Anna Youngman has to wear a mask on her property due to the risk of crystalline silica from the neighbouring quarry.

A toy giraffe wearing a dust mask reminds Anna Youngman's grandchildren of the potential danger in the air outside.

Families living by an expanding Christchurch quarry have been told to wear masks on their own properties after health officials discovered the quarry's dust posed a serious long-term health risk.

For the residents of Old West Coast Rd, a rural area of Yaldhurst made up of leafy lifestyle blocks, air pollution has been a concern for several years. Dust coated their homes, gardens, cars and pets in thick layers of grime.

ALDEN WILLIAMS/FAIRFAX NZ They put a mask on a toy giraffe by the front door, to remind their grandchildren when they go outside to play.

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After years of complaints, two recent independent tests showed the dust was not just a nuisance but a serious long-term health risk. It contains crystalline silica, which can cause lung cancer and silicosis, an irreversible disease, over a long period. It confirmed the residents' worst fears about the dust they had been breathing for years.

GOOGLE EARTH The quarry is expanding closer to the houses in the top right.

One has been prescribed an inhaler after a doctor raised serious concerns about the situation. Others have picked up symptoms of bronchitis and complained of shortness of breath.

Canterbury medical officer of health Dr Alistair Humphrey recently confirmed some residents had symptoms consistent with silica exposure.

For Youngman, who moved to the area to retire, the dust issue has been all-consuming.

SUPPLIED Dust accumulating on the windows of a house.

The dust was "killing us", she said. "We're not moaning because we don't like quarries. Business is business. But when your life's on the line, you'll speak."

Both tests – one commissioned by residents, the other by Environment Canterbury (ECan) – showed the dust contained 30 per cent silica.

"We knew it was toxic – we didn't know how bad, though," Youngman said.

SUPPLIED Dust accumulating on outdoor furniture.

"You come home from a place like China and you think thank God I live in a country that's clean and green with fresh air. This is worse."

Other experts have acknowledged the seriousness of the risk, too.

Dr Kelvin Duncan, an independent microbiologist and former dean of science at the University of Canterbury, said he was alarmed when he learned about the situation and now works with the residents pro-bono.

"This quarry would not exist anywhere else in New Zealand, let alone the world, that close to a major facility like a road and residences," he said.

"I came out here for five minutes, saw what they [the quarry] were doing, and thought this was unacceptable and a serious health risk."

A UNIQUE SITUATION

Christchurch is unusual in allowing quarries to exist so to close homes.

The quarry, run by Winstone Aggregates, was given permission in 2015 to expand onto rural zoned land. It is now within 90 metres of one house and 150m from several others. One couple would have shared a boundary with the extension, so they moved.

Other quarries want to do the same. A proposed quarry in Eyrewell, which has yet to formally apply for resource consent, would be 40m from a house.

Quarries have been in high demand in recent years due to the aggregate needed for the region's rebuild.

Christchurch's city plan has no requirement for setback distances from quarries, but the Ministry for the Environment's good practice guidelines recommend a setback distance of 500m from those containing crystalline silica.

Some countries, such as India and Pakistan, insist on a 1-kilometre minimum setback.

When Annell McDonagh and her family moved to Old West Coast Rd, they were about 600m from the quarry. Now they are around 150m away.

"It's just bizarre that we have to wear dust masks on our property," she said. "People just look at you like, what the hell is going on?"

ECan has committed to a new testing regime to make sure dust does not leave the quarry's boundaries. Because the dust was now known to have a health impact, the rules became stricter.

"We have told all quarry operators that no visible dust beyond the boundary is acceptable given the potential health effects," ECan senior manager service delivery Brett Aldridge said.

There would be officers on site two or three times a day during quarry operating hours.

The city council said the consent's conditions could be reviewed if ECan's investigation found unanticipated adverse effects or if incorrect information had been supplied.

"While the council is conscious of the serious nature of the issues being raised, there does need to be a robust evidential basis for initiating a review of conditions," council consenting and compliance general manager Leonie Rae said.

The quarry's managers said they took health and safety very seriously and were working to improve its dust management procedures.

"We are committed to making further improvements and are investigating different options to help further control dust," GBC Winstone general manager Ian Jones said.

"These include, but are not limited to, changing truck movements, options to further seal internal roading, and further enclosing processing plant on-site."