Burning silicone, a synthetic polymer based on silicon, oxygen, carbon, and hydrogen, releases potentially harmful byproducts. Unlike conventional, carbon-based plastics, silicone has a unique inorganic backbone that grants it high thermal stability. When exposed to extreme heat, however, the material undergoes decomposition that generates toxic smoke, making safety dependent on the temperature and environment.
How Silicone Reacts to High Heat
Silicone is prized for its heat resistance, maintaining its structure far beyond the limits of many other polymers. Unlike many plastics, silicone rubber does not melt into a liquid form. It maintains its solid structure until thermal decomposition begins, generally around 400°C (752°F) or higher. This high temperature resistance is due to the strong bonds in its silicon-oxygen backbone.
When combustion occurs, the material decomposes rather than melting and flowing away. A key characteristic of burning silicone is the formation of a non-combustible residue known as silica ash (silicon dioxide). This white, glass-like layer deposits on the surface, serving as a temporary barrier that slows the rate of further decomposition. This process means that, in a fire, silicone often generates less visible smoke than many common organic materials.
Identifying the Toxic Fumes
Despite its relatively good fire-resistant profile compared to many organic polymers, the thermal decomposition of silicone still releases several toxic byproducts. The primary health risks stem from the organic side chains, typically methyl groups, attached to the silicon-oxygen backbone. These groups break down when exposed to high heat in the presence of oxygen, leading to the formation of gaseous hazards.
One of the most immediate threats is the production of Carbon Monoxide (CO), a colorless and odorless asphyxiant gas. Like any organic material undergoing incomplete combustion, silicone’s carbon-containing parts yield CO, which interferes with the blood’s ability to carry oxygen. Another significant byproduct is Formaldehyde, a flammable, pungent gas that acts as a severe irritant to the eyes, nose, and respiratory tract.
Formaldehyde generation can begin at temperatures as low as 149°C (300°F), though the rate of release increases substantially above 200°C (392°F). While silicone typically produces a lower fraction of formaldehyde compared to some other materials, the presence of this irritant poses a clear health risk upon inhalation. Trace amounts of other volatile organic compounds (VOCs), like methanol and formic acid, can also be released during this thermal breakdown.
The white ash residue created during burning, known as silica fume, is composed of amorphous silicon dioxide. While this material is considered less hazardous than crystalline silica, inhaling the fine, dispersed particles can still irritate the respiratory system. Exposure to this fine dust can lead to irritation, and prolonged exposure is linked to lung inflammation and conditions like chronic bronchitis.
Safety and Exposure Response
The most important step upon encountering burning silicone is to prioritize personal safety and limit exposure to the fumes. If the burning material is indoors, immediate ventilation is paramount to disperse the concentrated gases. Open windows and doors to establish airflow and evacuate the area promptly.
Because Carbon Monoxide is invisible and odorless, its presence is indicated by symptoms or a specialized detector. If you or others experience symptoms like persistent coughing, shortness of breath, dizziness, headache, or nausea, seek fresh air immediately and contact emergency medical services. These symptoms indicate potential asphyxiation or severe respiratory irritation from the fumes.
Do not attempt to extinguish the fire if it is unsafe or producing heavy smoke. If the source is small and safe to approach, use an appropriate fire extinguisher, ensuring the area is well-ventilated immediately afterward. Once the fire is out, avoid disturbing the white silica ash, as this can release fine, irritating dust particles. Professional cleanup is often recommended to safely remove the residue and eliminate contamination.