An ethanol fire is combustion fueled by ethyl alcohol, a clear, volatile, and highly flammable liquid. Ethanol, often sold as bioethanol, is increasingly used in ventless decorative appliances like bio-fireplaces and tabletop heaters. Understanding its specific chemical nature is important, as its fire characteristics differ significantly from traditional materials like wood or paper, demanding specialized knowledge for safe use and proper suppression.
Defining Ethanol and Its Combustion Process
Ethanol is an organic chemical compound with the molecular formula C2H5OH. It is one of the most widely produced chemicals globally and is commonly known as ethyl alcohol or grain alcohol. As a liquid fuel, it possesses a high energy content that is readily released during combustion.
The combustion process is a reaction with oxygen, producing predictable byproducts and heat. One molecule of ethanol reacts with three molecules of oxygen (O2) to yield two molecules of carbon dioxide (CO2), three molecules of water vapor (H2O), and heat energy. The full reaction is C2H5OH + 3O2 \(\rightarrow\) 2CO2 + 3H2O + Heat.
This complete reaction explains why ethanol is considered a clean-burning fuel. Unlike wood or coal, ethanol leaves minimal residue, ash, or soot. The lack of uncombusted carbon particles determines the flame’s unique appearance and the small amount of smoke produced.
Distinctive Properties of the Ethanol Flame
The most hazardous property of an ethanol fire is the near-invisibility of its flame in bright environments. Traditional fires are visible because they produce soot, consisting of incandescent carbon particles that glow orange or yellow. Since ethanol combustion is clean and produces little soot, the energy is released as a pale blue or mauve flame that is difficult to distinguish against daylight.
The absence of a visible flame poses a serious safety risk, as a person may unknowingly walk into or place an object over a burning surface. The heat produced is substantial, with the adiabatic flame temperature reaching approximately 2082°C (3779°F). In consumer bio-fireplaces, the heat output is often localized, providing supplementary heating typically ranging from two to three kilowatts.
The primary combustion products are carbon dioxide and water vapor. Since ventless appliances release CO2 directly into the living space, proper ventilation is necessary to prevent CO2 buildup, which can displace breathable oxygen. Although the clean-burning nature means no harmful smoke or fumes requiring a chimney are created, the constant consumption of oxygen indoors must still be managed.
Specialized Methods for Extinguishing an Ethanol Fire
Extinguishing an ethanol fire requires methods that address its specific chemical properties, especially its water-miscibility. Unlike petroleum-based fuels, ethanol mixes readily with water. Attempting to extinguish a large, concentrated ethanol fire with a stream of water can be counterproductive because the water dilutes the fuel, allowing the fire to spread across a wider surface area while remaining combustible.
For smaller ethanol fires, such as those in a tabletop burner, the manufacturer-supplied lid or snuffer is the most effective tool. This method works by smothering the flame, cutting off the supply of oxygen and breaking the fire triangle. Wait until the fuel tray has cooled before attempting to handle the burner or add more fuel.
When dealing with a larger spill fire, the recommended tool is a dry chemical fire extinguisher rated for Class B or ABC fires, which interrupt the chemical chain reaction. Firefighters rely on specialized Alcohol-Resistant Foam (ARF). This foam uses polymers to create a stable, impermeable barrier over the burning liquid, preventing the foam’s water content from mixing with the alcohol and smothering the fire.