A founder member of Birmingham rock group Electric Light Orchestra died when a 63 stone (400kg) bale of silage rolled nearly 200ft (60m) down a steep field on to his moving car.
Michael Edwards, 62, the band's former cellist, died instantly when the bale landed on the cab of his bottled-water delivery van on a rural road in September last year.
An inquest jury in Plymouth has returned a verdict of accidental death despite an independent expert and a Health and Safety Executive inspector casting doubt on how the independent contractor carrying out the work had secured the bale to stop it rolling down towards the road.
In a statement released after the inquest, Mr Edwards' brother David said: "Michael's death was totally unnecessary and preventable if a proper assessment of the risks of carrying out a baling operation on a steeply-sloping field adjoining a public road had been carried out.
"I would like to ask the coroner to consider making a recommendation to the HSE to revise its guidelines to include the hazards of a baling operation on sloping ground, so that similar tragedies may be prevented in future."
The bale crashed on to Mr Edwards' van as he drove down the A381 at Halwell, near Totnes, in South Devon, just after noon on Friday September 3.
Despite the efforts of a doctor who was caught in the traffic leading to the crash site and a local GP he died at the scene from massive head injuries.
He had lived in nearby Totnes for many years.
Simon Jones, the HSE inspector who examined the scene, told the jury: "My gut reaction was that there was a dangerous slope on that field.
"There was the potential for a round bale to roll. The steeper the slope, the greater the potential for it to roll."
Plymouth and West Devon deputy coroner Andrew Cox said that he would write to the HSE urging it to issue guidance on the use of baling machinery on steep slopes, as none is currently available.
