According to Sjaak Van Loo and Jaap Koppejan in the "Handbook of Biomass Combustion and Co-firing," wood pellet-fired equipment is susceptible to burn back into the storage hopper and feed auger. Back burning from a poor quality wood stove presents a significant fire hazard and can lead to large-scale house fires. This risk greatly aggravates if the stove has not been adequately serviced/cleaned and if poor quality wood pellets are used for burning.
Low quality wood pellet burners and stoves emit noxious gases, including carbon monoxide, oxides of nitrogen, volatile organic compounds and unburned or partially burnt hydrocarbons. The burners can also emit significant amounts of particulate matter, also called soot, the inhalation of which causes lung cancer, asthma, cardiovascular problems and premature death.
Incomplete burning of wood pellets releases particulate matter, tiny droplets of organic wood tar vapors and gases. Exposure to particulate matter aggravates respiratory illnesses and contributes to cancer and lung diseases.
Wood pellets cause significant environmental risks and contribute to air pollution. Incomplete burning produces carbon compounds which react with oxides of nitrogen in the presence of sunlight to form photochemical smog, otherwise known as ozone. Ozone makes breathing difficult and injures the lungs, especially in old people and children. Oxides of nitrogen generated from wood pellet burning combines with water vapor and volatile organic compounds to produce acid fog and acid rain. Wood pellets encourage tree extraction from forests, causing deforestation, which results in an imbalance in the ecological equilibrium.
According to Sina Ebnesajjad in the "Adhesives Technology Handbook," some wood pellets test positive for formaldehyde--a known carcinogen, which is defined as a substance directly involved in causing cancer. Formaldehyde is a pungent, toxic adhesive used to bond wood fibers to make wood pellets. According to Harish Kumar in the book "Environmental Health Hazards," exposure to formaldehyde causes hypersensitivity, damages the linings of the alimentary and respiratory tracts and causes lung cancer. Its toxicity is mainly attributed to formic acid, its oxidation product.