Pretty ? Yes maybe for spectators but no one wants one of these. Why do they happen ?

A number of reasons, poorly maintained chimneys, standards of chimneys,blocked chimneys,and burning the wrong fuel,especially unseasoned wood. If the moisture content is above 20% it shouldnt be burnt as the sap/tar (creosote) will tar the flue up and it will ignite. So ensure that you only buy Wood at least 18 months old.If you are unsure use a meter to test it. If you want one contact me for details.