Most homeowners do not know that there are various stages of a substance called “creosote” that builds up from burning wood. This substance in large quantities is HIGHLY FLAMMABLE. Here are the various stages of creosote build-up:
The first stage is a feather-light, dull gray, brown or black soot.
The second stage is a black or brown granular accumulation that can be crusty and flaky.
The third stage of creosote is a drippy, sticky, road tar-like coating which is much harder to remove.
Above all (and most deadly) stage is a shiny, hardened, glaze-like coating on the fireplace flue that is virtually impossible to remove. At this stage the creosote is highly flammable and is often the cause of chimney fires.
Therefore, stages of creosote build-up two through four are all highly combustible forms of creosote. If allowed to build up in sufficient quantities with the internal flue temperature high enough.
is vital to your safety!
To keep chimney build-up at a minimum, sweep up ashes regularly, burn the proper fuel, and be sure your flue air supply isn’t restricted. In other words, hardwood firewood burns cleaner than softwood, and manufactured wood burns much cleaner than hardwood. Call a professional chimney sweep before the start of each season to inspect and repair any issues in your fireplace.
In conclusion, NEVER burn paper products (example cardboard, huge amounts of newspapers or other paper type of products) as these tend to float the ashes upward that can be lodged in the walls of the chimney and create flash fire.