Five people were checked in with symptoms of exposure to hazardous gases and a further nine people working in the vicinity were taken to hospital as a precaution.

They have now been released as a full investigation into the source of hazardous gas continues.

A Department of Employment, Economic Development and Innovation spokesman reportedly said the mine was already operating under a directive issued by the Queensland Mines Inspectorate on February 24 in relation to gas fume issues at the mine.

“The directive requires the mine operator to review its site safety and health management system in respect to the development and implementation of a plan to further mitigate risk of gas-related incidents and heating of exposed coal seams,” the spokesperson is reported as saying in the Daily Mercury.

Thiess Australian mining executive general manager Michael Wright said Thiess was continuing to work closely with employees to monitor and mitigate hazardous gases onsite by increasing awareness of the issue.

“The safety of our people is our number one focus [and] we are working with the mines inspector and leading independent experts to get to the bottom of this issue,” Wright said.

Thiess is continuing to work with the government agency Safety in Mines Testing and Research Station and other technical experts to carry out additional testing.

“Thiess has also engaged an independent occupational physician to assist with any medical queries our team has,” Wright said.

“We will continue to communicate monitoring results and findings of specialists and technical experts including timeframes for the implementation of recommendations to our employees.”

Hazardous gases can be generated when coal and some other materials are exposed to oxygen.

Thiess said it continually planned mining activities and implemented identification, monitoring and response procedures to mitigate any potential impacts of mining in this type of environment.

Collinsville mine is part of the NCA project, a mining, processing and exporting partnership that delivers export quality coal to international customers.

The NCA project includes the Newlands open cut operation and underground longwall operation, the Collinsville open cut mine and the Abbot Point coal terminal.

The Collinsville mine produces a variety of coking and steaming coal products for both overseas and domestic markets.

The project is a joint venture between Xstrata Coal (55%), Itochu Coal Resources (35%) and Sumitomo (10%).

The current workforce includes 350 Thiess employees and approximately 160 subcontractors.

Mine planning and operation is complex, requiring the blending of eight coal seams to comply with the client’s product coal specifications.

Thiess’ work scope includes the operation and maintenance of the existing mine infrastructure, including a 550 tonnes per hour coal handling preparation plant, administration and workshop buildings.

The mining area covers approximately 2750 hectares and includes eight operational pits with 628km of coal haul roads to maintain.

The mine produces 4.5 million tonnes per annum of product coal, made up of coking and thermal coal.

The overburden removal of 35 million bank cubic metres per annum is performed by a combination of drilling, cast blasting, dragline operations, bulk dozing push and truck/excavator removal.