Mark Isaacs was only 24, with no social work training, when the Salvation Army offered him an overseas welfare job in late September, 2012.
He was told he would fly almost immediately to work with asylum seekers on Nauru, where a panicked Gillard government had just reopened the mothballed offshore detention centre originally set up by the Howard government.
As Mr Isaacs tells it in a searing expose of nine months spent working inside the offshore camp, it seemed in those first weeks the Salvos had hired ''a collection of misfits''.
''I joined a motley crew of seniors, 18-year-olds, university students, mothers, social workers, religious experts, atheists,'' he writes in a book to be released on Monday, titled The Undesirables.
''Many of the staff, me included, were underqualified. Some arrived in Nauru not knowing what an asylum seeker was,'' he said. ''We were thrown, without guidance, into a camp of angry, depressed men.''
In a response on Friday, the Salvation Army, which has not yet seen the book, said Mr Isaacs was hired to carry out ''unskilled duties'' which ''do not require individuals to have particular skills or experience''.
It added: ''In the early days of the Salvation Army's work on Nauru and Manus Island … the Department of Immigration and Border Protection required an incredibly rapid start-up, which meant that a formal induction was not developed prior to [the Army] getting its first people on the ground.''
Mr Isaacs said the atmosphere at the detention centre, which was under the overall control of the Department of Immigration, was oppressive. Workers felt that they were under surveillance from security staff, and that ''often if you assisted an asylum seeker you were made to feel like you were on the 'wrong' side''.
The camp, known on Nauru as ''Topside'', threw together hundreds of internees from Sri Lanka, Afghanistan, Iraq, Iran, Pakistan and elsewhere in the Middle East.
In the early weeks, before accommodation blocks were built, the men lived in 35-year-old army tents. And Mr Isaacs said the tents had once been soaked in kerosene for waterproofing purposes, making them highly flammable.
With many of the men suspected of having cigarette lighters in their possession, he said, ''we were sitting on an army-supplied bomb''.
He said staff were rocked almost daily by self-harm or suicide attempts by the asylum seekers.
Riots occurred on Nauru soon after Mr Isaacs left in June last year.
The Salvation Army's $74 million federal government contract for services on Manus and Nauru expired in February.