In my last post I link to a newspaper article featuring a young man who tragically died of hypoxia after inhaling pure nitrous oxide. The article emphasises that this was a consequence of substance abuse. However there is another situation where theoretically exactly the same situation could arise in what is perceived as a much more harmless practice.
Helium balloons are widely bought both for adults and children. How many people, including children, have opened the balloon and inhaled the gas to produce an amusing squeaky voice? There's no oxygen in them either.