At least 27 revellers have been hospitalised with carbon monoxide poisoning after they were sickened during an illegal rave inside an underground bunker.
Five people were in a critical condition and two police officers who helped the revellers were among those who were poisoned at the “Rave Cave” event in Oslo, Norway.
The carbon monoxide level in parts of the bunker was “many times” more than the lethal level, and the oxygen level was barely 16%, below the minimum safe concentration of 19.5%, said officials.
Investigators have blamed fumes from portable diesel generators, which were used to power the sound system and lights in the venue which is about 230ft (70 metres) underground.
About 200 people were attending the party in the capital when officers on patrol happened upon a group of young people who were confused, and several people then emerged from the bunker and asked for help in the early hours of Sunday.
The victims were mainly aged between 20 and 30.
Carbon monoxide is a poisonous gas that has no smell or taste, and it can be fatal to those exposed to high levels.
It stops the blood from carrying oxygen, and the lack of oxygen causes cells and tissue to die.
Police said a number of partygoers told officers they had taken drugs, including cocaine and MDMA, and the outcome for them could have been much worse.
One partygoer, who was in hospital, told broadcaster NRK he rescued a number of victims by carrying them out.
The man said: “They were unconscious, and it was very dark inside.
“In retrospect, I think it was stupid [attending the rave]. But when you start drinking, you become a little less [aware].”
A woman who attended the rave added: “We could have ended up with permanent injuries A doctor called it a collective suicide attempt. It’s totally sick even to think about it.”
A man who left the rave before police arrived told NRK had to leave the bunker several times to get fresh air.
He said other parties had been held in the same bunker this summer. Bars in Norway are banned from serving alcohol after midnight as part of coronavirus restrictions.
The only way in and out of the bunker was through a hole measuring about one metre by one metre. It was reported to be a former Civil Defence bunker, and the new owners were not aware of the party until police discovered it.
Police launched a search for the organisers of the rave, which was reportedly planned three weeks in advance on Facebook. Two people have been arrested, the force announced on Monday.
The force is also carrying out an internal investigation for not acting on a tip-off.
Local resident Matt Vestengen-Cox, 34, told TV 2 that he reported the party to police several hours before police came upon it by chance, and said several people outside the bunker’s entrance looked “very drunk”.
Seven people were discovered unconscious in the bunker, while almost 20 others were sickened.
Many were suffering from dizziness, nausea and headaches, local media reported.
Five were in a critical condition in hospital, but it is understood all of the victims are out of danger.
Three remained in intensive care on Monday.
In a blog post, Oslo University Hospital said it had 100 staff members helping the 25-plus patients after a major incident was declared.
Police have issued an appeal to people who were at the party to go to a hospital if they are feeling unwell.
Lars Magne Hovtun, chief of staff of Oslo’s fire service, said it was fortunate there were no fatalities.
He said many people would have died had a fire broken out inside the bunker.
He added: “This party could have had major consequences.”