For safety reasons, never burn any type of treated or painted wood, as it can release toxic fumes when heated. It is also important to refrain from burning plastic, rubber, or synthetic materials, as they release toxic chemicals when burned. Additionally, never put flammable liquids, such as gasoline or lighter fluid, in the fireplace as they can cause explosive and uncontrollable fires. Lastly, do not overload the fireplace with too much wood or other fuel, as this can lead to excessive heat and potential damage to the fireplace and chimney. It's always best to stick to natural firewood and follow proper safety guidelines for a safe and enjoyable fireplace experience.