Miss Jones' said her father, uncle and great-uncle had to look on as thousands of dollars of equipment was destroyed - unable to do anything as huge flames took hold.
Emergency services were called to the fire on Waitao Rd at 10.10pm, with firefighters from Papamoa, Te Puke and Mount Maunganui attending.
Miss Jones said her father was also treated at the scene for minor burns to his hand.
She believed Graham would have been trying to save family heirlooms - such as his mother's 1920s diaries - when he was burned.
Strong winds fanned the flames, which gained momentum with fuels and oils stored in the shed, she said.
"It went up much faster than a house fire would."
Only charcoal and disfigured remains of machinery were left on the site yesterday where the large barn had stood.
The farm had been in the family for at least three generations and her grandfather had spent most days "pottering" in the workshop, Miss Jones said.
"I think my grandad is the most upset because he was in the workshop every day.
"I think that's the hardest part, just all the memories.
"The shed held a collection of about three generations of projects, equipment and tools."
Neighbours had come to the family's aid with basic equipment to get them through the day and continue the farm running as usual.
"Any support we've had has been awesome and I know it means a lot to dad ... He's just gutted but he doesn't have time to stop and think about it because he has to keep working on the farm."
Her father, Kevin Jones, was not new to disasters. He had to take down his sheds after a mini tornado destroyed another shed on his farm a few years ago.
Fire investigators from Pumicelands Rural Fire were at the farm yesterday investigating the fire but western zone manager Allan Pearce said a cause had not yet been established.
"It's been so badly burned it's hard to know where it started."
Mr Pearce said the injured man was lucky to get out.
Miss Jones had organised a working bee for the weekend to help her parents out.
