The Sydney air quality was bad enough for a few days to force key infrastructure as the Sydney port to stop work as conditions were unsafe for their workers. This has never happened before. There were also over 100 buildings which had their fire alarms triggered by the smoke (including the HQ for the fire service, ironically enough). Unprecedented conditions. The good news is that it is wood smoke, and not nitrous oxide or burning plastic for the most part, so not carcinogenic as some fires can be. The wind conditions were unusual and in the past not likely to occur in January -- however the past weather patterns are changed this year, and the worst fires tend to hit in Feb or March, so the worst may yet to come. Melbourne is somewhat safer for air quality, but again there have been fires in the US which have been as bad or worse, just not near major tourist areas (the last one was the Berkeley fire in 1991, which was a rare urban forest fire and would have burned the city to the SF Bay except for a wind change -- Sydney is not exposed to that event).