BAL12.5 - 2014, part of AS3959 - 2009 for domestic building standards sets maximum apertures for home cladding, screens, roof sealing etc for bushfire protection in low risk areas. The aperture size recommended is 2 mm. It may be mandatory for new homes but not much is being done for existing older ones. Checking my 30 year old brick veneer home in the Blue Mountains recently I found most gaps closely met this limit, but I noticed that my two whirly bird (generic name) roof ventilators had curved entry apertures in the impellor 20 mm wide and about 250 mm long. Inside the impellor and the tube connecting it to the roof there was no mesh to catch any objects entering the unit. They simply fall down directly onto a dusty ceiling. The potential for a fire to start from a falling ember seems high. Just how high is not possible to determine without some testing. But some reports from California and within Australia place house fires from ember attack as high as 90%. Most houses burn down from fires starting within.
I checked various web sites concerned with building standards including BAL12.5 and there was no discussion of the design of whirly birds and their performance in bushfires. I wrote to a major manufacturer of whirly birds and to my surprise obtained a rapid telephone response and long discussion. I was told this anomaly in design has been recognised and that company was considering making stainless steel mesh disk screens for fitting within the vertical tubes. These will be offered as optional extras with new units. So far this company has not advertised these screens for retrofitting to their 350,000 existing installations.
BAL12.5 second edition was published in 2014, so at least 6 years has elapsed with no action taken to fix this anomaly, and no publication of laboratory testing of these units in simulated bushfire conditions to show that they are in fact safe. So I recommend that the relevant building standards authority and councils in bushfire prone areas investigate this matter, and Choice members can in fact take their own protective action by buying at least ember rated Al wire gauze, or stainless steel gauze and cutting and fitting screens to their own whirly birds. They should be glued in with silicone cement or equivalent to keep them in place.