Welder Keith Wharton, 41, was killed instantly and his colleague Christopher Cansfield, 31, sustained severe injuries including a broken neck and leg in the incident in March 2007.
The court heard that a steel lifting frame, weighing more than half a ton, fell from an overhead crane onto the workers.
It is understood there was no safety catch on the hook of the crane, which could have prevented the load from falling.
The firm – which was trading as Stackright Building Systems, in Kirby – pleaded guilty to breaching the Health and Safety at Work Act.
HSE inspector Iain Evans said: "Keith Wharton should not have died. His was an avoidable, pointless and unnecessary death in an environment where there were numerous safety issues.
"If the company which employed him had dutifully exercised its responsibility to ensure their safety, his family would not be here at court today grieving their loss."
The firm was also ordered to pay £16,941 in costs.