Sandy Haining, 33, died after the quad he was moving accelerated into a wall at his work's garage.
A fatal accident inquiry into his death has heard from colleagues who were working with him and saw his last moments in May 2012.
Hamilton Sheriff Court heard the vehicle belonged to the garage owner's son.
Mechanic Mark Sproule, 35, said Mr Haining, of Wishaw, Lanarkshire, had asked how to put the quad into reverse before hearing a "big bang" at the Brigbrae Garage in Mossend.
He said: "We had to move it [the quad bike] every day to get space in the workshop and Jack would usually drive it out. If he wasn't there then we would just push it out. I have no idea why Sandy chose to drive it that day."
Mr Sproule told how he tried to help Mr Haining as he waited for an ambulance to arrive. He said: "He was choking on his own blood so I turned him on his side into the recovery position."
Mr Haining lived with his fiancée Claire Anderson and their six-week-old daughter Katie when he died.
Mr Haining's father Alex said later: "It was a tragic accident."
Sheriff Carole Cunninghame will deliver her findings later.