Engineer slams inaction over usage of dental trailers despite wheel issues

An arrow on a photo of a dental clinic trailer wheel shows where a wheel stud is close to being shorn through.
An arrow on a photo of a dental clinic trailer wheel shows where a wheel stud is close to being shorn through. Photo credit: RNZ/Supplied

Phil Pennington for RNZ

Heavy dental clinic trailers are still being towed between schools even after an investigation found their wheel studs are likely to snap off after just 3000km of use.

The investigating engineer called it "really scary".

Two have already failed, sending wheels flying across the road, just missing cars.

A Tauranga towing company is refusing to move them anymore, even on the back of a truck.

Another, in Otago, said it is taking a risk every time it tows one but that the hospitals that own the 23 trailers nationwide still want them moved.

"The risk is still there," Doug Moller of Dental and Medical in Dunedin said Thursday.

The five-tonne trailers are also still getting certificates of fitness, official records show.

Waka Kotahi has not banned them or made sure they are fixed.

This is six years after the first wheel snapped off near Cromwell, "at about 70kph on the highway with catastrophic explosion as the wheel broke off and ripped all the body skirt off".

"The wheel shot across in front of a car travelling at 100Kph and bounced into the lake", said a 2020 email from Moller.

It is one of dozens of emails newly released by Waka Kotahi to RNZ that finally reveal the risks.

Read the emails here (11 pages), and here (72 pages).

One email, from an engineer, said hospitals had been instructed last November not to tow the trailers, and only move them around on the back of a flatbed truck.

But Moller said yesterday: "We are still towing them."

They had instituted stringent checks of the wheels since 2017, but "I know I'm taking a risk even doing it".

"I'm not happy about it. We are asking for changes. Nothing has been seen to be done."

Threat to dental health

The danger to motorists is, bizarrely, twinned with a threat to children's dental health.

The emails show Lakes District Health in Rotorua saying it was having to cut down on school visits by the mobile clinics.

This was after Tauranga towing company Medworx began moving the trailers on a flatbed truck after a wheel snapped off, bounding across Cameron Rd, in 2020.

Medworx then stopped moving them altogether in January this year.

Lakes Health told NZTA a few weeks ago that Medworx had told it did not want to cause a possibly fatal accident.

"Lakes position is no different, we have been doing everything possible to minimize risk, assuming extra costs in our operation and additionally limiting the schools visited due to the size of the truck that we must use to move them now," the Lakes manager wrote.

"With this news, what happens is that we have to stop the operation of these units, which implies that our children will not be able to receive care until the problem is resolved.

"Which, of course, will have consequences for their oral health, and this is very serious for us and it should be for everyone."

A Waka Kotahi manager said two days later: "The DHB are sending me emails wanting answers and asking what we are doing about this.

"This is impacting child oral health."

But Medworx owner Terry Williams said Thursday that Waka Kotahi had done way too little, way too late.

"There's been no word back to the hospitals that they shouldn't be towed," he said.

"So we're just in this constant, backwards and forwards, about towing them when we can't."

The trailer maker, Action Manufacturing of Hamilton, told RNZ Thursday the trailers could be fixed in April.

It had been hard getting parts, but stronger wheels and studs had finally arrived, Action said.

A wheel snapped off a trailer near Cromwell in 2017, flying into Lake Dunstan.
A wheel snapped off a trailer near Cromwell in 2017, flying into Lake Dunstan. Photo credit: Supplied/RNZ

Inaction for years

Six years ago, straight after the 2017 snap-off, independent engineers identified a likely flaw with the trailers' wheel assembly, the emails show.

Checks found three other trailer wheels had cracks.

Doug Moller then emailed CI Munro, now Action Manufacturing, telling it to check all the trailers' wheel rims and nuts.

But the trailer components were shown to be genuinely compliant with road rules.

So Action and its engineer, TSV Consultants, looked elsewhere for a cause, even going as far as to suggest to Waka Kotahi in 2021 that maybe the movers were towing them badly.

Waka Kotahi got involved in Action's investigation in 2021. It said it did not know about the trailers till 2020, after Medworx alerted it to the Tauranga crash.

Last September, Te Whatu Ora warned hospitals to take care having the trailers towed - and it blamed the wheel assemblies.

'It all gets really scary'

Finally, last November, the investigation reported back, this time with the heft of NZTA behind it.

"What we are quite clearly seeing is that rim flex is inducing fatigue load into the bolts," TSV said in a 7 November email about the findings.

The bolts or studs, where they suffered 50 percent more loading, also had their durability cut "by a factor of three".

"Where it all gets really scary is .... [in] simulating cornering," it said.

"This increases the rim flex considerably and therefore fatigue into the studs, giving a very short life, as was seen by the in-service units" - which both failed around 1500km.

A month later, last December, TSV announced a solution, to fit stronger rims and studs:

"Our analysis improves the stud life from 2996kms to 409,000kms" - or by 140 times, it said, an email shows.

Moller told RNZ he has never been told about those findings.

Medworx's chief executive Terry Williams said the same - that he only got a watered-down version of them after he lodged an Official Information request with Waka Kotahi.

"It's shocking. I'm speechless," Williams said Thursday.

"These trailers are just such a risk to be on the road. They shouldn't be there."

Te Whatu Ora told RNZ last November that some trailers had already been modified to make them safe, but this was a month before TSV even reported back on its solution.

The emails show Medworx has fought since 2020 for the regulator to act.

TSV said yesterday it focused on "other possible causes" because the trailer components were up to spec.

"I feel we acted appropriately and professionally throughout this process, and Action Manufacturing was also very committed to finding the cause and solution," its director Chris Deakin said yesterday.

"I don't feel the responsibility of the fault lies with either myself or the manufacturer as we were ultimately able to prove it was a component-related issue."

Action's Chris Devoy said it was hard to pinpoint the cause especially as they got little help from the component suppliers.

"Action has since agreed without prejudice to deliver this solution at its costs even though we strongly believe the fault lies with the components, not the assembly of the vehicles, a view also supported by TSV," he said.

Of the 2017 warning from Dental and Medical about the wheels, Devoy said his supplier at the time, BNT, came to a different conclusion, which Action "in good faith" accepted.

Waka Kotahi can choose to put a "ban flag" on a trailer or vehicle but did not in this case.

"The option to apply flags to these trailers was not considered necessary as the trailers are in known ownership, and communication has been ongoing between the manufacturer and Te Whatu Ora in regard to this issue and the repair solution," it told RNZ Thursday.

"The option to flag these trailers may need to be reconsidered if there are further delays to the delivery of parts and completion of repairs."