The case relates to an 89-year-old coal worker who has been diagnosed with mixed dust pneumoconiosis.
The worker spent much of his career in the Southern coalfields in NSW, but retired in the late 1980s.
The regulator's Major Investigation Unit is investigating the case to determine whether there were breaches of the work health and safety laws and to see if there are any learnings to further strengthen the regulatory framework.
Chief compliance officer Anthony Keon said the worker was detected through health surveillance screening, which was provided to all current and retired coal workers, as part of the NSW regulatory framework.
"While the worker has been out of the industry for some 30 years, it demonstrates the need to remain vigilant, so that this insidious disease does not continue to appear into the future," Keon said.
"The NSW regulatory framework of delivering prevention, detection, enforcement and education strategies are essential to protect workers in the NSW coal industry from harm in the future.
"Controlling dust exposure, monitoring and ongoing health surveillance are vital components of prevention and detection strategies that are in place and strictly enforced."
The results of the regulator's investigation into the first reported case of dust disease in NSW since the 1970s found the worker had a spontaneous form of lung disease known as Idiopathic Pulmonary Fibrosis, not mixed dust pneumoconiosis as first diagnosed.
Further, no evidence was found that the worker was exposed to hazardous levels of atmospheric contaminant at any of his workplaces.
Therefore, based on the available information and in the absence of further medical evidence, the regulator did not consider the worker's death to be workplace related.