Various news outlets are claiming that people suffered from poisoning after liquid nitrogen was poured into a swimming pool. The intended effect was to produce mist.
For example,the telegraph reported (text directly below the headline, above the video):
"21-year-old man was in a coma in Mexico and eight other people were treated in hospital after liquid nitrogen reacted with chlorine at a pool party ...",
This doesn't jive with my high-school level knowledge of chemistry, but I can't be 100% sure that there isn't some reaction to produce something toxic.
I totally expect that the cause of the injuries is due to asphyxiation, but I have not found a reputable source to rule out the possibility of a significant chemical reaction.