A 16-year-old boy who was found unresponsive in his prison cell died of natural causes, a coroner has concluded.
Daniel Adewole suffered a sudden unexpected death in epilepsy at Cookham Wood jail in Kent in 2015.
The inquest in Maidstone heard that despite repeated attempts to rouse him by kicking his locked door, officers did not enter the cell for 38 minutes.
They assumed he was asleep on the floor, hidden by his bed cover.
One officer went for a cigarette in between checking on him, the inquest heard, and another did not use her emergency key because she feared she might be attacked.
Medical experts told the hearing it was likely Daniel had been dead for any time between half an hour and several hours before he was found.
Senior coroner Patricia Harding said she was not satisfied Daniel's death could have been prevented had his cell been entered earlier.
Giving her conclusion, she said the events were of "significant concern", but she had received information from the prison estate that changes had been made to prevent similar cases.
After the hearing, a Ministry of Justice spokeswoman said: "Our thoughts are with the family and friends of Mr Adewole and we will carefully consider the findings of the inquest."