The Senate inquiry into conditions at the Nauru immigration detention facility revealed that physical abuse, including sexual abuse, poor sanitation and unhygienic living conditions characterise this Australian government-sponsored centre.

What is clear – despite protests from the Abbott government, the operator Transfield, and the Nauruan government – is that detainees in the centre are likely to be exposed to serious mental and physical harm because of the way the centre is run, and the primitive conditions of the centre itself.

So who is legally responsible for the physical and mental harm caused to detainees? Where does the buck stop? asks Greg Barns, a barrister and a spokesman for the Australian Lawyers Alliance, in a comment piece in The Guardian newspaper this week.

The answer to that line of questioning is clear – the Commonwealth government.

It owes a duty of care to detainees to ensure they are well cared for mentally and physically. It has a legal obligation to ensure that the centre, as a workplace, is safe for employees, contractors and detainees.

Case law in Australia, including high court decisions, makes it clear that when a person is in a position of vulnerability the duty of care owed by the party that placed them in that position is non-delegable.

Detainees in immigration detention centres are inherently vulnerable. They cannot come and go as they please. It is known by the Commonwealth government, because of expert reports over many years, that detention can make detainees vulnerable to mental illness.

The Commonwealth cannot out source or delegate that duty of care to a contractor.

It does not matter that the Commonwealth’s facility is outside of Australia. So long as the Commonwealth is the entity that detains individuals pursuant to a particular Commonwealth law then it remains responsible for their wellbeing.

The medical care provided on Nauru is also relevant to the question of the Commonwealth’s liability.

It is no excuse that because the detention centre is on a small, poverty-stricken island in the Pacific, health care must be compromised. The law here is clear.

As Justice Paul Finn of the federal court said in 2005, of a case involving the remote Baxter detention centre in South Australia: “Having made its choice of location, the Commonwealth, not the detainees, should bear the consequences of it insofar as that choice has affected or compromised the medical services that could be made available to meet the known needs of detainees.”

The Commonwealth is also liable under Commonwealth occupational health and safety legislation for detainees in detention centres.

The Work Health and Safety Act, introduced in 2012, makes it clear that the Commonwealth as the entity that runs the Nauru detention centre “must ensure, so far as is reasonably practicable, that the health and safety of other persons is not put at risk from work carried out as part of the conduct of” the detention centre.

Non-compliance with its obligations under this Act is a criminal offence carrying fines up to $3 million and jail for up to five years.

Comcare is the Commonwealth government agency responsible for ensuring that the detention facilities on Nauru comply with workplace safety laws.

Max Costello, a former senior workplace safety prosecutor in Victoria, has pointed out the Commonwealth is bound by workplace safety laws even though it has out sourced the day-to-day running of the detention centre of Nauru and that it is situated in a foreign jurisdiction.

“By means of sections 10 and 12F(3) the Work Health and Safety Act’s criminal offence provisions apply to the Commonwealth, both within Australia and overseas – while sections 14 and 272 close off any attempt by the Commonwealth to avoid its duties by ‘offshoring’ them to Nauru and PNG, or ‘outsourcing’ them to contractors,” Costello wrote on the legal website Justinian.

The Senate’s Nauru inquiry needs to focus on issues of legal liability. Unlike the victims of Catholic Church abuse – who have been met with legal complexities that make suing the Church difficult – in the case of asylum seekers on Nauru there is no such obstacle.

Any asylum seeker who suffers mental and, or, physical harm on Nauru is likely to have a decent chance of a successful claim against the Commonwealth for breach of duty of care.

The risk to taxpayers of having to pay out hundreds of millions of dollars in successful claims needs to be examined by the current Senate committee.

It must also ask Comcare why it is not in Nauru collecting evidence on what, according to first hand reports, appear to be clear breaches of workplace standards by the Commonwealth.

There is a legal price to pay for bipartisan policies of cruelty to asylum seekers and the Australian public needs to be made aware of just how substantial that price is and will be in years to come.