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Christchurch Tsunami Sirens Face Axe After Failed Test, Communication Breakdowns
The number of tsunami sirens along the Christchurch coast could be cut to as few as four, after an alert system review that found they cause confusion and delays during emergencies.
The city has 45 sirens between Brooklands and Taylors Mistake, but next week, Christchurch city councillors will consider a recommendation that would see them only positioned in evacuation zones with limited cell phone coverage.
The report recommended the council primarily uses emergency mobile alerts to raise the alarm, in accordance with national and international best practice, moving from a "fragile, unreliable, over-complicated and inconsistent" alerting system to one that was "straightforward and effective".
Fewer strategically positioned sirens - in the range of 4-6 - and emergency services, television, radio, website and social media messages would become the secondary alerting method.
Christchurch's tsunami sirens failed to sound during a planned test in April, because the Auckland-based contractor responsible was dealing with a car crash outside their property at the time.
The council initially blamed human error, then conceded having an emergency system so dependent on one person was unacceptable. The test was rescheduled for 13 July.
The council said a "local-source" tsunami could inundate Christchurch and Banks Peninsula evacuation zones in less than 60 minutes, so its top priority was preventing loss of life with an alert system that gave a clear message to evacuate.
The review noted sirens caused confusion and delays because:
- Warnings could be mistaken for different hazards, because of multi-purpose sirens like rural fire alarms
- Sirens could create a false sense of security, with people waiting for official warnings that might not be issued in time
- Sirens could distract from public education messages about responding to natural tsunami warning signs
- Limited information was provided, requiring the public to seek further information before evacuating
- Sirens were prone to damage or failure in an earthquake
- Sirens could be inaudible in windy conditions
- Sirens were established on ageing technology and infrastructure, and the network trigger could not be operated locally
Civil Defence and Emergency Management manager Brenden Winder said the emergency mobile alert method aimed to minimise confusion.
"In the rare event of a tsunami, our top priority is preventing loss of life," he said. "This relies on having a straightforward and effective alerting system, giving residents a clear message to evacuate.
"Sirens are no longer considered to be a suitable primary tsunami alerting method, as they cause confusion and delay communities responding effectively.
"Mobile alerts are used nationally as the main alerting method in an emergency. This sends a clear message straight to the user's phone on what action to take.
"We want people to act quickly and decisively in an emergency, and a text alert provides that direction."
Staff said another option to upgrade the existing 45 sirens and add 41 sirens for adequate coverage across a new national tsunami evacuation zone issued by the National Emergency Management Agency would come at a substantial cost to the council.
Following the magnitude 7.8 Kaikōura earthquake in 2016, a communication breakdown meant Christchurch's sirens did not sound until two hours afterwards at 2am - an hour after Civil Defence issued an alert.
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