Wood pellets, popular for heating in France, pose a carbon monoxide (CO) risk even when not in use due to natural chemical reactions, primarily the oxidation of fatty acids, as reported by the French Agency for Food, Environmental and Occupational Health & Safety (ANSES). These reactions can cause stored pellets to heat up and release CO, along with other gases like CO₂, CH₄, and VOCs, while also reducing oxygen levels. While emissions are typically low and decrease over time, they can increase in higher temperatures and become dangerous in confined, poorly ventilated spaces, as exemplified by a case in Haut-Rhin where an 87-year-old man was found intoxicated due to CO buildup from pellets stored in his basement. ANSES advises storing pellets in cool, dry, well-ventilated areas, using airtight containers for opened bags indoors, elevating them outdoors, and keeping them away from heat sources to mitigate this odorless, toxic risk.