The new organisation replacing DHBs is urging authorities to think carefully before closing Hutt Hospital's main block.
Photo: RNZ / Dom Thomas
Hutt District Health Board (DHB) has released advice it has received on the earthquake-prone building that houses wards, maternity and vital radiology services.
Reviews confirm the stairs, floors, columns and beams are the weakest points.
All four elements rate just 15 percent of New Building Standard (NBS), according to documents released today.
The DHB has released the engineering advice it got over the last few weeks on its earthquake-prone medical block.
If a building has a low NBS percentage rating, it doesn't mean it will not be damaged but it does mean people are more likely to be harmed in a significant quake.
Engineers have found the seven-storey block's frames do not have enough strength to resist a one-in-1000-year earthquake - called a "design-level earthquake".
Various reviews say the columns and beams on the third and fourth floor, and at the roof are most prone to fail.
However, Health New Zealand said the engineers "do not necessarily expect a life safety hazard to arise in more frequent moderate earthquakes".
Health NZ, which takes over from DHBs next month, said in advice last month the block was not considered dangerous or at imminent risk of collapse, and the DHB should not make any hasty decisions about closing it - that would demand an evaluation of the impact on services, it said.
The risk to occupants over the next one to two years was considered low.
"From an engineering risk perspective, there is considered to be no reason why this building should not continue to be used in the short-term while options to provide for the delivery of medical services in alternative locations are developed," Health New Zealand's engineer said.
Maternity and vital radiology services housed in the block mean it should be considered an Importance Level 4 (IL4) building, which ramps up the seismic loading by 40 percent, review engineers Silverster Clark said.
At IL4, it would not be worth fixing, lead engineers Aurecon said last month, when it detailed an elaborate series of strengthening options to the DHB.
It "would be excessive in terms of cost" at IL4 level, it said.
Fixing it would be very difficult, and take two to three years even if it was fully emptied out, while a staged remediation would take much longer again, Aurecon said.
The Health Ministry has been looking for months at upgrading any building with radiology to IL4 status.
The DHB knew the ministry was doing this, when it presented a 10-year-old seismic assessment last year to persuade Hutt City Council the block was not earthquake-prone (under 34 percent NBS). The council accepted the outdated DSA.
That 2011 DSA found similar weaknesses, and identified undesirable ways the tower block might "collapse", but rated the building 43 percent NBS.
The various assessments and reviews now released note the stairs could collapse and heavy concrete panels on the outside fall on the people in a significant quake.
"Failure of these items potentially poses life safety risk due to the items themselves falling," Silvester Clark said.
The firm has still to complete a full review of Aurecon's detailed seismic assessment (DSA).
As well as weak points in the superstructure, the foundations are poor too, rated just 20 percent NBS on ground prone to liquefaction.
"Under liquefaction, the lateral strength of the piles was adversely affected which contributes to the poor percentage NBS rating of the foundation," Aurecon told the DHB last month.
"This failure is likely to result in a softening of the building response, which may reduce the impact of the earthquake of the superstructure of the building but would also result in permanent lateral and vertical displacement of the building."
The floor was designed in such a way that in itself it is strong, however, the engineers say the floors at roof level, first floor and ground floor would move in a way that might jeopardise the vertical parts of the structure.
Elsewhere, they state, "in addition, Heretaunga Block has a flat slab floor slab system that was observed to perform poorly in past earthquakes".
The target NBS of 100 percent equates to a one in a million chance of a fatality in a design-level quake; the Heretaunga at 15 percent has a one in 40,000 chance, on 25 times greater risk.
On 2 June, the health board agreed to ask Health NZ and the Ministry of Health to commit to rebuilding on the hospital site "a fit for purpose building that meets the current and future healthcare needs of the community in the Hutt Valley".
As for getting out of the tower block, the DHB wants that to happen soon.
"The option to stay in the Heretaunga building for any longer than is required to vacate practicably is not appropriate or viable," its minutes say.
It should be cleared out "to the maximum extent practicable and as soon as reasonably practicable".
A plan to implement this is due by 22 June, as well as planning for engineers to identify and implement temporary steps to minimise risks to people's lives in the meantime.