The Prison Governors Association has called on the government to set up an independent public inquiry into the state of prisons in England and Wales.
It follows what the association describes as an "unprecedented" rise in violence and suicides in prisons.
The association's members voted unanimously for a public inquiry at the body's annual conference in Derby.
Justice Secretary Elizabeth Truss last week promised an extra £14m to recruit more prison officers.
The association, which represents 1,021 governors across the UK, said that in the 12 months to June there were 105 self-inflicted deaths - almost double the number five years ago.
Serious assaults on staff have increased by 146% in the same period and self-harm incidents increased by more than 10,000, it added.
BBC Home Affairs Correspondent Danny Shaw said the call for a public inquiry was a symbolic gesture by an organisation that didn't usually bang the drum.
It was a sign of the alarm felt among governors about safety in prisons, he said.
The association said levels of safety in prisons had declined since the introduction of "benchmarking" - a programme to drive down costs by reducing staffing and simplifying the prison regime.
It said it had a number of questions, including "why resources continued to be depleted when evidence showed that it was not working".
The purpose of requesting a public inquiry was "not about apportioning blame but understanding what went wrong," it said.
The association added: "Unless we understand what has contributed to the creation of this brutal environment that staff and prisoners are working and living in it is likely to continue.
"The PGA believes an independent public inquiry is the only way we will get to the truth."
A Ministry of Justice spokesperson said the justice secretary had been clear that safety in prisons was fundamental to the justice system working and to its reform.
"We are fully committed to addressing the significant increase in violence, self-harm and self-inflicted deaths in our prisons," they said.
The additional £14m in 10 of the most challenging prisons would increase staff levels by more than 400 prison officers and a white paper setting out plans for prison safety and reform was due to be published, they added.