It's not within the scope of DAMP to fire someone on a first offence,
Is that a general statement for all DAMPS or specific to the RFDS DAMP?
If an operator has it documented in their DAMP and the employees are informed of the dismissal action as the result an initial positive and confirmatory positive tests, anyone failing a drug or alcohol test can be dismissed.
There is plenty of precedent for dismissal after the first positive test in other industries where staff operate complex machinery.