Authorities say an incident in which underground miners were engulfed in a wall of flame should have been avoided.

The NSW Resources Regulator has been investigating an incident at the Chain Valley Colliery in January, in which a group of underground workers were exposed to flames when methane gas was ignited.

The regulator’s initial report has found that the gas ignition sent a wall of fire over the workers operating mining machines from an underground panel.

“Based on information provided by mine workers, the flame width was 2 metres to 2.5 metres and came back over the head of the machine for 2 metres to 2.5 metres,” the regulator said.

“Inspectors immediately attended the site and issued a notice prohibiting all workers from entering the site's underground workings.”

The regulator has issued a prohibition notice that stops the operation until such time as it is satisfied that appropriate risk controls had been implemented.

The report lists a number of safety failings.

“The mine did not have a frictional ignition management plan,” it said.

“The ventilation system in the panel was not at an acceptable standard, with vent rubbers missing and numerous vent tubes damaged.

“Fan and vent tube sizing was marginal to ensure adequate ventilation at the face to dilute accumulations of gas.

“The mine ventilation control plan did not stipulate requirements for supervisors to verify ventilation quantities at the face.”

The authority found that the incident could have been deadly.

“If ventilation quantities are insufficient to prevent a methane layer from forming, and this layer goes undetected, an incendiary spark can ignite the gas,” the regulator said.

“If the flame path reaches an accumulation of methane in the general body, it can explode with devastating consequences.”

The report specifically recommends that frictional ignition risks be assessed.

“Ventilation design should ensure that the air quality, quantity and velocity at each working place is sufficient to prevent the formation of methane layers,” it said.

“Continuous miners should have methane sensor heads positioned to maximise the likelihood of detecting gas.”

LakeCoal, the operator of the Lake Macquarie mine, says it is working on better protocols.

“The circumstances surrounding the incident are still being investigated by LakeCoal, the NSW Resources Regulator and the Construction Forestry Mining and Energy Union,” the company said.

“LakeCoal, in consultation with the NSW Resources Regulator, has implemented additional controls to address the incident.”