... Its not the breathing part that'll kill you... its just water vapor... which can open nasal passages and your bronchi, which makes it easier to breather. But the heat is the threat, causing dehydration and overheating, like bimjob said...
Here is what Frank jarnbar who Work at the steam industry had to say
"I work with steam in industrial settings that will cut a human in half haha. also interesting is superheated steam is completely invisible, not like your typical steam full of water droplets. but in general no it wont kill you just breathing it in, the heat is the only danger of steam, steam is just the gas form of water, only achieved with heat. Heat as you know can kill you."
