Poison ivy can be dangerous even when you're disposing of it in a fire. During burning, urushiol is carried by smoke and dust particles. Airborne particles may coat surrounding surfaces with urushiol and cause diffuse dermatitis and potentially severe airway irritation.
Prevention is the best defense.
You should always be alert for poison ivy when walking and especially look down before you sit down. It is frequently found along streams or lakeshores, its growth encouraged by moisture. Protective clothing may help, but contaminated clothing and tools must be disposed of or cleaned to avoid additional contact. Diligent washing of the skin with soap and water or swabbing with alcohol is only helpful if done soon after exposure. There are some protective agents available.