Duraflame logs are safe to burn in a zero-clearance fireplace. Duraflame logs do not release any toxins when burned and are not a fire hazard, making them safe for use.
The concern over using Duraflame and other manufactured fire logs is caused by the warning present on many zero-clearance fireplaces. Before a fireplace is considered safe to manufacture, sell, and use, it must pass a rigorous safety check, the UL-certification test. Because most fireplaces did not test for manufactured logs when they received their UL-certification tests, manufacturers were required to include this warning label.
Additionally, Duraflame logs have only been manufactured for the last 40 years. Because fireplaces have such a long life, many older models still have this warning. Manufactured logs have since received their own individual UL-certifications.
While older fireplaces with original labels will still warn against burning anything but natural logs, newer models have removed this warning label.