Although black walnut wood produces a toxin called juglone, it can be burned safely. It is not most people's first choice for firewood because it is expensive and is mainly used for furniture.
Many people are skeptical about the safety of burning black walnut wood because the tree itself produces juglone. This toxin can be dangerous when it is exposed to plants, animals and children. The wood shavings of black walnut wood are also toxic, so care should be taken when children or plants are around a fire. Once juglone comes into contact with air, water or bacteria, the toxin dissipates. This makes it safe to burn because the toxin is not carried in the smoke.