27 poisoned with carbon monoxide at illegal Oslo rave

27 people were poisoned with carbon monoxide given off by portable generators at a secret rave in Oslo, Norway last weekend.

The “Rave Cave” event took place at a secret bunker with around 200 attendees in their 20s and 30s, starting late Saturday night. The rave was only discovered in the early hours of Sunday when a patrol happened across a group of confused young people.

Emergency services found seven people lying unconscious in the bunker.

Out of the 27 poisoned, five people were hospitalized in critical condition, including two police officers who were first on the scene. All are now improving and out of danger—two of the five were released from the ICU today— although authorities have urged attendees to seek medical help in the event they experience dizziness, headaches or nausea.

Portable diesel generators were used to power the lighting and sound systems at the event, and neither participants or organizers appeared to know the potential dangers of using a diesel generator in a confined space.

The company that owns the bunker described the secret rave as a “serious break-in” and said they did not bear any responsibility, Norway’s VG newspaper reported.

An unidentified man who attended the party reported that the air quality declined throughout the night, causing him to leave the bunker for fresh air on several occasions. Several events have taken place at the space in the last several months, he says, but this party was unprecedented in its number of attendees and generators. The event remains under investigation.

Carbon monoxide is a colorless, odorless gas produced by the incomplete burning of carbon-based fuels. The gas displaces oxygen from the body’s red blood cells, depriving the heart, brain and other vital organs of oxygen. Inhaling carbon monoxide in large amounts can lead to unconsciousness or even death.