Two prison officers entered the prisoner's cell after hearing a small explosion at around 6.30pm on Saturday. They found the back of the metal cell door scorched and discovered wires and a battery.
The device had been attached to the door near the hatch used by staff for checking on the prisoner.
Neil Mason, secretary of the Parkhurst Prison Officers Association, said the explosion was either intended as a warning, or it went off prematurely.
"This could have killed or maimed a member of staff. We believe it may have been detonated by battery."
Mr Mason said he was unaware whether the explosive used was a mixture match heads or milk powder in sachets, which can be highly inflammable. He said there was also concern that a book had been found in the cell from the prison library, which apparently gave details on how to make explosive devices.
"If this is true then it's just stupid," said Mr Mason. "Our population is due to rise by around 20 per cent, while the number of staff is dropping by 25 per cent.This incident underlines our concern about staffing levels."Reuse content