What is a Rail Industry Worker National Block resulting from a medically recorded drug failure?

Where a Rail Industry Worker health assessment requires a drug and alcohol test, if the drug test comes back as confirmed positive, the Authorised Health Professional (AHP) records the results and the system automatically places a National/Rail Industry Worker Program Block on the Rail Industry Worker. Whilst this is recorded on each Network Operator Australia-wide, if any of the Network Operators has a rehabilitation mechanism or policy to support lifting the block on their network, the Network Operator can lift the block for their network only (the block remains for all other Network Operators).