The former NSW chief scientist wants a meeting with NSW Health to "talk this out", after expressing some frustration with advice there are no safe levels of particulate matter in humans, as the commission considers a proposal to extend Rix's Creek coal mine for 21 years until 2040.

"They always say, every time I've been involved in a case, that there's no safe level of particulate matter, and yet... as we know, even in the Hunter, it's not Beijing," Professor O'Kane said on July 9 while the commission questioned Department of Planning director of resources assessments Howard Reed.

Hunter New England Local Health District's population health unit raised concerns the mine's proximity to Singleton and another 21 years of open cut operations would add to the cumulative impacts of mining in the area and "the resultant health risks to a community".

The Bloomfield mine applied to operate for another 21 years after its previous approval expired in June.

Mr Reed revealed some employees within government agencies are more likely to give "strong and straightforward" advice to the Department of Planning on major projects than others who "perhaps are a bit more accepting of what happens in other parts of government".

Some health employees might place "great significance" on an "epidemiological study that would suggest there is no threshold limit for human health impacts from particulate matter", and they "will not be entirely satisfied whether we address their concerns or not", Mr Reed said.

The department recommended three new air quality conditions but supported an "adaptive approach to air quality management" which would change over the life of the mine.

Mr Reed conceded the department's use of the phrase "best practice for the management of coal mining" to describe proposed conditions at Rix's Creek was "not as transparent as it could be".

The conditions were only "best practice" because the department's assessment of mine proposals had improved over the past 10 years so "the current practice is best practice", Mr Reed told the commission.

He said there was no trigger to force mine closure plans in the event of a Global Financial Crisis-type threat to multiple Hunter coal mines at the same time, after Professor O'Kane questioned if there was "resilience to deal with uncertainty", including responses to climate change.

Lock the Gate spokesperson Georgia Woods said the Independent Planning Commission deserved credit for posting a transcript of its meeting with the Department of Planning on its website, but some of the responses were extremely concerning.

"We're grateful to NSW Health for continuing to raise the issue of the cumulative impacts of coal mining in the Upper Hunter," Ms Woods.

But Mr Reed's evidence about different responses from individuals within different agencies showed there were public servants who "go in to bat for the health of people living in the Hunter and there are others who get with the program", Ms Woods said.

The transcript showed "the department conceded there might be a whole bunch of mines close suddenly because of the economic uncertainties of coal" which was "an admission the government doesn't have its hands on the wheel in directing the mining industry".

While the Hunter's air quality issues are not as bad as Beijing's, "we have a right to expect the IPC and the Department of Planning to have regard to Australian standards when they consider these issues", Ms Woods said.

The commission will hold a public hearing at Singleton on July 29 before making a final determination on the Rix's Creek mine continuation.