The leak occurred in connection with valve testing on the drilling, production and accommodation facility HMP1 on the Heimdal field.
It has not yet been determined how much gas leaked out, but the gas leak was substantial and resulted in a serious situation on the facility.
There were 98 people on the facility when the leak was discovered. No one was injured in the incident.
The PSA has decided to conduct an investigation due to, among other factors, the significant potential of the incident.
The PSA investigation team will be travelling to the Heimdal field on Wednesday this week.
The purpose of the investigation is to ascertain the course of events and identify trigger factors and underlying causes. The investigation will result in a report which will be published at www.ptil.no.
The Heimdal gas field is located in the central part of the North Sea and has been developed with an integrated drilling, production and accommodation facility (HMP1). HMP1 is connected to the riser facility HRP by a bridge, which was constructed when the Heimdal Gas Centre (HGS) was established.
Today Heimdal is primarily a process centre for other tied-in fields. Huldra, Skirne and Vale deliver gas to Heimdal, and gas from Oseberg is also transported via Heimdal.
Statoil is the operator for Heimdal.