Why Does Wood Spark?

Moisture

• Moisture from living trees is retained as the wood is cut. Burning fresh, or green, logs causes the moisture pockets that remain in the wood to heat up. These pockets contain water vapor and gasses. When the gasses inside the pockets explode, debris is emitted from the wood in the form of sparks. Allowing cut firewood proper time to dry out before use eliminates gas and moisture pockets, thus eliminating the potential for sparks.

  Firewood such as red cedar and various pine species hold moisture and are quicker to ignite, according to the University of Missouri. If you hear popping noises, this is the audible portion of the spark igniting.

Resin

• According to Oklahoma State University, resin is found in trees with a highly flammable sap concentration such as poplar, pines, conifers and red cedar. Resin is found in both hardwood and softwood. Look for dry, amber colored sap that has oozed out onto the surface of the log. Logs with this condition contain noticeable resin and will throw sparks.

Decomposition

• Burning firewood decomposes as it is consumed by the flame. Part of the decomposition is creosote and soot. Look for dark, thick smoke as a sign of creosote tar forming inside the chimney. As wood burns, the water evaporates, leaving the gasses and other chemicals. The chemicals break down into charcoal. The charcoal forms carbon dioxide and then carbon monoxide through burning. As pockets of chemicals, gasses and volatile liquids explode, the charcoal and other debris not completely decomposed shoot into the air as sparks. If a spark ignites the creosote or tar in the chimney, it can cause a secondary fire, or chimney fire, feeding off the soot and tar built up in the chimney.

Precautions

• Using wet wood, green wood (freshly cut) or only a species that burns hot can cause an abundance of sparks. Mixing hardwood with softwood, using dry wood and chopping wood into smaller pieces helps reduce the potential sparking.

  Seasoning firewood is a method of drying the wood outdoors. Dry your firewood by stacking it in alternating directions per layer to achieve airflow around the logs. Oklahoma State University has a test that wood burners can use to determine dryness of their firewood; strike two logs together and listen to the sound. A sharp cracking noise indicates drier wood. A dull thud indicates higher moisture content remains in the wood.