How does presumptive legislation work in regards to workers' compensation for occupational exposure to firefighters? The firefighter has the burden of proving their ailment was the result of occupational exposure. More than one firefighter in a single agency must present cancer diagnoses before workers' compensation can be applied. The employer must prove that the firefighter's working conditions were not a significant contributing factor to the development of cancer. Occupational exposure is presumed for firefighters and therefore is a personal risk of each individual firefighter; workers' compensation cannot be awarded