As mentioned elsewhere earlier in the thread, Blacks are officially not considered dangerous to humans. They are typically quite placid in temperament and unlikely to bite, but if they do bite, the venom is of relatively low toxicity, so won't do much more than make you feel rotten for a while.
Browns on the other hand.... quite unpredictable, not averse to having a go, and highly toxic, requiring urgent attention if you're chomped.
And for the record, there are no venomous lizards in Australia. Just to buck the trend....