Three people have died and more are in hospital after a birthday surprise at a Moscow party had unforeseen consequences. Video shows dry ice being poured into a pool for effect, inadvertently creating a carbon dioxide gas chamber.

The chilling incident occurred at a Moscow sauna late on Friday. Ekaterina Didenko, an Instagram blogger with over a million subscribers, was celebrating her 29th birthday with her family and friends.

No-one expected the festivities to turn into a tragedy when the blogger’s husband Valentin presented the guests with a surprise treat. The man brought out a large amount of dry ice – solid carbon dioxide – and after everyone donned symbolic ‘protection’, he poured it into a pool to create the fancy mist effect for everyone to take photos and videos.

Footage of the fateful moment emerged online on Saturday. It shows the revelers wearing improvised protective costumes and goggles and gathered by a small indoor pool. One of them reads the instructions aloud, jokingly warning that the dry ice might be very dangerous before pouring the substance into the pool. The guests then proceed to jump in, with the bravest one submerging himself completely – while one of the onlookers jokes “He’s dead, he’s not with us anymore.”

The joke, however, turned grim within moments. Upon coming into contact with the water, the dry ice evaporated, creating a thick plume of carbon dioxide – effectively turning the pool into a gas chamber.

Three people, including Valentin, were left dead in the aftermath of the stunt, while several others remain in hospital. The small indoors location, as well as the large amount – 25 to 30 kilograms – of dry ice used, created a lethal concentration of the gas. The ‘protective equipment’ the revelers sported proved completely useless, as it didn’t include full-body wetsuits and rebreathers.

The tragic accident promptly went viral on the Russian-language portion of the internet. Some expressed condolences to the widowed blogger, whose two children are now left without a father. Many others attacked her over the “stupidity” of the stunt and the couple’s “ignorance.”

Didenko is a certified pharmacist, blogging about pharmacies and drugs, and her late husband had a higher technical education, so there have been questions raised as to whether the two should have known better than to play with dry ice.

It remains unclear where Valentin procured such a large amount of dry ice – and some earlier Instagram posts by Didenko suggested that he might have cooked it himself.

Russian law enforcement has launched a probe into the accident, which will likely target both Didenko and the owners of the sauna, who were reportedly aware of – but had not stopped – the deadly stunt.

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