A supplier of air-raid type tsunami sirens is challenging the city council to literally hear them out in a siren sound off.

City enginer Howard Severinsen told councillors an offer to supply air-raid type sirens to Tauranga was declined because it ‘lacked credibility'.

'As the design engineers and suppliers that offered sirens to TCC, we are left with little option other than to respond to the article, especially given that the council have never told us they had any issues with our credibility, nor hinted at it,” says Gary Lewis from siren manufacturer Tactical Tooling Ltd.

'Nor have they tested our sirens despite our repeated offers to bring sirens to Tauranga and test them, at no cost to Council. We would have thought it was an offer a prospective buyer of sirens couldn't refuse, and that offer still stands indefinitely.

'If we can execute a test demonstration of our machines at Papamoa, there will be no further dispute about reach and sound character because these machines are, without exaggeration, quite spectacular. We challenge council to take up this offer at no cost to ratepayers.”

The story reported councillor Bill Grainger's ongoing opposition to the electronic sirens that have been recommended by council staff. He was commenting after a test of the same sirens in Christchurch was criticised because they were unheard by residents.

Bill wants the howlers because they have a sound that will go through walls and wake people up.

Gary Lewis says Tauranga will need only 6-8 sirens because they can be heard up to 32 km in good conditions.

'Why not just put it to the test?”

Because the boosted sirens are very loud with four times the reach of a conventional rotary air raid siren, they are intended to be 'blip” started which makes them emit a loud grunting sound to warn nearby people to cover their ears and move away when they are about to start up.

'There is no comparison between sinusoidal hooters (electronic sirens), and the Carter type air raid siren because the electronic hooters produce waves that are continuous tones, whereas the boosted Carter siren produces individual shock waves at a rate of up to 550 shocks per second,” says Gary.

'Each shock is a sonic boom caused by instantaneous air reversal exceeding velocity of sound. Electronic hooters are incapable of producing that kind of wave shape.

'A good analogy is the small but famous Vancouver 9 oclock gun which has been firing a single shot every day for more than a hundred years. The shock wave from it is heard 70km away under ideal conditions, and regularly heard at 50km.”

A recent installation of tsunami sirens at Moera in Lower Hutt city, took less than 4 hours, including re-programming the SCADA radio control system to cycle the siren against hearing damage to passers-by, says Gary.

Tauranga already has identical SCADA control terminals to those used universally by councils, so the 'design and build” referred to by Howard Severinsen is actually little more than digging holes for poles.

Councils have more than enough resources to carry out simple installation work, plus access to local contractors, says Gary.

As for the resource consent objection, emergency sirens are specifically exempted from local body bylaws and regulations, and there is an implied exemption from the RMA.

Tactical Tooling recommends powering its sirens from a propane gas generator, because unlike diesel and petrol, propane has an indefinite shelf life in storage, and the use of a generator means the siren is not dependent on mains electricity.

The article also prompted comment from Wilfried Roding, CEO at Meerkat Alert Systems Limited. Meerkat alarms are the one that will probably be used.

He says the Tauranga tsunami system based on multiple strategically located short-range directional electronic outdoor sirens, is intended to target only the vulnerable communities within the innundation zones, to minimise unnecessarily alarming persons not at risk.

This type of system has been successfully operating in Auckland and other regions in NZ since 2007.

He says claims for the loudness of the air raid type sirens is a little far fetched.

A 4kW double-ended Carter type air-raid siren will have a rated output of about 129dBA @ 1m, whereas the 200W Meerkat electronic horns proposed for Tauranga are each rated at about 134dBA @ 1m.

And, electronic sirens can copy any sound including speech and the wail of a WW-ll siren, if that were to be required.

The ability to generate different signals in succession allows for multiple messages such as, for example, ‘Alert', ‘Evacuate' and ‘All Clear' to be broadcast.

The determining factor is: ‘How big' is practical and permissible for a siren to be installed within legislative constraints and to avoid exposure to hearing damage, says Wilfried.

A house will typically attenuate sound by 20-50dBA depending on construction , open windows, ambient noise, siren sound frequency, irrespective of whether the source is a mechanical or an electronic siren.

'Outdoor sirens will therefore warn some, but not all people indoors, and are consequently and essentially that – outdoor warning sirens,” says Wilfried. 'It is important to understand that sirens, although a primary alerting tool, operate hand in hand with other media and alerting systems, as part of a multi-tiered and integrated emergency notification process.”

The mission critical nature of a tsunami siren system demands that it is continuously and automatically monitored and always guaranteed to function, including during power outages. This is much more easily achieved and less costly with electronic sirens, says Wilfried.

'If we believed that if mechanical sirens were a better solution, we would be supplying these instead. It only takes a few minutes in Google to verify that mechanical siren systems are progressively being superseded by electronic versions, for good reason.”