Ethanol, also known as ethyl alcohol, is a colorless, volatile organic compound that is highly flammable. It is a common ingredient in alcoholic beverages, hand sanitizers, and as a fuel additive in gasoline, often labeled as E85. Because ethanol is a solvent that easily evaporates, its vapors present the primary fire hazard.
The Key Flammability Metrics
Ethanol’s flammability is defined by three specific metrics. The Flash Point is the minimum temperature at which the liquid releases enough vapor to form an ignitable mixture with the air near its surface. For pure, 100% ethanol, this temperature is very low, ranging from approximately 13°C to 16.6°C (55°F to 62°F). This low flash point means that ethanol can easily ignite at typical room temperatures if an ignition source is present.
The Autoignition Temperature is the point at which ethanol vapor will spontaneously ignite without a spark or flame. This temperature is significantly higher, falling between 363°C and 369°C (685°F and 696°F). While the flash point requires an external spark, the autoignition temperature represents the point where a hot surface alone can cause combustion.
The Flammable Range defines the concentration of ethanol vapor in the air that will allow combustion to occur. Ethanol has a wide flammable range, with a Lower Explosive Limit (LEL) of approximately 3.3% vapor by volume in the air and an Upper Explosive Limit (UEL) of about 19%. If the vapor concentration is below the LEL, the mixture is too lean to burn, but if it is above the UEL, it is too rich in fuel and lacks the necessary oxygen.
Impact of Water Concentration on Flammability
Ethanol is completely miscible with water, which has a direct effect on the substance’s fire risk. The presence of water absorbs heat and reduces the concentration of ethanol, making it more difficult for the mixture to produce enough flammable vapor to ignite. For example, 70% ethanol has a slightly higher flash point of about 16°C (61°F) compared to pure ethanol.
As the water content increases, the flash point of the solution rises, requiring a much higher ambient temperature for the solution to become flammable. Practically, ethanol solutions below 50% to 60% concentration by volume are extremely difficult to ignite at normal room temperature. This is why low-proof alcoholic beverages pose a much smaller fire risk than high-proof spirits or laboratory-grade ethanol.
Even with high water content, the mixture may still be flammable if the temperature is elevated, such as during a fire. However, the presence of water significantly reduces the heat release rate and the overall fire hazard. This principle is why hand sanitizers, which often contain 60% to 90% ethanol, still represent a considerable fire risk, while a diluted cleaning solution with a low alcohol concentration does not.
Necessary Precautions for Handling and Storage
Proper ventilation is paramount, as ethanol vapor is heavier than air and can travel along floors or settle in low-lying areas, creating a fire hazard far from the liquid source. Mechanical or passive airflow systems must be adequate to disperse these vapors and keep the concentration well below the LEL.
All potential ignition sources must be rigorously eliminated from the vicinity of ethanol storage and handling areas. This includes open flames, sparks from tools, and static electricity, which can easily be generated during the transfer of the liquid. Containers must be properly grounded and bonded during dispensing to prevent static discharge from igniting the vapors.
Ethanol should be stored in containers made of appropriate materials, such as stainless steel, glass, or high-density polyethylene (HDPE), and must be securely sealed to prevent evaporation. Storage temperature should be maintained in a cool environment, ideally between 15°C and 25°C (59°F and 77°F). Elevated temperatures increase the rate of vapor production, significantly raising the risk of fire.
Methods for Extinguishing Ethanol Fires
Ethanol fires are classified as Class B fires, which involve flammable liquids. Standard firefighting techniques, such as applying plain water, can be ineffective or even counterproductive. Because water mixes readily with ethanol, a strong water stream may simply dilute the burning fuel, causing the fire to spread rather than extinguish it.
The preferred method for extinguishing large ethanol fires is the use of Alcohol-Resistant (AR) foam. AR foams are specially formulated to create a stable blanket over the liquid surface, which suppresses the flammable vapors and smothers the fire without being broken down by the alcohol. This foam is crucial in industrial settings where large quantities of ethanol are present.
For smaller ethanol fires, such as those in a laboratory or small spill, dry chemical extinguishers marked ABC or BC are effective options. These extinguishers interrupt the chemical reaction of the fire by coating the fuel with a non-flammable powder. Alternatively, a carbon dioxide (CO2) extinguisher can be used to displace the oxygen and smother the flame.