The operator of the Hazelwood open-cut coalmine failed to maintain a permanent 50-metre wide firebreak around the perimeter of the mine, even though it was one of its own procedures for fire control, according to the Victorian WorkCover Authority.

During a visit to the mine on March 20 – many weeks after the disastrous fire ignited – WorkCover inspector Kevin Hayes observed that a permanent and continuous firebreak corridor was not in place.

After his visit, Mr Hayes issued mine operator GDF Suez with a notice to implement the 50-metre firebreak, giving it until June 23 to comply.

The inquiry heard on Wednesday that the Hazelwood mine, which burnt for 45 days from February 9 and shrouded the 14,000 residents of Morwell in smoke and burnt coal ash, was considered one of the most hazardous mines in Victoria. It also heard repeated concerns that there were gaps in the regulatory regime covering the mine.

Counsel assisting the inquiry Peter Rozen said one of the ''controls'' at the site was for a ''continuous 50-metre wide and permanently maintained firebreak corridor around the perimeter of the mine, to exist all year round''.