On April 16, the site was closed while the 25m-high brick chimney stack was assessed after structural changes were noticed during a routine visual inspection.
Dunedin City Council property services group manager Anna Nilsen said drone footage taken earlier this month confirmed the changes and council staff instructed the Gasworks Museum to close the facility while an engineer’s assessment was undertaken.
"The advice we have since received is that there is an imminent risk to public safety," Ms Nilsen said.
Following specialist advice on a range of options, council staff and Dunedin Gasworks Museum Trust members agreed the best way forward was to deconstruct the chimney above the visual crack line, she said.
"Temporarily securing the structure may reduce the risk of collapse, but deconstruction would still be required at some point in the future."
Naylor Love had been contracted to carry out the urgent deconstruction work which — "all going well" — was expected to begin next week.
A safety barrier had been erected to exclude access to the area immediately around the chimney and deconstruction was expected to take a "number of weeks", Ms Nilsen said.
The site is a category 1 historic place owned by the council, which assists the trust with maintenance and refurbishment.
"We know this is not the outcome the trust or heritage lovers want, but public safety needs to come first," she said.
However, reconstruction would also depend on funding and feasibility assessments.
Until recently, cracks in the 118-year-old chimney structure were not considered a major issue and it was not at risk of immediate failure, despite some age-related maintenance, Ms Nilsen said.
Earlier this month, the council said the 6.8-magnitude earthquake off Southland’s coast in March caused new cracks and aggravated the existing ones.
Neighbouring Woolworths Dunedin South was issued with an Affected Building Notice on April 17, requiring it to manage any potential risks from a collapse in one corner of its building.
The work had been completed and the notice amended, allowing unrestricted access to all parts of the supermarket again.
