Corn oil is a common ingredient, often used for frying and high-heat cooking applications. While it is a liquid that can certainly burn and cause a dangerous fire, the answer to whether it is “flammable” is technically no. Corn oil, like all vegetable oils, is scientifically classified as a combustible liquid. This means it requires significantly more energy and heat to ignite than true flammable liquids. Understanding this distinction, along with the specific temperatures involved, is important for kitchen safety.
Defining the Difference Between Flammable and Combustible
The terms “flammable” and “combustible” are not interchangeable in a scientific and regulatory context; the difference is defined by a measurement called the flash point. A liquid is legally classified as flammable if its flash point is below 100°F (37.8°C). These liquids, such as gasoline or acetone, produce enough ignitable vapor at or near room temperature to catch fire easily when exposed to a spark or flame.
Combustible liquids, conversely, have a flash point at or above 100°F (37.8°C) and require preheating to generate sufficient ignitable vapor. Corn oil falls into this latter category, as its flash point is well above 200°F (93°C). For corn oil to burn, its temperature must first be raised high enough to release these vapors, as it is the vapor, not the liquid itself, that combusts.
The Critical Temperatures: Flash Point and Fire Point
The thermal properties of corn oil confirm its combustible classification and high ignition barrier. The flash point is the lowest temperature at which the liquid produces enough vapor to ignite briefly, or “flash,” when an external ignition source is applied. For corn oil, this temperature is typically very high, hovering around 600°F (315°C).
If the oil temperature continues to rise past the flash point, it will reach the fire point. The fire point is the temperature at which the oil produces enough sustained vapor to continue burning for at least five seconds after ignition. For most vegetable oils, including corn oil, the fire point is approximately 700°F (375°C). This sustained burning is why an oil fire is so dangerous; the fire can feed itself without further heat input from the stove once this temperature is reached.
The autoignition temperature is the point at which the oil ignites spontaneously without any external spark or flame. This is the highest of the thermal benchmarks, with corn oil’s autoignition temperature being around 737.6°F (392°C). These high temperatures illustrate why corn oil is not a fire risk under normal circumstances, but they also emphasize the danger of overheating oil during deep frying.
Preventing and Extinguishing Cooking Oil Fires
Prevention
Because corn oil is combustible, the primary safety focus in the kitchen is preventing it from reaching its high ignition temperatures. The most effective prevention method is constant supervision; never leave heating oil unattended on the stovetop. If the oil begins to smoke, which happens around 450°F for corn oil, this is a clear sign the temperature is approaching dangerous levels, and the heat should be reduced immediately.
Another common cause of oil fires is adding water to hot oil, which can happen when frying wet foods. Water instantly vaporizes into steam when it hits the hot oil, causing the oil to violently splash out of the pan and spread the fire. To prevent this, ensure all food items are completely dry before placing them into heated oil.
Extinguishing Small Fires
If a grease fire does occur, it is important to react quickly and calmly with the correct extinguishing method. First, turn off the heat source immediately, but do not attempt to move the pot, as this can splash the burning oil and spread the fire. The most effective initial action is to smother the flames by sliding a non-glass metal lid or a baking sheet over the pan to cut off the fire’s oxygen supply.
For very small fires, a generous amount of baking soda or salt can be carefully poured onto the flames. Baking soda works by releasing carbon dioxide when heated, which helps to smother the fire. However, never use flour or baking powder, as these substances can worsen the fire.
Using a Fire Extinguisher
Never pour water on a grease fire, as this will result in a rapid and dangerous fireball explosion that spreads the oil and flames. For a fire that cannot be smothered or is growing beyond the pan, a Class K fire extinguisher is the correct tool. These extinguishers contain specialized chemicals designed to suppress fires involving high-temperature cooking oils and fats.