In the case of Argon, it's both inert and non-toxic. The main danger is that it's heavier than air (so you can asphyxiate yourself if you try).

As such, "food" grade argon is actually less pure than industrial argon - food grade is 99.996 and industrial grade is 99.998

The practical difference is what contaminants exist - because argon is non-reactive, in food grade argon they are just trying to remove contaminants you don't want in food.

In industrial grade argon, mainly used for welding, almost any kind of impurity can cause issues, whether it would be "safe to eat" or not.