All of what Russel says is true, but it is important to note that while non-toxic, the fact that it is heavier than air means the risk of suffocation is much greater.
Think about it; when you breath out with helium, it all rushes out as soon as you open your lungs. With this, it will sink to the bottom of your lungs, and may not be breathed out for quite some time (the deepest you can breath out is around 70%).