Shell E&P Ireland has said today that it is investigating the circumstances around the activation of a safety alarm in the Corrib tunnel at Aughoose in north Mayo last Monday.
The company halted tunneling work and evacuated workers as a precautionary measure when the alarm sounded at 5.45 pm.
Fire services were called to the Aughoose site.
After a full inspection of the tunnel, work resumed at 11 am on Tuesday morning.
A company spokesperson said an internal investigation is now underway as to the cause of the alarm sounding.