Background: Bushfire fighters are potentially subject to risks from bushfire smoke. Although many different protective masks and filters are available, it is not clear which is the most effective from a health and safety perspective. The effect of protective filters on the respiratory health of Western Australian urban career fire fighters under controlled simulated conditions is investigated.Methods: Sixty-four healthy Fire and Emergency Services Authority of Western Australia (FESA) urban career fire fighters were subjected to controlled simulated bushfire smoke in an open smoke chamber for 15 min. The firefighters were allocated one of the three types of protective filters: particulate only (P), particulate/organic vapor (POV), and a particulate/ organic vapor/formaldehyde (POVF) filter using a double-blind randomized procedure. Personal air sampling inside the fire fighters' masks, spirometry, oximetry. and self-reported symptom data were collected at baseline and at two time intervals after the smoke exposure.Results: A significant decline in oxygen saturation was seen immediately after exposure, however, the decline was small and no significant relationships could be established between this and the type of filter used. A significantly higher number of participants in the P and POV filter groups self-reported an increase in coughing, wheezing, and shortness of breath compared to the POVF group. Air sampling demonstrated a significantly higher level of formaldehyde and acrolein inside the masks fitted with P filters compared to POV and POVF filters.Conclusions: Testing the effectiveness of P, POV, and POVF filters under controlled conditions has demonstrated that the POVF filter provides statistically significant better protection for the fire fighters' airways in a simulated bushfire exposure chamber.