Fighting or fleeing police could be lethal but the risks of being shot by a stun gun are extremely low, an expert has told a conference in Wellington.
The findings of a decade of Taser trials were outlined to police at an Australasian stun gun conference today.
The devices have proved controversial since they were rolled out nationally in 2010, despite no reports of significant injuries in the more than 200 times they have been used here.
Their use has also raised questions in Australia after Brazilian student Roberto Laudisio Curti, 21, died in March after police shot him with a stun gun when he was suspected of shoplifting.
University of Minnesota emergency medicine researcher Jeffrey Ho, who is also Taser International's medical director, told the conference today that the risk of a stun gun causing a cardiac arrest was extremely low.
His peer-reviewed research, funded by Taser, involved studying the physiological effects on about 800 people who were shocked for between five and 15 seconds.
The test subjects, some of whom had pre-existing heart conditions, underwent blood tests, heart monitoring, breath analysis and real-time cardiac ultrasounds.
They suffered increased heart and breathing rates, which was consistent with anxiety or pain, but their hearts and lungs continued to work.
Dr Ho said the findings showed the cardiac risks were "extremely low", although it would be foolish to say the risk was zero.
He said it was important to consider the context in which Tasers were used, such as fighting or fleeing police, which were high-risk activities.
Tasers were just one of a number of risk factors which could lead to deaths when someone was being arrested - including deliriousness, dehydration, intoxication and drug use.
"We try to think of different ways that you could possibly kill somebody when somebody is resisting arrest, independent of using a Taser device," Dr Ho said.
One hypothesis was that people fighting or fleeing police suffered from exhaustion and a massive spike in stress hormones, increasing their risk of a cardiac arrest.
To test the hypothesis, Dr Ho's team subjected people to several different scenarios including being shot by a stun gun, fleeing a police dog, running and scaling a wall, and being pepper-sprayed.
They found the worst thing was to allow offenders to continue to fight or run.
"These can be life-threatening."
Dr Ho said resisting arrest was the most dangerous of all.
Half the volunteers who got into an intense 45-second simulated struggle either vomited or passed out immediately.
"We couldn't figure out what was going on - we almost stopped the test because I thought we were going to kill somebody."
Dr Ho said allowing offenders to continue to run or struggle just made the situation worse.
"I am not advocating holding somebody down for 120 seconds with a Taser device or anything like that.
"I am advocating for smart use, where you've got somebody who is going to fight you for the next 10 or 15 minutes, you need to put them down right now and get them medical help."
Police national operations manager Superintendent Barry Taylor said the conference was a chance to discuss emerging trends and issues relating to the use of the Taser.
The stun guns had proved extremely successful in de-escalating dangerous and potentially life-threatening situations, but Mr Taylor added that improving understanding of their use was critical to their continued safety.
The conference comes after police announced they would introduce a double-shot Taser that fires two high-powered charges without officers having to reload.
The older model failed to work on armed suspects in several incidents in the past few years.
The three-day conference will hear from technical, medical, policy and academic experts, with police representatives from Australia and Singapore among those attending.
TASERS IN NZ:
* Rolled out nationally in March 2010
* 908 in use
* 4700 police staff trained to use them
* Discharged 212 times
* No life-threatening injuries