sabenaboy:
"The problem is that no lower level acceptable ash concentration has been defined and decision makers are greatly overreacting"
That comment sums up the heart of the problem. As no lower level acceptable ash concentration has ever been defined, then how can you assert that the decision-makers are greatly overreacting? They don't know and you don't know.
I agree that the fact that this is so represents a historical failure of both the industry and the regulators, but given the current state, then there is really no choice than to use a highly conservative risk assessment.