I agree with the comments above, that the only reason to cross the track would be if a person was in danger.
I've only had to cross a live track once, and that was to attend a Caterham driver who wasn't moving in the car after a heavy impact. We crossed only because it was the first lap and could be reasonably sure we had a safe gap to do so before the pack came back around, and we got the nod from the Observer.
I was still green, however, and stupidly backed up my colleague by taking an extinguisher. After the incident was cleared up (driver was fine, just shaken), I quite rightly had a lecture from the Observer on crossing the track with a bottle. I took on board what I was told and learnt from it. And I expect the Aussie fire marshal has learnt from his mis-adventure also. We're all human at the end of the day and will make bad judgement calls from time to time, and just have to learn from them. So rather than pointing fingers and apportioning blame, it's more constructive if we accept what's done is done and learn from it.
(Climbs down from high horse
)