Department of Planning representatives inspected a number of Upper Hunter mines after complaints of blasting and operations after 2pm on August 8, before coarse particle PM10 dust levels were recorded in the hazardous range of up to 275 microns per cubic metre by 4pm. A good air quality level is between 17 and 35 microns per cubic metre and hazardous is greater than 100.

Wild winds pushed Camberwell dust levels from 46.6 microns per cubic metre at 2pm on August 8 to an extraordinary 461.9 at 3pm. The 24-hour Camberwell average was hazardous at 117.8 microns per cubic metre. Doctors have previously strongly criticised the Hunter's air quality regime as "trivial and ineffective".

The department confirmed it was investigating complaints of blasting contrary to consent conditions at Mount Arthur and Bengalla mines near Muswellbrook, poor dust management during the extreme weather and spontaneous combustion at Mount Arthur.

The complaints included photos showing heavy dust associated with truck movements at the top of overburden emplacements after 3pm on August 8 when winds from the south west directed dust towards the town of Muswellbrook.

In a statement in response to questions Muswellbrook Shire Council said it received a "steady flow of complaints from the early afternoon about trucks continuing to dump overburden in very blustery conditions in alleged breach of its duty to do all things reasonably practicable to minimise dust over the community".

"The council forwarded information to both the Department of Planning's compliance unit and the Environment Protection Authority."

The council noted Mount Pleasant coal mine north of the town suspended operations from 3pm.

A Mount Arthur spokesperson said the mine took action on August 8 to mitigate the impact of the high winds.

"We did stop dumping at heights at around 2pm, and there was a temporary suspension in several parts of the operation including the ROM, which ceased operating for an hour," the spokesperson said.

"The re-start was slow and staged over a number of hours, in response to the wind conditions. We also decided not to proceed with blasting activities as scheduled due to the conditions."

Bengalla general manager Cam Halfpenny said the mine modified operations from mid-morning on August 8 because of the weather conditions, and department inspectors were on site later that day when the mine was not operating because of high winds.

"Bengalla is a long term member of the local community with most of our employees living locally. We always seek to minimise our impact on the community through operating in accordance with our environmental consent conditions," Mr Halfpenny said.

A spokesperson for Glencore's Mangoola mine near Muswellbrook said steps were taken to minimise dust levels during extreme winds on Thursday, Friday and Saturday including reducing dust generating activities and parking up equipment as necessary.

"As a result of Mangoola's proactive approach, our operation was below all compliance limits for dust on Thursday, August 8, despite the challenging conditions," the spokesperson said.

The Department of Planning declined to comment on complaints "as all investigations are ongoing", but confirmed a complaint against Mount Arthur about spontaneous combustion on part of the mine site.

Minutes of the May community consultative committee meeting show questions about "heating" of coal in a section of the mine and whether "spontaneous combustion was likely to be an issue for the community".

The spontaneous combustion of coal is known to produce toxic gases including carbon monoxide and sulphur dioxide which can cause breathing difficulties, particularly for asthmatics, the young and elderly.

The minutes show a mine employee confirmed "heating" of coal within an area of tailing emplacement which had delayed rehabilitation.

"The area does not have smoke issuing and does not have visible, active spontaneous combustion but the heating has been identified during thermal surveys and requires further work prior to rehabilitation," the mine employee told the committee meeting.

Under its environmental licence the mine is required to report spontaneous combustion and address "heating" incidents by removing affected material before spontaneous combustion can occur.

Mount Arthur did not respond to questions about spontaneous combustion.

Bulga resident and community representative on the Upper Hunter air quality monitoring network, John Krey, said the extreme dust readings "shows the result of the Department of Planning's approval for open cut mines over recent years, without considering the cumulative effect and the effect on residents' health".

"The EPA has the almost impossible task of trying to keep the mining industry within reasonable boundaries when the department continues to recommend and approve more open cut mines. The Camberwell PM10 figure of 461 mid-afternoon indicates how serious the problems are."

Mr Krey said the NSW Government's own air quality monitoring showed "a trend of the last three to four years for an increase in dust each year".

"The mining industry and the government cannot keep blaming the drought for these dust storms in the Hunter Valley," he said.

Mr Krey and Bulga resident Alan Leslie criticised the department and EPA for being based away from the Upper Hunter, leaving residents and Muswellbrook Council to raise the alarm.

"The mines and the government will say dust levels are high because of the high winds, and that is true, but if there weren't so many unbelievably high, uncovered mountains of dusty rubble lying around because of open cut mines, the dust problem would be nothing like as bad as it is," Mr Leslie said.

"The dust has to be there to get blown around."

Environmental Justice Australia researcher James Whelan said air pollution was out of control in the Hunter Valley because there was no safe level of exposure to the particle pollution from the region's coal mines and coal-fired power stations.

"The NSW government knows what it needs to do. It needs to set strict pollution controls when it assesses and licences polluters, implement a strong 'polluter pays' scheme that penalises polluters for every tonne of pollution they create and shut polluters down when they cause excessive pollution like last week," Dr Whelan said.

"The standard $15,000 penalty infringement notice that the EPA serves coal mining companies are a slap on the wrist that will never protect community health."

A BHP spokesperson said Mount Arthur did not "currently have a live spontaneous combustion incident" at the mine site.

"We are required to notify the Resources Regulator when spontaneous combustion occurs. We recently advised the regulator of a small spontaneous combustion event at the northern end of our lease, which was extinguished when it occurred some months ago. It does not present any ongoing threat, and has no impact off-site," the spokesperson said.

"This occurrence is being actively managed, and we will complete remediation with removal of the affected area in the coming weeks. We also report such occurrences to the NSW EPA every six months."

An EPA spokesperson said its records did not contain specific reference to heating as described in the Mount Arthur minutes, but "the reports the EPA receives from Mt Arthur do provide details of the location of spontaneous combustion across the site".