Michael McLean, 17, died in hospital in August 2015 after an incident at Denholm MacNamee in Inverurie, Aberdeenshire.
Dean Reynolds, 23, of Keith, has gone on trial accused of culpable homicide.
He denies culpably and recklessly operating a cable spooner machine while Mr McLean was in the drum.
Mr Reynolds faces an alternative charge of breaching Health and Safety guidelines as an employee.
He also faces a charge of attempting to pervert the ends of justice by discarding two pairs of work boots.
The first witness in the trial, Denholm MacNamee managing director Brian Ritchie, told the High Court in Aberdeen how he became aware of an emergency at the workplace on 14 August, 2015.
The teenager was spending his second summer at the firm, and 14 August was his last day before he was due to return to school.
Around 12.20pm bosses were alerted to an “emergency” in a paint shed at the yard in Inverurie Business Park - where the firm carried out water jet cleaning and industrial painting for oil firm clients.
Mr Ritchie said he was sitting in his office when a staff member burst in shouting “Mikey is unconscious”.
Mr Ritchie and other staff rushed to the paint shed - a short distance from the firm’s main building - where Michael was lying unconscious.
Mr Ritchie, 49, said: “I thought he was dead. He was blueish-white and bleeding from the ear.”
Mark McLean, the teenager’s father, also worked at the company.
Mr Ritchie said: “Mark - Mikey’s dad - came running out and started giving him CPR.”
Mr Ritchie said it was “instantly” clear it was serious.
Mr Ritchie said he asked Mr Reynolds what had happened but he said he didn’t know, and that he may have “taken a turn”.
He said Mr Reynolds later said the teenager had been chewing gum so might have choked.
Mr Ritchie said the teenager had been very safety-conscious. His nickname at work was “PPE Mikey” because of his dedication to always wearing the correct personal protective equipment.
The trial, before Lord Beckett, continues.