Since 2000, it is estimated that at least 20 people have died from poor air quality due to manmade burns, with hundreds of emergency hospital visits. A study from the WA Department of Health has confirmed that prescribed burns contribute significantly more to hospitalisations than wildfires (autumn and spring periods in the report).
In contrast, over this same time period, 4 people have died from bushfires in the south-west. These four tragic deaths all occurred in farmland, not forest.
Data from Borchers Arriagada N, Palmer AJ, Bowman DMJS, Johnston FH. 2020. Exceedances of national air quality standards for particulate matter in Western Australia: sources and health-related impacts. Med J Aust. 213(6):280–281. doi:10.5694/mja2.50547.