disability and continues to endure significant pain.
“The incident could have been avoided had Elland Steel fulfilled its responsibilities to fully assess the risks involved with this heavy lifting, and then put measures in place to mitigate those risks.
"Lifting operations need to be properly planned by a competent person and all staff need to be trained and adequately supervised. The lack of a robust system of work will inevitably mean that risk is not properly controlled and the consequences can be devastating."
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