Foxes have a significant impact on native fauna and urban pets. Fox control can be difficult to achieve in urban areas. Fumigation of breeding, or natal dens with carbon monoxide (CO) gas is sometimes used to destroy young cubs. Carbon monoxide is a colourless, odourless gas that causes oxygen depletion leading to unconsciousness and rapid death without pain or discernible discomfort. The gas is generated by the incomplete combustion of carbon using sodium nitrate within a fumigant cartridge.