Stuart McNaught, a joiner for William Fulton Building Services Ltd, was putting up plasterboard inside an extension at a house in Cochno Road East, Duntocher, when the incident happened in icy conditions on 6 January 2011.
Dumbarton Sheriff Court heard that his employer, William Fulton, had brought more plasterboard sheets for the job and was using a forklift truck to lift the load onto the site.
Fulton drove the unsecured load of 82 plasterboard sheets, weighing 1925kg, down the road towards the extension and began to lower them into a courtyard.
The court heard that the forks were iced up and the road had not been gritted.
McNaught, then 36, and another employee were in the courtyard below the forklift and watched the boom extend over a demolished wall.
As the workers began to guide the load from the forklift to the ground McNaught, who was not wearing a hi-vis vest and could not see Mr Fulton, noticed the plasterboard move.
As he tried to get out of the way, he slipped. The load fell off the forks and landed on McNaught trapping him.
On hearing his screams, the other site workers tried to lift the plasterboard but as it was too heavy, Fulton drove the forklift into the courtyard to lift the boards off Mr McNaught.
He was taken to hospital with a broken rib, pelvis, punctured lung and fractures to his right ankle and both legs.
He returned to work after five months but continued to suffer from chronic pain and resigned a year later. However, he returned to the company in April this year.
William Fulton Building Services Ltd was prosecuted after a HSE investigation found that the company failed to address how the plasterboard could be lifted and moved safely, particularly at the time when the site was badly affected by ice.
The court was told Fulton had not received basic training in using a forklift truck. A trained operator would have considered the safest route and ensured that people would not be working in the area while material was being unloaded.
He would also have recognised that there was ice on the forks of the truck which would make the load more likely to move.
William Fulton Building Services Ltd, of Bearsden, Glasgow, was fined £8,000 after pleading guilty to breaching safety laws.
Following the case, HSE Inspector Moira Jennings said: “This incident was clearly foreseeable and therefore readily avoidable.
Working below a forklift truck is dangerous and the company should have carried out a proper risk assessment.
“This would have identified the risks of moving materials around the site and to employees standing near the plasterboard while it was being unloaded from an elevated position.
“The plasterboard should have been placed flat on the ground in the yard or at the entrance rather than expecting people to collect them from an elevated position on the raised forks of the vehicle.
“William Fulton should have ensured he had good visual contact and communications with Mr McNaught, who should have been wearing a hi-vis vest and standing well away from the forklift as the load was lowered.”