These materials contain chemicals that give off toxic fumes when burned. Never light a fire in a fireplace with flammable liquids such as gasoline, lighter fluid, etc. Learn to start a fire with kindling wood or starters designed for use in a fireplace. Never burn Christmas trees. Always use a firescreen.
Sparks flying out from a fireplace can set fire to floors, carpets, furniture, etc.
Never leave small children unattended in a room with a fire going. Keep flammables away from the fireplace. For example, don't store old newspapers next to the hearth. Don't let the flames get too high. The flames should never be so high that they reach into the chimney.