Brucewayne
If you can tell me the difference between a volcanic ash cloud and airspace that "could" have ash particulates in it then that would solve the huge multimillion quid probelm that airlines in Europe face.
I dont want to get hard-nosed on logic but you cannot use burden of proof on the fact that accidents have not occurred. Burden of proof can only be validly applied on an event that has actually happened. My Latin is a bit rusty but reductio ab absurdum is the term which fits. In this context it means that you would accept any risk because you do not recognise it as a problem.