Food grade mineral oil (FGMO) is a common household product used to condition wooden cutting boards, butcher blocks, and metal kitchen equipment. It prevents degradation and rust and is also used in pharmaceuticals as a laxative, demonstrating its safety for human contact. Since FGMO is derived from petroleum, a common safety concern is its flammability, especially when stored in a kitchen environment. This article addresses the combustion properties of food grade mineral oil and outlines practical safety measures for its use and storage.
Understanding Food Grade Mineral Oil
Food grade mineral oil is a highly refined, non-volatile liquid originating from crude petroleum oil. It is colorless, odorless, and tasteless, distinguishing it from industrial-grade oils that contain impurities and additives. The rigorous purification process removes harmful compounds like aromatic rings and sulfur, ensuring it meets strict safety standards.
This refinement results in a product certified as safe for food contact, typically designated with USP or NF grades. The liquid consists of saturated aliphatic and alicyclic nonpolar hydrocarbons, contributing to its chemical inertness and stability. This composition prevents it from going rancid like vegetable oils and allows it to serve as an effective, protective barrier for wood and metal.
Conditions Required for Ignition
Food grade mineral oil is classified as combustible, not flammable, based on the temperature required for ignition. A liquid is legally considered flammable if its flash point is below 100°F (38°C), meaning it produces enough vapor to ignite easily at room temperature. Combustible liquids, like FGMO, require significant external heat to begin burning.
The flash point of food grade mineral oil is typically very high, often ranging from 300°F to 380°F (149°C to 193°C), though some grades exceed 420°F (215°C). The flash point is the minimum temperature at which the oil produces enough vapor to briefly ignite when exposed to an ignition source. For sustained burning to occur, the temperature must reach the fire point, which is slightly higher.
Accidental ignition under normal household conditions is highly unlikely due to these high temperature requirements. The oil must be significantly preheated before it poses a fire risk, unlike volatile liquids such as gasoline. The auto-ignition temperature—the temperature at which the oil ignites without an external spark or flame—is even higher, generally around 500°F (260°C).
Safe Use and Storage Practices
The primary safety precaution is storing food grade mineral oil away from high heat sources and open flames. Containers should be kept sealed in a cool, dry location to prevent exposure to elevated temperatures. Avoiding contamination with other flammable liquids, such as solvents, is also important, as this can drastically lower the oil’s flash point.
If a mineral oil fire occurs, water is not an effective extinguishing agent and can spread the burning oil. For small oil fires, recommended extinguishers include dry chemical, carbon dioxide (CO2), or alcohol foam, which are effective against Class B fires. Since FGMO is used for food contact surfaces, the safest approach for household fires is to smother the flames or use a multi-purpose dry chemical extinguisher.