An annual Independent Monitoring Board (IMB) report for the 12 months to the end of October 2017 for the west London YOI found that inmates spend too much time in their cells and are not taking part frequently enough in education classes and other activities.
This is causing frustration among inmates, which the IMB believes is leading to increased incidents of violence.
There were 405 incidents where staff had to use physical restraint over the period covered in the report. Of these, 229 involved "multi-perpetrator" fights, 204 involved a young offender attacking another inmate and 28 involved an attack on a member of staff.
"At the beginning of the reporting period all prisoners endured frequent and unpredictable daily regime changes, often caused by a shortage of uniformed staff," states the report.
"They spent far too much time in their cells, and too little time in education, purposeful activity and association. This led to much frustration and in the IMB's view, to increased and sometimes explosive violence."
It adds: "It is an unusual week that passes without several violent incidents."
When activities are provided sometimes these had to be abandoned due to issues around violence.
A Bounce Back scheme, where young offenders carry out building work in the prison and learn new skills from its building contractor, had to be temporarily stopped amid Prison Officer Association concerns around prisoners having access to "potentially dangerous tools".
This scheme is now up and running with painting replacing plastering and construction.
"This is regrettable as the full scheme would have given prisoners much greater eligibility for building trade apprenticeships after release," states the IMB report.
Bullying is another concern highlighted in the report, as is the increased importing of drugs.
The condition of the buildings is also criticised by the IMB, in particular the poor state of some cells.
"These issues include leaking roofs, broken washing machines and tumble dryers, broken lighting in corridors and an inefficient central heating system," states the IMB report.
"Two prisoners reported having to sleep fully clothed in winter because cell windows would not close and another reported having to sleep on the floor to avoid condensation dripping from walls and the ceiling."
Despite the concerns the report praises the staff "for another year of dedicated and committed work caring for some of the most challenging, complex and vulnerable young men in Britain".
Staffing problems had also improved, with the shortfall of officers falling from 72 in October 2016 to 50 by November last year.
The IMB also notes that efforts to reduce incidents of violence are proving successful. This includes managers and officers focusing more on addressing the causes of such incidents.
Since January 2017 the number of prisoner-on-prisoner assaults has dropped by a third.
The report covers both Feltham A, for 15- to 18-year-olds, and Feltham B, for 18- to 21-year-olds. Feltham B currently holds around 150 young people, with the YOI overall having capacity for around 560 young offenders.
Figures published by parliament last month show that the average number of hours young offenders in YOIs spend in the classroom has fallen in the past two years. This comes despite a focus by the government in recent years to place education at the heart of youth custody.
Last July HM Chief Inspector of Prisons Peter Clarke warned that youth custody is so dangerous that tragedy is "inevitable".
Earlier this month it emerged that the use of custody for under-18s is to be reviewed as part of efforts to more effectively deal with young offenders in London.
The review is set out in a memorandum of understanding between the Ministry of Justice, London Councils and the Mayor's Office for Policing and Crime.
The MoJ has been contacted for comment.
