Are certain species of firewood unsafe or unsuitable to burn?
No there is no dangerous firewood that we know of. There are woods with sticky sap in their bark and others that can’t be split by hand and so are not as desirable as others. But creosote is a product of combustion, not a component of wood. If burned in bright, hot fires, much less creosote is formed from whatever wood is burned uncured firewood can also produce smoky fires. If you have some very dry wood available, mix it with regular firewood to avoid excessive smoke. Burn bright, hot fires.
