Suncor has confirmed that an “operational issue” that occurred on Sunday at Syncrude’s upgrading area at Mildred Lake Site north of Fort McMurray did not result in an H2S gas leak.

Hydrogen sulfide (H2S) is an extremely flammable and toxic gas that is one of the leading causes of workplace gas inhalation deaths according to the Occupational Safety and Health Administration.

Suncor spokesperson Leithan Slade confirmed on Monday that there has not been any release of H2S gas.

“Syncrude is responding to an operational issue in the upgrading area at our Mildred Lake site north of Fort McMurray. Our focus is on the safety of our people and resolving this issue as quickly and safely as possible. There have been no safety incidents and no release has occurred. As a precautionary measure the immediate area was evacuated yesterday and today the number of people working on that site has been limited to those critical to operations. We continue to work with and update the appropriate Regulators as well as nearby communities.”

Slade did not confirm the nature of the “operational issue,” but did confirm that staff had been limited to critical persons on Sunday and that the number of people on-site would continue to be reduced on Monday as a precautionary measure.