Failure-prone safety netting allowed a tramper to fall from the height of three storeys into a West Coast river, sparking nationwide checks and upgrades of almost 150 swingbridges in 2020.
The Department of Conservation kept the lid on this until RNZ's inquiries under the Official Information Act.
The department's own files show the plastic netting was prone to wear and tear and commonly came loose, leaving a gap someone could fall through.
"Nylon mesh wears through at these sites, and maybe not the best type to use, especially where we are relying on it to prevent fall," a report said.
But it was not begun to be replaced on bridges until after the accident in May 2020.
The internal reports, not released until now, describe a tramper falling through such a gap, then hanging from his packstraps 16m above the Whitcombe River near Hokitika.
He survived the drop from the Collier Gorge swingbridge into the river near rocks, making it to the bank with only scrapes, bruises and a cut hand.
A Department of Conservation ranger had checked the plastic safety netting on the narrow swingbridge just four months before.
An initial report behind closed doors at DoC said the bridge design, maintenance and inspection regime were "good".
However, an investigation straight after concluded:
"Polyethylene netting has been widely used as barrier-infill netting, but problems with it wearing and detaching are common across DoC's bridging network."
It "has been used because it is light, easy to handle, and doesn't corrode, but it hasn't proved reliable enough as a fall prevention measure".
The reports said a party of five experienced trampers from Christchurch Tramping Club were on their way to Frew Hut on a fine day on 30 May.
The last in line "got about halfway across the bridge and slipped ... and was left hanging by his tramping pack caught on the swing bridge".
One friend scrambled out to him but could not pull him up. The others feared putting any more weight on the one-person-wide bridge.
The man eventually unclipped his waistbelt and slid out of the trapped pack, "then dropped approx. 16.5m into a deep river pool, narrowly avoiding rocks".
Swept downstream, with the river at low flow, he managed to get out.
The trampers continued and alerted DoC on 2 June when they got out.
A repair crew got there within 48 hours and found "a 5m length of netting had detached" near the middle, though it had been okay four months prior.
A 13-page June 2020 investigation, only now made public, said the netting on the bridge had been fixed "multiple times" before.
"Problems with the polyethylene barrier netting on this bridge had been recurring and are common across DoC's bridging infrastructure," it said.
"Regardless of how polyethylene barrier-infill netting is fixed, problems with the netting detaching are common."
The 2020 accident also prompted the department to set up a formal system to record accidents.
"DoC doesn't record visitor accidents in a centralised database," said investigators.
"There is no ability to analyse visitor accidents for frequency and common cause, or determine if risk reduction measures are effective."
On the swingbridges, rangers had begun using ring staples in place of bag ties to tie the netting on, but the staples seemed to wear through the netting, reports said.
The netting at Colliers gave way in between inspections, but other trampers - if they saw it had failed - did not tell DoC, the report said.
The bridge was as stable and no more slippery than any other bridge of this type, the repair crew reported.
A separate short incident report said "perhaps a formal safety alert" should be issued, but it was not.
It also at one point said: "Design of bridge is engineered, and 'safe'."
Some netting replaced
After the internal investigations, DoC ordered the plastic netting be progressively swapped out for steel chainlink at 147 swingbridges of the Forest Service (NZFS) type, and at other types of bridge, too.
It has given itself five years to do this, as "problems recur or when deterioration is widespread".
Work to check the netting has almost been completed, DoC told RNZ.
It had been replaced with steel netting "where required". It did not say how many bridges had needed it.
"Each region ... built a plan around prioritising netting replacement and installation," said director of heritage and visitors Catherine Wilson.
Two bridges still needed work and were either temporarily closed or "low risk", it said.
Of the 147 NZFS bridges, 31 had no safety netting at all before this; 116 had polyethylene.
There was no specific policy saying they had to have safety netting.
The newer model of swingbridge has more horizontal cables to prevent a fall, a solid timber anti-slip deck and was "generally considered more user-friendly".
The NZFS have slippery chain-link decks that trampers walk on.
But putting non-slip decks on all 147 NZFS bridges was "not considered practical or economic".
DoC also ordered a change to how the safety netting was held on - to start using steel wire loop - as what they had been using tended to wear through the plastic netting.
The reports said trampers should be reminded to stash any walking poles in their packs on bridges, as these could be a distraction. The man who fell was holding a pair of poles in one hand.
Asked by RNZ why external workplace inspectors had not been involved, DoC said, "WorkSafe has not been notified as there have been no incidents involving staff on these bridges."
The exposure of staff to risks is also a health and safety matter.
In 2015, four tourists fell 8m into a river when a cable snapped on a bridge at Lake Waikaremoana. It was captured on video:
DoC then checked 111 bridges that used such cable.
The Colliers Gorge bridge had no netting at all up till 2014, when trampers crossing in high winds got a scare, prompting the upgrade.
The only other account of a fall from a swingbridge - a fatal one - was on the St James walkway near Hanmer in the 1970s, the DoC reports said.
This prompted the Forest Service to put in netting on some, but not all, its swingbridges.
The Colliers Gorge bridge was built in 2004 after a flood took out a 1982 bridge, and upgraded in 2016. Its most recent load test was in 2016.
It had had maintenance done 11 months before the 2020 fall, when it needed its netting refixed, and inspections were scheduled for at least every two years.
RNZ
