OK, we all know that dry ice will keep things cool in your cooler, and even freeze things rock hard. You can also make that cool smoke coming out of a glass of water or maybe a centerpiece for a banquet or some such. Guess what? It can also kill you.
It seems that at a birthday party in Moscow, they wanted to cool the pool down to take a nice bracing dip. So, they dumped some dry ice in. It cooled the water but also created a cloud over the top. Bet it looked really, well, cool.
The problem is that dry ice is the solid form of carbon dioxide (CO2). That's the gas your body exhales through the lungs in order to get rid of it. High CO2 levels in the body are deadly. Normal ambient air is about 21% oxygen but contains only 0.04% CO2. So when the cloud of CO2 gas collected over the pool that obviously increased the level of CO2 while decreasing the level of oxygen (O2) by simple replacement. That is, each liter of air above the pool now contained a reduced amount of O2 and a greatly increased level of CO2. As the people breathed this mixture they became weak and dizzy and ultimately lost consciousness simply because they were not getting enough oxygen through their lungs to the bloodstream and ultimately to the brain. Apparently three of them died and many others were close. The take-home message is: don't do this.
https://www.newser.com/story/287606/dumping-dry-ice-into-pool-kills-3-people-at-moscow-party.htmlIn 1986, a similar thing happened on a much larger scale at Lake Nyos in Cameroon. Some sort of geological event--there is still controversy over exactly what happened--created a CO2 cloud that spread across the area, killing over 1700 people. CO2 is heavier than air, so tends to hug the ground and settle in valleys and low areas. That's what happened here. And at that Russian swimming pool.
https://en.wikipedia.org/wiki/Lake_Nyos_disaster