Robert Ramsey, 19, of Dundee, an agency worker, had been working at Forfar Galvanisers premises in Carseview Road, for four months when the incident happened on 20 November 2013.
Forfar Sheriff Court heard that Mr Ramsey had been helping colleagues move the large A-frame, which measured 3.82m by 1.6m and weighed almost half a tonne.
The A-frame was lifted and moved outside, where it was raining, on the forks of a forklift truck. It was then turned and was being moved into the correct position with Mr Ramsey and another colleague on opposite sides of the A-frame to steady it.
However, the A-frame was not secured to the forks and it began to slip.The forklift driver shouted repeated warnings, and although his colleague heeded them moving out of the way, Mr Ramsey took hold of the A-frame to steady it, but it continued to slip and fell onto him.
Mr Ramsey suffered serious injuries to his legs including bruised bones, trapped nerves, muscle and tissue damage as well as severe swelling and external bruising. He was off work for several months and could only walk short distances. He has now made a full recovery
An investigation by the Health and Safety Executive (HSE) revealed Forfar Galvanisers did not have in place a safe system of work for the task. The company had developed a procedure for moving ungainly loads following a similar incident in 2007, but this had not been implemented.
HSE had also offered advice to the company in 2007, which recommended that when lifting and moving unstable loads, additional securing arrangements should be used when moving items on forklift trucks. It was also recommended that if operators were required to steady loads in transit, tag lines should be used rather than direct contact, to keep operators well out of harm's way.
Since the incident the company has issued instructions that loads should preferably be carried flat rather than suspended and has commissioned a specialist company to investigate whether a clamping attachment could be used to enable loads to be secured to the forks of the forklift.
Forfar Galvanisers Ltd, of Carseview Road, Forfar, pleaded guilty to breaching Section 3(1) of the Health and Safety at Work etc Act 1974.
HSE principal inspector Niall Miller, said: "Forfar Galvanisers Ltd's failure to act to make sure its employees and agency workers were adequately protected during such movement operations, has led to serious injuries for Mr Ramsey, which could have been so easily prevented.
"The issues with unsecured loads on forklift trucks are well-known in all relevant industries. It was entirely foreseeable that loads which are unsecured will become unstable when they are moved and that metal will become slippery if wet, especially when placed on another wet metal object.
"Around a quarter of all workplace transport incidents involve forklift trucks, with 50% of these happening because someone is hit either by the vehicle or a falling load.
"It was clear there was a risk of death or serious injury if the A-frame fell from the forklift truck, particularly as the company was aware of previous incidents of loads falling. Had the company acted on this and the advice of HSE, Mr Ramsey would not have been injured."