The Independent Police Conduct Authority is pushing for the establishment of detoxification centres or temporary shelters for heavily intoxicated people as a way to prevent deaths in police custody.
The recommendation comes after a review of 27 deaths during arrest or detention by the police between 2000 and 2010. It found 20 of those who died were affected by alcohol, drugs or both.
The authority carried out the review following several deaths of heavily intoxicated detainees. Its main aim was to identify any recurring issues or developing trends.
All except one of the 27 people who died were male, and almost half were Maori. The most common cause of death was suicide by hanging, accounting for 10 deaths.
Seven of the deaths followed the use of restraint by police during arrest, and seven were caused by the detainee's medical condition. Three had drug-related causes.
Fourteen of those who died had mental health issues, 13 were affected by alcohol at the time of their arrest, and nine were affected by drugs. Five people were only in custody for detoxification.
No formal risk evaluation had been carried out on eight people, while 15 had been assessed as being at no risk.
In four cases there was serious neglect of duty or breaches of policy by police, the review said.
The authority made 20 recommendations, headed by a call for police to work with the Ministry of Health and others towards the establishment of detoxification centres or temporary shelters.
Calls had long been made for such places where extremely intoxicated people could be medically supervised while they sobered up, the review said.
Detoxification centres or shelters had been contemplated by laws since the 1960s but had not been set up. So police had to take heavily intoxicated people into custody as a last resort.
"This means that at times custody staff have to deal with a large number of intoxicated and vulnerable detainees who are only being detained due to their level of intoxication."
Deaths in custody may be prevented if heavily intoxicated people could be taken to facilities where staff were able to provide health care and were medically trained to detect whether alcohol may be masking a more serious medical condition.
Two other recommendations at the top of the list relate to methods used by police to restrain people.
Police should ensure training reinforced dangers associated with restraining people in a prone position with their hands tied behind their back, the review said.
It should also reinforce the risks of positional asphyxia and other restraint-related medical conditions, and the appropriate tactical options for dealing with people who may be affected by those conditions.
Authority chair Judge Sir David Carruthers said deaths in custody were uncommon and did not necessarily reflect the quality of care generally provided by the police.
"While it is rare in New Zealand for people to die while in police custody, such deaths can be controversial," he said.
"There may be issues around the use of force by police during an arrest, or with the standard of care police provide to a detainee."
The review found that five of the seven people who died following the use of restraint by police had underlying medical conditions, including heart disease and a lung tumour. In four cases the underlying health problems appeared to have contributed to the deaths, while four of those who died suffered from schizophrenia.
Suicides in custody had become less common since 2004, with seven between 2000 and 2004, and three since.
But it appeared the number of suicides following custody had increased. The nine during the 10-year review period all happened from 2004 onwards, indicating some people continued to be in danger from suicidal feelings after being released, the review said.
Of the 20 people affected by alcohol, drugs or both, three died after being restrained by police, eight committed suicide, three died of drug-related causes, and six died from a medical condition.